Uploaded by بن شكر

Design Criteria for Infrastructure Projects, Rev 03 Nov 2010[1]

advertisement
Guidance Document
Design Criteria for Infrastructure Projects
Revision No. 3 - November 2010
Prepared for:
The Great Socialist People’s Libyan Arab Jamahiriya
Housing and Infrastructure Board (HIB)
Program Management Department (PMD)
Contents
LIST OF TABLES ........................................................................................................................... TAB-1
LIST OF FIGURES ........................................................................................................................... FIG-1
REVISION TRACKING .................................................................................................................... REV-1
ACRONYMS AND ABBREVIATIONS ............................................................................................... AA-1
INTRODUCTION ......................................................................................................................... INTRO-1
1
WATER DESIGN STANDARDS.......................................................................................... 1-1
1.1
1.1.2
OBJECTIVES ...................................................................................................................... 1-1
Operation and Maintenance Aspects ...................................................................................... 1-1
1.2
POTABLE WATER DEMAND .............................................................................................. 1-1
1.3
WATER TRANSPORT AND DISTRIBUTION SYSTEM ....................................................... 1-2
1.3.1
Reservoir Design ................................................................................................................... 1-2
1.3.2
Ground Level Tanks............................................................................................................... 1-2
1.3.3
Elevated Water Tanks ............................................................................................................ 1-2
1.3.4
Transport Water Lines............................................................................................................ 1-3
1.3.5
Distribution Water Lines ......................................................................................................... 1-4
1.3.6
Fire Hydrants ......................................................................................................................... 1-5
1.3.7
Laterals ................................................................................................................................. 1-6
1.3.8
Backflow Prevention .............................................................................................................. 1-6
1.3.9
Operation and Maintenance ................................................................................................... 1-6
1.4
WATER WELL DESIGN ...................................................................................................... 1-6
1.5
SURFACE WATER, GROUND WATER, AND SEAWATER TREATMENT .......................... 1-6
1.5.1
Purpose................................................................................................................................. 1-6
1.5.2
Water Treatment Design Criteria ............................................................................................ 1-7
1.6
STRUCTURAL DESIGN ...................................................................................................... 1-9
ATTACHMENT 1-1 : CRITERIA FOR ESTABLISHING WATER DEMAND.................................... 1-10
ATTACHMENT 1-2. TRANSPORT WATER LINE DESIGN PARAMETERS .................................. 1-12
ATTACHMENT 1-3. DISTRIBUTION WATER LINE DESIGN PARAMETERS ............................... 1-13
ATTACHMENT 1-4: WATER WELL DESIGN CRITERIA............................................................... 1-14
ATTACHMENT 1-5: TREATED WATER QUALITY PARAMETERS............................................... 1-17
ATTACHMENT 1-6: SECONDARY MAXIMUM CONTAINMENT LEVELS..................................... 1-19
ATTACHMENT 1-7: TREATMENT PROCESS OPERATIONS ...................................................... 1-20
ATTACHMENT 1-8: PIPE MATERIALS FOR WATER TREATMENT PLANTS .............................. 1-23
2
SEWERAGE ....................................................................................................................... 2-1
2.1
SEWER DESIGN CRITERIA ............................................................................................... 2-1
2.1.1
Sewage Flow ......................................................................................................................... 2-1
2.1.2
Hydraulic Analyses ................................................................................................................ 2-2
2.1.3
Flow Velocities....................................................................................................................... 2-2
AUGUST 2010
REVISION NO. 03
TOC-1
2.1.4
Depth of Flow ........................................................................................................................ 2-2
2.1.5
Pipe Gradients ....................................................................................................................... 2-2
2.1.6
Pipe Materials ........................................................................................................................ 2-3
2.1.7
Minimum Cover Requirements ............................................................................................... 2-3
2.1.8
Utility Crossings ..................................................................................................................... 2-3
2.1.9
Manholes .............................................................................................................................. 2-3
2.2
PUMPING STATIONS ......................................................................................................... 2-4
2.2.1
Pumping Station Type ............................................................................................................ 2-4
2.2.2
Pump Selection ..................................................................................................................... 2-5
2.2.3
Pumping Station Structures .................................................................................................... 2-5
2.2.4
Surge Protection .................................................................................................................... 2-6
2.2.5
Electrical and Instrumentation Systems .................................................................................. 2-6
2.2.6
Odor Control .......................................................................................................................... 2-6
2.2.7
Gas Monitoring ...................................................................................................................... 2-6
2.2.8
Rising Mains .......................................................................................................................... 2-7
2.2.9
Air Valves and Washouts ....................................................................................................... 2-7
2.2.10
Pumping Stations Operations and Maintenance ...................................................................... 2-8
2.3
STRUCTURAL DESIGN ...................................................................................................... 2-8
ATTACHMENT 2-1 LAND USE BASED FLOWS FOR SEWERAGE ............................................... 2-9
ATTACHMENT 2-2 PIPE GRADIENTS ......................................................................................... 2-11
ATTACHMENT 2-3 SEWER MANHOLE DESIGN CRITERIA........................................................ 2-12
3
SEWAGE TREATMENT ..................................................................................................... 3-1
3.1
PURPOSE .......................................................................................................................... 3-1
3.2
SEWAGE TREATMENT DESIGN CRITERIA ...................................................................... 3-2
3.2.2
Population and Growth Projections ......................................................................................... 3-2
3.2.3
Sewage Flow Generation ....................................................................................................... 3-2
3.2.4
Sewage Loadings .................................................................................................................. 3-3
3.2.5
Design Discharge Quality Limitations...................................................................................... 3-3
3.3
SITE SPECIFIC DESIGN CONSIDERATIONS .................................................................... 3-4
3.4
TREATMENT PROCESS DESIGN CRITERIA ..................................................................... 3-4
3.4.1
Mechanical Treatment Systems.............................................................................................. 3-4
3.4.2
Lagoon Treatment Systems ................................................................................................... 3-5
3.4.3
Package Treatment Plant ....................................................................................................... 3-5
3.4.4
Mobile Package Treatment Plant ............................................................................................ 3-5
3.5
STRUCTURAL DESIGN ...................................................................................................... 3-6
ATTACHMENT 3-1 LIQUID PROCESS DESIGN CRITERIA ........................................................... 3-7
ATTACHMENT 3-2 LIQUID PROCESS HYDRAULIC SYSTEM CRITERIA ................................... 3-12
ATTACHMENT 3-3 BIOSOLIDS SYSTEM CRITERIA ................................................................... 3-14
ATTACHMENT 3-4 BIOSOLIDS SYSTEM CRITERIA ................................................................... 3-16
ATTACHMENT 3-5 MECHANICAL ODOR CONTROL SYSTEM CRITERIA ................................. 3-17
ATTACHMENT 3-6 LAGOON TREATMENT SYSTEM GENERAL GUIDELINES .......................... 3-18
ATTACHMENT 3-7 AERATED LAGOONS CRITERIA .................................................................. 3-19
AUGUST 2010
REVISION NO. 03
TOC-2
ATTACHMENT 3-8 FACULTATIVE LAGOON TREATMENT SYSTEM CRITERIA ........................ 3-20
ATTACHMENT 3-9 TERTIARY TREATMENT CRITERIA ............................................................. 3-21
4
STORM WATER ................................................................................................................. 4-1
4.1
STORM WATER MANAGEMENT POLICY.......................................................................... 4-1
4.1.1
Storm Water Quantity Management ........................................................................................ 4-1
4.1.2
Enhancing Storm Water Quality.............................................................................................. 4-2
4.2
STORM WATER DESIGN CRITERIA .................................................................................. 4-2
4.2.1
Design Storm ......................................................................................................................... 4-2
4.2.2
Runoff Coefficients ................................................................................................................ 4-3
4.2.3
Runoff Volumes ..................................................................................................................... 4-3
4.3
HYDRAULIC ANALYSES .................................................................................................... 4-4
4.3.1
Flow Velocities....................................................................................................................... 4-4
4.3.2
Clear Times ........................................................................................................................... 4-4
4.3.3
Depth of Flow ........................................................................................................................ 4-5
4.4
PIPE MATERIALS ............................................................................................................... 4-5
4.4.1
Pipe Gradients ....................................................................................................................... 4-5
4.4.2
Minimum Cover Requirements ............................................................................................... 4-6
4.4.3
Manholes .............................................................................................................................. 4-6
4.4.4
Connection Chambers ........................................................................................................... 4-7
4.4.5
Catch Basins and Trench Drains ............................................................................................ 4-7
4.4.6
Utility Crossings ..................................................................................................................... 4-7
4.5
DETENTION PONDS (SEPARATE STORM DRAINAGE ONLY) ......................................... 4-7
4.5.1
Pond Inlet and Outlet Structures ............................................................................................. 4-8
4.5.2
Discharge Control Structures.................................................................................................. 4-8
4.5.3
Pond Depth ........................................................................................................................... 4-8
4.5.4
Detention Pond Emptying ....................................................................................................... 4-8
4.5.5
Dry Detention Ponds .............................................................................................................. 4-9
4.5.6
Wet Detention Ponds ............................................................................................................. 4-9
4.5.7
Retention Ponds .................................................................................................................... 4-9
4.5.8
Buried Detention Chambers ................................................................................................... 4-9
4.6
OIL-WATER SEPARATORS ............................................................................................... 4-9
4.7
STORM WATER MANAGEMENT WITHIN AN AIRPORT .................................................. 4-11
4.7.1
Bird Scare ........................................................................................................................... 4-11
4.8
GROUNDWATER DEWATERING ..................................................................................... 4-11
4.9
PUMPING STATIONS AND RISING MAINS...................................................................... 4-11
4.9.1
Pumping Station Type .......................................................................................................... 4-12
4.9.2
Wet Well Volume ................................................................................................................. 4-12
4.9.3
Wet Well Depth.................................................................................................................... 4-12
4.9.4
Pump Selection ................................................................................................................... 4-12
4.9.5
Pumping Station Structures .................................................................................................. 4-13
4.9.6
Surge Protection .................................................................................................................. 4-13
4.9.7
Rising Mains ........................................................................................................................ 4-13
4.9.8
Air Valves and Washouts ..................................................................................................... 4-13
AUGUST 2010
REVISION NO. 03
TOC-3
4.9.9
Reliability ............................................................................................................................. 4-14
ATTACHMENT 4-1 INTENSITY-DURATION DATA - TRIPOLI...................................................... 4-15
ATTACHMENT 4-2 INTENSITY-DURATION TABLE AND CURVE, MISRATA .............................. 4-16
ATTACHMENT 4-3 INTENSITY-DURATION DATA, BENGHAZI................................................... 4-17
ATTACHMENT 4-4 INTENSITY-DURATION DATA, DERNA ........................................................ 4-18
ATTACHMENT 4-5 METEOROLOGICAL STATIONS LOCATIONS .............................................. 4-19
ATTACHMENT 4-6 RUNOFF COEFFICIENT VALUES................................................................. 4-20
ATTACHMENT 4-7 SAMPLE HYDRAULIC ANALYSES CALCULATIONS .................................... 4-21
5
WATER REUSE FOR LANDSCAPE IRRIGATION ............................................................. 5-1
5.1
GENERAL ........................................................................................................................... 5-1
5.1.1
Irrigation Supply ..................................................................................................................... 5-1
5.1.2
Transmission Network............................................................................................................ 5-1
5.1.3
Distribution Network ............................................................................................................... 5-1
5.1.4
Irrigation Water Quality Standards .......................................................................................... 5-2
5.2
IRRIGATION DESIGN CRITERIA........................................................................................ 5-2
5.2.1
Irrigation Demands ................................................................................................................ 5-2
5.2.2
Distribution Network ............................................................................................................... 5-3
5.2.3
Flow Meters and Structures.................................................................................................... 5-5
5.2.4
Storage ................................................................................................................................. 5-5
5.2.5
Pumping Stations................................................................................................................... 5-6
5.2.6
Fire Hydrants ......................................................................................................................... 5-7
6
STANDARDS FOR BARRIER-FREE DESIGN .................................................................... 6-1
6.1
INTRODUCTION ................................................................................................................. 6-1
6.1.1
Purpose................................................................................................................................. 6-1
6.1.2
Application ............................................................................................................................. 6-1
6.1.3
Definition of Significant Renovation ........................................................................................ 6-1
6.1.4
Maintenance .......................................................................................................................... 6-1
6.1.5
Emergency Evacuation Planning ............................................................................................ 6-1
6.2
EXTERIOR AREAS ............................................................................................................. 6-1
6.2.1
Parking and Drop-Off Areas ................................................................................................... 6-1
6.2.2
Walkways and Ramps............................................................................................................ 6-5
6.2.3
Entrances and Exits ............................................................................................................... 6-8
6.2.4
Exterior Amenities ................................................................................................................ 6-10
6.3
INTERIOR AREAS ............................................................................................................ 6-10
6.3.1
Stairs and Ramps ................................................................................................................ 6-10
6.3.2
Lobbies and Corridors .......................................................................................................... 6-12
6.3.3
Elevators and Lifts ............................................................................................................... 6-12
6.3.4
Interior Doors and Doorways ................................................................................................ 6-13
6.4
FACILITIES ....................................................................................................................... 6-14
6.4.1
Washrooms/Bathrooms/Toilets ............................................................................................. 6-14
6.4.2
Shower and Bath Facilities ................................................................................................... 6-17
6.4.3
Drinking Fountains ............................................................................................................... 6-20
AUGUST 2010
REVISION NO. 03
TOC-4
6.4.4
Public Pay Telephones ........................................................................................................ 6-21
6.4.5
Controls............................................................................................................................... 6-21
6.4.6
Signage ............................................................................................................................... 6-22
6.4.7
Tactile Warnings .................................................................................................................. 6-23
6.4.8
Counters and Line up Guides ............................................................................................... 6-24
6.4.9
Places of Assembly.............................................................................................................. 6-24
6.4.10
Assisted Listening Devices ................................................................................................... 6-26
6.4.11
Visual and Audible Alarms ................................................................................................... 6-26
6.4.12
Life Safety ........................................................................................................................... 6-26
6.4.13
Cooking & Laundry Facilities ................................................................................................ 6-26
7
SURVEYING STANDARDS ................................................................................................ 7-1
7.1
PURPOSE .......................................................................................................................... 7-1
7.2
HORIZONTAL CONTROL SURVEYS ................................................................................. 7-1
7.2.1
Definition ............................................................................................................................... 7-1
7.2.2
Field Methods ........................................................................................................................ 7-1
7.2.3
Coordinate Adjustment........................................................................................................... 7-2
7.3
VERTICAL CONTROL SURVEYS ....................................................................................... 7-2
7.3.1
Definition ............................................................................................................................... 7-2
7.3.2
GPS Network Design Example: .............................................................................................. 7-3
7.3.3
Benchmarks .......................................................................................................................... 7-4
7.4
TOPOGRAPHIC SURVEYS ................................................................................................ 7-4
7.4.1
Definition ............................................................................................................................... 7-4
7.4.2
Utility Surveys ........................................................................................................................ 7-4
7.4.3
Digital Terrain Model (DTM) ................................................................................................... 7-5
7.4.4
Route Survey ......................................................................................................................... 7-5
7.4.5
Considerations - Other Technology ........................................................................................ 7-6
7.4.6
Work Product ......................................................................................................................... 7-6
7.4.7
Information Required ............................................................................................................. 7-6
7.4.8
Monuments ........................................................................................................................... 7-6
7.4.9
Field Procedures.................................................................................................................... 7-7
7.4.10
Topographic Features ............................................................................................................ 7-8
7.4.11
Electronic Data ...................................................................................................................... 7-8
7.4.12
Data Collection ...................................................................................................................... 7-8
7.5
7.5.1
7.6
CONSTRUCTION STAKING ............................................................................................... 7-9
Field Methods ........................................................................................................................ 7-9
AS-BUILT SURVEYS .......................................................................................................... 7-9
7.6.1
Definition ............................................................................................................................... 7-9
7.6.2
Deliverable ............................................................................................................................ 7-9
7.7
SURVEY MAP CHECK LIST ............................................................................................... 7-9
ATTACHMENT 7-1 GPS LOG SHEET.......................................................................................... 7-10
ATTACHMENT 7-2 SURVEY REPORT GUIDELINES .................................................................. 7-11
ATTACHMENT 7-3 TOLERANCES FOR CONVENTIONAL TRAVERSE FOR 2
ND
RD
AND 3
ORDER ..................................................................................................................... 7-13
AUGUST 2010
REVISION NO. 03
TOC-5
8
ROADWAY ......................................................................................................................... 8-1
8.1
HIGHWAY SYSTEMS ......................................................................................................... 8-1
8.1.1
Functional Classification......................................................................................................... 8-1
8.1.2
Freeways .............................................................................................................................. 8-1
8.1.3
Expressways ......................................................................................................................... 8-1
8.1.4
Arterials ................................................................................................................................. 8-1
8.1.5
Collectors .............................................................................................................................. 8-2
8.1.6
Local Roads .......................................................................................................................... 8-2
8.2
TRAFFIC............................................................................................................................. 8-2
8.2.1
Level of Service ..................................................................................................................... 8-2
8.2.2
Design Vehicles ..................................................................................................................... 8-3
8.3
SPEED................................................................................................................................ 8-3
8.3.1
Design Speed ........................................................................................................................ 8-4
8.3.2
Posted Speed ........................................................................................................................ 8-4
8.3.3
Ramps .................................................................................................................................. 8-5
8.4
SIGHT DISTANCE .............................................................................................................. 8-5
8.4.1
Stopping Sight Distance (SSD)............................................................................................... 8-5
8.4.2
Passing Sight Distance (PSD) ................................................................................................ 8-7
8.4.3
Decision Sight Distance ......................................................................................................... 8-7
8.5
HORIZONTAL ALIGNMENT................................................................................................ 8-8
8.5.1
General ................................................................................................................................. 8-8
8.5.2
Types of Horizontal Curvature ................................................................................................ 8-9
8.5.3
Minimum Curvature.............................................................................................................. 8-11
8.5.4
Spiral Curve Transition......................................................................................................... 8-12
8.5.5
Horizontal Stopping Sight Distance....................................................................................... 8-14
8.5.6
Superelevation..................................................................................................................... 8-14
8.5.7
Minimum Lane Width on Curves ........................................................................................... 8-19
8.6
VERTICAL ALIGNMENT ................................................................................................... 8-19
8.6.1
Grades ................................................................................................................................ 8-20
8.6.2
Vertical Curves .................................................................................................................... 8-21
8.6.3
Combining Horizontal and Vertical Alignments ...................................................................... 8-25
8.6.4
Vertical Clearances .............................................................................................................. 8-27
8.7
CROSS SECTION ELEMENTS ......................................................................................... 8-27
8.7.1
General ............................................................................................................................... 8-27
8.7.2
Travel Lanes........................................................................................................................ 8-28
8.7.3
Shoulders ............................................................................................................................ 8-29
8.7.4
Curbing ............................................................................................................................... 8-29
8.7.5
Borders, Buffer Strips and Sidewalks .................................................................................... 8-29
8.7.6
Medians .............................................................................................................................. 8-29
8.7.7
Cross Slopes ....................................................................................................................... 8-31
8.7.8
Side Slopes ......................................................................................................................... 8-31
8.7.9
Ditch Sections ..................................................................................................................... 8-31
8.7.10
Right-of-Way Limits.............................................................................................................. 8-32
8.7.11
Horizontal Clearances .......................................................................................................... 8-32
AUGUST 2010
REVISION NO. 03
TOC-6
8.7.12
8.8
Others ................................................................................................................................. 8-34
GRADE SEPARATIONS AND INTERCHANGES .............................................................. 8-36
8.8.1
Warrants ............................................................................................................................. 8-36
8.8.2
Interchange Types ............................................................................................................... 8-36
8.8.3
Interchange Analysis ............................................................................................................ 8-41
8.8.4
Traffic Lane Principles.......................................................................................................... 8-42
8.8.5
Lane Balance ...................................................................................................................... 8-42
8.8.6
Freeway/Ramp Junctions ..................................................................................................... 8-44
8.8.7
Capacity and Level of Service .............................................................................................. 8-56
8.8.8
Ramp Design ....................................................................................................................... 8-59
8.8.9
Spacing of Ramp Terminals ................................................................................................. 8-61
8.8.10
Appendices ......................................................................................................................... 8-63
8.9
SUMMARY OF DESIGN PARAMETERS........................................................................... 8-72
8.9.1
Local Roads and Streets ...................................................................................................... 8-73
8.9.2
Collectors ............................................................................................................................ 8-73
8.9.3
Arterials ............................................................................................................................... 8-74
8.9.4
Freeways/Expressways ....................................................................................................... 8-74
8.10
HIGHWAY FACILITIES ..................................................................................................... 8-75
8.10.1
General ............................................................................................................................... 8-75
8.10.2
Public Transport Facilities .................................................................................................... 8-76
8.10.3
Parking Facilities.................................................................................................................. 8-78
8.10.4
Safety Barriers ..................................................................................................................... 8-81
8.10.5
Impact Attenuator Systems .................................................................................................. 8-89
8.10.6
Traffic Calming .................................................................................................................... 8-90
8.11
INTERSECTIONS ............................................................................................................. 8-93
8.11.1
General Design Considerations ............................................................................................ 8-93
8.11.2
Intersection Sight Distance ................................................................................................... 8-97
8.11.3
Intersection Turns .............................................................................................................. 8-105
8.12
ROUNDABOUTS ............................................................................................................ 8-133
8.12.1
General ............................................................................................................................. 8-133
8.12.2
Design Principles ............................................................................................................... 8-133
8.12.3
General Features of a Roundabout..................................................................................... 8-134
8.12.4
Speeds through the Roundabout ........................................................................................ 8-136
8.12.5
Design Vehicle................................................................................................................... 8-138
8.12.6
Inscribed Circle Diameter ................................................................................................... 8-139
8.12.7
Circulating Roadway Width ................................................................................................ 8-140
8.12.8
Entry Width........................................................................................................................ 8-141
8.12.9
Entry Curves...................................................................................................................... 8-142
8.12.10
Exit Curves ........................................................................................................................ 8-143
8.12.11
Vertical Considerations ...................................................................................................... 8-145
8.12.12
Visibility ............................................................................................................................. 8-148
8.12.13
Entry Curbing .................................................................................................................... 8-150
8.12.14
Safety at Roundabouts ....................................................................................................... 8-151
AUGUST 2010
REVISION NO. 03
TOC-7
9
FLEXIBLE PAVEMENT DESIGN MANUAL ........................................................................ 9-1
9.1
PURPOSE .......................................................................................................................... 9-1
9.2
GENERAL ........................................................................................................................... 9-1
9.3
DESIGN PROCESS ............................................................................................................ 9-1
9.4
REFERENCES.................................................................................................................... 9-1
9.5
PAVEMENT TYPES, DEFINITIONS AND ABBREVIATIONS ............................................... 9-2
9.5.1
Flexible Pavement ................................................................................................................. 9-2
9.5.2
Pavement Design Terms and Definitions ................................................................................ 9-3
9.6
TYPICAL PAVEMENT DESIGN PROCEDURES FOR 30% SUBMITTAL ............................ 9-4
9.6.1
Step 1 – Determine Scope of Work......................................................................................... 9-5
9.6.2
Step 2 – Collect Basic Project Data ........................................................................................ 9-6
9.6.3
Step 3 – Determine Design Bearing Ratio (DBR) .................................................................... 9-6
9.6.4
Step 4 – HIB Reviews Scope of Work and DBR Determination ................................................ 9-7
9.6.5
9.7
Step 5 - HIB Reviews/Comments on the 30% Design .............................................................. 9-8
NEW AND RECONSTRUCTED PAVEMENT ...................................................................... 9-8
9.7.1
Pavement Design Cover Sheet .............................................................................................. 9-8
9.7.2
Data Sheet 1: Pavement Structural Design Data .................................................................... 9-8
9.7.3
Design Bearing Ratio (DBR) Determination ............................................................................ 9-8
9.7.4
Data Sheet 2: Determining Structural Number (SN)................................................................. 9-8
9.7.5
Data Sheet 3: Pavements Structural Number (SN) ................................................................ 9-10
9.8
RECLAMATION ................................................................................................................ 9-13
9.9
PAVEMENT RESURFACING ............................................................................................ 9-13
9.9.1
Pavement Resurfacing Design Cover Sheet ......................................................................... 9-13
9.9.2
Data Sheet 1: Pavement Structural Design Data ................................................................... 9-13
9.9.3
Data Sheet 2: Actual SN of Existing Pavement ..................................................................... 9-15
9.9.4
Data Sheet 3: Determination of Resurfacing Thickness ......................................................... 9-15
9.10
LIMITED ACCESS HIGHWAY PAVEMENT RESURFACING DESIGN .............................. 9-15
9.10.1
Design Method .................................................................................................................... 9-15
9.10.2
Serviceability ....................................................................................................................... 9-15
9.10.3
Reliability ............................................................................................................................. 9-15
9.10.4
Back-Calculation .................................................................................................................. 9-16
9.10.5
1993 AASHTO Pavement Resurfacing Design ...................................................................... 9-16
9.11
9.11.1
9.12
TYPICAL PAVEMENT DESIGN FOR LOW VOLUME ROADS .......................................... 9-16
Design Procedures .............................................................................................................. 9-16
FOR FURTHER INFORMATION ....................................................................................... 9-16
ATTACHMENT 9-1 PAVEMENT DESIGN CHECKLIST ................................................................ 9-17
ATTACHMENT 9-2 NEW OR RECONSTRUCTED PAVEMENT FORM ........................................ 9-19
ATTACHMENT 9-3 OVERLAY DESIGN FORM ........................................................................... 9-23
ATTACHMENT 9-4 SAMPLE PROBLEMS AND COMPLETED FORMS ....................................... 9-27
10
UNIFORM TRAFFIC CONTROL DEVICES ....................................................................... 10-1
10.1
TRAFFIC CONTROL FOR WORK AREA (SUPPLEMENTS) ............................................. 10-1
10.2
ROADWAY CONSTRUCTION .......................................................................................... 10-1
AUGUST 2010
REVISION NO. 03
TOC-8
10.2.1
Corridor and Network-wide Constructions ............................................................................. 10-1
10.2.2
Authority .............................................................................................................................. 10-1
10.3
TRAFFIC CONTROL ZONES ............................................................................................ 10-2
10.3.1
Application ........................................................................................................................... 10-3
10.3.2
Guideline ............................................................................................................................. 10-3
10.3.3
Traffic Management Plans ................................................................................................... 10-5
10.3.4
Components of Temporary Traffic Control Zones .................................................................. 10-6
ATTACHMENT 10-1 TRAFFIC MANAGEMENT PLAN (SAMPLE) NO. 1 ...................................... 10-9
ATTACHMENT 10-2 : TRAFFIC MANAGEMENT PLAN (SAMPLE) NO. 2 .................................. 10-12
11
LANDSCAPE DESIGN CRITERIA .................................................................................... 11-1
11.1
LANDSCAPE DESIGN CRITERIA ..................................................................................... 11-1
11.1.1
Landscape and Planting ....................................................................................................... 11-1
11.1.2
Planting on Private Development Parcels ............................................................................. 11-4
11.1.3
Planting on Public Streets and Streets within Private Developments ...................................... 11-5
11.1.4
Planting on Public Parks and Landscaped Open Areas ......................................................... 11-6
11.2
LANDSCAPING PLANS SUBMITTALS REQUIREMENTS ................................................ 11-6
11.3
LANDSCAPE GRADING PLAN ......................................................................................... 11-7
11.3.2
Tree and Plant Maintenance .............................................................................................. 11-10
11.3.3
Indigenous Species............................................................................................................ 11-10
12
STREETSCAPE ................................................................................................................ 12-1
12.1
INTRODUCTION ............................................................................................................... 12-1
12.2
GOOD DESIGN ................................................................................................................ 12-1
12.3
OBJECTIVE ...................................................................................................................... 12-2
12.4
PRINCIPLES..................................................................................................................... 12-2
12.5
DESIGN GUIDELINES AND CRITERIA............................................................................. 12-3
12.5.1
Planting Regimes................................................................................................................. 12-3
12.5.2
Footway layout .................................................................................................................... 12-3
12.5.3
Paving ................................................................................................................................. 12-4
12.5.4
Street Furniture and Features............................................................................................... 12-5
12.5.5
Lighting ............................................................................................................................... 12-5
12.5.6
Benches .............................................................................................................................. 12-5
12.5.7
Planters ............................................................................................................................... 12-6
12.5.8
Playground Equipment ......................................................................................................... 12-6
12.5.9
Water Features in Public Open Spaces ................................................................................ 12-6
12.5.10
Shading Strategies .............................................................................................................. 12-6
12.5.11
Signage ............................................................................................................................... 12-6
12.6
13
DELIVERING THE PRINCIPLES....................................................................................... 12-6
BRIDGE INSPECTION...................................................................................................... 13-1
13.1
INTRODUCTION ............................................................................................................... 13-1
13.1.1
References .......................................................................................................................... 13-1
13.1.2
AASHTO Inspection Manuals ............................................................................................... 13-2
AUGUST 2010
REVISION NO. 03
TOC-9
13.1.3
13.2
Inspection Procedures ......................................................................................................... 13-5
BRIDGE INSPECTION PERSONNEL ............................................................................... 13-6
13.2.1
Requirements ...................................................................................................................... 13-6
13.2.2
Bridge Inspection Personnel................................................................................................. 13-7
13.2.3
Bridge Inspections by Contractors ........................................................................................ 13-7
13.2.4
Use of the Contractor Pool ................................................................................................... 13-8
13.3
FIELD INSPECTION REQUIREMENTS ............................................................................ 13-9
13.3.1
Types of Bridge Inspection ................................................................................................... 13-9
13.3.2
Initial Inspections ................................................................................................................. 13-9
13.3.3
Routine Inspections ............................................................................................................. 13-9
13.3.4
Damage Inspections .......................................................................................................... 13-10
13.3.5
In-Depth Inspections .......................................................................................................... 13-10
13.3.6
Special Inspections ............................................................................................................ 13-16
13.4
RATINGS AND LOAD POSTING..................................................................................... 13-16
13.4.1
Overview ........................................................................................................................... 13-16
13.4.2
Condition Ratings .............................................................................................................. 13-16
13.4.3
Appraisal Ratings............................................................................................................... 13-17
13.4.4
Load Ratings ..................................................................................................................... 13-21
13.4.5
Legal Loads and Load Posting ........................................................................................... 13-25
13.5
ROUTING AND PERMITS............................................................................................... 13-30
13.5.1
Overview ........................................................................................................................... 13-30
13.5.2
Role of Inspection Engineers and the Traffic Authorities ...................................................... 13-30
13.5.3
Permits.............................................................................................................................. 13-31
13.5.4
Example of Inventory, Operating, and Permit Loads ............................................................ 13-33
13.6
BRIDGE PROGRAMMING .............................................................................................. 13-36
13.6.1
Basis for Bridge Rehabilitation or Replacement................................................................... 13-36
13.6.2
Bridge Program ................................................................................................................. 13-37
13.6.3
Sufficiency Ratings ............................................................................................................ 13-38
13.7
BRIDGE RECORDS ........................................................................................................ 13-41
13.7.1
Overview ........................................................................................................................... 13-41
13.7.2
Definition of Terms............................................................................................................. 13-41
13.7.3
Contractor Requirements ................................................................................................... 13-43
13.7.4
Coding Guidelines ............................................................................................................. 13-43
13.7.5
Forms................................................................................................................................ 13-44
13.7.6
Calculations ....................................................................................................................... 13-46
13.7.7
Data Submittal ................................................................................................................... 13-49
13.7.8
The Bridge Folder .............................................................................................................. 13-52
13.8
ATTACHMENTS ............................................................................................................. 13-53
ATTACHMENT 13-1 BRIDGE INSPECTION REPORT ................................................................ 13-54
ATTACHMENT 13-2 BRIDGE APPRAISAL WORKSHEET .......................................................... 13-57
ATTACHMENT 13-3 BRIDGE STRUCTURAL CONDITION HISTORY ........................................ 13-58
ATTACHMENT 13-4 BRIDGE INSPECTION FOLLOW-UP ACTION WORKSHEET .................... 13-59
ATTACHMENT 13-5 BRIDGE INVENTORY RECORD ................................................................ 13-61
AUGUST 2010
REVISION NO. 03
TOC-10
ATTACHMENT 13-6 BRIDGE INVENTORY RECORD SKETCH ................................................. 13-62
ATTACHMENT 13-7 REVISION TO BRIDGE INVENTORY RECORD ......................................... 13-63
ATTACHMENT 13-8 CHANNEL CROSS-SECTION MEASUREMENTS RECORD ...................... 13-64
ATTACHMENT 13-9 UNDERCLEARANCE RECORD ................................................................. 13-66
ATTACHMENT 13-10 BRIDGE SUMMARY SHEET .................................................................... 13-67
ATTACHMENT 13-11 RECOMMENDED CHANGE IN BRIDGE LOAD POSTING ....................... 13-68
14
ELECTRICAL, INSTRUMENTATION, CONTROL AND AUTOMATION (EICA) ................ 14-1
14.1
APPLICABILITY ................................................................................................................ 14-1
14.2
GENERAL REQUIREMENTS ............................................................................................ 14-1
14.3
ENVIRONMENTAL PROTECTION .................................................................................... 14-1
14.4
EQUIPMENT STANDARDS AND CERTIFICATION .......................................................... 14-2
14.5
SYSTEM VOLTAGES ....................................................................................................... 14-2
14.6
SUPPLY DESIGN CONSIDERATIONS ............................................................................. 14-2
14.7
HARMONICS .................................................................................................................... 14-2
14.7.1
Harmonics - General ............................................................................................................ 14-2
14.7.2
Earthing and Bonding .......................................................................................................... 14-3
14.7.3
Exposed Conductive Parts ................................................................................................... 14-3
14.7.4
Functional Earths (Instrument earths) ................................................................................... 14-3
14.8
LIGHTNING PROTECTION ............................................................................................... 14-3
14.9
LOW VOLTAGE SWITCHGEAR AND CONTROL GEAR .................................................. 14-3
14.9.1
Form 1 or Form 2 Panels ..................................................................................................... 14-4
14.9.2
Form 3b Type 2 Panels ........................................................................................................ 14-4
14.9.3
Form 4a Type 2 Panels ........................................................................................................ 14-4
14.10
ROTATING ELECTRICAL MACHINERY ........................................................................... 14-4
14.11
FACTORY ASSEMBLED DISTRIBUTION BOARDS ......................................................... 14-4
14.12
MINIATURE CIRCUIT BREAKERS (MCBS) ...................................................................... 14-4
14.13
LOW VOLTAGE INDUSTRIAL CIRCUIT BREAKERS........................................................ 14-5
14.14
ELECTRICAL ISOLATION ................................................................................................ 14-5
14.15
STANDBY GENERATOR .................................................................................................. 14-5
14.15.1
Standby Generators – Design Standards .............................................................................. 14-5
14.15.2
Standby Generator Ratings .................................................................................................. 14-5
14.16
UNINTERRUPTIBLE POWER SUPPLIES (UPS) .............................................................. 14-6
14.17
EQUIPMENT FOR USE IN HAZARDOUS AREAS ............................................................ 14-6
14.18
SWITCHGEAR ROOMS AND LV SUBSTATIONS ............................................................. 14-6
14.19
CABLING AND CONTAINMENT SYSTEMS ...................................................................... 14-6
14.20
LIGHTING ......................................................................................................................... 14-7
14.20.1
Street Lighting ..................................................................................................................... 14-7
14.20.2
Lamp Types......................................................................................................................... 14-7
14.20.3
Considerations..................................................................................................................... 14-7
14.20.4
Emergency Lighting ............................................................................................................. 14-7
14.21
AUGUST 2010
ELECTRICAL ROOMS AND KIOSKS................................................................................ 14-7
REVISION NO. 03
TOC-11
14.22
INSTRUMENTATION ........................................................................................................ 14-8
14.23
FLOW MEASUREMENT ................................................................................................... 14-8
14.23.1
Electromagnetic Flowmeter .................................................................................................. 14-8
14.23.2
Open Channel Measurement (OCM) .................................................................................... 14-8
14.23.3
Variable Area Flowmeter (VA) .............................................................................................. 14-8
14.24
LEVEL MEASUREMENT................................................................................................... 14-8
14.25
TEMPERATURE MEASUREMENT ................................................................................... 14-9
14.26
PRESSURE MEASUREMENT .......................................................................................... 14-9
14.27
PH MEASUREMENT......................................................................................................... 14-9
14.28
DISSOLVED OXYGEN (DO) MEASUREMENT ................................................................. 14-9
14.29
PROCESS ANALYZERS AND CONTINUOUS SAMPLING SYSTEMS.............................. 14-9
14.30
CONTROL VALVE ACTUATORS ...................................................................................... 14-9
14.31
PLANT CONTROL AND AUTOMATION ............................................................................ 14-9
14.31.1
Functional Design Specification ............................................................................................ 14-9
14.31.2
SCADA System Architecture .............................................................................................. 14-10
14.31.3
Telemetry Outstation.......................................................................................................... 14-10
15
TELECOMMUNICATION .................................................................................................. 15-1
16
GAS DISTRIBUTION ........................................................................................................ 16-1
17
GREAT MANMADE RIVER REQUIREMENTS.................................................................. 17-1
AUGUST 2010
REVISION NO. 03
TOC-12
List of Tables
Table 2-1 Wastewater Unit Flow Rates .......................................................................................... 2-1
Table 2-2 Typical Roughness Coefficients ..................................................................................... 2-2
Table 2-3 Minimum and Maximum Velocities in Sewer Pipes ......................................................... 2-2
Table 2-4 Minimum and Maximum Depth of Flow in Sewers at Peak Flows .................................... 2-2
Table 2-5 Utility Crossings for Sewer Pipes.................................................................................... 2-3
Table 3-1 Calculated Peak Flow Factors for Specific Populations................................................... 3-2
Table 3-2 Typical Sewage Loading Values..................................................................................... 3-3
Table 3-3 Sewage Discharge Quality Limitations ........................................................................... 3-3
Table 4-1 Typical Roughness Coefficients ..................................................................................... 4-4
Table 4-2 Minimum & Maximum Velocities ..................................................................................... 4-4
Table 4-3 Allowable Clear Times ................................................................................................... 4-5
Table 4-4 Allowable Pipe Materials ................................................................................................ 4-5
Table 4-5 Minimum Pipe Gradients ................................................................................................ 4-6
Table 4-6 Utility Crossing for Storm Drains..................................................................................... 4-7
Table 5-1 Permissible Water Classes for Irrigation Methods ........................................................... 5-2
Table 5-2 Irrigation Demand by Plant Type .................................................................................... 5-3
Table 5-3 Utility Crossing for Irrigation Pipes.................................................................................. 5-4
Table 6-1 Barrier Free Parking Spaces .......................................................................................... 6-2
Table 6-2 Barrier Free Parking Spaces (Vans) ............................................................................... 6-4
Table 6-3 Seating Requirements.................................................................................................. 6-25
Table 7-1 Third Order Differential Leveling Requirements .............................................................. 7-2
Table 8-1 Functional System Characteristics ................................................................................. 8-1
Table 8-2 Minimum Level of Service Guidelines ............................................................................. 8-2
Table 8-3 General Definitions of Levels of Service ......................................................................... 8-2
Table 8-4 Design Vehicle Parameters (meters) .............................................................................. 8-3
Table 8-5 Design Speeds .............................................................................................................. 8-4
Table 8-6 Recommended Posted Speeds ...................................................................................... 8-4
Table 8-7 Minimum Design Speed for Connecting Roadways ........................................................ 8-5
Table 8-8 Stopping Sight Distances ............................................................................................... 8-6
Table 8-9 Passing Sight Distances................................................................................................. 8-7
Table 8-10 Decision Sight Distance ............................................................................................... 8-8
Table 8-11 Minimum Horizontal Curvature ................................................................................... 8-12
Table 8-12 Spiral Lengths for Minimum Radii at 6% Superelevation ............................................. 8-13
Table 8-13 Maximum Superelevation ........................................................................................... 8-15
Table 8-14 Maximum Relative Gradients ..................................................................................... 8-16
Table 8-15 Minimum Lane Width on Curves ................................................................................. 8-19
Table 8-16 Recommended Maximum Grades .............................................................................. 8-20
Table 8-17 Critical Grade Lengths ............................................................................................... 8-21
Table 8-18 Maximum Change in Grade without Vertical Curves ................................................... 8-21
Table 8-19 Design Controls for Crest and Sag Vertical Curves ..................................................... 8-25
AUGUST 2010
REVISION NO. 03
TAB-1
Table 8-20(a) Additional Clearance for Sag Curves ...................................................................... 8-27
Table 8-20(b) Recommended Roadway Section Widths Freeways/Expressways ......................... 8-28
Table 8-21(a) Arterials Minimum Lane and Shoulder Widths ........................................................ 8-28
Table 8-21(b) Minimum Median Widths for Certain Functions (m) ................................................ 8-30
Table 8-22 Typical Median Widths (m) ......................................................................................... 8-30
Table 8-23 Clear Zone Width (m) ................................................................................................. 8-32
Table 8-24 Horizontal Curve Adjustments .................................................................................... 8-33
Table 8-25 Speed Change Lane Adjustment Factors as a Function of Grade ............................... 8-55
Table 8-26 Design Speeds for Connecting Roadways.................................................................. 8-59
Table 8-27 Minimum Radii for Intersection Curves ....................................................................... 8-60
Table 8-28 Ramp Gradient Guidelines ......................................................................................... 8-61
Table 8-29 Service Volumes for Single-Lane Ramps ................................................................... 8-61
Table 8-30 Minimum Spacing between Successive Exits ............................................................. 8-62
Table 8-31 Minimum Spacing between Successive Entries .......................................................... 8-62
Table 8-32 Minimum Spacing between an Exit and an Entry ........................................................ 8-62
Table 8-33 Spacing Criteria for Entry/Exit .................................................................................... 8-63
Table 8-34 Summary of Geometric Parameters for Local Roads and Streets ............................... 8-73
Table 8-35 Summary of Geometric Parameters for Collectors ...................................................... 8-73
Table 8-36 Summary of Geometric Parameters for Arterials ......................................................... 8-74
Table 8-37 Summary of Geometric Parameters for Freeways/Expressways ................................. 8-74
Table 8-38 Curbside Angled Parking – Width Occupied ............................................................... 8-79
Table 8-39 Curbside Angled Parking Minimum Width................................................................... 8-79
Table 8-40 Parking Lot Dimensions (m) ....................................................................................... 8-81
Table 8-41 Selection Criteria for Roadside Barriers ...................................................................... 8-82
Table 8-42 Barrier Warrants for Non-Traversable Terrain and Roadside Obstacles ...................... 8-84
Table 8-43 Suggested Setback from Edge of Traveled Way......................................................... 8-86
Table 8-44 Clearance between Barrier and Object Being Protected ............................................. 8-87
Table 8-45 Minimum Intersection Spacing (Measured center-to-center) ....................................... 8-94
Table 8-46 Acceleration Rates for Passenger Vehicles .............................................................. 8-104
Table 8-47 Effect of Gradient on Accelerating Time (ta) at Intersections ..................................... 8-105
Table 8-48 Minimum Edge of Traveled Way Designs for Turns at Intersection............................ 8-106
Table 8-49 Cross Street Width Occupied by Turning Vehicle...................................................... 8-110
Table 8-50 Designs for Turning Roadways................................................................................. 8-116
Table 8-51 Minimum Designs for Turning Roadways.................................................................. 8-118
Table 8-52 Minimum Lengths of Spirals for Intersection Curves ................................................. 8-119
Table 8-53 Guide for Left-Turn Lanes on Two-Lane Highways ................................................... 8-123
Table 8-54 Minimum Design of Median Openings (SU Design Vehicle) ...................................... 8-130
Table 8-55 Minimum Design of Median Openings (WB-12 Design Vehicle) ................................ 8-130
Table 8-56 Effect of Skew on Minimum Design for Median Openings ......................................... 8-131
Table 8-57 Design Controls for Minimum Median Openings ....................................................... 8-133
Table 8-58 Recommended Maximum Entry Design Speeds ....................................................... 8-137
AUGUST 2010
REVISION NO. 03
TAB-2
Table 8-59 Recommended Inscribed Circle Diameters ............................................................... 8-140
Table 8-60 Minimum Width of Circulating Pavement .................................................................. 8-140
Table 8-61 Visibility at Roundabouts .......................................................................................... 8-149
Table 9-1 Equivalent 80 kN axle applications per 1000 trucks flexible pavements (ESAL) .............. 9-4
Table 9-2 Design Bearing Ratio Determination............................................................................... 9-7
Table 9-3 DBR Based on AASHTO Soils Classification .................................................................. 9-7
Table 9-4 Pavement Thickness .................................................................................................... 9-11
Table 9-5 Layer Coefficients for New and Reconstructed Pavements ........................................... 9-11
Table 9-6 Minimum Pavement Thickness (New and Reconstructed Flexible Pavements) ............. 9-12
Table 9-7 Layer Coefficients for Existing Pavements .................................................................... 9-14
Table 9-8 Reduction Factors for Existing Pavement ..................................................................... 9-14
Table 13-1 Changing Load Posting of an On-System Bridge ...................................................... 13-29
Table 13-2 Emergency Load Posting of an On-System Bridge ................................................... 13-29
Table 13-3(a) Off-System Closure Procedures ........................................................................... 13-30
Table 13-3(b) Comparison of Analyses for Example Bridge ........................................................ 13-36
Table 13-4 Functionally Obsolete ............................................................................................... 13-37
Table 13-5 Adjusted Inventory Tonnage..................................................................................... 13-38
Table 13-6 Load Posting Tables ................................................................................................ 13-48
Table 13-7 Load Posting Signage .............................................................................................. 13-49
AUGUST 2010
REVISION NO. 03
TAB-3
List of Figures
Figure 1-1 Typical Treatment Process Seawater Desalination ........................................................ 1-9
Figure 6-1 Barrier-Free Car Parking Spaces .................................................................................. 6-2
Figure 6-2 Symbols ....................................................................................................................... 6-3
Figure 6-3 Barrier-Free Van Parking Spaces.................................................................................. 6-4
Figure 6-4 Vertical Parking Sign..................................................................................................... 6-5
Figure 6-5 Overhead Hazards........................................................................................................ 6-6
Figure 6-6 Cane Detectable Obstructions ...................................................................................... 6-6
Figure 6-7 Edge Ramp Protection .................................................................................................. 6-7
Figure 6-8 Curb Ramps ................................................................................................................. 6-8
Figure 6-9 Vestibule Clearance ...................................................................................................... 6-9
Figure 6-10 Door Clear Width ........................................................................................................ 6-9
Figure 6-11 Cane Detectable Railing ........................................................................................... 6-10
Figure 6-12 Handrails .................................................................................................................. 6-12
Figure 6-13 Door Clearances ....................................................................................................... 6-14
Figure 6-14 Barrier-Free Showers................................................................................................ 6-17
Figure 6-15 Barrier-Free Bathtubs ............................................................................................... 6-19
Figure 6-16 Water Closet Details ................................................................................................. 6-20
Figure 6-17 Toilet Partition Details ............................................................................................... 6-20
Figure 6-18 Cantilevered Drinking Fountain ................................................................................. 6-21
Figure 6-19 Control Locations ...................................................................................................... 6-22
Figure 6-20 Signs ........................................................................................................................ 6-23
Figure 6-21 Detectable Warning Indicator Location ...................................................................... 6-23
Figure 6-22 Tactile Warnings Indicator Location........................................................................... 6-24
Figure 6-23 Tactile Warnings & Detectable Warning Indicator ...................................................... 6-24
Figure 6-24 Wheel Chair Viewing Space ...................................................................................... 6-25
Figure 6-25 Washers & Dryers..................................................................................................... 6-27
Figure 6-26 Kitchen Layouts ........................................................................................................ 6-27
Figure 6-27 Elevator Clearances.................................................................................................. 6-28
Figure 8-1 Visibility Envelope for Stopping Sight Distance .............................................................. 8-6
Figure 8-2 Simple Curve ................................................................................................................ 8-9
Figure 8-3 Compound Curve........................................................................................................ 8-10
Figure 8-4 Compound Curve Transition ....................................................................................... 8-11
Figure 8-5 Typical Spiral Transition Curve.................................................................................... 8-13
Figure 8-6 Components for Determining Horizontal Sight Distance .............................................. 8-14
Figure 8-7 Development of Superelevation .................................................................................. 8-17
Figure 8-8 Highway with Paved Shoulders ................................................................................... 8-19
Figure 8-9(a) Parabolic Vertical Curves........................................................................................ 8-22
Figure 8-9(b) Parabolic Vertical Curves........................................................................................ 8-23
Figure 8-9(c) Parabolic Vertical Curves ........................................................................................ 8-24
Figure 8-10(a) Summary of Undesirable Alignment Combinations ................................................ 8-26
AUGUST 2010
REVISION NO. 03
FIG-1
Figure 8-10(b) Summary of Desirable Alignment Combinations.................................................... 8-27
Figure 8-11 Typical Ditch Section ................................................................................................ 8-32
Figure 8-12(a) Example of parallel fill slope design ...................................................................... 8-34
Figure 8-12(b) Three-Leg Interchanges........................................................................................ 8-37
Figure 8-13 Typical Diamond Interchange (Schematic) ................................................................ 8-38
Figure 8-14 Full Cloverleafs ......................................................................................................... 8-39
Figure 8-15 Partial Cloverleaf Arrangements................................................................................ 8-40
Figure 8-16 Grade-separated Roundabout ................................................................................... 8-41
Figure 8-17 Coordination of Lane Balance and Basic Number of Lanes ....................................... 8-43
Figure 8-18 Alternatives in Dropping Auxiliary Lanes ................................................................... 8-44
Figure 8-19 Taper Type Exit Ramp (1-Lane) ................................................................................ 8-45
Figure 8-20 Parallel Type Exit Ramp (1-Lane).............................................................................. 8-46
Figure 8-21 Taper Type Exit Ramp (2-Lane with Lane Drop) ........................................................ 8-47
Figure 8-22 Parallel Type Exit Ramp (2-Lane without Lane Drop) ................................................ 8-48
Figure 8-23 Minimum Deceleration Lengths for Exit Terminals with Grades of 2% or Less ........... 8-49
Figure 8-24 Taper Type Entrance Ramp (1-Lane) ........................................................................ 8-50
Figure 8-25 Parallel Type Entrance Ramp (1-Lane) ..................................................................... 8-51
Figure 8-26 Taper Type Entrance Ramp (2-Lane with Lane Gain) ................................................ 8-52
Figure 8-27 Parallel Type Entrance Ramp (2-Lane with Lane Gain) ............................................. 8-53
Figure 8-28 Minimum Acceleration Lengths for Entrance Terminals With Grades of 2% or Less ... 8-54
Figure 8-29 Weaving Sections ..................................................................................................... 8-56
Figure 8-30 Capacity of Ramp Configurations .............................................................................. 8-57
Figure 8-31 Major Forks............................................................................................................... 8-58
Figure 8-32 Branch Connections.................................................................................................. 8-58
Figure 8-33 Freeway Exit at Interchange...................................................................................... 8-64
Figure 8-34 Freeway Exit at Interchange (From Inner Loop Cloverleaf Type Ramp) ..................... 8-65
Figure 8-35 Freeway Exit at Diamond Interchange ....................................................................... 8-66
Figure 8-36 Freeway Entrance at Interchange (from outer) .......................................................... 8-67
Figure 8-37 Freeway Entrance at Interchange (from Inner) .......................................................... 8-68
Figure 8-38 Freeway Entrance at Interchange (Diamond Type Ramps) ........................................ 8-69
Figure 8-39 Freeway Entrance – Exit at Interchange .................................................................... 8-70
Figure 8-40 Exit at Interchange .................................................................................................... 8-71
Figure 8-41 Diamond Ramps (Minor Roadway Exits and Entrances) ............................................ 8-72
Figure 8-42 Handicap Ramp with Landing Area ........................................................................... 8-76
Figure 8-43 Preferred Bus Bay Layout ......................................................................................... 8-77
Figure 8-44 Bus Stops at Intersections......................................................................................... 8-78
Figure 8-45 Parking Lot Laid-out with a 90-Degree Angle............................................................. 8-80
Figure 8-46 Parking Bay Dimensions ........................................................................................... 8-80
Figure 8-47 Comparative Risk Warrants for Embankments .......................................................... 8-84
Figure 8-48 Barrier Length of Need.............................................................................................. 8-88
Figure 8-49 Impact Attenuator Protection to Obstruction Located in the Gore Area....................... 8-90
AUGUST 2010
REVISION NO. 03
FIG-2
Figure 8-50(a) Traffic Calming Layout Using Planted Median ........................................................ 8-92
Figure 8-50(b) Traffic Calming Layout Using Pinch Point .............................................................. 8-92
Figure 8-51 Sight Distance at Intersections Minimum Sight Triangle............................................. 8-99
Figure 8-52 Sight Distance at Intersections ................................................................................ 8-100
Figure 8-53 Sight Distance at Intersections, Case III .................................................................. 8-101
Figure 8-54 Intersection Sight Distance at At-Grade Intersections .............................................. 8-102
Figure 8-55 Intersection Sight Distances .................................................................................... 8-103
Figure 8-56 Sight Distance at Skewed Intersections................................................................... 8-104
Figure 8-57 Minimum Designs for Simple Curves ....................................................................... 8-111
Figure 8-58 Detailed Layout of Simple Curve Radius, Taper Offset (90 Degree)......................... 8-112
Figure 8-59 Detailed Layout of Simple Curve Radius, Taper Offset ( ‹ 90 Degrees) .................... 8-113
Figure 8-60 Detailed Layout of Simple Curve Radius, Taper Offset ( › 90 Degrees) .................... 8-114
Figure 8-61 Effect of Curb Radii on Turning Paths ..................................................................... 8-115
Figure 8-62 Typical Design for Turning Roadway ....................................................................... 8-117
Figure 8-63 Designs for Turning Roadways with Minimum Corner Islands .................................. 8-120
Figure 8-64 Right-Turn Warrants at Unsignalized Intersections on 2-Lane Highways ................. 8-121
Figure 8-65 Typical Right and Left Turn Lanes on Divided Highway ........................................... 8-124
Figure 8-66 Typical Left-Turn Lane on an Undivided Highway .................................................... 8-125
Figure 8-67 By-Pass Lane in Highly Developed Areas ............................................................... 8-125
Figure 8-68 Minimum Design of Median Openings (SU Design Vehicle) ..................................... 8-128
Figure 8-69 Minimum Design of Median Openings (WB-12 Design Vehicle) ............................... 8-129
Figure 8-70 Deflection of Entering Traffic ................................................................................... 8-134
Figure 8-71 Typical Roundabout Design .................................................................................... 8-135
Figure 8-72 Basic Geometric Elements of a Roundabout ........................................................... 8-135
Figure 8-73 Sample Theoretical Speed Profile (Urban Compact Roundabout) ............................ 8-136
Figure 8-74 Fastest Vehicle Path through Single-lane Roundabout ............................................ 8-137
Figure 8-75 Fastest Vehicle Path through Double-lane Roundabout ........................................... 8-138
Figure 8-76 Example of Critical Right-turn Movement................................................................. 8-138
Figure 8-77 Design Vehicle with the Use of an Apron................................................................. 8-139
Figure 8-78 Approach Widening by Adding Full Lane ................................................................. 8-142
Figure 8-79 Approach Widening by Entry Flaring ....................................................................... 8-142
Figure 8-80 Typical Roundabout Entrance Geometry ................................................................. 8-143
Figure 8-81 Vehicle Path Radii .................................................................................................. 8-144
Figure 8-82 Typical Roundabout Exit Geometry ......................................................................... 8-144
Figure 8-83 Sample Plan View ................................................................................................... 8-145
Figure 8-84 Sample Approach Profile ........................................................................................ 8-146
Figure 8-85 Sample Central Island Profile .................................................................................. 8-146
Figure 8-86 Typical Circulatory Roadway Section ...................................................................... 8-147
Figure 8-87 Typical Section with a Truck Apron ......................................................................... 8-147
Figure 8-88 Stopping Sight Distance on Approach to Roundabout ............................................. 8-148
Figure 8-89 Visibility to the Left from the “Give Way” Line .......................................................... 8-149
AUGUST 2010
REVISION NO. 03
FIG-3
Figure 8-90 Visibility to the Left over the 15m before the Give Way Line..................................... 8-150
Figure 8-91 Shoulder Run-out on an Undivided Road ................................................................ 8-150
Figure 8-92 Shoulder Run-out on a Divided Road ...................................................................... 8-151
Figure 9-1 Pavement Courses for Flexible Pavement Structure...................................................... 9-3
Figure 9-2 30% Design Activities ................................................................................................... 9-5
Figure 9-3 DBR vs. SSV ................................................................................................................ 9-9
Figure 9-4 Structural Number (SN) Nomograph (For Flexible Pavement P = 2.5) ......................... 9-10
Figure 10-1 Network Traffic Management Program ...................................................................... 10-2
Figure 10-2 Component Parts of a Temporary Traffic Control Zone .............................................. 10-7
Figure 11-1 Use of Raised Beds .................................................................................................. 11-2
Figure 11-2 Use of Colorful Flowers ............................................................................................. 11-3
Figure 11-3 Tree Grate in Paved Area ......................................................................................... 11-3
Figure 11-4(a) Landscaping around the home (1)......................................................................... 11-5
Figure 11-4(b) Landscaping around the home (2)......................................................................... 11-5
Figure 11-5 Shrub and Tree Planting Details (1) .......................................................................... 11-8
Figure 11-6 Shrub and Tree Planting Details (2) .......................................................................... 11-8
Figure 11-7 Planting Details – Tree on Pavement ........................................................................ 11-9
Figure 11-8 Hedge Planting Detail ............................................................................................... 11-9
Figure 11-9 Planting Details – Palm on Pavement...................................................................... 11-10
Figure 13-1 AASHTO Design Loads .......................................................................................... 13-20
Figure 13-2 Load Ratings for Concrete Bridges without Plans .................................................... 13-24
Figure 13-3 On-System Load Posting Guidelines ....................................................................... 13-26
Figure 13-4 Off-System Load Posting Guidelines ....................................................................... 13-27
Figure 13-5 Typical Load Posting Signs ..................................................................................... 13-28
Figure 13-6 Typical I-Beam Bridge Elevation and Cross-Section ................................................ 13-34
AUGUST 2010
REVISION NO. 03
FIG-4
Revision Tracking
Revision No.:
Description
Date
Revision No. 00
DRAFT Version
01-July-08
Revision No. 01
Working Copy
21-Aug-08
Revision No. 02
Working Copy
June 2009
Revision No. 03
Working Copy
Nov. 2010
Summary of Changes to Revision 02 in Revision 03
This section describes changes to the Revision 02 of this document incorporated in Revision 03. All
sections have had formatting modifications. For clarity and ease of use, formatting and minor
typographical changes are not included in this description.
Introduction
Designs shall be in accordance with the following guidelines and all other applicable criteria.
Section 1
General: Electrical, instrumentation, control and automation criteria have been deleted from this
section and described in Section 14. The tables have been moved to the end of the section as
attachments for ease of reference.
Table 1-2 (Attachment 1-2): A minimum slope of 0.2% is required of transport lines.
Section 1.3.3, Elevated Water Tanks: Equations are clarified.
Section 1.3.4, Suction Pipes: Design velocity v
2.5 m/s.
Section 1.3.4, Pumps: Fittings include an electromagnetic flowmeter.
Section 1.3.5, Distribution Water Lines, Valves: Valve installation and types of valves for different
water line diameters is updated.
Section 1.5.1: Plant process basins, walkways, and stairways shall be equipped with a railing system
designed with two rails, not three.
Section 1.5.1: This section now refers to surface water under the influence of groundwater and
requires secondary disinfection at all treatment plants.
Section 1.5.1 no. 3: Treatment processes are to be designed for N+1 redundancy.
Sections 1.5.1 no. 17 and 18: Deleted.
Section 1.6: Section on structural design requirements for water and wastewater systems added.
Table 1-7 (Attachment 1-7):
Number of units for Rapid Mix and Flocculation is 2 minimum.
-1
Velocity gradient, G, = 600-1000 secs .
Separate pH level requirements specified for calcium and magnesium hardness.
AUGUST 2010
REVISION NO. 03
REV-1
“Plain” Sedimentation Basins renamed “Conventional” Sedimentation Basins.
Tube or plate settler application rate shall be < 4.8 m/hr for total sedimentation basin surface
area.
Section 2
General: Electrical, instrumentation, control and automation criteria have been deleted from this
section and described in Section 14. Several tables have been moved to the end of the section as
attachments for ease of reference.
Section 2.1.6: Material requirements for less than or more than 315 mm pipe size changed to less
than or more than 800 mm pipe size.
Table 2-8 (Attachment 2-3): Maximum spacing between manholes changed to 50 m for pipes less
than 600 mm in diameter. Materials of construction for manhole access shaft and barrel shall be
reinforced concrete.
Section 2.1.9, Manholes: Requirements for location of manholes modified.
Section 2.2: Add requirement for stainless steel components for metal submerged in or in intermittent
contact with raw sewage.
Section 2.2.1: Pump control shall be by ultrasonic level control.
Section 2.2.1.1: Formula corrected from V = CT x Q/4 to V = CT x Q/2.
Section 2.2.2 no. 3: Change “high” to “low.”
Section 2.2.2 no. 4: Delete “POR and AOR.”
Section 2.2.2 no. 5: Deleted.
Section 2.2.2: Pump configuration requirement modified from lead/lag to duty-standby with assist
pumps as needed.
Section 2.2.3 no. 7: Deleted.
Section 2.2.5: Wet-well level controls described. Other electrical and control information deleted.
Section 2.2.7: New section on Gas Monitoring requirements provided.
Section 2.2.10 no. 3: Plant process basins, walkways, and stairways shall be equipped with a railing
system designed with two rails, not three.
Section 2.2.10: Delete nos. 5, 6, and 7.
Section 2.3: Structural design requirements added.
Section 3
General: Electrical, instrumentation, control and automation criteria have been deleted from this
section and described in Section 14. Several tables have been moved to the end of the section as
attachments for ease of reference.
Section 3.1: Delete nos. 5 and 6.
Section 3.1 no. 7: Delete the first words “Electrical and.” Replace requirement for SRT of 30 days
with requirement of 37 days.
Section 3.1: Add no. 15 regarding requirement for stainless steel components and renumber
following items.
Section 3.2: Add “Aerobic digesters, 2 minimum’ to required number of process units for treatment
plants.
Section 3.2: Delete nos. 1 and 2.
Section 3.4.3 no. 2: Change SRT requirement of 30 days to 20 days.
Tables 3-4 through 3-12 (Attachments 3-1 through 3-9): Vendor names replaced with equipment
types.
Table 3-4 (Attachment 3-1):
Requirement for waste container with 5-day storage capacity added to Coarse Bar Screens,
Fine Screening, and Aerated Grit Chambers.Aerated grit chamber aeration rates updated.
AUGUST 2010
REVISION NO. 03
REV-2
Primary Clarifier weir plates shall be adjustable.
Minimum freeboard requirement of 0.5 m added to Primary Clarifiers, Aeration Basins,
Secondary Clarifiers, and Aerobic Digesters
Aeration Basin (CAS, EA, OD) design HRT updated and minimum sidewater depth added.
Secondary Clarifier surface overflow rates, solids loading rates, and weir loading rates
updated.
Disinfection enclosure requirements updated.
Supplemental disinfection tank size updated.
Table 3-5 (Attachment 3-2):
Return Activated Sludge Pump and Waste Activated Pump allowable pumps updated.
Waste Activated Sludge Pump design flow updated to 5% of ADF.
Secondary Sludge Thickening System Design Flow description updated.
Aerobic Digesters (EA and OD Systems) with design solids retention time less than 30 days
Design SRT updated and Decanting requirement modified.
Table 3-7 (Attachment 3-4): Sludge and scum system piping changed to cement-mortar lined ductile
iron.
Tables 3-10 and 3-11 (Attachments 3-7 and 3-8): Excavation and embankment slope requirements
changed to 3:1.
Table 3-11 (Attachment 3-8): Anaerobic Lagoon followed by Stabilization Ponds (SP) and Maturation
Ponds approximate site area requirement changed to 15 ha.
Table 3-12 (Attachment 3-9): Tertiary Wetlands requirements updated.
Section 3.5: Structural design requirements added.
Section 4
General: Electrical, instrumentation, control and automation criteria have been deleted from this
section and described in Section 14.
Section 4.3.1 Table 4-4: Gravity pipe minimum velocity requirement increased.
Section 4.4 Table 4-6: Minimum pipe diameter updated for uPVC and HDPE.
Section 5
General: Electrical, instrumentation, control and automation criteria have been deleted from this
section and described in Section 14. Requirements for SCADA system deleted.
Section 5.2.1: Irrigation Demands subsection rewritten to clarify determination of irrigation demands.
Section 5.2.2.8: Requirement for control valve changed from motorized to actuated.
Section 5.2.5.1: Design considerations for irrigation pumping system: added “Net Positive Suction
Head Available (NPSHA)” and “Power required for pump drive.”
Section 5.2.6: Added requirement for appropriate identification of recycled water fire hydrants.
Section 6
This section had no significant changes.
Section 7
General: Clarifications of terms added throughout.
Section 7.2.3: Requirements for Coordinate Adjustment updated and reference added to Survey
Department of Libya (SDL).
Section 7.3.1: Clarifications and Table 7-1 added regarding third-order leveling.
Section 7.3.2: Reference to SDL added.
Section 7.3.3: Definition of benchmark added.
Section 7.4.1: Clarifications and requirements for spot elevations for contours added.
Section 7.4.3: Clarifications of methodology added.
Section 7.4.9: Recommendation for calibration of instruments and clarification of two-peg test added.
AUGUST 2010
REVISION NO. 03
REV-3
Section 7.6.2: Requirements for as-builts modified.
Attachment 7-A renamed Attachment 7-1.
Attachment 7-2, Survey Report Guidelines: Added.
Attachment 7-3, Tolerances for Conventional Traverse for 2nd and 3rd Order: Added.
Section 8
General: Reference made to AASHTO – A Policy on Geometric Design of Highways and Streets
as supplemental to this document.
Section 8.7.11 Table 8.7.4: “Clear Zone Width” revised with updated footnotes.
Section 8.7.11 Table 8.7.5: “Horizontal Curve Adjustments” and Figure 8.7.2 added.
Section 8.9 Summary of Design Parameters: Typical sections shown for each roadway classification
have been deleted.
Section 8.10.1.4 Pedestrian Overpasses: This section has been modified.
Section 8.10.3.4: Figure 8-46 Comparative Risk Warrants for Embankments added.
Section 8.10.4.2: Table 8-42 Barrier Warrants for Non-traversable Terrain and Roadside Obstacles
added.
Section 8.10.4.2 Roadside Obstacles: This section has been modified.
Section 8.10.5 Impact Attenuator Systems: Delineation paragraph added.
Section 9
General: Reference made to AASHTO – A Policy on Geometric Design of Highways and Streets
as supplemental to this document.
Section replaced in its entirety to accommodate local conditions.
Section 10
This section had no significant changes.
Section 11
General: Clarifications of terms added throughout.
Section 11: Delete “the use of qualified designers, engineers, technicians, and other specialists is
required as standard.”
Section 11.1.1 Grassy areas item c: Add “and put in place management and maintenance schemes.”
Section 11.1.1 Turf areas: Delete item f.
Section 11.1.2 item j: Add “Permitted plants for use in hedge fences are provided in species list in this
section.”
Section 11.3.2 Tree and Plant Maintenance has been added, including a suggested plant species list.
Section 12
This section had no significant changes.
Section 13
This section had no significant changes.
Section 14
This section previously consisted of one paragraph referencing GECOL standards. The section has
been replaced with detailed electrical, instrumentation, control and automation criteria.
Section 15
This section had no significant changes.
Section 16
This section had no significant changes.
AUGUST 2010
REVISION NO. 03
REV-4
Section 17
This section is new.
AUGUST 2010
REVISION NO. 03
REV-5
Acronyms and Abbreviations
2WLTL
Two-Way Left-Turn Lane
ADT
Average Daily Traffic
AL
Aerated Lagoon
ANSI
American National Standards Institute
AOR
Actual Oxygenation Rate
ATEX
‘Atmosphere Explosives’ regulations
AWWA
American Water Works Association
BOD5
Biochemical Oxygen Demand (5-day)
CAS
Conventional Activated Sludge
CBD
Central Business District
C-D
Collector-Distributor
CE
Certificate European
CIE
The International Commission on Illumination
cm
Centimeter(s)
COD
Chemical Oxygen Demand
Cs
Carbon steel
CT
Contact Time
D
nominal pipe Diameter
D
Depth
DHV
Design Hourly Volume
DIN
German Institute for Standardisation
DIP
Ductile Iron Pipe
DO
Dissolved Oxygen
DSEAR
Dangerous Substances and Explosive Atmosphere Regulations
EA
Extended Aeration
EN
European Norm (standards)
E. coli
Escherichia coli
EWT
Elevated Water Tank
FAA
Federal Aviation Administration
FDS
Functional Design Specification
FOG
Fats Oils and Greases
FRP
Fiberglass Reinforced Plastic
AUGUST 2010
REVISION NO. 03
AA-1
Fs
side Friction factor
GECOL
General Electric Company of Libya
GLT
Ground Level Tanks
GMR
Great Man-made River
GPRS
General Packet Radio Service
GPS
Global Positioning System
GRP
Glass Fiber Reinforced Plastic
GSM
Global System for Mobile Communications
GWA
General Water Authority
H
Height
HDPE
High Density Polyethylene
HI
Hydraulic Institute
HIB
Housing and Infrastructure Board
HMI
Human Machine Interface
HRT
Hydraulic Retention Time
ICD
Inscribed Circle Diameter
IEC
International Electrotechnical Commission
ISO
International Standards Organization
kVA
kiloVolt Ampere
kW
kiloWatt
LAN
Local Area Network
l/d/c
liters per day per capita
LED
Light Emitting Diode
LV
Low Voltage
km/h
kilometers per hour
m
meters
m3
cubic meters
MCB
Miniature Circuit Breaker
MCC
Motor Control Centre
MCCB
Moulded Case Circuit Breaker
MCL
Maximum Contaminant Level
MET
Main Earth Terminal
mg/l
milligrams per liter
AUGUST 2010
REVISION NO. 03
AA-2
ml
Milliliters
MLSS
Mix Liquor Suspended Solids
mm
millimeters
MPN
Most Probable Number
NH3
Ammonia
NPSHR
Net Positive Suction Head Required
NTU
Nephelometric Turbidity Unit
OCM
Open Channel Measurement
OD
Oxidation Ditch
pc/h
passenger cars per hour
PCC
Point of Compound Curvature, Point of Common Contact
PF
Peaking Factor
PLC
Programmable Logic Controller
PRD
Perception/Reaction Distance
PSC
Point of Spiral to Curve
PSCC
Prospective Short Circuit Current
PSD
Passing Sight Distance
PT
Point of Tangency
PVC
Polyvinyl Chloride
Q
Flow
RAS
Return Activated Sludge
RCP
Reinforced Concrete Pipe
ROW
Right-Of-Way
rpm
revolutions per minute
RSR
Rapid Sludge Return
RTD
Resistance Temperature Detector
RTU
Remote Terminal Unit
SCADA
Supervisory Control And Data Acquisition
SOR
Standard Oxygenation Rate
SRT
Solids Retention Time
SSD
Stopping Sight Distance
STP
Sewage Treatment Plant
TDS
Total Dissolved Solids
AUGUST 2010
REVISION NO. 03
AA-3
TKN
Total Kjeldahl Nitrogen
TN
Total Nitrogen
TP
Total Phosphorus
TSE
treated sewage effluent
TSS
Total Suspended Solids
UI
longitudinal uniformity ratio
UPS
Uninterruptible Power Supply
uPVC
unplasticised Polyvinyl Chloride
USEPA
United States Environmental Protection Agency
VA
Variable Area Flowmeter
VCP
Vitrified Clay Pipe
WAS
Waste Activated Sludge
WEF
Water Environment Federation
WRP
Water Reuse Plant
WSP
Welded Steel Pipe
AUGUST 2010
REVISION NO. 03
AA-4
Introduction
This Design Criteria for Infrastructure presents design criteria for water, sewage, storm water, barrierfree, surveying, roadways, pavement design, uniform traffic control devices, landscape, bridge
inspection, electrical, telecommunication and gas systems. The criteria presented in the following
sections are provided as the basis for all infrastructure designs prepared for the Libya Housing and
Infrastructure Board (HIB).
These design criteria are presented to support the design intent of the HIB infrastructure planning.
Designs shall be in accordance with the following guidelines and with all other applicable criteria.
These design criteria should be implemented in conjunction with the Housing and Infrastructure
Master Specifications and Standard Details and the Design Criteria for Housing Projects. The
geotechnical design criteria for treatment plants and pump stations shall be in accordance with the
Section 5.6 of the Design Criteria for Housing Projects.
AUGUST 2010
REVISION NO. 03
INTRO-1
1
Water Design Standards
1.1 Objectives
The objective of the Libya Housing and Infrastructure Board (HIB) water supply system is to provide
safe, potable, adequate, reliable, efficient, and effective water supply facilities. Water service is to be
provided in an economically and environmentally sustainable manner in terms of both water treatment
and water distribution. The objective of the water treatment is to produce and maintain finished water
quality that is hygienically safe and aesthetically pleasing, in an economic manner while complying
with water quality standards provided by the World Health Organization (WHO) and/or the United
States Environmental Protection Agency (USEPA). The evaluation of water quality should not be
limited to the treatment facilities, but should extend the distribution system to the point of consumer
consumption. The distribution system should maintain adequate pressure and safe water quality,
while meeting fire protection needs.
Specific goals of the HIB are:
1.
Land distribution delivery systems with sufficient capacity to supply current and future
water demands;
2.
Provide adequate and reliable water distribution facilities (supply mains, pump
stations, service reservoirs, transmission, and distribution systems) that meet peak
hour demands and sustained periods of high demand while maintaining adequate
delivery pressures and water quality.
3.
Provide a level of fire fighting capability adequate in relation to the recommendations
defined in this document;
4.
Maintain a safe, potable, adequate, and reliable water supply for consumers.
The water system design must be compatible with the overall community master development plan.
The system layout shall be designed for, and take into account, water quality, pressure, flow rate, and
long-term planning. Hydraulic calculations performed by the designer shall be submitted to HIB for
review and approval in support of the design.
1.1.2
Operation and Maintenance Aspects
Water supply systems should be designed with consideration of the system’s current and future
operation and maintenance requirements. The result will be a system that can be easily and
economically operated and maintained using standard techniques and equipment essential for the
reliability of the water system.
1.2 Potable Water Demand
Water demand determination is the starting point for the design of water supply systems. Water
demand is typically based on population data and population growth projections, combined with
established values of the water demand per capita along with the specific needs of large water users.
The water demand per capita is usually based on historical data and is typically dependent on the
size of the community. Smaller community water use is predominantly residential, while larger
community water use can include significant requirements for commercial and industrial water
demand. For smaller communities with significant commercial or industrial components, special
consideration should be given to the commercial and industrial water needs.
Other factors in water demand calculations for facilities design are the seasonal and daily variations in
demand with particular emphasis on maximum daily demand, maximum hourly demand, and fire
fighting demand.
Water systems are typically designed to serve both the current and the projected population for 20 to
25 years in the future. To limit the immediate capital costs, designs are usually prepared for phased
implementation, with system upgrades added as the demand increases over time.
The Criteria for Establishing Water Demand is included as Attachment 1-1.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-1
1.3
Water Transport and Distribution System
1.3.1
Reservoir Design
This section addresses reservoir sizing of Ground Level Tanks (GLT) and Elevated Water Tanks
(EWT). Values from the water demand projections, as previously addressed, shall be used to
calculate the design capacity of the GLT and EWT.
1.3.2
Ground Level Tanks
Ground Level Tanks shall be designed to handle storage volume for the maximum day demand. The
volume shall be calculated using the differences between the cumulative curves of constant pumping
and hourly consumption during a maximum day. Fire fighting volume shall also be added to this
calculated amount and calculated volumes shall be based on the following equation:
V = ((Qmaxd – Qp) + 80% of fire fight demand)*4 hours (assume two fires for 2 hours duration
each)
Where:
3
V
is the Volume (m )
Qmaxd
is the maximum daily demand (m /d)
Qp
is the constant water supply pumping rate (m /d)
3
3
When GLT is filled from a water treatment plant, Qp would be the average treatment capacity of the
plant. When the GLT is filled from groundwater wells, Qp would be the well output with the largest
well out of service. When the supply of water to fill the tank is intermittent, then Qp should be
considered to be zero. Tanks filled directly from the distribution system, either from a different
pressure zone or via a pressure reduction valve should consider Qp to be zero. These types of tanks
should be filled in four hours or less during the night or early morning hours when other demands are
low.
The minimum storage capacity for systems not providing fire protection shall be equal to the average
daily consumption. This requirement may be reduced when the source and treatment facilities have
sufficient capacity with standby power to supplement peak demands of the system. Ground level
storage tanks are generally used for storage only and not for setting hydraulic gradients in the system.
These types of tanks serve as wet wells for booster pumps that serve the customers in a service area.
If an existing reservoir is in good condition and able to handle the proposed design storage
requirements, a new reservoir shall not be required.
In addition, the residence time and internal mixing in tanks must be considered to avoid dead zones
where stagnation may occur and to provide a sufficient turnover rate of the tank’s contents. In
general, the tank’s contents should be replenished at least once every 3 days. Where possible,
separate inlet and outlet pipes should be provided for all tanks.
1.3.3
Elevated Water Tanks
EWT shall be designed to provide storage for 35% of maximum day demand. The volume shall be
calculated using the differences between the cumulative curves of constant pumping and hourly
consumption during a maximum day. Fire fighting volume shall also be added to this calculated
amount. The greater of the two calculated volumes shall be used based on the following equations:
V = ((Qmaxh – Qmaxd) + 20% of fire fight demand)*4 hours, or
V = ((Qmaxh – Qp) + 20% of fire fight demand)*4 hours
Where:
V
is the Volume (m3)
Qmaxd
is the maximum daily demand (m /h)
Qmaxh
is the maximum hourly demand (m3/h)
Qp
is the constant water supply pumping rate (m /h)
3
3
Elevated water tanks shall be designed similar to ground storage tanks and are intended to minimize
the unusable storage below the minimum acceptable level. The height (h) of the EWT shall be
designed to meet the water distribution system pressure requirements, as determined by the hydraulic
modeling of the system. In absence of modeling, the following criteria may be used. The minimum
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-2
level in the tank is based on providing a minimum pressure in the distribution system in accordance
with the following:
Normal demands based on providing a minimum pressure equal to 25 m at the highest ground
elevation within the service area of the tank
Fire fighting demands based on providing a minimum pressure equal to 15 m at the highest ground
elevation within the service area of the tank
Volumes in the tank below the minimum level for firefighting are considered emergency reserves and
may require temporary pumping to be delivered. In cases where sufficiently high ground levels are
available, a ground storage tank may be used. In general, elevated tanks may be used in conjunction
with supply pumps that can provide more than 65 percent of the demand in the tank’s service area.
1.3.4
Transport Water Lines
Transport water lines are intended to deliver water from the main supply source to storage reservoirs
and distribution networks. These lines are not intended to distribute water directly to service
connections. Delivery pressures shall be maintained by pressure sustaining valves at ground
reservoirs and by the hydrostatic head at elevated water tanks.
Network Analyses
Network analyses of the water system shall be performed to ensure that an adequate and safe water
supply is available to all consumers connected to the system for all defined modes of operation.
The Transport Water Line Design Parameters are included as Attachment 1-2.
Fittings
The following fittings shall be included along the water transport lines for facilitating the operation,
control, and maintenance:
1.
Air release, Air/Vacuum, Combination Air and Vacuum relief Valves: Air release and
vacuum relief valves are often needed along transmission mains. Air release valves
shall be provided at summits along the pipe profile and along long stretches with
uniform slope to purge out accumulated air in the pipe system. Air must be bled
slowly from high points to prevent (1) “air binding” and (2) the reduction of the cross
section of the pipe at high points. Combination air release valves are used to vent
large quantities of air from the pipeline when the pipe in being filled as well as
releasing the small quantities of accumulated air during normal operations.
Air/vacuum valves are used to prevent excessively low pressures when the pump
head drops quickly (as in power failures) to prevent column separation and at
extreme high points in pipelines to prevent potential pipeline collapse due to vacuum.
Vacuum relief valves can be as large as one-sixth of the diameter of the transmission
main, whereas air release valves may be as small as one-fiftieth of the diameter of
the pipe. The selection of the sizes of these valves shall be in accordance with
AWWA’s Manual of Water Supply Practice M51 Air-Release, Air/Vacuum &
Combination Air Valves.
2.
A combination of air and vacuum valves shall be provided at appropriate locations for
quick air entry or vent to prevent cavitations and facilitate quick filling of the pipe. In
general, air-valves are to be installed at crest points, change in elevations and in case
of constant rising mains having moderate slope, at a maximum spacing of 500 m to
750 m.
3.
Washout valves: These valves will be provided at low points or sags along the pipe
profile. These valves facilitate flushing, repair or maintenance of the pipe wherever
necessary. In cases where the static head on these valves exceeds 15m, proper
energy dissipation devices and erosion control shall be provided.
4.
Isolating valves: The location of these valves shall consider the profile of the pipeline
and the location of washout and air valves. Isolating valves shall be provided at a
maximum distance of every 2 to 3 kilometers.
5.
Isolating Valves with diameter smaller than 300 mm shall be gate valves and larger
diameter shall be butterfly valves.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-3
6.
Non-Return Valves (Check Valves): These valves will be provided in the pump station
to prevent a reverse flow into the pumps and shall be of noiseless non-slam type.
7.
Tapping Sleeves and tees: These fittings are used to add branches for the pipe line.
In general, tapping sleeves shall not be used where the branch size is greater than or
equal to one half of the main pipe diameter. In such cases, standard tees should be
used.
The pressure ratings of all fittings shall equal or exceed the maximum design pressure requirement
for the pipeline.
All transport line valves not located in a pump station structure shall be installed inside reinforced
concrete valve chambers.
Suction Pipes
Suction pipe diameters shall be sized with due regard for the pumping net positive suction head
requirement (NPSHR), and shall generally provide for a flow velocity, v 2.5 m/s.
Pumps
Pump capacity shall be designed to meet the required water demand, Q, and total dynamic head, H.
Elevated water tanks provide a buffer for constant speed pumps. For distribution systems without an
elevated water tank, a variable running speed drive is required to allow the pumping rate to maintain a
constant discharge pressure as the system demands are provided.
The following fittings shall be provided with each pump:
1.
Isolation valves (one provided upstream and downstream of each pump to protect
pumps and all associated fittings)
2.
Non-return valve or a hydraulically actuated control valve designed to close more
slowly than a non-return valve. If a hydraulically actuated control valve is used, a
special hydraulic transient analysis must be performed to demonstrate that excessive
surge pressures will be controlled. These valve shall be placed directly downstream
of the pumps
3.
Electromagnetic flow meter (downstream of pump)
4.
Pressure gage (downstream of pump)
5.
Sampling tap (downstream of pump)
6.
Air valve on discharge pressure main (downstream of pump)
Reliability
For reliability, provide installed spares for all rotating equipment shall be provided to provide N+1
reliability (duplicate of largest pump). All equipment shall be supplied with the manufacturer’s
recommended spare parts.
1.3.5
Distribution Water Lines
Distribution water lines shall provide service to commercial and residential developments. Distribution
lines, sized according to calculated demand, are divided into three categories: Main Lines,
Secondary Lines, and Laterals.
Distribution Lines Network Analyses
Network analyses of the water system shall be performed to ensure that an adequate and safe water
supply is available to all consumers connected to the system for all defined modes of operation. The
system shall be in designed in accordance with the hydraulic design parameters listed in
The Distribution Line Water Parameters are included as Attachment 1-3.
Alignment
For distribution systems downstream of reservoirs, a ‘looped’ rather than ‘branched’ layout should be
used to provide more than one supply route on distribution systems wherever possible. The valve
arrangement shall be designed to limit the area needing to be shut down when isolating and repairing
any section of water line is necessary.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-4
Deviation of a pipeline around an obstruction can be achieved by deflection at pipe joints or in
combination with bends or connectors. The deflection angle permitted at a flexible joint shall be in
accordance with the pipe manufacturer’s recommendation. For laying plastic pipes on curves,
minimum radii are to be as per pipe manufacturer’s recommendations. If deflection of joints does not
provide the necessary deviation, bends and other fittings shall be used.
Pipe Cover and Placement
The pipe cover depth must follow the pipe manufacturer’s recommendations and protection
requirements or meet the following criteria (whichever is greater):
Pipe Under Traffic: Cover Depth 1.0 m (Pipe thickness design shall consider the maximum
expected traffic loading on the pipeline).
Pipe Outside Traffic: Cover Depth
0.8 m
Any pipe placed less than the minimum cover requirements shall be encased in concrete.
Water lines shall be placed a minimum of 3 m horizontally from any existing or proposed gravity sewer
line, storm water line, septic tank or subsoil treatment system. The horizontal distance shall be
measured from the outside edge of the water line to the outside edge of the line or structure.
Water lines crossing above or below sewer lines shall be placed a minimum of 0.5 m apart vertically.
The vertical distance shall be measured from the outside edge of the water line to the outside edge of
the sewer line. A full-length section of the water line shall be placed at the crossing so as to maximize
the distance of the joints from the sewer line. When the water line is placed below the sewer line, the
water line shall be encased in concrete for a total length of 3 m centered on the crossing point.
Thrust Blocks
Thrust or anchor blocks of plain or reinforced concrete, which have been designed to resist
unbalanced hydraulic forces, shall be provided at all bends, tees, tapers, in-line stop valves and dead
ends. Thrust blocks shall be designed according to the water line pressure and soil horizontal bearing
capacity.
Valves
Isolation valves shall be located approximately every 500 m and shall also be located near each tee
connection. Installation shall be underground with spindle and surface box. The following valve types
should be used for different water line diameters:
Ø < 400 mm: Gate valve
Ø
1.3.6
400 mm: Gate or butterfly valve
Fire Hydrants
The requirement for water for fire-fighting purposes shall be determined in accordance with local
regulations and Infrastructure Design Criteria.
Location of fire hydrants shall avoid lot entrances and obstruction to pedestrian movement or
generally be placed at the corner of street intersections and property corners. Criteria for fire hydrant
assembly spacing are as follows:
1.
Limited-Access Roads (Ring Roads), 300 m on alternating sides of the road
2.
Divided Roads With Medians or Barrier Dividers, 75 m on alternating sides of the
road
3.
2-Lane Local Roads, 150 m
4.
2-Lane Residential Roads, 120 m
5.
Hydrants shall be located at a maximum spacing of 150 m in single family residential
areas, 120 m in multiple family areas, and 75 m in commercial, school and industrial
areas.
6.
Hydrant location shall be such that the distance to any building does not exceed 75 m
and not less than 12 m.
7.
Hydrant shall be located within 2.5 m of finished curbing on the end of paved surface.
Distances shall be measured along road centerline or fire lane. Hydrant assemblies shall be located
within public road rights-of-way unless otherwise approved by the fire department.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-5
Fire hydrants leads shall be a minimum of 150 mm diameter. Hydrants shall not be connected to
pipelines less than 200 mm in diameter. Hydrants shall be dry barrel type with isolation valves.
Hydrants may also be used for operational purposes, such as filling, draining, venting, and flushing of
the water main. These requirements are to be considered while selecting location and type of
hydrants.
1.3.7
Laterals
Laterals (house connections) shall be designed to provide a flow equal to 0.3 l/s. The maximum
velocity shall be no greater than 1.0 m/s. Each house connection must be installed with a flow meter
used to measure the amount of water supplied. No house connections shall be made to water lines
with diameter greater than 300 mm.
Pipe material should be PE except in rocky soil where galvanized steel pipe or copper may be used.
If PE pipe is used in rocky soil, the pipe must be protected by a 200 mm thick sand layer on all sides.
For copper pipe; solders, flux, and pipe fittings containing lead shall not be allowed.
1.3.8
Backflow Prevention
Backflow prevention shall be provided to eliminate any connection between the water distribution
system and any system of pipes, pumps, hydrants, or tanks that have the potential to allow
contaminated materials into the drinking water supply. To prevent cross-contamination of drinking
water, suitable backflow prevention devices must be installed. Backflow prevention devices shall
comply with appropriate AWWA standard.
1.3.9
Operation and Maintenance
Follow the guidelines included in AWWA Standard G200-04: AWWA Standard for Distribution
Systems Operation and Management.
1.4 Water Well Design
Groundwater is the typical water supply source for communities and settlements not served by the
Great Man-made River (GMR) water supply. For the security and reliability of water supply to these
communities and settlements, it is important that water supply wells be constructed to an acceptable
standard of reliability and performance. A series of design criteria have been established for potable
water supply wells in Libya.
The Water Well Design Criteria are included as Attachment 1-4.
1.5 Surface Water, Ground Water, and Seawater Treatment
1.5.1
Purpose
The purpose of the Design Criteria is to establish the common criteria for the process design of Libya
HIB water treatment plants. Following is a list of goals and objectives for water treatment plant
design.
3
Treatment plants for average daily demand less than 10,000 m /day shall be designed based on the
characteristics of the specific water supply. Types of process and general sizing criteria are
presented in this document.
Water treatment plant design is dependent on the quantity and quality of water to be treated to meet
finished water criteria suitable for potable water consumption.
1.
Plant buildings shall be architecturally designed structures with adequate heating,
ventilating, and air conditioning systems. The buildings shall be constructed of
concrete or masonry with concrete roofs.
2.
All treatment facilities shall be equipped with automatic changeover diesel generators
suitably sized to operate the water treatment facility at normal demand and to meet
peak electrical load.
3.
All treatment processes shall be designed for N+1 redundancy, meaning that the
facility shall be able to provide the maximum daily demand with one process train out
of service.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-6
1.5.2
4.
Surface water treatment plants shall consist of typical conventional treatment
processes such as rapid mix/coagulation, flocculation, sedimentation, filtration,
disinfection and fluoridation, meeting generally accepted design standards (i.e.,
Health Research Incorporated Recommended Standards for Water Works, 2007).
5.
Groundwater treatment plants shall consist of processes based on treating
constituents in the groundwater. For Libya, the typical constituents are iron,
manganese, and high total dissolved solids (TDS).
6.
Electrical and Mechanical Reliability standards shall be equivalent to United States
Environmental Protection Agency (USEPA) Reliability Class II.
7.
All plant process basins, walkways, and stairways shall be equipped with a railing
system designed with two rails and toe plate. The design shall be based on
equivalent standards established by the Occupational Health & Safety Administration
(OSHA) or National Examination Board Occupational Health & Safety (NEBOSH).
8.
Pipe galleries and below grade pump rooms shall be ventilated in accordance with
normal practice to reduce moisture buildup and potential for toxic gas buildup.
9.
All plants shall be equipped with a Supervisory Control and Data Acquisition
(SCADA) system to facilitate process control and monitoring of the facility. Flow
meters shall be provided to monitor raw water, individual filtered water, and finished
water.
10.
Water treatment plants will have continuous online monitoring of raw water
temperature, flow, turbidity, and pH; individual filtered water turbidity and flow filter
headloss; finished water temperature, turbidity, pH, and chlorine residual. Plants
shall also be equipped with laboratory equipment for monitoring water quality of grab
samples throughout the treatment process.
11.
Process design shall consider overall water conservation. Conservation of raw water
supply can be achieved through the treatment and recycle of spent filter backwash
water. Conservation of finished water supply for filter backwash can be achieved
through the use of a combined air and water backwash system.
12.
Low Pressure Membrane filtration with air backwash can be considered as an
alternative to conventional water treatment with appropriate pretreatment units ahead
of the membrane filtration units.
13.
All treatment plants treating surface water or ground water under the influence of
surface water shall have primary disinfection with either ultraviolet disinfection for
pathogens and chlorine for viruses, or chlorination alone. The primary disinfection
shall satisfy the virus and Giardia inactivation requirements as established by the CT
product method (USEPA Surface Water Treatment Rule). Secondary disinfection
shall be provided in all treatment plants via chlorination for maintaining free chlorine
residual in the distribution system of not less than 0.2 mg/L as free available chlorine.
14.
Water storage facilities shall be sized to meet the required contact time (CT) prior to
distribution to the first customer downstream of the water treatment plant, unless the
water treatment plant is the first customer. If the water treatment plant is the first
customer, then provide CT prior to sending the water back into the water treatment
plant.
Water Treatment Design Criteria
Population and Growth Projections
Population and growth projections shall be based on the saturated population of the Third Generation
Master Plan area with the water supply sources and treatment capacity according to projected
population to 2025.
Water Demand
Water treatment plants shall be designed considering average daily demand and maximum
instantaneous daily demand. The plant hydraulics shall be designed for maximum daily demand and
future expansion. The maximum daily demand for small residential areas can range from 1.0 to 2.0
times the average daily demand. Storage capacity at water treatment plants shall be determined
based on demand in the distribution system, the water need at the plant such as backwashing,
service water at the plant site, and for allowing adequate contact time for disinfection. At a minimum,
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-7
the plant should have 10 percent of its daily capacity available for storage over and above the volume
needed for internal uses and disinfection. Fire flow demand is not included in the typical calculations
for average and maximum daily water demands, but should be included when sizing finished water
storage facilities.
Finished or Treated Water Quality
Finished or treated water must meet water quality standards with mean concentrations at or below the
following maximum contaminant levels (MCLs). There are several available treatment technologies
that are commonly effective at reducing contaminants of concern. It should be noted that
combinations of unit processes may be required. The source water must be sampled for the
constituents below in order to establish the appropriate treatment technology.
The Treated Water Quality Parameters are included as Attachment 1-5.
Secondary Maximum Contaminant Levels
Secondary Maximum contaminant levels are not considered to present a risk to human health at the
maximum levels given in the table, but are related to the aesthetic quality of the water. If these
contaminants are present at the levels above these standards, the contaminants may cause the water
to appear cloudy or colored, or to taste or smell bad, resulting in a significant number of consumer
complaints. The available treatment technologies for removal of secondary contaminants vary. Many
secondary contaminants can be removed through conventional processes.
The Secondary Maximum Contaminant Levels are included as Attachment 1-6.
Treatment Process Operations
Other unit processes that are typically included are used in solids handling applications. This may
include gravity thickeners, lagoons, dewatering equipment, and solids drying.
The Treatment Process Operations are included as Attachment 1-7.
Treatment Plant Layout
A typical conventional water treatment plant can be configured for a campus-style layout with
separate buildings and structures for each treatment process or can be a compact design with
shared-wall construction. The layout of the facility is based on the availability of land and the existing
topography.
Desalination Plants
There are two principal types of desalination plant processes, membrane desalination including
electrodialysis reversal, nanofiltration, and reverse osmosis; and thermal methods including multi
stage flash distillation, multiple effect distillation, and vapor compression. These types of plants may
be used for sea water, brackish water in estuaries or in shallow aquifers near shorelines. For both
desalination processes, seawater intake points must be located in a current environment that is
directed seaward. The intake line must be situated at a depth to prevent interference with shipping
operations and designed to prevent fish from entering the intake.
Reverse Osmosis (or High Pressure Membrane Process)
Pretreatment units may be required prior to the reverse osmosis process to condition the water before
being treated by the membranes. Chlorine, phosphorus, and iron substantially shorten the membrane
life and must be removed prior to membrane treatment. Organics must not be applied to the
membranes because they cause biofouling and will also shorten membrane life.
Reverse Osmosis Membranes are spiral wound membranes offered by numerous manufacturers
worldwide. For Mediterranean seawater with a total dissolved solids estimated at 30,000 mg/l, these
membranes are designed to operate at operational pressures up to 60 bar.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-8
Figure 1-1 Typical Treatment Process Seawater Desalination
Distillation uses heat exchangers to heat the water to be treated to a boiling point. Water is boiled off
of the exchanger and based though a condensing unit that produces finished water free of pathogens.
Only residual chlorination of the finished water is required.
Both types of desalination plants produce brine waste that is 30 to 60 percent of the water flow. Brine
should be captured in percolation or evaporation ponds. For special conditions, brine may be
discharged back to the sea. These discharge pipelines must be designed with similar considerations
as the intake line. The discharge pipe must terminate in an area where currents flow away from the
shoreline and away from the plant intake screening system.
Pipe Materials
Pipe Materials for Water Treatment Plants are included as Attachment 1-8.
1.6 Structural Design
The structural design criteria have been developed to provide general guidelines and requirements for
the structural design of water/wastewater facilities for Housing and Infrastructure Board (HIB). The
Contractor shall design and construct all projects to meet or exceed these guidelines and
requirements. The design criteria are based on International Standards and Libyan Codes.
The structural design shall conform to the requirements and guidelines outlined herein. However, the
criteria presented in this section describe minimum requirements and do not preclude independent
thinking by the engineer. Descriptions of alternatives, advantages, calculations, economic analysis, if
required, and cost information must be included. The final decision on any changes will be made by
the CM/CS after consultation with the HIB and PMD.
Structure design shall meet the following requirements:
All concrete water and wastewater holding structures shall be designed in accordance with ACI 35006 Code Requirements for Environmental Engineering Concrete Structures and Commentary and with
guidance from ACI 350.4R-04 Design Considerations for Environmental Engineering Structures.
All non-water holding structures and building structures shall meet the requirements of Section Five of
the Design Criteria for Housing Projects.
All concrete water holding structures shall be design for seismic loading in accordance with ACI
350.3-06 Seismic Design of Liquid-Containing Concrete Structures and Commentary. Seismic
accelerations shall meet or exceed the values from Table 5-1 Seismic Accelerations and Figure 5-1
Seismic Zones Libya from the Design Criteria for Housing Projects.
All water and wastewater structures shall be leaked tested in accordance with ACI 350.1/350.1R
Tightness testing of Environmental Engineering Concrete Structures and Commentary. All water &
wastewater structures shall meet the tightness criterion requirements of visual inspection only
(Designation HST-VIO), unless required by contract to meet higher designation.
Durability of the structural system, minimum life expectancy 50 years.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-9
Attachment 1-1 : Criteria for Establishing Water Demand
Component
Design Criteria
Average Water Demand
Average water
demand m3/d
[Qave]
(Water distribution
pipe leakage, pipe
flushing, lawn
irrigation etc.
included.)
Population [inhabitants]
Demand [Q]
<3,000
Q= 150 l/d/c
3,000 – 20,000
Q= 180 l/d/c
20,000 – 50,000
Q= 200 l/d/c
50,000 – 100,000
Q= 250 l/d/c
100,000 – 500,000
Q=300 l/d/c
>500,000
Q=350 l/d/c
Maximum Daily Demand Factor
Maximum daily
demand m3/d
[Qmaxd=kmaxd
*Qave]
Population [inhabitants]
Factor kmaxd [-]
<10,000
1.8
10,000 – 30,000
1.5
30,000 – 100,000
1.4
> 100,000
1.3
Maximum Hour Demand Factor
Maximum Peak
hour demand m3/h
[Qhmax=khmax* Qave]
Population [inhabitants]
Factor khmax [-]
<10,000
3.0
10,000 –30,000
2.7
30,000 – 100,000
2.5
> 100,000
2.0
Using any suitable fire fighting equation (i.e. AWWA M31 Distribution System
Requirements for Fire Fighting) with a total duration of 4 hours (assume two fires
at the same time with 2 hour duration each).
Fire fighting
demand Qff [l/s]
AUGUST 2010
Population [inhabitants]
Qff, Fire Demand (l/s)
Up to 10,000
20
10,000 – 25,000
25
25,000 – 50,000
30
50,000 – 100,000
40
100,000 – 200,000
45
greater than 200,000
50
REVISION NO. 03
W ATER DESIGN STANDARDS 1-10
Component
Design Criteria
Minimum demand
[Qdmin] [Qhmin]
Qdmin = 0.6 to 0. 7*Qave
Qhmin = 0.3*Qave
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-11
Attachment 1-2. Transport Water Line Design Parameters
Component
Design Criteria
Design Flow
Qdes (average flow)
Use the greater of the following values:
Qdes = Qave, v = 1.0 m/s, or
Qdes = Qmaxd, v = 2.5 m/s
Minimum Pressure
5 m (0.5 bar) above the highest point in system (provided there are no
customers serviced by this line)
Maximum Operating
Pressure
100 m (10 bar)
Design Maximum
Pressure
Maximum Expected Operating pressure x 2 + water hammer allowance of 70
m (7 bar)
Minimum Velocity
0.6 m/s
Maximum Velocity
2.5 m/s
Minimum Slope
0.2 %
2
Materials
Ø 150 mm - 400 mm: PVC or HDPE
Ø >400 mm: DIP, FRP or HDPE
Roughness Coefficient
Per pipe specifications and formulas. Not to exceed a Hazen-Williams
roughness coefficient of 140
1
1
Consideration must be taken for aggressive soil conditions and economical comparison.
2
Minimum slope allows washouts and air relief valves to better function.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-12
Attachment 1-3. Distribution Water Line Design Parameters
Component
Design Criteria
Secondary Line
Main Line
Line Diameter Size
< 200 mm
> 200 mm
(All water lines used for firefighting shall be at
least 200 mm)
Design Flow
Qdes (average flow)
Use the greater of the following values:
Qdes = Qave x Khmax
Qdes = Qmaxd+ Qff
Minimum Pressure Head
1.5 bar (15 m)
Maximum Pressure Head
60 m (6.0 bar)
Minimum Design Velocity
0.1 m/s
0.6 m/s
Maximum Design Velocity 1.5 m/s
2.5 m/s
1
Ø 150 mm - 400 mm: PVC, HDPE
Ø > 400 mm: Ductile Iron
Materials
PVC, HDPE
Gradient
Not less than 0.1%
Roughness Coefficient
Per pipe specifications and formulas
1
Consideration must be taken for aggressive soil conditions and economical comparison.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-13
Attachment 1-4: Water Well Design Criteria
Component
Design Criteria
Approval of New Wells
All new wells and well designs should be approved by the General Water
Authority (GWA).
Design life
Normally 25 years, except if used as a temporary source. Wells deeper
than 350 m should be designed for 50 years.
Number of wells
Minimum of two wells per settlement, except where there is a reliable
alternative backup source of water. The number of wells should be
sufficient to satisfy water demand even when there are interruptions due to
maintenance. The number of wells should allow for meeting the average
daily demand with the largest capacity well out of service.
Depth of wells
Ideally wells should penetrate the entire aquifer, except where there are
financial constraints (e.g. deep Kiklah aquifer) or a deterioration of water
quality with depth. The final drill depth should be sufficient to prevent
possible cave in before the placement of screens and casing.
Distance between wells To be determined by hydrogeological studies, based on pumping tests in
existing wells. The distance should be sufficient to minimize interference
effects between adjacent wells.
Drilling diameter
Should be sufficient to allow a minimum of 5 cm gap between the borehole
and the casing/screen for placing the gravel pack and cement grout.
Casing/screen material
Choice of material should be based on technical constraints (well depth,
aquifer and groundwater characteristics), and economic analysis. Corrosive
resistant materials [e.g. glass fiber reinforced plastic (GRP), polyvinyl
chloride (PVC), unplasticised polyvinyl chloride (uPVC), stainless steel (SS),
etc.] to be used in areas of aggressive groundwater.
Cement grout
Only neat cement grout to be used (no sand/gravel).
Well head
A conductor casing of minimum length 6 m grouted into position to avoid
surface contamination of the well. A concrete protection pad of minimum
1 m high around the top of the wellhead, of which 0.75 m is below ground
level. The top of the casing should extend minimum 0.8 m above ground
level. The casing should be locked shut/spot welded after completion to
avoid contamination/vandalism of the well.
Disinfection of Wells
All wells should be disinfected after completion by chlorination (sodium
hypochlorite or calcium hypochlorite) at a concentration no less than 10
mg/L as free chlorine for 24 hrs. The wells should then be purged by
pumping to waste until the presence of chlorine is reduced, as verified
through testing or until the water no longer smells of chlorine. Note that the
presence of chlorine in groundwater will tend to oxidize metals such as iron
and manganese, creating dark particulates in the pump-to-waste water.
Flushing shall continue until these particulates are removed.
Well Head Protection
The well should be protected by a well house that also contains the control
panel. An area of 15 m radius around the well should be fenced. In areas
of shallow aquifers, no water degradation activities such as agriculture to be
allowed in a 120 m radius. No cesspools or septic tanks within 60 day travel
time as defined by hydrogeological studies. No use of dangerous chemicals
(e.g. pesticides) within the catchment zone of the well as defined by
hydrogeological studies.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-14
Component
Design Criteria
Pumping Tests
All production wells should be tested by:
A variable discharge rate pumping test (min 4 steps of min 60 minutes
each).
A constant discharge rate pumping test (rate based on results of variable
rate test). The length of the test to be decided based on aquifer
characteristics and size of settlement to be supplied. Minimum length is 24
hours for small settlements (<1000 population), 72 hours (1000-10,000
population), 120 hours (>10,000 population). In unconfined aquifers, the
pumping test must be long enough to include delayed yield, and the final
drawdown curve.
A recovery test (continued until a minimum 95% recovery is reached,
minimum test duration is 24 hours)
During the pumping tests hydrochemical parameters (including, at a
minimum, pH, Temperature and Conductivity) should be monitored at
regular intervals.
Water Analysis
Water quality to be analyzed for all parameters in the Libyan Standard
No. 82 and as included herein.
Pump capacity/type
Pump capacity to be chosen based on well completion report and calculated
using results of pumping tests. The capacity should not exceed 70% of the
maximum pumping test rate. Pump material should be based on technical
constraints and economic analysis. Corrosive resistant materials to be used
in areas of aggressive groundwater. Aggressive groundwaters are usually
very low alkalinity and or low TDS waters. These conditions generally do
not exist in Libya.
Pump Setting Depth
The pump setting depth is calculated based on the pumping test results,
and allowing for a decline in the water table due to the pumping from the
well, and adjacent wells. A safely margin of 5 m should be added to this
depth.
Rising Main
Size is determined by pump characteristics.
Rising main material should be based on technical constraints and
economic analysis. Corrosive resistant materials to be used in areas of
aggressive groundwater.
Dipper tube
All production wells must have a 1" (25 mm) dipper tube, to enable water
levels to be measured using an electronic water level dipper. The dipper
tube can be hanging separately from the rising main (e.g. GI pipe), or
attached to it if it is flexible (e.g. PVC/PET tube). The dipper tube should
extend to minimum 10 m below the expected water level during maximum
pumping rate. Corrosive resistant materials to be used in areas of
aggressive groundwater.
Records
A record of the construction details shall be prepared for all production
wells. Recorded information must include well location; borehole diameter
and depth; well casing details (diameters, materials, schedules, and depths
of all permanent casings); well screen details (diameters, materials, opening
widths, and depths); depth of grouted and sand-packed intervals; original
yield/drawdown; original water level.
Surface Fittings
Minimum controls/fittings at the surface are flow control valve, flow meter,
pressure gauge, non-return valve, sampling tap.
Monitoring
All wells to be monitored on at least a monthly basis for pumping water
levels, well yield and water quality (minimum measurement = conductivity).
Record to be kept of daily pumping hours and daily total flows for each well.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-15
Component
Design Criteria
Emergency power
supply
If the existing power supply is unreliable the wells in a well field should have
access to an emergency power source such as a standby generator with
automatic changeover.
Spare parts
Full stock of spare parts to be available so that interruptions in the supply for
maintenance works are minimized.
Decommissioning of old Wells to be plugged at depth with cement/bentonite if they traverse more
wells
than one aquifer. Backfilling of the well with non-contaminated materials
and protection by a surface cement or bentonite plug over the top 10 m of
the well.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-16
Attachment 1-5: Treated Water Quality Parameters
Contaminant Microbials
Turbidity
(1)
Available Treatment Technologies
MCL
Finished water < 0.3 NTU in
95 % of measurements
Not to exceed 1 NTU at any
time
In-line, direct, or conventional filtration, or low
pressure membranes, UF or MF. Groundwater
sources that meet turbidity and other standards
may require no treatment through unit processes.
Primary disinfection for surface water systems,
Total Coliforms
No more than 5 % positive
and maintain distribution system residual > 0.2
(including fecal
samples in distribution system mg/l free available chlorine. Groundwater system
coliform and E. coli)
per month
may also be required to chlorinate to comply with
MCL depending on source water quality.
Giardia and Viruses
Contaminant Inorganic
Chemicals
Antimony
Arsenic
Achieve 3-log and 4-log
removal respectively
For surface water systems using conventional
filtration, provide 0.5 log removal of Giardia
through primary disinfection. For direct filtration,
provide 1-log inactivation of Giardia through
primary disinfection. For groundwater systems,
provide 4-log removal of viruses prior to first user
through chlorination, if groundwater shows
.(2)
evidence of fecal contamination of source
Available Treatment Technologies(1)
MCL
0.006 mg/L
Granular activated carbon
0.01 mg/l
Oxidation and then coagulation with ferric sulfate
or alum (pH dependent)
7 million fibers/liter
(longer than 10 µm)
Coagulation/filtration
2 mg/L
Lime softening or ion exchange
Beryllium
0.004 mg/L
Chemical precipitation
Cadmium
0.005 mg/L
Ferric sulfate coagulation or lime softening
Chromium (total)
0.1 mg/L
Ferric sulfate coagulation or lime softening
Copper 1
1.3 mg/L
Ferric sulfate coagulation
Cyanide (as free
cyanide)
0.2 mg/l
Fluoride
4 mg/L
Chemical precipitation or ion exchange
Mercury
0.002 mg/L
Ferric sulfate coagulation
GAC
Nitrate
10 (as Nitrogen)
Ion exchange or nanofiltration
Nitrite
1 (as Nitrogen)
Ion exchange or nanofiltration
Asbestos
Barium
AUGUST 2010
GAC and chemical oxidation
REVISION NO. 03
W ATER DESIGN STANDARDS 1-17
Contaminant Inorganic
Chemicals
(1)
Available Treatment Technologies
MCL
Selenium
0.05 mg/L
Ferric sulfate coagulation,
or Ion exchange,
or reverse osmosis
Thallium
0.002 mg/L
Chemical precipitation followed by filtration
Contaminant Organic Chemicals
(1)
Available Treatment Technologies
MCL
Synthetic organic
Generally, aeration, air-stripping, GAC
Chemicals (SOC’s)
adsorption, or combinations thereof are required.
Comply with the USEPA
and Volatile
Drinking Water Contaminants Advanced oxidation may be required for certain
Organic
and Maximum Contaminant
compounds.
Compounds
Levels
(VOC’s)
(1)
Other treatment technologies may also apply. It may be necessary to install multiple unit processes
depending on source water quality.
(2)
Conventional filtration is defined as having the following unit processes: coagulation (i.e., chemical
mixing), flocculation, sedimentation, and filtration. Direct filtration consists of coagulation, flocculation,
and filtration. In-line filtration consists of coagulation and filtration.
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-18
Attachment 1-6: Secondary Maximum Containment Levels
Contaminant
Secondary
MCL
Noticeable Effects above
the Secondary MCL
Available Treatment Technologies
Aluminum
0.05 to 0.2
mg/L*
colored water
Coagulation & clarification
Chloride
250 mg/L
salty taste
Reverse osmosis
Color
15 color units
visible tint
Conventional or direct filtration
Corrosivity
Non-corrosive
metallic taste; corroded
pipes/ fixtures staining
pH adjustment or sequestration
Fluoride
2.0 mg/L
tooth discoloration
Chemical precipitation or ion
exchange
Foaming agents
0.5 mg/L
frothy, cloudy; bitter taste;
odor
Iron
0.3 mg/L
rusty color; sediment;
metallic taste; reddish or
orange staining
Oxidation and filtration
Manganese
0.05 mg/L
black to brown color; black
staining; bitter metallic
taste
Oxidation and filtration
3 TON
(threshold odor
number)
"rotten-egg", musty or
chemical smell
Powdered or granular activated
carbon
pH
6.5 - 8.5
low pH: bitter metallic
taste; corrosion
high pH: slippery feel;
soda taste; deposits
pH adjustment
Silver
0.1 mg/L
skin discoloration; graying
of the white part of the
eye
Coagulation with ferric sulfate or
alum, or lime softening
Sulfate
250 mg/L
salty taste
Lime softening or reverse osmosis
Total Dissolved
Solids (TDS)
500 mg/L
hardness; deposits;
colored water; staining;
salty taste
Lime softening for hardness
reduction (Ca, Mg, and sulfates) or
reverse osmosis for sodium,
chloride, nitrates
5 mg/L
metallic taste
Coagulation
Odor
Zinc
* mg/L is milligrams of substance per liter of water
AUGUST 2010
REVISION NO. 03
W ATER DESIGN STANDARDS 1-19
Attachment 1-7: Treatment Process Operations
BASIC TREATMENT PROCESS OPERATIONS
Rapid Mix
Number of Units
2 minimum
Design Flow
Maximum Daily Flow
Vertical shaft mechanical mixing, jet mixers, static
mixers, or In-line mixers
Allowable Types
-1
Velocity Gradient, G
600-1000 secs
Hydraulic Retention Time
30 sec for mechanical mixing
Recommended Pre-treatment Chemicals for reduction of:
Turbidity
Aluminum sulphate, ferric or ferrous sulfate or ferric
chloride, polyaluminum chloride, flocculant aid polymer
Metals
Ferric sulphate, lime softening, sodium hydroxide for ph
adjustment
Lime and/or lime/soda ash to elevate pH to 9.5 for
calcium hardness and pH 10.5 for calcium and
magnesium hardness
Hardness
General Pre-treatment requirement ahead
of Reverse Osmosis Membranes (also
consult with RO system supplier)
Sulfuric acid and/or antiscalant
Flocculation
Number of Units
2 minimum
Design Flow
Maximum Daily Flow
Flow-through velocity
0.15 m/min to 0.50 m/min
Detention Time
20-30 minutes total through minimum of two stages
Allowable Mixing Devices
Axial flow propellers or turbines, flat blade turbines,
reciprocating units (walking beam)
-1
Velocity Gradient, G
10-70 sec , tapered flocculation (diminishing G)
preferred
Conventional Sedimentation Basins
Number of Units
Design Flow
2 minimum
Maximum Daily Demand
Average Daily Demand (one unit out of service)
4 hours
2 hours (lime-soda softening)
Detention Time
Surface loading rate
1.22 m/hr
Weir Overflow Rate
250 m per day per meter of weir length
AUGUST 2010
3
REVISION NO. 03
W ATER DESIGN STANDARDS 1-20
BASIC TREATMENT PROCESS OPERATIONS
Flow-through Velocity
0.15 m/min
Minimum Sidewater Depth
3m
Freeboard
0.5 m
Absorption Clarifiers (or other high-rate clarifiers)
Design Size
Sized by manufacturer (typically smaller footprint than
conventional sedimentation basin. Suitable for influent
turbidities less than 30 NTU)
Tube or Plate Settlers
Design Size
Application Rate
Sized by manufacturer
< 4.8 m/hr for a total sedimentation basin surface area
Granular Media Filters
Number of Units
2 minimum
Design Flow
Maximum Daily Demand (with one unit out of service)
Filter Media
Dual media (anthracite, sand), mono media (sand or
anthracite) or granular activated carbon (GAC)
Loading Rate
4.9 to 9.8 m/hr (2-4 gpm/sf)
Media Depth
1 - 2 m depending on water quality
Underdrains
Ceramic perforated blocks, nozzles and false floor
decking, folded steel plate,
Backwash rates
Up to 49 m/hr depending on temperature and media
Backwash bed expansion
Surface wash rate
20-30 %
1.22 to 9.76 m/hr depending on arm diameter and nozzle
orientation
Air wash rate
37 to 91 m/hr air
Finished Water Clearwell
Design Flow
Maximum Daily Demand
Include system storage and fire fighting demands if not
provided in distribution system.
Process Functions
Chlorine contact time needed for C(t) (see below) plus 2
backwash cycles for all filter and process units requiring
water backwash
Disinfection
Design Flow
AUGUST 2010
Maximum Daily Demand and lowest temperature
REVISION NO. 03
W ATER DESIGN STANDARDS 1-21
BASIC TREATMENT PROCESS OPERATIONS
Minimum Contact Time
Based on effective contact time times concentration [CT]
required. The effective contact time is a fraction of the
theoretical contact time. This fraction is dependent on :
baffling, finished water pH, finished water chlorine
residual, water temperature, maximum flow and minimum
clearwell depth
Internal Baffling Dimension Ratio
10 length to 1 width
Filter Control Valves
Purpose
Regulate filter feed and backwash operation
Allowable Valve Type
Electrically operated butterfly valve
Backwash Pump
Capacity
Capable of supplying 49 m/hr of filter area
Vertical turbine pumps sized to create 30% expansion of
the filter bed.
Variable speed drives.
Allowable Type
AUGUST 2010
Elevated storage tank sufficient to hold at least 2
backwash cycles with a minimum level sufficient to
provide driving head to furnish design backwash flow
rate.
REVISION NO. 03
W ATER DESIGN STANDARDS 1-22
Attachment 1-8: Pipe Materials for Water Treatment Plants
Pipe Component
Allowable Material
5 mm opening size, 316 stainless steel
Air Purgable Inlet and
Brine Outlet Screens
316 stainless steel wedgewire screen
Screen hydraulics designed for 50% obstruction
Fiberglass Reinforced Plastic (FRP) per AWWA C950 (requires ballasting
or anchors to prevent flotation)
Inlet/Brine Outlet Pipe
(material dependent upon
size)
High Density Polyethylene (HDPE) per AWWA C901 and C906 (requires
ballasting or anchors to prevent flotation)
Ductile iron (per ANSI/AWWA C151/A21.5)
Polyvinyl Chloride (PVC) (per AWWA C900)
Mechanical joint pressure class 350 ductile iron pipe(per ANSI/AWWA
C151/A21.5)
Underground Site Pipe
Precast concrete cylinder pipe (for pipes larger than 1200mm) per AWWA
standards C300, C301, C302, C303, and C304)
In-Plant Mechanical
Process Pipe
Chemical Feed Lines
AUGUST 2010
Pressure class 350 ductile iron pipe with 125 psi flanges
Non corrosive HDPE
REVISION NO. 03
W ATER DESIGN STANDARDS 1-23
2
Sewerage
This section presents standard design criteria for sewerage systems.
The criteria presented have been standardized to reflect typical installations. It is understood that
certain situations may require deviation from the criteria herein.
2.1 Sewer Design Criteria
Sewerage systems include collection of wastewater from each source, transport, including pumping
stations, delivery to a treatment facility, treatment, and disposal of solids generated during the
treatment process. Storage and handling of Treated Sewage Effluent (TSE) is considered part of the
irrigation system and is covered in Section 4.0.
In general, sewer capacity should be designed for the estimated ultimate contributing population and
the full expected development of industrial and commercial areas.
2.1.1
Sewage Flow
For community wide design average wastewater flows are determined as 80% of the design average
water demand. Table 2-1 lists average water and wastewater flow rates based on community
population size.
Table 2-1 Wastewater Unit Flow Rates
Average Water
3
Demand m /d [Qave]
(Water distribution pipe
leakage, pipe flushing,
lawn irrigation etc.
included.)
Population
[Inhabitants]
Average Potable
Water Demand [Q]
Domestic
Sewage Flow [Q]
<3,000
Q= 150 l/d/c
Q= 120 l/d/c
3,000 – 20,000
Q= 180 l/d/c
Q= 145 l/d/c
20,000 – 50,000
Q= 200 l/d/c
Q= 160 l/d/c
50,000 – 100,000
Q= 250 l/d/c
Q= 200 l/d/c
100,000 – 500,000
Q= 300 l/d/c
Q= 240 l/d/c
>500,000
Q= 350 l/d/c
Q= 280 l/d/c
Design peak hourly sewage flows shall be calculated by using a Peaking Factor (PF) for all sewage
flows from a known or assumed tributary population, based on the Babbitt Formula, as follows:
PF = 4.25 × (Population ÷ 1000)
-1/6
The PF shall be used to project peak hourly sewage flows from tributary areas with contributing
population equal to or greater than 500 persons, up to 90,000 persons. For tributary areas with fewer
than 500 persons, an alternative method of estimating peak flows is allowable.
For example, the peaking factor for a population of 3,000 using the Babbitt Formula is PF = 3.5
For populations 90,000 and above, or sewage flows of 18,000 m3/d or greater, the peaking factor shall
never be less than 2.0.
Land Use Based Flows for Sewage are included as Attachment 2-1.
For other commercial and industrial sewage flow projection, a detailed evaluation is required by type
on a case-by-case basis subject to occupancy regulations.
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-1
2.1.2
Hydraulic Analyses
Hydraulic analyses shall be carried out using approved computer modeling software. Acceptable
models are Infoworks, SewerCAD, Mouse Model, InfoSewer, and other equivalent commercially
available models.
Roughness coefficients based on the pipe material as shown in Table 2- shall be used. The
roughness coefficient is a measure of the variation and magnitude of protuberances on the interior
surface of the pipe. The roughness therefore is a function of the pipe material, age, and condition.
Poor pipe conditions are to be assumed for sewage system designs.
Table 2-2 Typical Roughness Coefficients
Manning’s Coefficient, n
Pipe Material
2.1.3
Normal
Maximum
uPVC
0.010
0.013
GRP
0.010
0.013
HDPE
0.010
0.018
RCP
0.012
0.016
DIP (with mortar lining)
0.012
0.016
Flow Velocities
The design flow velocity limits are listed below.
Table 2-3 Minimum and Maximum Velocities in Sewer Pipes
Pipe Description
Gravity pipe
Pressure pipe
2.1.4
Minimum Velocity
(m/s)
Maximum Velocity
(m/s)
Design Velocity
(m/s)
0.5
2.5
0.75
0.6 to 1.0
2.5
1.5
Depth of Flow
The following table shows the recommended depth of flow in gravity sewer lines. The ratio d/D is the
ratio of the flow depth (d) to the nominal pipe diameter (D).
Table 2-4 Minimum and Maximum Depth of Flow in Sewers at Peak Flows
Description
Maximum (d/D)
Minimum (d/D)
Trunk sewer lines
0.75
0.50
Main and lateral sewer lines
0.85
0.50
2.1.5
Pipe Gradients
In order to achieve the required minimum velocity in sewer lines, pipes should be designed by
observing the minimum gradients.
Pipe Gradients are included as Attachment 2-2.
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-2
2.1.6
Pipe Materials
Sewer pipe materials have been selected to be consistent with local standard practices, based on
economics and local availability. The following materials shall be used for various pipe sizes:
2.1.7
1.
For sewer mains equal to or less than 800 mm in diameter, uPVC shall be used. For
sewer mains larger than 800 mm in diameter, GRP shall be used. Other corrosion
resistant materials, such as PVC greater than 800 mm, high density polyethylene
pipe (HDPE) or vitrified clay pipe (VCP) may be considered.
2.
For pressure mains, GRP, HDPE or PVC shall be used. DIP with mortar lining or
ceramic epoxy lining may be considered for special circumstances.
Minimum Cover Requirements
The minimum cover recommended is 1.2 m above the pipe crown, in order to protect from external
loads. If the available cover is less than 1.2 m, then additional protection such as full concrete
encasement or the use of concrete protection slabs shall be provided. In special areas with heavy
loading, specific protection may be required based on structural evaluations.
The actual cover required for construction and access may be greater than that required solely for
structural integrity. For example, the minimum cover required by the physical dimensions of a typical
access manhole is 2 m above the pipe crown. However, for small pipes less than or equal to 315 mm
in diameter, the required cover may be less than 1.2 m. If inspection chambers are installed rather
than manholes, 1.0 m of cover will suffice.
The maximum cover depth recommended is approximately 10 m. This maximum depth is consistent
with typical pipe installation standards and manufacturer recommendations. Should the actual cover
be greater than 10 m, pipe materials and loads should be evaluated and a higher strength class of
pipe utilized.
For pipes installed at less than these minimum values or at excessive depths, concrete encasement
may be required to protect the pipe from damage. Alternatives of different pipe size at a different
slope should be considered before designing the pipelines outside of the specified depth ranges.
In all cases, the pipe minimum and maximum depths shall be in conformance with the pipe
manufacturers’ recommendations
2.1.8
Utility Crossings
Utility crossings for this project shall follow the guidelines shown in Table 2-5.
Table 2-5 Utility Crossings for Sewer Pipes
Parameter
Minimum Criteria
Vertical Clearance
50 cm; if less than 50 cm, use concrete saddle and provide
concrete encasement to first joint on each side of crossing
Horizontal Clearance
3.0 m
Where available corridor space is limited, minimum clearance may
be reduced to 1.2 m assuming structures can overlap into adjacent
corridors.
If in same trench, place other utility on separate bench on
undisturbed soil above sewage line
Potable Water Lines
Always place sewage lines below potable water lines
Pipes shall be aligned to cross under roads at 90 degrees or perpendicular to the road.
2.1.9
Manholes
Manholes are required to provide access to the sewer mains. They are also provided at each change
in direction (vertical or horizontal), change in diameter, and connection of two or more lines. Sewage
manholes are to be installed a maximum of 100 m apart. Sewage manholes shall be constructed of
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-3
reinforced concrete with GRP, epoxy mortar (min. 5 mm), or flexible PVC lining for corrosion
protection.
These structures shall be circular in shape and designed in accordance with the established design
criteria.
Sewer Manhole Design Criteria are included as Attachment 2-3.
Alternative manhole designs are required where there are multiple pipeline crossings.
In general, gravity sewers alignment shall be adjusted such that all manholes are located outside of
vehicular travel lanes, if feasible. Manholes may be placed in paved shoulders where available.
2.2
Pumping Stations
Pumping stations are required when sewerage collection network depths exceed the practical or
economic constructability limit. Sewerage facilities will typically consist of gravity driven systems;
however, due to topography and the need to limit sewer depths to a practical maximum, pumping
stations may need to be included in the system.
All sewage pressure pipes within the site limits of the pumping station shall be GRP with minimum
2
pipe stiffness of 10,000 N/m . Foul air pipes may be either uPVC or GRP.
All metal components that are submerged or in intermittent contact with raw sewage shall be made of
316 stainless steel. Galvanized steel shall not be permitted.
2.2.1
Pumping Station Type
The design philosophy includes the minimization of the total number of sewage pumping stations in
the collection system. Where pumping is required, the number of times a given flow is pumped
should also be minimized.
Three types of sewage pumping stations shall be used: (1) submersible stations for small to medium
size facilities, (2) wet well-dry well stations for large facilities, and (3) screw pump stations in situations
where the required head is just to lift into a higher elevation gravity flow pipe.
Pumping stations shall be designed to handle flows greater than or equal to the projected peak
influent flow rate which is determined by applying the Peaking Factor to the average flow. Peak flows
shall be validated using hydraulic modeling software with accurate modeling of the actual sewer
collection system.
Wet well sizing is a function of the incoming flow, the control strategy for the station, the selected
pumps, whether single speed or variable speed drive, and the number of starts per hour permissible
for the pumps. Recommended cycling frequency depends on the type of pump being used, the motor
size, and pump operating efficiency. For design purposes, submersible pumping stations shall have a
minimum cycle time of 6 minutes or a maximum of 10 starts per hour. Pump controls shall be based
primarily on water elevations in the wet well of the station. Constant speed pump operation shall be
by wet well elevation with ultrasonic level control wet well alarms and shutoff. Variable speed pumps
may be provided to maintain a set water level in the wetwell.
2.2.1.1
Wet Well Volume
For constant speed pumps, wet well volume is calculated based on cycling frequency when inflow to
the station is 50 percent of the pumping rate with a single pump operating.
The wet well volume shall be calculated from the basic formula:
CT
=
[V/(D-Q)+(V/Q)] where
D
=
Pump rate (m /min.)
Q
=
Inflow rate (m3/min.)
CT
=
cycle time (min.)
V
=
volume (m )
3
3
Since “minimum” cycle time is of concern (Q=D/2), the formula reduces to V = CT x Q/2.
2.2.1.2
Wet Well Depth
The operating depth of wet well is a function of the following:
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-4
1.
Required submergence to prevent vortexing in the pump suction piping or the pump
inlet, which may cause unbalanced loading on impellers & bearings, thereby reducing
pump life.
2.
The Net Positive Suction Head Required (NPSHR) plus a 1.5 meter margin. The
NPSHR is based on the particular pump, impeller selection, and requirements
provided by the pump manufacturer.
3.
Priming: The minimum wet well level must be set 150 mm above the top of the pump
volute.
4.
The elevation of influent sewer shall be designed to prevent turbulence and air
entrainment in the wetwell.
5.
High liquid level in the wet well shall be set at 0.8 times the inlet pipe diameter above
the invert. This allows the inlet pipe to be emptied frequently, preventing buildup of
settled material in the gravity inlet pipes.
The required submergence refers to minimum liquid level above a vertical pump inlet, flare inlet, or
fitting, and above the centerline of the flare if positioned horizontally.
The minimum submergence determination, priming, and NPSHR shall be verified during the wet well
sizing.
2.2.2
Pump Selection
Pump selection should be made to optimize conditions over the minimum, average, and maximum
projected range of flows. Selection is made to minimize holding times in the wet well before pumping
and to maximize efficiency. Actual pump selection is made after a system head capacity curve is
developed for the proposed installation. The following are to be considered:
1.
Required range of flows
2.
Range of friction coefficient values for old and new pipe
3.
Range of static head, note that the low wet well elevation is to be used for the pump
design rating point
4.
Number of pumps based on pump selection
5.
Operating and control strategy
6.
Efficiency
7.
Potential for upgrading capacity
All pumping stations shall have a minimum of two pumps to operate as duty-standby. Additional
‘assist’ pumps shall be included as required. All pump systems shall have a facility for duty rotation.
If screw pumps are used, a minimum of two pumps shall be installed. Screw pumps automatically
pump with a variable output to match the incoming flow (up to a maximum capacity). Pump selection
is primarily a function of number of pumps, pump maximum capacity, number of flights, and lift.
2.2.3
Pumping Station Structures
Pumping station structures shall be designed to ensure a safe working environment for operation and
maintenance staff, as well as to maximize performance and to minimize construction and operation
costs. The following shall be incorporated:
1.
Wet wells shall be isolated from dry wells and/or superstructures by impermeable
walls.
2.
Independent ventilation systems for shall be used for the wet well and the dry well to
meet applicable standards.
3.
Provisions shall be made to facilitate removing pumps, motors, and other mechanical
and electrical equipment.
4.
Suitable, separate, and safe means of access shall be provided to dry wells and to
wet wells.
5.
Wet wells and pump suction inlets shall be configured to minimize turbulence.
Trench type wet wells shall be used.
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-5
2.2.4
6.
A minimum of two wet wells shall be used except for pumping systems with a
capacity less than 35 L/sec or self-cleaning trench wet well if approved
7.
All pumping stations shall provide a valved connection point downstream of the pump
isolation valves to allow temporary bypass pumping
8.
Wet wells shall be GRP lined with factory fabricated materials
Surge Protection
Surges can be generated in the sewage force main following power failures, pump starting, or
stopping and sudden valve operations. The need for surge limiting equipment to protect the force
main due to possible transient pressure variation shall be considered. The calculation of surge shall
be carried out by appropriate methods and using the relevant general equations and surge flow
calculation software according to the conditions specified by the designer and based on the most
unfavorable operating conditions. Where surge protection is found to be necessary, the designer
shall size and specify the appropriate surge protection equipment. Surge tanks are the preferred
method and can be bladder tanks or air tanks.
2.2.5
Electrical and Instrumentation Systems
All pumping stations shall be designed and constructed based on Section 14 criteria in this document.
Wet well level controls shall meet the following criteria:
1.
Two-pump pumping stations
2.
Ultrasonic level control system with a single sensor
3.
Encapsulated-type float switches for:
i
ii
iii
4.
Three or more pump pumping stations
5.
Ultrasonic level sensor control system with redundant sensors
6.
Encapsulated-type float switches for:
i
ii
7.
LOW-LOW Wet Well Level to stop all operating pumps and initiate an alarm
HIGH-HIGH Wet Well Level to initiate an alarm
The float switches shall be firmly supported from the top of the wet well, suspended in
a stilling well and fixed to the stilling well wall so that the float switches cannot
become entangled. Stilling wells shall be
i
ii
iii
iv
2.2.6
LOW-LOW Wet Well Level to stop all operating pumps and initiate an alarm
HIGH-HIGH Wet Well Level to initiate an alarm
HIGH level for backup to start a pump in case an ultrasonic unit fails
Large enough to allow free movement of the float switch
Constructed of GRP or other non-corrosive material
Securely fixed to the wet well wall with 316 stainless steel supports and
fasteners
Vented at the top and bottom to avoid trapping air bubbles
Odor Control
Odor control measures shall be provided to ensure that noxious gases and odors are in
concentrations lower than the detection level. Chemical odor control systems shall comprise of
chemical scrubbers with packed counter current or cross current, two or three stage chemical type
and/or a bulk activated carbon deodorizer. Biofilter odor control is also acceptable and preferable in
locations where chemical replacement may not be reliable. Ventilation shall be designed for one
complete air change per hour consistent. Ventilation of submersible pump wet wells shall be a
minimum of 12 air changes per hour.
2.2.7
Gas Monitoring
Gas monitoring is required in confined spaces that are classified as “permit-required.”
A confined space is defined as a space that “has limited or restricted means of entry or exit, is large
enough for an employee to enter and perform assigned work, and is not designed for continuous
occupancy by the employee.”
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-6
A permit-required confined space is a confined space that “contains or has the potential to contain a
hazardous atmosphere, contains a material that has the potential for engulfing the entrant, has an
internal configuration that might cause an entrant to be trapped or asphyxiated by inwardly converging
walls or by a floor that is sloped downward and tapers to a smaller cross-section, and/or contains any
other recognized serious safety or health concerns.”
Areas accessible to operating personnel, such as a dry well in a pump station, that have the potential
to build up toxic and/or explosive gases or dangerously low oxygen levels, must have permanently
mounted gas monitoring units. The units shall be able to monitor lower explosive limit (LEL),
hydrogen sulfide (H2S), and oxygen (O2). The gas monitoring unit shall initiate a local alarm (audible
and visual) and send a discrete signal for an alarm to the SCADA system.
Potable gas monitoring units for monitoring LEL, H2S, and O2 shall be provided and used by
operations and maintenance personnel when entering less accessible areas, such as wet wells,
chemical tanks, manholes, and valve chambers.
2.2.8
Rising Mains
Rising mains shall be sized to maintain velocities with an acceptable range for a variety of flow
conditions. Rising main pipe diameters shall not be less than 200 mm. Selection of the diameter is
dependent on the maximum and minimum flow rates required through the pipe, and the
characteristics of the pipe (length, material, and route). The head loss in the system should be
minimized.
Minimum and maximum velocities for sewer rising mains have been established as 0.6 to 1.0 and
2.5 m/s, respectively, with a target design velocity of 1.5 m/s. The maximum velocity restriction is
related to minimizing the effects of scour on the interior of the pipe as well as minimization of friction
head losses. The design velocity is based on the ability to re-suspend settled solids within the rising
main. The minimum velocity must be achieved with only one pump in operation since this will be the
condition during low-flow periods.
2.2.9
Air Valves and Washouts
The raising mains shall be equipped with the following valves for facilitating the operation, control, and
maintenance:
1.
Air and Vacuum Valves: These valves shall be provided at summits along the pipe
profile and along long stretches with uniform slope to purge out accumulated air in the
pipe system. Air release and vacuum relief valves are often needed along
transmission mains and may sometimes be unavoidable in sewage force mains. Air
must be bled slowly from high points to prevent (1) “air binding” and (2) the reduction
of the cross section of the pipe at high points. Vacuum conditions must be prevented
when the pump head drops quickly (as in power failures) to prevent column
separation and at extreme high points in pipelines to prevent potential pipeline
collapse due to vacuum. Vacuum relief valves can be as large as one-sixth of the
diameter of the transmission main, whereas air release valves may be as small as
one-fiftieth of the diameter of the pipe.
2.
A combination of air and vacuum valves shall be provided at appropriate locations for
quick air entry or vent to prevent cavitations and facilitate quick filling of the pipe. In
general, air-valves are to be provided at crest points, changes in elevations and in
case of constant rising mains having moderate slope, at a maximum spacing of
600 m.
3.
Washout valves: These valves will be provided at low points or sags along the pipe
profile. These valves facilitate flushing, repair or maintenance of the pipe wherever
necessary.
4.
Isolating valves: The location of these valves shall consider the profile of the pipeline
and the location of washout and air valves. Isolating valves shall be provided at a
maximum distance of every 2 to 3 kilometers.
5.
Isolating Valves with diameter smaller than 300 mm shall be solid wedge or double
revolving disc gate valves and larger diameter shall be eccentric plug valves or
double revolving disc gate valves.
6.
Non-Return Valves: These valves will be provided in the pumping station to prevent a
reverse flow into the pumps and shall be rubber flapper type with position indication
and backflow device.
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-7
All valves not located in a pumping station structure shall be installed inside reinforced concrete valve
chambers, consisting of an access manhole, vent, a ladder, and a sump.
2.2.10
Pumping Stations Operations and Maintenance
1.
Pumping station buildings shall be architecturally designed structures with adequate
heating, ventilating, and air conditioning systems. Prefabricated structures shall not
be allowed. All buildings shall be of concrete or masonry construction.
2.
Electrical and Mechanical Reliability standards shall be equivalent to USEPA
Reliability Class II.
3.
All pumping station wet wells, walkways, and stairways shall be equipped with a
railing system designed with two rails and a toe plate. The design shall be based on
standards established by the US Occupational Health & Safety Administration
(OSHA) or UK National Examination Board in Occupational Safety and Health
(NEBOSH).
4.
Pipe galleries and below grade pump rooms shall be force ventilated (powered in and
out) sufficiently to minimize potential for toxic gas buildup. Unless otherwise directed,
all buildings and structures shall comply with US National Fire Protection Association
820 standards.
2.3 Structural Design
Structural design of water and wastewater facilities shall meet the requirements described in
Section 1.
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-8
Attachment 2-1 Land Use Based Flows for Sewerage
Type/Activity
Unit
Unit Flow Rate
(l/unit/day)
School – Kindergarten
Child
Employee
25
50
School – Daily School
Student
Employee
40
50
Institutes and medium schools
Student
Employee
50
50
Universities and higher
Student
Employee
60
50
Intern Quarters
Resident
120
Institutions with beds (other than
hospitals)
Employee
Bed
50
200
Hospital - Psychological
Employee
Bed
60
300
Hospital – Medical
Employee
Bed
60
400
Senior Care Residence
Employee
Resident
100
400
Care Houses (economy)
Employee
Resident
60
120
Public Administrative Buildings
Person
50
Camps with toilet & shower
Person
200
Visitor
Employee
10
50
Mosques
Person
30
Sports Club (with toilets only)
Member
50
Sports Club (with toilets and shower)
Employee
Member
50
200
Cultural Club (with toilets only)
Employee
Visitor
50
10
Recreational Club (with toilets only)
Employee
Visitor
50
25
Museums and Monument Buildings
Factories & Commercial
Varies according to industry type
Parks (with toilets only)
Employee
Visitor
50
10
Offices (with toilets only)
Employee
Visitor
50
10
Hotels
Room
Employee
380
50
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-9
Type/Activity
Unit
Unit Flow Rate
(l/unit/day)
Exhibition Halls
Employee
Visitor
50
20
Airport
Passenger
Employee
18
54
Car
100
Petrol (Fuel) Stations
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-10
Attachment 2-2 Pipe Gradients
AUGUST 2010
Pipe Diameter
(mm)
Minimum Gradient (m/m)
(Velocity 0.75 m/s)
200
0.00500
250
0.00370
315
0.00270
400
0.00200
500
0.00150
600
0.00120
700
0.00100
800
0.00085
900
0.00070
1000
0.00060
1100
0.00055
1200 and larger
0.00050
REVISION NO. 03
SEWERAGE 2-11
Attachment 2-3 Sewer Manhole Design Criteria
Description
Standard
Maximum Spacing between
manholes
For pipes up to 600 mm in diameter - 50 m
For pipes of 600 mm or greater in diameter - 100 m
Benching
Minimum 0.50 m width on at least one side of flow channel. Ladder
stops to be incorporated into surface.
Manhole Access
Access by electric winch and tripod or portable ladder. Ladder
stops to be incorporated in benching for emergency access. No
built-in ladder rungs or permanent ladders.
Manhole Frame and Cover
Circular opening 0.60 m minimum diameter. Cover and frame to be
machined and tagged to prevent rocking. All covers and frames in
roadways to be rated for maximum vehicle loads.
Access Shaft
Diameter 1.0 m
Length 2.5 m maximum
Barrel
Diameter 1.5 m except as otherwise noted. Based on pipe
diameter plus minimum benching of 0.5 m on one side
Safety Chains
Provide on all manholes with pipe diameter 600 mm or larger
Materials of Construction:
Access Shaft
Top Slab
Barrel
Bottom Slab
Benching
Lining
Exterior Corrosion Protection
Reinforced concrete
Reinforced concrete
Reinforced concrete
Reinforced concrete
Granolithic concrete base
GRP factory-fabricated and hand lay-up seams.
Bituminous impregnated membrane with flexible fabric
Testing
Hydrostatic and Infiltration (as specified)
AUGUST 2010
REVISION NO. 03
SEWERAGE 2-12
3
Sewage Treatment
3.1 Purpose
The purpose of the principal Design Criteria is to establish the common criteria for the process design
of Libya HIB sewage treatment plants. Following is a list of goals and objectives for these treatment
plant projects. Contractors shall provide evidence of compliance with each of these objectives in their
proposals.
1.
Sewage treatment plant processes shall be based on the following flow criteria:
2.
Up to 2,000 m /d: Aerated lagoons (AL), Stabilization Ponds (SP), or Extended
Aeration (EA)
3.
2,001 to 12,000 m /d: EA or Oxidation Ditches (OD)
4.
12,001 to 50,000 m3/d: OD
5.
Over 50,000 m /d: Conventional Activated Sludge (CAS)
6.
Conventional activated sludge sewage treatment plants shall have waste activated
sludge (WAS) thickening with gravity-belt thickeners prior to anaerobic digestion of
WAS and primary sludge. Final dewatering shall be with belt filter presses.
7.
Extended Aeration and OD plants with 37 day solids retention time can be
constructed without formal sludge digestion systems. With solids retention times <37
days, EA and OD plants will require sludge digestion, such that the combined
aeration tank and aerobic digestion SRT is at least 37 days.
8.
Plant buildings shall be architecturally designed structures with adequate heating,
ventilating, and air conditioning systems. Prefabricated structures will not be allowed.
All buildings shall be of concrete or masonry construction.
9.
Mechanical reliability standards will be equivalent to USEPA Reliability Class II.
Biological reactors and clarification shall have a minimum of two tanks for each
3
process component. For all facilities larger than 15,000 m /day, full treatment shall
be provided with any one process tank out of service. No processes shall be
bypassed under any reliability condition.
10.
All plant process basins, walkways, and stairways shall be equipped with a railing
system designed with three rails and a toe plate. The design shall be based on
standards established by the US Occupational Health and Safety Administration
(OSHA) or UK National Examination Board in Occupational Safety and Health
(NEBOSH).
11.
Pipe galleries and below grade pump rooms shall be force ventilated (powered in and
out) sufficiently to minimize potential for toxic gas buildup. Unless otherwise directed,
all buildings and structures shall comply with US National Fire Protection Association
820 standards.
12.
Water reuse will be planned for all sewage treatment plants in Libya, unless
specifically indicated otherwise. All treatment facilities shall be equipped with effluent
filtration by disc filters, continuous backwash sand filters or membrane filters.
13.
Each plant shall be equipped with a plant water system for washdown purposes, and
other uses. The system should be a non-potable water system using filtered
treatment plant effluent as a water source. The system shall include a
hydropneumatic system using either air tanks and compressors or bladder tanks.
14.
All treatment channels and basins will be reinforced concrete. All concrete structures
shall have a corrosion protective coating that extends from 0.33 m below the water
surface to the top of the tank.
15.
All metal components that are submerged or in intermittent contact with raw sewage,
including waste containers for grit and solids, shall be made of 316 stainless steel.
Galvanized steel shall not be permitted.
16.
Minimum velocities at low flow in channels shall be 0.8 m/sec.
AUGUST 2010
3
3
3
REVISION NO. 03
SEWAGE TREATMENT 3-1
17.
For long sewage pipelines, a means of oxidation of the sewage to prevent odors shall
be considered in the design.
3.2 Sewage Treatment Design Criteria
Minimum number of process units: Treatment plants shall be required to have the following minimum
number of process units or unit operation.
3
1.
Coarse Screens for plants over 2,000 m /day: (Minimum two active and one bypass)
2.
Fine Screens: 2 minimum
3.
Traveling bridge type rectangular aerated grit chambers: Single grit chamber for
lagoons and package treatment plants <2,000m3/day and two parallel grit chambers
for EA, OD, and CAS sewage treatment plants.
4.
Conventional velocity controlled grit chambers (SP): 2 minimum
5.
Primary Clarifiers (CAS): 2 minimum
6.
Aeration Tanks (CAS, OD, EA plants): 2 minimum
7.
Filter disc chambers or concrete filter chambers: 2 minimum
8.
Pump and air blower systems will have one standby unit equal in size to the largest
pump or air blower in the system
9.
Aerobic digesters: 2 minimum
All treatment plants shall be designed to allow for ease of operation and maintenance.
The treatment plants will be specifically designed to treat to water reuse standard quality and
designed to be monitored for daily performance.
All treatment plant processes will be designed in such a manner that discharge quality will be
maintained with service outage in any of the major equipment groupings including pumps, air blowers,
and mechanical mixers, sludge thickening and dewatering devices. For each surface aerator and
aerator mixer there shall be one extra mixer in each aeration basin or aerobic digester to assure
compliance with one slow speed line shaft aerator or aerator mixer out of service.
3.2.2
Population and Growth Projections
Population and growth projections shall be based on the saturated population of the Second
Generation (or Third Generation) Master Plan area with sources and requirement according to
projected population till 2025.
3.2.3
Sewage Flow Generation
Sewage treatment plants shall be designed to accommodate both the average daily flow and peak
hourly flow. Treatment plant hydraulic systems shall be designed to accommodate the peak hourly
flow.
The peak flow factor shall be based on the Babbitt formula listed in Section 2 and as calculated in
Table 3-1. The peak hourly flow can range from 2.0 to 4.0 times the average daily flow rate of the
facility. For populations above 90,000, the maximum design flow shall be based on a 2.0 peaking
factor. For populations less than 1,500, the design peak flow shall be based on a peaking factor of
4.0.
The following table presents a basis for calculating design flows for sewage facilities that include
pipelines, pumping stations, and sewage treatment plants.
Table 3-1 Calculated Peak Flow Factors for Specific Populations
AUGUST 2010
Population
Sewage Flow
< 1,500
Q < 220 m /d
4.0
2,000
Q = 290 m3/d
3.78
5,000
Q = 725 m /d
3
3
REVISION NO. 03
Peak Flow Factor
3.25
SEWAGE TREATMENT 3-2
Population
Sewage Flow
Peak Flow Factor
10,000
Q = 1,450 m3/d
2.90
20,000
Q = 4,000 m /d
2.58
50,000
Q = 10,000 m3/d
2.21
3
3
90,000
3.2.4
Q = 18,000 m /d
2.00
Sewage Loadings
Table 3-2 lists typical sewage loading values for planning and design purposes. Whenever possible,
laboratory analysis of the sewage shall be made to establish actual values for design.
Table 3-2 Typical Sewage Loading Values
3.2.5
Parameter
Value
BOD5
60 g/cap-day
TSS
80 g/cap-day
NH3
10 g/cap-day
TP
1.2 g/cap-day
COD
150 g/cap-day
pH
6.5 - 7.5
TKN
13 g/cap-day
FOG
30 g/cap-day
Design Discharge Quality Limitations
Table 3-3 lists sewage design discharge quality limitation values:
Table 3-3 Sewage Discharge Quality Limitations
AUGUST 2010
Parameter
Value
BOD5
10 mg/l
TSS
10 mg/l
NH3
1 mg/l
TP
10 mg/l
pH
6.0-9.0
TN
20 mg/l
FOG
5 mg/l
Total Coliform
MPN < 23/100 ml
REVISION NO. 03
SEWAGE TREATMENT 3-3
3.3
Site Specific Design Considerations
Sewage treatment plants shall be sited for full access to all process units, equipment, and ancillary
facilities. Following is a list of considerations in site specific treatment plant design.
1.
Altitude of site: This is important to properly design biological and oxygen transfer
systems in activated sludge sewage treatment plants. Aeration compressors shall be
sized for the ratio of actual oxygenation rate to standard oxygenation rate. Standard
oxygenation rates assume operation at sea level and 20 degrees C water
temperature.
2.
Proximity to floodplains: Treatment sites must not be vulnerable to flooding and
should be specifically designed to operate and remain in regulatory compliance
during flood events as great as that with a 4 percent probability (25-year flood). For
events with less than 1 percent probability of occurrence in any given year (100-year
flood), treatment facilities shall be protected from damage during the flood, but are
not required to meet effluent quality limitations.
3.
Temperature of influent sewage: Water temperature greatly influences the biological
reactions that occur in the activated sludge aeration basins. Higher water
temperatures (up to 35 degrees C) provide higher biological kinetics. At low water
temperatures (below 20 degrees C), bacterial growth is hindered. Process
calculations shall be performed for the maximum monthly average water temperature
and minimum monthly average water temperature.
4.
Availability of process equipment: All equipment shall be provided by vendors who
can readily service their equipment installations in Libya. It is preferable that
equipment be provided where spare or replacement parts can be delivered within two
business days.
5.
Ambient considerations: With potential for dust and sand storms and ambient
temperatures as high as 50 degrees C, certain process equipment including dry pit
pumps, aeration blowers, chemical feed systems and generators, shall be placed in
ventilated buildings. For installations in the coastal areas, shade structures may be
allowed if they have barriers protecting the equipment from wind storms.
6.
Proximity of population: Sewage treatment plants shall be sited such that they are a
minimum distance of 1,000 m from populated areas. If this cannot be accomplished
because of site availability, treatment plant design shall include mechanical odor
control measures that can include containment and odor scrubbing of off-gases from
plant pumping stations, headworks systems, primary clarifiers, and anaerobic sludge
handling processes at a minimum. Alternative sludge drying systems may be
required if odors cannot be contained within the site. Odor control methods may
include biofiltration, granular activated carbon, or multiple stage chemical scrubbers
(for extreme cases only).
7.
Structural foundation design: Subsurface geotechnical investigations shall be
conducted for treatment plant designs to enable the development of site specific
design criteria. For facilities in areas of soft or expansive soils, water bearing
structures shall incorporate the use of friction piles, bearing piles, or equivalent
structural supports. Foundation design shall be in accord with the recommendations
made in the geotechnical investigations report.
8.
Proximity of water supply wells. Sewage plants shall not be sited within 300 m of
potable water supply wells.
9.
Minimum Flows. Minimum flows will be considered in channels, pipelines, and
process mechanical systems operating ranges.
3.4 Treatment Process Design Criteria
3.4.1
Mechanical Treatment Systems
The design criteria for sewage treatment processes is categorized into many sections and have been
separated into attachments for ease of reference and use. The sections are:
Liquid Process Criteria are included as Attachment 3-1.
AUGUST 2010
REVISION NO. 03
SEWAGE TREATMENT 3-4
Liquid Process Hydraulic System Criteria are included as Attachment 3-2.
Biosolids System Criteria are included as Attachment 3-3.
Treatment Plant Piping Criteria are included as Attachment 3-4.
Mechanical Odor Control System Criteria are included as Attachment 3-5.
3.4.2
Lagoon Treatment Systems
Lagoon Treatment Systems are mostly non-mechanical. These have also been categorized into
sections and separated into attachments for ease of reference and use. The sections are:
Lagoon Treatment System General Guidelines are included as Attachment 3-6.
Aerated Lagoon Criteria are included as Attachment 3-7.
Facultative Lagoon Treatment System Criteria are included as Attachment 3-8.
Tertiary Treatment for Lagoons are included as Attachment 3-9.
3.4.3
3.4.4
Package Treatment Plant
1.
Small Package sewage treatment plants shall be pre-engineered. The treatment
plant manufacturers and equipment suppliers shall have at least 10 years experience
in the design and construction of package sewage treatment plants and the specific
treatment plants offered shall have at least 5 years of acceptable performance in the
field. The plants are intended for permanent use.
2.
The wastewater treatment process shall consist of a headworks facility suitable for
the proposed process, followed by extended aeration activated sludge with an SRT of
at least 20 days at design loadings. The treatment process types may be
conventional extended aeration or an equivalent process technology using Activated
Moving Bed (AMB) Biomedia, Fixed Activated Sludge Treatment (FAST), or
Membrane Bioreactor (MBR). With exception of the MBR plants, all small package
treatment plants shall include tertiary filtration by disk filters, or equivalent.
3.
All plant types shall have UV disinfection and chlorine dosing for residual. For all
plant types, the treatment process performance shall be equivalent to a conventional
extended aeration plant and capable of producing a stabilized waste sludge at the
stipulated loadings. Aerobic sludge digestion may be included for a lower SRT plant
as an alternative to achieving the desired sludge stabilization results. All treatment
plant types shall achieve full nitrification and substantial denitrification, as indicated by
the effluent standards to be met.
Mobile Package Treatment Plant
1.
Small and mobile package sewage treatment plants shall be pre-engineered. The
treatment plant manufacturers shall have at least 10 years experience in the design
and construction of package sewage treatment plants and the specific treatment
plants offered shall have at least 5 years of acceptable performance in the field.
Tankage shall be high quality structural steel with the best available coatings for
corrosion protection. Sacrificial anodes shall be supplied with every steel tank or
structure. The plants are intended for temporary use while permanent facilities are
under construction. When no longer needed, the plants are intended to be relocated
by others either to storage or to another location in need of a temporary treatment
plant.
2.
The wastewater treatment process shall consist of a headworks facility suitable for
the proposed process, followed by activated sludge using Activated Moving Bed
(AMB) Biomedia, Fixed Activated Sludge Treatment (FAST), or Membrane Bioreactor
(MBR). The FAST and AMB Biomedia treatment plants shall include tertiary filtration
by disk filters, or equivalent. All plant types shall have UV disinfection and chlorine
dosing for residual. The treatment process reactors shall have an F:M ratio (food to
microorganism ratio) equivalent to an extended aeration plant and minimum SRT of
20 days, capable of producing a stabilized waste sludge at the stipulated loadings.
AUGUST 2010
REVISION NO. 03
SEWAGE TREATMENT 3-5
3.5 Structural Design
Structural design of water and wastewater facilities shall meet the requirements described in
Section 1.
AUGUST 2010
REVISION NO. 03
SEWAGE TREATMENT 3-6
Attachment 3-1 Liquid Process Design Criteria
Coarse Bar Screens for all plant types
Opening Size Coarse Screens
15 to 25 mm
Location
Influent pump station, headworks bypass channel
Maximum Head Loss, Clean Screen
0.3 m
Operation
Manually cleaned bar racks shall be limited to facilities with
3
capacities less than 15,000 m /day with larger facilities being
the mechanical type. Drum screens and mechanical rakestyle screens mechanical screens are acceptable.
Auxiliary Equipment
For mechanically cleaned screens, screenings conveyor and
screenings compactor are required. All installations require
screenings waste container with 5-day storage capacity.
Fine Screening for CAS, EA, and OD systems
Opening Size Fine Screens
Range 6-10 mm (fine)
Maximum Head Loss, clean screen
0.3 m
Bar screen, step screen, band screen, or perforated plate
screen.
Screen Types
Step screens shall include a continuous flushing system for
the bottom step.
Drum screen with 2.5-5mm opening size (plants larger than
3
15,000 m /day- OD and CAS only)
Screen and wetted parts
316 stainless steel
Auxiliary Equipment
Screenings conveyor, screenings compactor and screenings
waste container. Systems to be a simple as possible with
screenings dropping from screens into containers where
practical. Waste container shall have 5-day storage capacity.
Coarse screens followed by fine screens.
Operation
Underwater Bearings
Automatically cleaned. Screen systems to be simple, drop
directly to containers. Provide screenings washer compactor
systems on screens 12 mm and smaller opening size. Use
conveyors only where required.
May be allowed for selected screens
Aerated Grit Chambers
Design Hydraulic Detention Time
10 min at peak hourly flow
Minimum Depth
2m
Length to Width Ratio
3:1 or more
JULY 2010
REVISION NO. 03
Sewage Treatment 3-7
Aerated Grit Chambers
Aeration
Coarse bubble diffused aeration
Aeration Rate
0.2 to 0.5 m3/m-min
Grease Removal
Grit removal and grease removal shall be integrated in an
aerated channel system
Grit Pump
Centrifugal recessed impeller of hardened materials, or air lift
for traveling bridge
Air Blowers for aerated grit chamber Tri-lobe positive displacement air blowers
Grit Washer
316L stainless steel and capable of producing grit with less than
3-5% organics in the treated grit for all grit systems.
Auxiliary Equipment
Grit container with 5-day storage capacity
Primary Clarifiers (CAS only)
Treatment
>50,000 m3/d
Configuration
Circular
Surface Overflow Rate – average
(peak)
30-50 m3/m2-day (80-120 m3/m2-day)
Minimum Sidewater Depth
3m
Minimum Freeboard
0.5 m
Weir and Launder System
Adjustable 316 stainless steel weir plate and peripheral
launder.
Weir Loading Rate – average (peak)
125-250 m /m-day (250-500 m /m-day)
Mechanism Type
Center or rim drive with spiral blade collectors
Scum Skimmer
Single scum skimmer with 1200 mm wide beach. Scum
system will include chopper pumps with recirculation
provision.
Spray Systems
Primary clarifiers will have spray systems for scum removal
Scum Baffle depth
600 mm
Sidewater depth
3.5 m to 6 m
JULY 2010
3
REVISION NO. 03
3
Sewage Treatment 3-8
Aeration Basins (CAS, EA, OD)
Design Hydraulic Retention Time
(HRT)
8 hrs (CAS) with all units in service; 30 hours (EA and
OD)with all units in service
Design Mixed Liquor Suspended
Solids (MLSS)
1,000-3,000 mg/L (CAS); 2,000-5,000 mg/L (EA ); and 3,0005,000 (OD)
Design Solids Retention Time (SRT)
3-15 days (CAS); 15-30 days (OD ); and 20-40 days (EA)
Design Food to Microorganism Ratio
(F/M) (kg BOD/kg MLVSS-d)
0.04-0.10 (OD and EA ) and 0.2-0.4 (CAS)
Bridge mounted aerator mixers (CAS, EA).
Brush or disk rotor and orbal aerators (OD)
Types of Aeration Systems
Fixed slow speed or two-speed surface aerators mounted on
concrete bridges or bottom mounted aerator and sparge ring
mounted on concrete platforms for CAS and EA systems.
Fine bubble diffusers are not acceptable due to diffuser
interference with cleaning of basin bottoms.
Minimum Sidewater Depth
3.5 m
Minimum Freeboard
0.5 m
Secondary Clarifiers
Configuration
Circular
3
Surface Overflow Rate – average
(peak)
2
3
2
3
2
16-28 m /m -day (40-64 m /m -day) (CAS); 8-16 m /m -day
3
2
(24-32 m /m -day) (EA and OD)
Long SRT systems produce lower density sludge requiring
shorter settling time clarifiers for EA and OD Systems
4-6 kg/m2-hour (8 kg/m2-hour )(CAS);
2
2
1-5 kg/m -hour (7 kg/m -hour) (EA and OD).
Solids Loading Rate – average (peak)
EA and OD sludge settles poorly and the loading rate has to
be lower than for CAS based on lower solids retention time
(SRT).
Minimum Sidewater Depth
4m
Minimum Freeboard
0.5 m
Weirs and Launder
External perimeter type. Launders to be concrete with FRP
weirs and scum baffles.
Weir Loading – average (peak)
125 m /m-day (300 m /m-day)
Scum Baffles
600 mm depth, minimum 1,200 mm wide scum beach
Mechanism Materials
All mechanism elements below water line shall be 316L
stainless steel
JULY 2010
3
REVISION NO. 03
3
Sewage Treatment 3-9
Secondary Clarifiers
Scum pump system
Chopper pump system with provisions with recirculation
mixing system for improving pumpability of mixture.
Scum spray system
Spray system required for scum removal
Clarifier baffles
Clarifiers to be equipped with impinging type baffles
Spiral scraper with center drives or rim drives.
Sludge Collector Mechanisms
Suction type similar to rapid sludge return (RSR) clarifier or
spiral blade type. Direct suction type through slotted tapered
tube.
Filters
Type of Filter
Hydraulic Loading Rate
Continuous backwash upflow filtration (fluidized bed type) or
stainless steel or fabric disc filters designed in accordance
with manufactures recommendations. These are designed for
maximum flow through the system.
3
2
3
2
15 m /m -h for fabric disc filter at max flow
15 m /m -h for fluidized bed filters at max flow
Disc filter submergence
60% maximum at max flow or per manufacturer
recommendations
Minimum Sand Media Depth
2.0 m
Single Filter Module Dimension
2 m x 2 m (fluidized bed)
Tankage
Reinforced concrete
Basin coating system
All concrete structures shall have a corrosion protective
coating that extends from 0.33m below the water surface to
the top of the tank.
Disinfection
Method
Ultraviolet radiation (UV)
Minimum dosage
80 mJoules/cm
Discharge limit
Total coliform: <23 colonies per 100 ml
Enclosure
UV systems shall be open channel type, housed in site-built
buildings
JULY 2010
2
REVISION NO. 03
Sewage Treatment 3-10
Supplemental Disinfection
Method
Sodium hypochlorite (12.5% solution)
Minimum dosage
2 mg/l at peak effluent flow rate
Tank Material, Size
Cross-linked fiberglass reinforced plastic (FRP), 6 m or 1
week supply whichever is greater
3
JULY 2010
REVISION NO. 03
Sewage Treatment 3-11
Attachment 3-2 Liquid Process Hydraulic System Criteria
Inlet Structures and Flow Splitting
Influent structure (Concrete)
Influent structures shall have concrete covers with positive
odor control.
Flow split structures (Concrete)
Provide weir slide gates or flumes for proportional split of
flow to individual process units.
Liquid Process Hydraulic Flow Distribution
Design Flow
Maximum flow
Channel Construction
Concrete with open grating above
Screening Channels features
Isolation gate valves upstream and downstream of each
screen
Ability to dewater any portion of the screening channel that
can be isolated
Screen channel shaped to sloped to prevent grit
accumulation at lower flowrates.
Channel Velocity, unaerated (minimum)
Raw sewage 0.8 m/sec; settled sewage 0.3m/sec
Gravity Pipe Velocity (minimum)
0.66 m/sec (partially filled)
Pressure Pipe Velocity (maximum)
3 m/sec
Distribution box gates
Provide to each process basin
Gate Materials
316 stainless steel
Return Activated Sludge Pumping
Return Activated Sludge Design Flow
0.25 to 1.5 x the Average Daily Flow, depending on
process
Archimedes screw pumps
Submersible (wet) pumps
Allowable Pumps
Solids handling single vane centrifugal pumps with VFDs
Dry pit solids handling submersible pumps with VFDs
Waste Activated Sludge Pumps
Design Flow
5% of treatment plant Average Daily Flow (variable)
Allowable pumps
Dry pit solids handling submersible pump
Submersible (wet) pumps
Solids handling single vane centrifugal pumps
JULY 2010
REVISION NO. 03
Sewage Treatment 3-12
Chemical Feed Pumps
Mechanical Diaphragm Pumps
<200 l/hr
Stainless Steel Progressive Cavity
Pumps for Polymer Only
200 l/hr to 1,000 l/hr
Hose Pumps
> 1,000 l/hr
JULY 2010
REVISION NO. 03
Sewage Treatment 3-13
Attachment 3-3 Biosolids System Criteria
Secondary Sludge Thickening Systems
Design Flow
Minimum 2% of plant Average Daily Flow, to be confirmed
by process modeling supplemented by empirical
calculations. For plants with capacity less than 5,000
m3/day, gravity thickeners cannot be used because the
flow is too small, and gravity belt thickeners cannot be
used because the sludge will be too thick for aeration in
the digester.
Solids Loading Rate
3 kg/m h
Acceptable Mechanisms
Center pivot type with rotating rakes and sludge collection
pockets (picket fence).
Gravity belt thickeners prior to anaerobic digesters
Rotary screw dewatering for plants with mixed anaerobic
digesters.
Typical Sidewall Depth
3 m for picket fence thickeners
Material
316 stainless steel mechanisms below water line
2-
Process to Thicken 0.7% Waste Activated Sludge to maximum 3% ahead of digesters
Aerobic Digesters (EA and OD Systems) with design solids retention time less than 30 days
Design Flow
2% of plant Average Daily Flow
Design Solids Retention Time
The SRT in days shall be equal to 37 minus the aeration
basin SRT in days.
Aeration
Coarse bubble air diffusion or line shaft surface aerators.
Allowable mixing systems with
prethickend sludge ( Picket Fence
prethickening)
Slow speed draft tube mechanical (35 rpm) for circular
reinforced concrete tank (with coarse bubble aeration only)
Decanting
Provide for plants with capacity less than 5,000 m3/day.
Telescoping valves are acceptable.
Minimum Freeboard
0.5 m
Anaerobic Sludge Digesters
Design Flow
2% of plant Average Daily Flow or as calculated.
Design Solids Retention Time
18 days, at 35 degree operating temperature.
Anaerobic Digester Mixing Options
Slow speed draft tube mechanical (35 rpm) for circular
reinforced concrete tank with concrete roof
Tangential pumped sludge mixing design for thickened
sludge concentration up to 5%
Circular reinforced concrete tank
Anaerobic Digester System Features
JULY 2010
Separate stainless steel gas holding tanks. Typical gas
storage 4-8 hours.
REVISION NO. 03
Sewage Treatment 3-14
Anaerobic Sludge Digesters
Energy recovery using dual fuel power generators.
Excess gas is to be flared or used to support power
generation
Sludge Drying Beds
Design Cycle Interval
25 days
Tankage
Concrete walls and floors
Wall Height
1.2 m
Max Cell Size for Sludge Removal
15 m x 30 m
Design Pan Evaporation
1 m/yr or as documented for specific location for winter
months
Population Based Area Estimation
0.2 m /population equivalent served, without pre-thickening
2
Belt Filter Press Systems
Material of Machine Housing - 316 stainless steel
Type of Enclosure - Site built building with odor control systems if located near populated areas.
JULY 2010
REVISION NO. 03
Sewage Treatment 3-15
Attachment 3-4 Biosolids System Criteria
Pumps and Piping For Treatment Plants
Raw sludge pumping
Constant speed recessed impeller pumps. Timer control
Secondary sludge pumping
Single vane, solids handling pumps for WAS
Screw centrifugal pumps for 0.25Q to 1.5 Q RAS range of
operation,
Archimedes screw pumps
Digested sludge pumping
Chopper pumps or rotary lobe pumps
Flanged ductile iron with cement mortar or ceramic epoxy
lining for exposed and buried. PVC, HDPE, or ductile iron
for buried piping
Liquid Process Piping
Solvent welded schedule 80 CPVC piping, flanged at
valves and equipment, when indoors for corrosive liquids
including all process chemicals
316L SS or PVC for Ø < 80 mm
Potable Water Pipe
Ductile iron for Ø > 80 mm
Sludge and scum system piping
Cement-mortar lined ductile iron
Process Air Piping
Schedule 5S T316L stainless steel for exposed, for buried
installation use Schedule 10.
Valves to be SS, HP butterfly valves for isolation.
Iris valves with mass flow meters for air control valves.
Chemical Piping
Use CPVC piping, solvent welded flanged only at valves
and equipment. No threaded connections permissible.
Valves on Gravity Pipelines
Eccentric cast iron plug valve, handwheel operated
Valves on Pressure Pipelines
Motor operated cast iron eccentric plug valves, check
valves to be Val Matic type
Influent Flow Monitoring
Magnetic flow meters or FRP parshall flume, cast-in-place
concrete
Flow monitoring on all Sludge Streams
Magnetic flow meters
Pipe Supports
All pipe supports that are not concrete saddles shall be
T316L stainless steel
Valve Operators
Geared operators for all plug valves, hand wheels for knife
gate valves, use electric actuators for 600 mm and larger
valves
JULY 2010
REVISION NO. 03
Sewage Treatment 3-16
Attachment 3-5 Mechanical Odor Control System Criteria
Mechanical Odor Control Systems
Terminal pumping station wetwells
Flow distribution chambers
Treatment Plants located within 2000 m
of Populated Areas will be equipped with Conventional grit chambers
Mechanical Odor Control Systems for the
Primary clarifiers (odor control dome or flat covers) for
following Process Areas
clarifiers within developed communities
Sludge thickening and mechanical sludge dewatering units
Biological filtration with activated carbon polishing for
normal loadings
Types of Treatment
Design Air changes
Wet chemical scrubbers for anticipated extreme odor
issues, as at inlet works receiving flow from long pipelines.
Chemical dosing along pipelines may also be needed to
control difficult odor problems.
1.5 air changes per hour plus aeration volume (tanks,
channels and wetwells)
12 air changes per hour continuous (rooms with open
sewage tanks)
30 air changes per hour intermittent (hazardous chemical
storage rooms), upon building entry.
Odor control systems shall be designed specifically for the constituents of the off-gases intercepted.
JULY 2010
REVISION NO. 03
Sewage Treatment 3-17
Attachment 3-6 Lagoon Treatment System General Guidelines
Lagoon Treatment Plants General Guidelines
3
Suitable for flows less than 2,000 m /day. Larger systems will be
considered on a case by case basis, provided that land is available
and the topography, geology, and site location is appropriate for
lagoon construction and operation.
Basic advanced wastewater
treatment using anaerobic and Suitable for large open areas more than 1,000 m away from
populated areas.
aerobic biological pond
systems
Pond systems can be very minimally mechanized for very low
operation and maintenance costs. They will require a full time
operation and maintenance staff for maintenance operations that
resemble farming operations.
Lagoon Plants shall be designed to treat to a level suitable for a
broad range of water reuse. Either continuous flow submerged
wetlands or intermittent sand filtration are appropriate for providing
the desired water reuse effluent quality. Other advanced treatment
methods will be considered on a case-by-case basis.
Tertiary Treatment
Lagoon treatment plants with maturation ponds and or constructed
tertiary wetlands will not be required to have disinfection.
Aerated lagoon plants with intermittent sand filters shall have
horizontal open channel ultraviolet disinfection systems.
JULY 2010
REVISION NO. 03
Sewage Treatment 3-18
Attachment 3-7 Aerated Lagoons Criteria
Anaerobic Lagoons followed by two-stage aerated lagoons (AL), and settlement ponds
Approximate size per 1,000 m3/day capacity 10 ha including tertiary
wetlands.
Anaerobic Lagoons
shall not be located
within 2,000 meters of
populated areas. Where
this is not possible
anaerobic lagoons shall
be covered as an odor
control measure.
Flow inlet and outlet chambers shall be diagonal from each other to prevent
short circuiting
Three flow channels, two mechanized, one non-mechanized
3- coarse screens, 2- mechanical fine screens
Grit chambers: 2 rectangular traveling bridge type aerated grit chambers
with coarse bubble air diffusers and grease removal. Ancillary systems
include cyclone separator and grit classifier, conveyor and 2-500 liter grit
storage bins
Aspect ratio 2:1
Excavation and embankment slopes 3:1
Anaerobic Lagoon
Pond depth 4 - 5 m
Detention time 4-5 days
Lining 150 mm concrete wearing surface panels over 60 mil thick HDPE
(high density polyethylene)
Aerated Lagoons
Stage 1 Aerated Lagoon – complete mix with air transfer sized for complete
oxidation of influent biochemical oxygen demand and ammonia (NH4). Five
day hydraulic residence time.
Stage 2 Aerated Lagoon – 50% complete mix. Primary role will be
nitrification and partial denitrification. Eight day hydraulic residence time.
Stage 3 Final settling of suspended solids. Two day hydraulic residence
time. Final settlement pond - depth 4-5 meters.
Aspect ratio 2:1
Minimum number of lagoon trains 2
Excavation and embankment slopes 3:1
Minimum water depth 4.0 meters
Freeboard 0.8-1.0 meters
Aeration Equipment
Floating, cable stayed slow speed line shaft surface aeration
One spare aerator for each 3 duty aerators
Aerated Lagoon Lining
1.5 mm HDPE (high density polyethylene) extended and anchored in top of
embankments.
JULY 2010
REVISION NO. 03
Sewage Treatment 3-19
Attachment 3-8 Facultative Lagoon Treatment System Criteria
Anaerobic Lagoon followed by Stabilization Ponds (SP) and Maturation Ponds
3
Approximate site area requirement 15 ha per 1,000 m /day
MINIMAL ENERGY AND MINIMUM MAINTENANCE REQUIREMENTS
Fixed 25 mm manually cleaned bar rack followed by
manually cleaned grit chamber
Screening and grit removal
Flow distribution chambers will be arranged with inlet and
outlet boxes diagonal from each other (AL) (SP)
Manual grit chambers (SP)velocity controlled at 0.4 m/sec
Aerated grit chambers (AL)
Anaerobic Lagoons provide primary
treatment, with an estimated 50%
removal efficiency for BOD5 and TSS
similar to the previously presented
Aerated Lagoon system
Stabilization Ponds, also called
Facultative Ponds. These ponds are
oxygenated by algal photosynthesis.
Maturation Ponds
(to provide additional solar based
oxidation and reduction of coliform
related bacteria, with some
denitrification)
JULY 2010
Nominal hydraulic detention time 5 days (AL) (SP)
Basin interior and exterior slopes 3:1 (AL) (SP)
Minimum number 2 for all pond treatment systems
(minimum 2 process trains)
Minimum number of lagoons 2 in series per process train
Slopes of excavation and embankments 3:1
Design water depth 1.5 meters with 0.8-1.0 meter
freeboard
1.5 mm thick high density polyethylene liner
Design hydraulic residence time 15 days .
Inlet and outlet boxes to be diagonal from each other for all
pond systems, to reduce short circuiting in the lagoons.
Design water depth 1.5 meter
Design hydraulic residence time 15 days
Design water depth 1 meter
Slope of excavation and embankment 3:1
Aspect ratio 2:1
Lining 1.5 mm thick HDPE
Minimum number of maturation ponds 2 in series per
process train
REVISION NO. 03
Sewage Treatment 3-20
Attachment 3-9 Tertiary Treatment Criteria
Tertiary Wetlands
Tertiary Wetlands shall be of the submerged flow-though Wetlands Type designed for the removal
of all nitrogen and phosphorus remaining in Lagoon treatment plant effluent. Effluent from the
wetlands can be piped to a earthen treated water reservoir equal in size to one day’s plant average
design flow that will be used for water reuse purposes.
Hydraulic flow distribution. This will be using at-grade level distribution channel with overflow
rectangular weirs placed at 4 meter intervals. Stop logs will be used to block off selected weirs to
facilitate uniform flow distribution.
Number of process trains shall be 2.
Number of wetland cells per train shall be 4.
Method of flow distribution is a concrete open channel system.
Aspect ratio (L:W) shall be 2:1.
Embankment slopes shall be 3:1.
Control gates shall be 316 stainless steel gates for primary channels and plastic stop logs for
regulating flow to wetland cells.
Design evapotranspiration rate using the Thornwaite Method is 0.84 m/year.
For annual precipitation data, use data from the World Weather Information Service for the area.
Wetlands plants shall be aquatic plants and grasses that are indigenous to the general location of
the treatment plant
Underlying gravel shall be 10 mm gravel, one meter deep. For horizontal subsurface flow (HSSF)
wetlands, depth shall be 0.3 m.
Alternative wetland systems such as open flow and subsurface flow wetlands can have surface flow
as well as subsurface flow.
Lining system for all wetland cells shall be 1.5 mm (60 mil) HDPE.
Groundwater shall be at least 1 meter below the wetlands.
JULY 2010
REVISION NO. 03
Sewage Treatment 3-21
Intermittent Sand Filtration
Intermittent Sand Filtration will be designed to filter out residual suspended solids and to reduce the
remaining nitrogen in lagoon effluents.
Hydraulic flow distribution. Duplex pump systems shall be used to pump the flow to alternating pairs
3
2
of sand filters. Filters shall be sized in accordance with published guidelines or 0.1 m /m -day,
which equates to 1 hectare filter area for 1,000 m3/d flow.
Intermittent sand filters shall be constructed with vertical concrete walls and bottom concrete slab.
0.25 – 0.35 mm Sand shall have a depth of 1.1 meters and shall be placed over 0.33 meters of 4
mm gravel. Effluent shall drain thru slotted pipes laid at the base of the gravel material.
Aspect ratio is 2:1
Minimum number of filters: 2 in parallel
JULY 2010
REVISION NO. 03
Sewage Treatment 3-22
4
Storm Water
HIB has developed design criteria for storm water drainage systems for use in their projects. The
criteria are presented to support the design intent of the HIB infrastructure. The intent of this section
is to provide design criteria for storm water only, free from sewage or other wastewaters. It is
understood that certain situations may require deviation from the criteria presented herein and under
this circumstance approval of the proposed criteria from HIB is required.
Since rainfall events in Libya are relatively infrequent, the design engineer should evaluate the best
storm management approach based on the information provided in this document to achieve a
balance between construction cost and an acceptable level of performance.
4.1 Storm Water Management Policy
Management of storm water is governed by Libyan Laws; two of the most pertinent articles from the
Libyan Law No. (15) of 1370 PD (2003) for Protecting and Improvement of the Environment are as
follows:
Article (34) prohibits discharge of polluted water to the sea. The Article reads:
“It is prohibited to discharge polluted water into the sea directly through drainage
pipes, whether the drainage is on the coast or therefrom or through canals or sewers,
including internal gravity flow water courses before treatment thereof as per the
effective legislations and regulation issued for implementing.”
Article (43) reads:
“The domestic and industrial drainage water is considered as a water sources and
shall not be wasted or disposed of after treatment thereof, unless it is proved that its
use is impractical. Then, it shall be disposed of under the rules and regulations issued
without causing any environmental pollution.”
In general, Libya receives little rainfall, most of the rainfall occurs in coastal areas. The average
annual total rainfall along the Mediterranean Coast ranges from 559 mm at Shahat in the eastern
0
coast line to 238 mm at Zwara close to the Tunisian boarder. South of 30 N Libya is almost all desert
with annual total rainfall ranging from 20 mm at Al Kutra to 9 mm in Sebha.
The Housing and Infrastructure Board (HIB) is building infrastructure throughout the country. The
infrastructures consist of housing, roads, and facilities for water distribution and treatment, for
wastewater collections and treatment, and for storm water collection. As development progresses the
land use of the area changes, increasing the impervious surface that do not readily absorb rainfall
runoff. Therefore, sound and practical storm water management practices must be implemented to
effectively utilize the precious resource - water.
4.1.1
Storm Water Quantity Management
As part of formulating a comprehensive Storm Water Management Policy, HIB has developed
background information and criteria and best management practices for storm water quality
enhancement. The storm water management objective is to eliminate or minimize discharge of storm
water runoff from the design storm to the Mediterranean Sea. Where this is not achievable HIB should
be consulted in advance and the project will be reviewed on case-by-case basis. As a general guide
line the options presented below should be taken into consideration. The items listed below are toolsin-a-tool-box and should be regarded as a general guidance and applied on a case-by-case basis for
a particular site.
Where topographic conditions of the site and project conditions allow, rain water should
be collected from roof tops into underground or ground level cisterns for onsite landscape
irrigation. The storage cisterns should be adequately sized based on the rainfall
information and amount of roof top area. Basic information such as runoff coefficient for
various land use can found in the in Section 4.2.
Storm water runoff from paved surfaces such as parking lots could be directed to sheet
flow to nearby landscaping areas or collected and stored during the rainy season for
landscape irrigation in the summer months. Runoff from the parking area may be
contaminated and requires per-treatment to remove sediment, sand, trash, and other
pollutants that are washed away from the paved surfaces. The treatment envisioned
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-1
should be simple and effective technique that reduces trash and sediment that could be
trapped or removed with extended detention.
Storm water runoff could be collected from the road ways through collector pipes and
stored and used for landscape irrigation at the appropriate locations after pre-treatment.
Guidance for sizing methodology of storm water collectors and conveyance system
including rain-fall intensity duration curve for several location in Libya is included in this
document.
Storm water could be collected from the impervious surfaces and allowed to infiltrate into
the ground to recharge the ground water. Guidance for sizing methodology is included in
this document.
4.1.2
Enhancing Storm Water Quality
Storm water from paved surfaces such as roads is contaminated with various pollutants such as trash,
sediment, oil and grease, bacteria and other pollutant as a result of human activity. Some degree of
treatment is required depending on the reuse objectives and receiving outfall such as ecologically
sensitive areas. The quality of storm water can be greatly improved by utilizing simple but effective
treatment technologies. Most of the pollutants in storm water runoff can be trapped at the source
before reaching the storm water collection and conveyance system. For pollutants that cannot be
trapped at the source, the storm water runoff could be collected and detained at strategic locations to
remove pollutant by gravity settling. When further enhancement is desired, the storm water runoff is
directed into a treatment system further enhancement.
The activity of enhancing the quality of storm water is generally referred as Best Management
Practice. Best Management Practices could be both non-structural and structural measures.
Non-structural measures include street sweeping, public education such as anti-litter campaign and
proper disposal of solid waste or trash. Non-structural measures could be very effective in reducing
gross pollutants such as plastics which do not bio-degrade. Proper and strategically placed signs and
billboards could be very effective methods of public educations. Structural measures require
construction of structures such as oil-and-water separators, detention basin, filter strips, grass swales,
and infiltration tranche and basin.
The above mentioned practices should be evaluated on a case-by-case basis for applicability in the
particular project site.
4.2 Storm Water Design Criteria
Storm water facilities design must be compatible with the appropriate storm water discharge and
disposal options. For example, it must be determined if the storm water will be collected and removed
from the site or if it will be retained on site and allowed to infiltrate into the ground and/or evaporate.
In general, Libya has a dry climate. Rainfalls in Libya are intense, short in duration, and infrequent.
Along the Mediterranean coast, the wettest months are from September to March. For example, the
average annual total rainfall in Tripoli is approximately 230 mm based on 40 years data recorded at
Tripoli International Airport. The maximum annual total rainfall in Tripoli during the same period was
560 mm recorded in 1982 and with a minimum annual total of 52 mm recorded in 1999. Other areas
in the country have significantly different rainfall records. Thus, the approach to storm water drainage
design must consider the local rainfall records for determining the appropriate design storm.
4.2.1
Design Storm
Design rain storms are typically determined based on long term rainfall records to develop values for
various recurrence intervals. For local drainage facilities such as subdivision collector roads, a storm
with a 5-year recurrence interval shall be used for calculating storm water runoff and sizing drainage
collectors and mains. For major drainage facilities, a 50-year storm event shall be used for calculating
storm water runoff and sizing the major drainage facilities. Major drainage facilities are large facilities
that receive inflows from multiple local drainage areas. Major drainage may also be critical drainage
areas, such as airports or underpasses, where localized flooding is unacceptable. A 25-year design
storm shall be used for sizing the collection system for freeway or major roads such as the Ring
Roads.
This section provides the design storm for sizing drainage facilities for different locations in Libya.
However, if the design storm is not available for a particular project location, the designer is
responsible for collecting and evaluating the available rainfall data and calculating the intensityduration of the design storm appropriate for the project location. The proposed design storm intensity
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-2
and duration shall be reviewed and approved by HIB before any detailed designs are undertaken.
Copies of all rainfall data used for determining the design storm shall be submitted together with the
calculated design storm intensity-duration for the design frequency.
Rainfall intensity-duration for the various frequencies for the City of Tripoli have been collected and
should and used for design purposes. An intensity curve is also provided and presents the same
information in a graphic form for 5 and 50 year recurrence intervals.
Intensity-Duration Data for Tripoli are included as Attachment 4-1.
Intensity-Duration Data for Misrata are included as Attachment 4-2.
Intensity-Duration Data for Benghazi are included as Attachment 4-3.
Intensity-Duration Data for Derna are included as Attachment 4-4.
Meteorological Station Locations are included as Attachment 4-5.
4.2.2
Runoff Coefficients
Runoff for the design storm event shall be calculated based on the Rational Method, whereby the
runoff flow, Q, equals a coefficient, C, times storm intensity, i, times the catchment area, A.
Where:
i - Rainfall intensity, m/sec
C – Runoff coefficient (dimensionless)
2
A – Drainage area, m
3
Q – Flow, m /sec
Runoff Coefficient Values and shall be used for design runoff flow calculations. Composite runoff
coefficients in each catchment can be determined by multiplying specific land use areas by their
respective coefficients and dividing the sum of these products by the total drainage area.
Runoff Coefficient Values are included as Attachment 4-6.
Sample Hydraulic Analyses Calculations are included as Attachment 4-7.
4.2.3
Runoff Volumes
Runoff volumes are calculated based on individual catchment areas, catchment characteristics and
the design storm(s). The equation for runoff flow volume for any given catchment is shown below:
Where:
V
C
d
A
3
is the runoff volume (m )
is the runoff coefficient (dimensionless)
is the total storm depth (m)
is the catchment area (m2)
Design flow rates are based on clearing the runoff volume within the required clear time after the end
of the storm event without exceeding the maximum allowable depth of localized flooding. Based on
hydraulic analyses, in locations where localized ponding does not exceed the maximum allowable
depth and with the required clear time, an average design flow may be used for sizing the drainage
conveyance and pumping stations. The average flow rate is determined by the following relationship:
=
Where:
Qavg
V
AUGUST 2010
)
average runoff flow rate (l/s)
3
runoff volume (m )
REVISION NO. 03
S TORM W ATER 4-3
ts
ct
storm duration (hours)
clear time (hours)
Where possible, sizing collection networks based on an average runoff rate can reduce the overall
size and cost of the collection system. Some facilities, such as roadway underpasses, require a zero
clear time. In such cases, the maximum peak flows should be accommodated by the drainage piping
and pumps.
4.3 Hydraulic Analyses
Hydraulic analyses shall be carried out using the Manning’s formula or approved computer modeling
software. Acceptable models are Infoworks, SewerCAD, Mouse Model, InfoSewer, and SWWM.
Other equivalent commercially available models may be used with prior written approval by HIB.
Roughness coefficients based on the pipe material shall be used. The roughness coefficient is a
measure of the friction resistance to flow by the interior surface of the pipe. The roughness therefore
is a function of the pipe material, age, and condition. Poor pipe conditions are to be assumed for
system designs. However, pumping facilities shall be designed to operate satisfactorily for either
normal or poor conditions.
4.3.1
Flow Velocities
The minimum design velocity allowed through drainage conduits (to prevent excessive settling of
solids) and the maximum flow allowed, to avoid abrasion of the gravity conduits, are as shown in
Table 4-4.
Table 4-1 Typical Roughness Coefficients
Manning’s, n
Pipe Material
Normal
Maximum
uPVC
0.010
0.013
GRP
0.010
0.013
HDPE
0.010
0.018
RCP
0.012
0.016
In situations where the minimum design velocity cannot be achieved for gravity pipe, the distance
between manholes should be reduced to better accommodate more frequent cleaning.
Table 4-2 Minimum & Maximum Velocities
4.3.2
Pipe Description
Minimum Velocity
(m/s)
Maximum Velocity
(m/s)
Gravity pipe
0.75
3.0
Pressure pipe
1.0
2.0
Clear Times
Allowable clear times have been established for the different types of areas where new storm water
drainage may be required. These times refer to the period of time after the end of a storm event
during which limited water ponding is permitted. Table 4-3 identify the clear time for each of the main
service areas. The maximum allowable depth of ponding along the roadway with curb and gutter is
the height of a road curb which is 150 mm.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-4
Table 4-3 Allowable Clear Times
Area Designation
Clear Time, hours
Comments
Freeways/Expressways
0
See Note 1
Arterial Roads
0
See Note 1
Collector Roads
1
Local Roads
1
Roadway Underpasses
0
Parking Lots
3
Airport Runways
0
See Note 1
Airport Taxiways
0
See Note 1
Airport Infield
24
See Note 2
See Note 1
Notes:
1. Water shall be cleared within the time frame of the storm, and flooding during the storm will be
minimized to avoid unnecessary disruption of traffic.
2. Shorter clear times shall be sought where possible.
4.3.3
Depth of Flow
The design depth of flow for all drainage pipes is assumed to be full, and when surcharged the energy
grade line should not be higher than the natural ground surface. The system may be designed to
operate under surcharge flow conditions for most pipes in order to achieve the required clear times.
4.4 Pipe Materials
Drainage pipe materials have been selected to be consistent with local standard practices, based on
economics and local availability. Table 4-4 lists allowable pipe materials for various pipe sizes.
Table 4-4 Allowable Pipe Materials
Pipe Material
Diameter (mm)
uPVC, HDPE
250 to 600
GRP, RCP
300 to 1400
RCP
Greater than 1400
The minimum pipe diameter permitted for drainage system gravity collection pipes is 300 mm. Land
subdrains under detention ponds and infiltration areas can be 200 mm in diameter. Connections to
street gutters and other inlets may also be 200 mm diameter, and shall have a slope of 2 percent or
greater.
RCP pipe shall be provided with protection from sulfide corrosion, such as PVC or GRP lining or
possibly a sacrificial lining of mortar with calcareous (limestone) aggregate.
4.4.1
Pipe Gradients
Minimum gradients are determined based on minimum scour velocity requirements. Larger pipe
diameter gradients are based on constructability as well as minimum velocity requirements.
Recommended minimum gradients are listed in Table 4-5. The minimum gradient considered
technically achievable during construction is 0.00050 m/m.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-5
Table 4-5 Minimum Pipe Gradients
4.4.2
Pipe Diameter (mm)
Minimum Gradient (m/m)
250
0.00246
300
0.00190
400
0.00132
500
0.00098
600
0.00077
700
0.00063
800
0.00053
900
0.00050
1000
0.00050
larger than 1000
0.00050
Minimum Cover Requirements
For gravity pipes, the minimum recommended cover in order to protect from external loads is 1.2 m
above the pipe crown. For pressure pipes, minimum cover is 0.8 m in unpaved areas with no
vehicular traffic and 1.0 m in paved areas with vehicular traffic. If the available cover is less than
specified, then additional protection such as full concrete encasement or the use of concrete
protection slabs may be required.
The actual cover required for construction and access may be greater than that required solely for
structural integrity. For example, the minimum cover required by the physical dimensions of a typical
access manhole is 2 m above the pipe crown. However, for small pipes less than or equal to 300 mm
in diameter, the required cover may be less than 1.2 m. In such cases, if inspection chambers are
installed rather than manholes, 1.0 m of cover may suffice.
The maximum cover depth recommended is approximately 10 m. This maximum depth is consistent
with typical pipe installation standards and manufacturer recommendations. Should the actual cover
be greater than 10 m, pipe material selection should be evaluated and a higher strength class of pipe
utilized.
For pipes installed less than the recommended minimum or more than maximum depths, concrete
encasement may be required to protect the pipe from damage or collapse. Alternatives of different
pipe size at a different slope should be considered before designing pipelines for installation outside
of the specified depth ranges.
In all cases, the pipe minimum and maximum depths shall be in conformance with the pipe
manufacturers’ recommendations.
4.4.3
Manholes
Manholes are used to provide access to drainage lines. They shall be provided at each change in
direction (vertical or horizontal) and connection of two or more lines. Manholes are to be placed at
least every 100 m or the limit of existing pipe cleaning equipment, whichever is smaller. In particular,
manholes should also be installed where necessary to facilitate cleaning and access. For pipe
diameters larger than 1500 mm where man entry is reasonably accommodated, maximum manhole
spacing may be increased to 200 m.
The manhole structures are normally circular in shape, with a minimum diameter of 1,000 mm.
Manholes shall be constructed of reinforced concrete with GRP or other corrosion proof lining with
prior written approval from HIB. Details of access and construction shall be in accordance with
established HIB or other equivalent standards and details.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-6
Manholes on gravity pipes shall be provided at any changes in horizontal direction and where pipe
sizes change. For transitions between pipes of different diameters, typical design is to match the
crown elevations of the pipes. In the event that this is not possible, the invert of the larger sewer pipe
can be raised to match the 0.8-depth point of both sewer pipes.
4.4.4
Connection Chambers
Special connection chambers shall be used in locations where manholes are not sufficient for the
required connection. This is most commonly the case where multiple large pipes must be connected
to equilibrate flows and/or flow control is to be implemented. Flow control shall be provided through
the use of penstocks.
4.4.5
Catch Basins and Trench Drains
Approved catch basins, trench drains, and gullies shall be used throughout the drainage projects.
Cast iron inlet grates shall be used throughout. Maximum spacing of catch basins in any major or
subdivision road shall be 25 m unless it is demonstrated by project specific calculations a wider
spacing is justified. Flush-mounted inlet structures may be used in areas without curbing.
Trench drains are required where sheet flow is likely, or where traffic loading is expected to exceed
standard highway loads. Standard details for trench drains shall be used throughout.
Inlets and gullies shall be provided with sediment traps with access for maintenance cleaning.
Inlet covers shall be provided with a sand trap to prevent accumulation of sand in curb inlet catch
basins.
4.4.6
Utility Crossings
Utility crossings for storm drains are to be consistent with internationally accepted standards, as
shown in Table 4-6.
Table 4-6 Utility Crossing for Storm Drains
Parameter
Minimum Criteria
Vertical Clearance
30 cm (if less than 30 cm, use concrete saddle)
Carry encasement to first joint on each side of crossing
Horizontal Clearance
3.0 m; if in same trench, place other utility on separate bench
on undisturbed soil above drainage line
Potable Water Lines
Always place above drainage lines
4.5 Detention Ponds (Separate Storm Drainage Only)
Storm water detention facilities, such as ponds, dry basins and underground chambers, can be
effective methods to attenuate peak flows by slowly releasing runoff volumes, and to improve water
quality by allowing pollutants to settle. Attenuating peak flows offer the benefit of reducing the
downstream pipe size and cost of construction of storm water management systems. Improving water
quality reduces the risk of collection systems becoming blocked or plugged with sediments and
debris, and the risk of releasing pollutants to the environment.
The ponds are typically located in areas that are at the naturally occurring lower elevations in the
catchment areas, with a minimum of one pond per catchment area. There are two types of storm
water detention basins: dry and wet. Dry detention basins are designed to be normally dry and
become temporarily inundated after a storm event. Dry detention ponds may be used for recreational
activities, such as soccer fields or the like, for all times except where there is a major rainfall event.
Wet detention ponds are designed to have a permanent pool at all times. In addition to runoff
calculation determining of evaporation rate should be performed to ensure there is a permanent pool
of water at the desired depth. Properly sized, designed, and maintained wet ponds also add an
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-7
amenity feature to the surrounding areas. Careful consideration should be given to provide a
minimum depth sufficient to avoid creating a mud pit. In some instance a supplemental water source
such as ground water or treated water may be needed. In areas of high groundwater, the
construction of detention ponds should be avoided.
The storm water detention facilities shall be designed to safely contain and slowly release runoff
volume from a 50-year, 24-hour rainfall event in order to accommodate a larger storm depth. It is
assumed that during the 50-year storm event, 15 percent of the total runoff is discharged from
detention facilities before water levels reach peak stage. Therefore, the detention facility is sized to
store a runoff volume equal to 85 percent of the total runoff volume from the 50-year, 24-hour rainfall
event.
4.5.1
Pond Inlet and Outlet Structures
Where the storm water collection system is discharged to ponds, side slopes are to be protected from
erosion with stone pitching or rip-rap. Where inflow velocities exceed 1.5 m/s, an energy dissipation
structure should be provided. Outlet structures should be sized adequately to empty the flow at the
desired time period. Discharge control structures shall be designed to release total runoff from the 5year 24-hour rainfall event over a period of 48 hours and to release the total runoff from the 50-year
24-hour rainfall event over a period of 72 hours. The outlet structures could be weir, orifice, or other
overflow structures.
4.5.2
Discharge Control Structures
Discharge control structures serve two purposes:
1.
To maintain surface water or groundwater levels and
2.
To release rainfall runoff at an attenuated peak discharge rate.
Discharge control structures are an integral part of a passive storm water management system. They
are used to maintain surface water levels and groundwater levels in detention ponds at target
elevations. The target elevation is typically set at not lower than the natural, pre-construction wet
season groundwater elevation. However, other factors may also be considered when selecting a
target elevation. The target elevation becomes the design control elevation. Each storm water pond
shall be assigned a design control elevation based on the best available groundwater data for that
specific location.
Discharge control structures shall be sized to release runoff from certain design storms over a
specified number of days without allowing the pond water surface levels to exceed the maximum
design high water levels. Discharge control structures release stored runoff through either an over
flow weir, or a circular orifice, or a combination of the two. Rectangular weirs and orifices shall be
designed using conventional formulas.
4.5.3
Pond Depth
The depth of water in a detention pond is an important consideration during design. While it is
possible and often desirable to minimize the land area required for a detention pond by increasing its
depth, the result may create conditions that can be hazardous. The depth influences both the safety
of operation and the quality of effluent from the pond. Pond side slopes generally should have a
stable slope with a gradient of 1 vertical to 5 horizontal (1V:5H). This gentle gradient allows vehicle
access for maintenance of the side slope and bottom. It also allows easy access for the possible
recreational use of the pond during dry months. During design, it may be desirable to adjust the side
slopes for aesthetic reasons. Pond side slope options include natural slope (1V:5H), hardened slope
terraced, and vertical retaining walls.
For wet ponds, the recommended pool of water should be a minimum of 1.5 meters at the deepest
location. The submerged side slope of the permanent pool could be increased to 3H:1V once the
depth in the permanent pool is greater than 0.5 meters. When site condition does not allow the above
recommendations, other values could be used with prior written approval from HIB.
4.5.4
Detention Pond Emptying
Efficient and complete clearing of dry detention ponds after a storm event is essential. Shallow,
stagnant pools promote breeding of nuisance insects. Deeper, wet ponds will develop plants and
may attract birds and other wildlife. Wet ponds may act as water features especially when associated
with pocket parks or other public use areas.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-8
4.5.5
Dry Detention Ponds
The following should be considered in sizing of all dry detention ponds:
4.5.6
1.
Size area to detain runoff volume from the design rainfall event plus 0.3 m of
freeboard
2.
Provide 5:1 side slopes or stable side slope as dictated by soil conditions
3.
Grade pond bottoms to central points to accumulate flows to central collection points.
A slope of two percent may be considered.
4.
Pond bottoms shall be at least 5 m above the average groundwater level.
5.
Provide perimeter land drain system to stabilize side slopes where groundwater
levels are expected to be higher elevation than the pond control elevation.
Wet Detention Ponds
The following should be incorporated in all wet detention ponds:
4.5.7
1.
Size area to detain runoff volume from the design storm plus 0.3 m of freeboard.
2.
Provide 5:1 side slopes or stable side slope as dictated by soil conditions.
3.
Pond bottom shall be at least 1.5 m below discharge control elevation.
4.
Consideration should be given to provide supplemental aeration and mixing within the
pond to enhance water quality.
5.
Provide perimeter land drain system to stabilize side slopes where groundwater
levels are expected to be higher elevation than the pond control elevation.
6.
Provide a gently sloping littoral shelf with aquatic vegetation along the wetted
perimeter of the pond for aesthetics and safety.
Retention Ponds
Retention ponds are intended to retain and impound all flow from twice the average annual rainfall
without overflow. They shall incorporate the following:
4.5.8
1.
Size volume to contain runoff from rainfall equal to two times the annual average
rainfall.
2.
Outlet via infiltration to groundwater, evaporation, or beneficial reuse such as
landscape irrigation.
3.
The depth is determined by inlet pipe levels.
Buried Detention Chambers
Where appropriate, consideration should be given to the use of buried detention chambers. These
chambers usually comprised of interconnected elements of perforated pipes or structures in a gravel
envelope.
1.
Size area required for detention chambers to detain runoff from the design storm
based on the estimated storage capacity for each chamber and gravel envelope.
2.
Provide oil-water separators at all inlets into the chambers
3.
Estimate pond areas assuming 0.66 m of storage per square meter of land area.
3
This method of storm water detention is only effective where the chambers are consistently above the
groundwater table with a positive outflow available at all times. The buried chambers will act as land
drains and keep the groundwater level below the chamber inlet.
Buried detention chambers are to be located using the same horizontal offset criteria as used for
storm water management basins within an airport.
4.6 Oil-Water Separators
Because rainfall events are infrequent, the first flush of storm water runoff from urbanized areas
typically contains a relatively high pollutant load. Oil-water separators may be required to reduce the
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-9
discharge of pollutants to the environment by capturing settling solids and floatable oils and grease.
Where required, oil-water separator designs shall meet the following requirements:
1.
Shall be constructed of impermeable materials and with minimum of three chambers
in series with access manholes into each chamber.
2.
For large catchment areas, provide a by-pass channel shall be provided to prevent
overflow of oil or contaminants as a result of heavy downpours.
3.
Provide a volume capacity from an average one-hour storm.
4.
A metal grill or appropriately designed screen shall be provided to prevent debris from
entering the oil-water separator.
5.
Separator discharge shall meet the following water quality criteria:
6.
No visible oil and grease.
7.
Suspended solids less than 50 mg/l during dry weather flow.
8.
Suspended solids less than 100 mg/l during wet weather flow.
9.
Maximum horizontal design velocity is 0.3 meters per second.
10.
For large catchment areas, size the separator to treat storm water runoff from the
“first flush.”
11.
Design depth of Separator shall be a minimum of 1.22 m and maximum of 2.44 m per
WEF MOP FD-3, “Pretreatment of Industrial Waste,” 1994.
12.
Provide access for regular maintenance to inspect units and remove accumulated oils
and settled solids.
13.
Depth-to-width ratio equal to 0.3 minimum and maximum 0.5 per WEF MOP FD-3,
“Pretreatment of Industrial Waste,” 1994.
14.
Velocity shall be based on the sustained peak storm water discharge rate from the 5year storm event.
15.
Flow in excess of runoff from 5-year storm event shall be bypassed around the
separator after coarse screening.
16.
Maximum width of a single Separator should be 10 m for reasonable constructability.
17.
Captured oil film and floatable solids in separator to be displaced into trough
collection system having weir crest elevation equals calculated High Water Level in
Separator plus 0.15 m.
18.
Sediment collected in Separator to be directed to sump for pumping to truck loading
station.
19.
Separator provided with inlet coarse screens consisting of in-channel manual bar
racks having 50 mm spacing between bars. Bar racks are to be vertical and have full
width depressed floor trench 0.4 m depth upstream of bar racks having overhead
hatch for vertical lift of debris from trench.
20.
Provide one sump pit with recessed channels in the bottom slab and one lift-out
submersible sump pump for dewatering each Separator cell.
21.
Provide one 100 mm diameter water supply line, from pond dewatering pump station
or other available water supply, into each parallel Separator for displacement of
waste floatable materials.
22.
Accumulated floatable waste and oils will be displaced through a weir opening
discharging into trough system to direct wastes to a sump. Sump pump shall
discharge to a truck filling station with spill containment and piping shall be fitted with
either disconnect couplings at grade or with an overhead tanker filling arrangement.
23.
For larger units, provide a one-ton jib crane for removal of screen, screenings, and
grit. Provide removable, motorized, one-ton wire rope hoist for use on the jib crane.
24.
For large oil-water separators, provide electric actuated sluice gates at the inlet and
outlet from the separator to isolate the units for maintenance and repairs.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-10
4.7
Storm water Management within an Airport
It may be desirable to route storm water runoff to shallow basins located in the areas of land between
runways and taxiways as part of a collection system. The basins shall have minimum horizontal
offsets from runways and taxiways in compliance with FAA regulations which specify offsets distances
to any changes in grade as follows:
1.
Minimum offset 23 m from edge of runway pavement.
2.
Minimum offset 110 m from centerline of taxiway.
3.
Minimum offset 20 m from end of blast pavement for taxiways.
4.
Maximum depth of basin 1.5 m
Maximum basin side slopes shall be 5H:1V. All runoff to the basins will flow freely into the collection
system. The basins are not intended to detain water for any period of time after the storm event.
(Reference is made to the following documents: Dubai Civil Aviation Report TD 75 – Storm water Master Plan for
Dubai International Airport and the U.S. Federal Aviation Administration Advisory Circular No. 150/5320-5B –
Airport Drainage.)
4.7.1
Bird Scare
For airports, bird control is a major priority for safe operation of the airport as birds are attracted to
standing pools of water such as detention ponds. Provisions to keep storm water detention ponds a
sufficient distance from airplane movements must be incorporated into the design. As such, no storm
water detention ponds will be located within an airport or within an airport fly zone.
4.8 Groundwater Dewatering
During construction continuous dewatering may be needed where ground water level is higher and
this section is included to provide guidance in dewatering. Possible groundwater rise due to future
irrigation and water supply system leakage must also be taken into account.
Dewatering time below the water table can be calculated using the following equation:
Where:
t=
dewatering time, days
A=
pond area, m2
Q’ =
groundwater discharge to pond per unit drawdown (to be obtained from
3
groundwater analysis or model), m /day/m
QP =
pumped
flow,
3
m /day
ZGW =
t
A
ln
Q'
gr
oundwater
table elevation, m
QP
Q'
QP
Q'
Z GW
Z P0
Z GW
ZP
ZP0 =
initial pond water surface elevation, m
ZP =
pond bottom elevation, m
Groundwater levels can be lowered by using active pumping and/or passive collection from the outfall
structures. The groundwater collected shall be disposed of in the storm water collection system or
pumped to Treated Sewage Effluent (TSE) storage tanks, if available and mixed with the TSE for use
as irrigation water. The extent to which groundwater can be blended with TSE must be evaluated on
a case-by-case basis.
4.9
Pumping Stations and Rising Mains
Storm water pumping stations are required when drainage collection network depths exceed the
practical or economic constructability limit. The first preference is to use gravity drainage systems;
however, due to topography and potential land use conflicts, there is the potential that some pumping
stations may be needed. Pumping stations may also be required where land drain systems are
employed and connections to gravity storm drainage systems are not possible.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-11
4.9.1
Pumping Station Type
The design philosophy is to maximize gravity flow and only use pumping where absolutely necessary.
Most storm water pumping stations shall be submersible pump type stations. Submersible pump
stations are well suited to drainage pumping given their low profile and low maintenance
requirements. Pumping stations shall be sized for the storm water flows but will also be used to
maintain the groundwater table below the desired elevation throughout the year.
For very large flows, storm water pumps may require use of low-head, high-volume axial flow pumps,
or possibly screw pumps where the required head is just a lift into a higher gravity flow pipe.
Storm water pumping stations shall be designed to handle the projected runoff for specific
catchments. However, their capacity may be larger in order to ensure that clear times for upstream
detention ponds are met. Pump controls shall be based on water elevations in the wet well of the
station.
4.9.2
Wet Well Volume
Wet well sizing is a function of the incoming flows, the control strategy for the station, the selected
pumps, and the number of starts per hour permissible for the pumps. Recommended cycling
frequency depends on the type of pump being used, the motor size and pump operating efficiency.
For submersible pumps in the range of capacities likely to be used, the recommended cycle time
ranges from 7 to 10 minutes; the equivalent of 6 to 10 starts per hour. For design purposes, pump
stations shall have a minimum cycle time of 10 minutes. Cycle times are with respect to dry weather
flows since during storm events there is little cycling of pumps.
For constant speed pumps, wet well volume is calculated based on cycling frequency when inflow to
the station is about 50 percent of the pumping rate with a single pump operating.
The wet well volume shall be calculated from the basic formula:
CT = [V/(D-Q)+(V/Q)] where
D
= Pump rate (m³/min.)
Q = Inflow rate (m³/min.)
CT = cycle time (minutes between pump starts)
V
= volume (m³)
Since “minimum” cycle time is of concern (Q = D/2), the formula reduces to CT = 2V/Q.
4.9.3
Wet Well Depth
The depth of wet well below the required invert of the inlet pipe is a function of the following:
1.
Required submergence to prevent vortexing in the pump suction piping which may
cause unbalanced loading on impellers & bearings, thereby reducing pump life.
2.
The minimum Net Positive Suction Head Required (NPSHR) by the particular pump
impeller selection. This requirement is provided by the pump supplier.
3.
High liquid level in the wet well being set at 0.8 times the inlet pipe diameter above
the invert. This allows the inlet pipe to be emptied frequently preventing buildup of
settled material in the gravity inlet pipes.
The required submergence refers to minimum liquid level above a vertical pump inlet flare or fitting
and above the centerline of the flare if positioned horizontally.
The submergence shall be calculated as per Hydraulic Institute Standards.
The minimum submergence determination and NPSHR shall be verified during the wet well sizing.
4.9.4
Pump Selection
Pump selection should be made to optimize conditions over the projected range of flows – minimum,
average, maximum. Selection is made to minimize holding times in the wet well before pumping and
maximizing efficiency. Actual pump selection can only be made after a system head capacity curve is
developed for the proposed installation. The following items are to be considered:
1.
Required range of head and flows
2.
Number of pumps
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-12
3.
Operating and control strategy
4.
Efficiency
5.
Potential for upgrading capacity
Multiple pumps will be used to achieve the required pumping capacity. Using multiple pumps permits
better station control and performance when flows vary from different intensity storm events. Also,
smaller capacity individual pumps for low flows will serve better during the dry season when the only
flows are from groundwater control.
If screw pumps are an appropriate option, a minimum of two pumps shall be installed. As screw
pumps automatically pump with a variable output to match the incoming flow (up to their maximum
capacity), pump selection is primarily a function of number of pumps and their maximum capacity.
4.9.5
Pumping Station Structures
Pumping station structures should be designed to ensure a safe working environment for operation
and maintenance staff as well as maximizing performance and minimizing costs. The following shall
be incorporated:
4.9.6
1.
Ventilation systems to meet applicable standards.
2.
Provisions to facilitate removing pumps, motors, and other mechanical and electrical
equipment.
3.
Suitable and safe means of access to dry wells and to wet wells.
4.
Wet wells configured to minimize turbulence.
Surge Protection
Surges can be generated in the pumped supply system following power failures, pump starting or
stopping and sudden valve operations. Need for surge limiting equipment to protect the supply
system due to possible transient pressure variation shall be considered. The calculation of surge
shall be carried out by appropriate methods and using the relevant general equations and surge
calculation software according to the conditions specified by the designer and based on the most
unfavorable operating conditions. Where surge protection is found to be necessary, the designer
shall size and specify the appropriate surge protection equipment.
4.9.7
Rising Mains
Rising mains shall be sized to maintain velocities within an acceptable range for a variety of flow
conditions. Rising main diameters should not be less than 200 mm. Selection of the diameter is
dependent on the maximum and minimum flow rates required through the pipe, the characteristics of
the pipe (length, material, and route) and velocity. Flows are set based on required clear times from
drainage areas and detention ponds. Pipe characteristics are important since the head loss in the
system should be minimized. Velocity is also a factor in the determination of head loss.
The minimum velocity must be achieved with only one pump in operation since this will be the
condition during low-flow periods.
All pressure service pipes beyond the limits of the pumping station shall be GRP with minimum pipe
2
2
stiffness of 10,000 N/m within the limits of the pumping station and 5,000 N/m beyond the limits of
the pumping station. As an alternative, ductile iron pipe and fittings may be used for pipes exposed in
the wet well and valve vaults.
4.9.8
Air Valves and Washouts
The rising mains shall be equipped with the following valves for facilitating the operation, control, and
maintenance.
1.
AUGUST 2010
Air and Vacuum Valves: These valves shall be provided at summits along the pipe
profile and along long stretches with uniform slope to purge out accumulated air in the
pipe system. Air release and vacuum relief valves are often needed along
transmission mains and may sometimes be unavoidable in sewage force mains. Air
must be bled slowly from high points to prevent (1) “air binding” and (2) the reduction
of the cross section of the pipe at high points. Vacuum conditions must be prevented
when the pump head drops quickly (as in power failures) to prevent column
separation and at extreme high points in pipelines to prevent potential pipeline
collapse due to vacuum. Vacuum relief valves can be as large as one-sixth of the
REVISION NO. 03
S TORM W ATER 4-13
diameter of the transmission main, whereas air release valves may be as small as
one-fiftieth of the diameter of the pipe.
2.
A combination of air and vacuum valves shall be provided at appropriate locations for
quick air entry or vent to prevent cavitations and facilitate quick filling of the pipe. In
general, air-valves are to be installed at crest points, changes in elevations and in
case of constant rising mains having moderate slope, at a maximum spacing of
1000 m to 1500 m.
3.
Washout valves: These valves will be provided at low points or sags along the pipe
profile. These valves facilitate flushing, repair or maintenance of the pipe wherever
necessary.
4.
Isolating valves: The location of these valves shall consider the profile of the pipeline
and the location of washout and air valves. Isolating valves shall be provided at a
maximum distance of every 2 to 3 kilometers.
5.
Isolating valves with diameter smaller than 300 mm shall be gate valves and larger
diameter shall be eccentric plug valves or globe valves.
6.
Non-return valves: These valves will be provided in the pump station to prevent a
reverse flow into the pumps and shall be of noiseless non-slam type.
All valves not located in a pump station structure shall be installed inside reinforced concrete valve
chambers.
4.9.9
Reliability
For reliability, provide on-line spares for all active equipment.
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-14
Attachment 4-1 Intensity-Duration Data - Tripoli
Time, Minutes
Intensity, mm/hr (for Tripoli, Libya)
2-year
5-year
10-year
25-year
50-year
100-year
5
94.8
116.5
134.6
147.0
158.7
165.7
10
57.9
73.7
85.8
95.0
104.0
109.3
15
43.4
56.4
65.9
73.6
81.2
85.7
30
26.6
35.7
42.0
47.5
53.2
56.5
60
16.2
22.6
26.8
30.7
34.8
37.3
90
12.2
17.3
20.6
23.8
27.2
29.2
120
9.9
14.3
17.1
19.8
22.8
24.6
180
7.4
10.9
13.1
15.4
17.8
19.3
360
4.5
6.9
8.4
9.9
11.7
12.7
720
2.8
4.4
5.3
6.4
7.7
8.4
1440
1.7
2.8
3.4
4.1
5.0
5.5
180
160
Intensity mm/hr
140
i 50= 423.5* t(-0.61)
120
50-Year
5-Year
100
80
60
i 5= 336.9* t(-0.66)
40
20
0
5
10 15
20
25
30
35 40
45 50
55
60
65
70 75
80
85
90
Time, Minutes
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-15
Attachment 4-2 Intensity-Duration Table and Curve, Misrata
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-16
Attachment 4-3 Intensity-Duration Data, Benghazi
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-17
Attachment 4-4 Intensity-Duration Data, Derna
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-18
Attachment 4-5 Meteorological Stations Locations
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-19
Attachment 4-6 Runoff Coefficient Values
Area Description
Runoff Coefficient, C
Categorized by Surface
Asphalt
0.7 to 0.95
Brick
0.7 to 0.85
Concrete
0.8 to 0.95
Sandy Soil
0.05 to 0.2
Clayey Soil
0.13 to 0.35
Categorized by use
Administration
0.5 to 0.75
Educational
0.6 to 0.8
Shopping Center
0.6 to 0.8
Medical Facilities
0.6 to 0.8
Religious and Cultural Facilities
0.7 to 0.8
Agricultural
0.3 to 0.5
Unimproved
0.1 to 0.3
Parks and Playgrounds, unpaved
0.1 to 0.25
Playground, unpaved
0.2 to 0.35
Business Districts
0.7 to 0.95
Residential
2
Small villas (<2500m )
0.3 to 0.5
2
Large villas (>2500 m )
0.25 to 0.4
Apartments
0.65 to 0.85
Industrial
AUGUST 2010
Light
0.5 to 0.8
Heavy
0.6 to 0.8
REVISION NO. 03
S TORM W ATER 4-20
Attachment 4-7 Sample Hydraulic Analyses Calculations
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-21
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-22
AUGUST 2010
REVISION NO. 03
S TORM W ATER 4-23
5
Water Reuse for Landscape Irrigation
HIB has developed standard design criteria for treated wastewater reuse and irrigation water
transmission and distribution systems. The criteria presented reflect typical installations in the region
and to support the design intent for treated wastewater reuse for landscape irrigation. It is understood
that certain situations may require deviation from the criteria presented herein. All deviations shall be
made only with the written HIB approval.
5.1 General
The primary source of water for landscape irrigation will be reclaimed water. For the purpose of this
document reclaimed water is defined as treated wastewater effluent that satisfies the minimum water
quality criteria for reuse as defined in Irrigation Water Quality Standards Section 5.1.4. Reclaimed
water can be augmented by other sources such as surface, groundwater and storm water runoff with
chloride and total dissolved solids concentrations and other water quality parameters consistent with
irrigation water quality criteria. Reclaimed water may also be used to supply water to fire hydrants
connected along the pipeline routes. Fire hydrants on reclaimed water shall be designed to
supplement rather than replace, or be used in lieu of, fire hydrants on potable water. Placement of
fire hydrants using reclaimed water shall supplement and not overlap or conflict with the locations of
fire hydrants on the water distribution system.
Regional irrigation water networks consist of three networks: supply, transmission, and distribution.
Irrigation water supply is pumped directly from wastewater treatment plants to large regional bulk
storage tanks equipped with irrigation transmission pumping stations. The transmission network
delivers irrigation water to local storage tanks, or lined ponds, equipped with fire and irrigation
distribution pumping stations. The distribution network delivers water to fire hydrants and local
irrigation users. To maintain the integrity of the operations and control strategy for the regional
irrigation water networks, neither the regional supply network, nor the transmission network, shall be
tapped for direct irrigation use. For smaller, non-regional irrigation networks, the supply network and
transmission network can combined into one network with HIB written approval.
5.1.1
Irrigation Supply
Reclaimed water supply system will consist of a network of pipes and pumping stations to deliver
reclaimed water from wastewater treatment plants to regional bulk storage and transmission pumping
facilities. This supply will be provided at a minimum pressure of 1.2 bars to points of delivery. End
users will be required to provide storage facilities with capacity to hold the volume equal to at least
one day of irrigation demand. A valve and meter chamber is required at the point of connection for
remote monitoring and control. End user storage facilities are required to be located adjacent to
existing road rights of way to allow maintenance access to the supply pipes. Connections to the
reclaimed water supply network for direct use in applying water for irrigation is not allowed.
The reclaimed water supply network shall be operated, maintained, and controlled by the owner of the
Sewage (wastewater) Treatment Plant or their designated authorized agency.
5.1.2
Transmission Network
Several regional bulk storage and irrigation transmission pumping facilities are planned to deliver low
pressure bulk water to end users 24 hours per day. Minimum transmission pressure will be 1.2 bar at
any point of connection. In-line booster pumping stations within the transmission network may be
necessary to achieve an economical balance between operation and capital cost of transmission
pumping. Irrigation water transmission piping system will deliver irrigation water to local storage
facilities. Valve and metering assemblies will be provided on the discharge to each local storage tank
for remote monitoring and control of delivery volumes, flows, and pressures. Metering assemblies will
consist of a flow meter, a back-pressure sustaining valve, and a solenoid-actuated flow control valve.
Connections to the reclaimed water transmission network for direct use in applying water for irrigation
is not allowed.
The reclaimed water transmission network shall be operated and controlled by the owner of the
regional reclaimed water transmission network or their designated authorized agency.
5.1.3
Distribution Network
Multiple local fire/irrigation storage and distribution pumping stations (provided by the end users) will
deliver water at sufficient pressure for irrigation service to points of application over a period of 8
AUGUST 2010
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-1
hours per day. Minimum distribution pressure will be 4.0 bar at the connection point for irrigation and
at fire hydrants in the event of fire flow. The irrigation distribution network shall be designed with
branches that can be isolated as needed for testing and cleaning. The distribution network should be
sized to supply the required peak day irrigation demand based on anticipated peak season usage
delivered over an 8-hour period plus fire flow.
The reclaimed water distribution network shall be operated and controlled by the local entity or an
authorized agency designated by HIB.
5.1.4
Irrigation Water Quality Standards
The minimum standards of treatment required for treated wastewater used in irrigation systems are
described below. The treated wastewater is divided into two classes:
1.
Class A waters: Treated to secondary standard, sand filtered and chlorinated. The
maximum E. coli level in the final effluent shall be less than 10 per 100 ml. This class
can be used for unrestricted irrigation.
2.
Class B waters: Treated to secondary standard and E. coli levels less than 1,000 per
ml. This class can be used for restricted irrigation.
The following table further describes the type of irrigation activities for which the two water classes
can be used.
Table 5-1 Permissible Water Classes for Irrigation Methods
Permissible
Water Class
Irrigation Method
Drip irrigation onto trees and bushes
A or B
Low mist hand spray
A or B
Spray irrigation in parks and green spaces (closed to public, after hours
of use, or at least 2 hours before public use)
A or B
Unlimited spray irrigation of public areas (with precautions to reduce
mist formation)
A only
In both cases the Total Dissolved Solids (TDS) of the treated wastewater shall be less than 1,000 mg/l
(which for reference is greater than potable water standard of 500 mg/l). Irrigation will either be
drip/subsurface irrigation (in public areas) or spray irrigation (in non-public areas). Thus, effluent
treated to Class B standards will be acceptable.
In addition to reclaimed water, other sources such as groundwater and captured storm water runoff of
acceptable quality, or potable water may be used to augment irrigation water supplies.
5.2 Irrigation Design Criteria
5.2.1
Irrigation Demands
Irrigation demand is based on the design of each landscape area within the service area of each
irrigation storage tank. Irrigation demand will vary dependent upon a number of interrelated issues,
including climate, location, soil, crop type, and season. Knowledge and assessment of all these
issues will be required in determining irrigation demands for a particular site or location.
The climate (humidity, rainfall, sunlight, temperature) will create different conditions and requirements
in the three primary climatic conditions (coast, desert and mountain) found in Libya. Different plants
will have different irrigation demands which, in turn,vary from season to season. The soil, too, will
affect requirements which in turn may have been influenced and changed by past agricultural
practices, erosion, man-made activities, etc.
This guidance provides an assessment framework to assist in understanding irrigation demand. No
two locations are the same; while basic parameters can be established, individual site assessments
AUGUST 2010
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-2
will be required. The contractor should source key available information, such as local weather data,
as well as undertake his own survey.
The network must be designed to meet the highest anticipated flow condition. An established practice
is to determine a reference crop evapotranspiration rate, which is basically the water used by freely
growing grasses, and then multiply by monthly crop coefficients to determine the need for other crops.
Coefficients rarely exceed 1.25 and can be much lower, e.g. for drought-tolerant species such as olive
trees, and can fall to zero, as in the case for deciduous trees with no leaves. Typical values can be
obtained from FAO publications and other sources.
For irrigation networks, the highest flow condition occurs during the season corresponding to peak
irrigation water demand. Peak demand usually occurs during the peak growing season and summer
months, with the highest evapotranspiration rates.
As an example for coastal areas only, typical peak irrigation demands (i.e. daily net depth required,
excluding losses) of different plant types are provided in Table 5-2.Error! Reference source not
found.
Table 5-2 Irrigation Demand by Plant Type
1
1
Plant type
Peak daily irrigation demand
Grass (Lawn)
10 mm/day
Deciduous Trees
7 mm/day
Olives Trees (high density)
5 mm/day
Citrus Trees
7 mm/day
Source: Libyan Agricultural Master Plan: Crop Gross Irrigation Requirements: Zone A (Coastal Areas)
Data are still required to expand this basic data into desert and mountain regions. Average annual
irrigation water demand will be substantially less than the peak season demand. That calculation
gives the depth (mm) that a crop needs, both total over the season and for peak daily use. To gain a
volume, multiply the depth by the area planted (one mm depth on 1 square meter requires 0.001 m3
or 1 liter). For trees, it is typical to use the area from the trunk out to the drip-line, or 1 m2 at a
minimum.
Contractors must also consider and allow for application losses. Irrigation efficiencies normally range
from 40% to 90% depending on the irrigation method used.
As plant palettes are developed, irrigation demand will become more defined for individual irrigation
areas. Salt tolerant plants and drought tolerant plants will be used in areas where appropriate in
order to decrease the overall irrigation demand.
5.2.2
Distribution Network
5.2.2.1
Hydraulic Calculations
Hydraulic calculations shall be carried out in order to demonstrate that the system will:
satisfy the estimated peak-day demand delivered over an 8-hour period plus fire flow;
operate at acceptable velocities;
operate within the required pressure range
5.2.2.2
Flow Velocities
All irrigation network pipelines are pressure mains. Mains should be sized to keep friction losses
under peak conditions to a manageable level. Selection of size requires an understanding of
projected flows for the service life of the system. Maximum velocities may range up to 2.5 m/s, or as
needed to not exceed a maximum head loss gradient of 10 m per kilometer.
5.2.2.3
Head Losses
The head loss resulting from flows through a single main may be calculated using the HazenWilliams Equation. Because most irrigation systems are networked, flows comes from several
directions and head losses cannot be determined directly. If the system is small a manual calculation
using a Hardy-Cross method may used. For larger networks, hydraulic design of all networked
AUGUST 2010
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-3
systems shall be carried out using approved computer modeling software. Acceptable models are
KYPIPE, PIPE2000, WaterCAD, H2ONet, Cybernet, EPAnet, and other equivalent commercially
available models. Designs should be evaluated over a range of C values (100 to 140) or equivalent,
to assess how the effects of pipe degradation will impact the overall system performance.
5.2.2.4
Pipe Materials
Irrigation mains shall be capable of accommodating the pressure required for fire flows. Irrigation
distribution mains from the end users’ secondary storage tanks shall be boosted with suitable pumps
to provide working pressures of up to 10 bar as needed to meet the minimum pressure for fire
protection. Pipes materials such as GRP, HDPE, or PVC shall be used.
5.2.2.5
Minimum Cover Requirements
For pressure pipes, minimum cover is 0.8 m below final finished or future grade in unpaved areas with
no vehicular traffic and 1.0 m below final finished or future grade in paved areas with vehicular traffic.
If the available cover is less than specified, then additional protection such as full concrete
encasement or the use of concrete protection slabs may be required
The actual cover required for construction may be greater than that required solely for structural
integrity. The maximum cover depth recommended is approximately 10 m. This maximum depth is
consistent with typical pipe installation standards and manufacturer recommendations. Should the
actual cover be greater than 10 m, pipe materials should be evaluated and a higher strength class of
pipe utilized.
For pipes at less than these minimum values or installed at excessive depths, concrete encasement
may be required to protect the pipe from damage. These should be looked at on an individual basis,
and alternatives of different pipe size should be considered before designing the pipelines outside of
the specified depth ranges. In all cases, the pipe minimum and maximum depths shall be in
conformance with the pipe manufacturers’ recommendations.
5.2.2.6
Utility Crossings
Utility crossings are recommended to be consistent with local standards and practices. The
guidelines, based on internationally accepted standards, are shown in Table 5-3.
Table 5-3 Utility Crossing for Irrigation Pipes
Parameter
Minimum Criteria
Vertical Clearance
30 cm (if less than 30 cm, use concrete saddle)
Carry encasement to first joint on each side of crossing
Horizontal Clearance
3.0 m
Where available corridor space is limited, minimum clearance may
be reduced to 1.2 m assuming structures can overlap into adjacent
corridors.
If in same trench, place other utility on separate bench on
undisturbed soil above the line
Potable Water Lines
Always place above irrigation lines
Irrigation pipes crossing under roads shall be aligned at 90 degrees or perpendicular to the road with
all bends located beyond the limits of the road pavement and curbs.
5.2.2.7
Thrust Blocks
Concrete thrust blocks shall be provided at tees, elbows, reducers, and other fittings in order to
prevent their movement due to pressure of the pipes. Design pressures for thrust restraint shall be
10 bar in all irrigation mains. Soils bearing allowances shall be according to normal allowances for
the type of soil encountered.
5.2.2.8
System Valves
The irrigation water mains and distribution system will be equipped with the following valves for
facilitating the operation, control, and maintenance of the system. The design consultant shall take
into account the proper distribution of valves along the system.
AUGUST 2010
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-4
Air Release Valves: These valves shall be provided at summits along the pipe profile and along long
stretches with uniform slope to purge out accumulated air in the pipe system. A combination of air
and vacuum valves shall be provided at appropriate locations for quick air entry or venting to prevent
cavitations and facilitate quick filling of the pipe. In general, air-valves shall be installed at crest
points, change in elevations and in case of constant rising mains having moderate slope, at a
maximum spacing of 600 m.
Washout valves: These valves shall be provided at low points or sags along the pipe profile. These
valves facilitate flushing, repair or maintenance of the pipe wherever necessary.
Isolating valves: shall be located at branching points on the network as a provision for flushing,
testing, and maintenance. The number and distribution of these valves shall be in a manner that
ensure minimum disturbance to the supply of irrigation water in case of maintenance or repair works.
The maximum allowable distance between isolating valves on the distribution lines shall not exceed
500 m. In general, isolation valves shall be provided on all branches from feeder mains and between
two washout valves. In the transmission mains where there are no intermediate branches, isolating
valves shall be provided at a maximum distance of every 2 to 3 kilometers. In the transmission mains,
profile of the pipeline and location of washout and air valves is also to be considered while locating
the isolation valves. Isolation Valves with diameter 300mm and smaller shall be gate valves and
larger diameter isolation values shall be butterfly valves.
Non-Return Valves: These check valves shall be provided in the pumping station to prevent a reverse
flow into the pumps and shall be of noiseless non-slam type.
Control valves: These valves shall be actuated butterfly or diaphragm type globe valves, operated to
control the flow and pressure at the consumer end while supplying to different tanks distribution
system with varying elevation and flow requirement.
All valves not located in a pumping station structure shall be installed inside reinforced concrete valve
chambers.
5.2.3
Flow Meters and Structures
Flow meters and structures shall be in accordance with electrical, instrumentation, and control
requirements of these criteria. .
5.2.4
Storage
There are two types of irrigation storage facilities planned. Bulk irrigation water storage will be
supplied with water directly from the supply network, with storage volume equal to a minimum of
one day of irrigation demand. Local fire/irrigation water storage will be supplied with water directly
from the irrigation water transmission network with storage volume equal to a minimum of one day of
irrigation demand plus two hours of fire flow.
Storage tanks are to be underground for aesthetic reasons. Above ground reservoirs or vertical tanks
may be used where the vertical profile of the storage facilities is consistent with the surrounding land
use and will not detract from the value of adjacent properties. Lined ponds may be used for storing
water for irrigation of large landscaped areas such as a golf course, and in some cases may even
provide an amenity feature.
Storage tanks shall be reinforced concrete structures with adequate safe access and cleanout
capabilities. If above ground storage is considered, it shall be hidden or screened from view from
outside the development. Above ground tanks may be reinforced concrete or glass-coated steel
structures. Storage tanks shall be completely covered to block exposure to sunlight to limit the
potential of algae growth. Pond storage facilities are exempted from this provision.
Storage tanks will be provided with wash-down capability. Storage tanks shall be compartmentalized
to allow one compartment to be taken out of service for cleaning while maintaining pumping
operations. Compartments will be isolated by motor-actuated sluice gates or penstocks. Tank
bottoms shall be sloped to one end to facilitate cleaning and draining. Multiple hose connections to
pressurized irrigation water shall be provided in close proximity to tank manhole access ports for
flushing and cleaning the tanks. Tank manhole access ports shall be located at spacing that will
facilitate the wash down and cleaning by a man holding a hose and nozzle from the top of the
structure without man-entry inside the tank being required.
Storage tank piping shall have mechanical float valves for protection from overflow on filling. All metal
components inside the storage tank or otherwise in contact with the treated wastewater shall be
constructed of corrosion resistant materials.
AUGUST 2010
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-5
5.2.5
Pumping Stations
Pumping stations at bulk irrigation water storage and transmission pumping stations will have a standalone building with a pump room, electrical room, generator room with fuel storage for back-up
emergency power, and a monitoring and control station. The pump room will include pumps, valves,
automatic backwash strainers, hydraulic surge protection, and a traveling bridge crane. For vertical
turbine pumps, provide roof hatches directly over the top of the pumps of sufficient size to allow
complete removal of the combined drive and pump using a mobile crane.
In-line booster pumping stations may also be used at several locations in the transmission mains
system to more efficiently maintain delivery pressures throughout the transmission network.
Pumping stations at Local Fire/Irrigation Water Storage and Distribution Pumping Stations will be a
scaled-down version of the Bulk Irrigation Water Storage and Transmission Pumping Station with
special provisions for additional fire pumps. In most cases, pumping stations will take their suction
directly from the storage tank. If a wet-well is designed separate from the storage tank or pond, it
should be sized using standard guidelines for such facilities. The wet-well and connection from the
storage facility shall be such that there is no chance for draining to the shutoff level during an
irrigation or fire flow event.
For vertical turbine pumps, verification that intakes are configured and sized in accordance with
applicable Hydraulic Institute standards is required during the design process. Verification of
compliance with Hydraulic Institute standards for vertical turbine pump intakes shall not be deferred to
the construction contractor.
The minimum required fuel storage capacity will be a function of the reliability of local power and fuel
delivery. Where local power and fuel delivery is consistently and reliably available, then a minimum of
one-day's fuel storage should be sufficient. Where power and fuel delivery is not consistent and
reliably available, then the capacity of fuel storage will need to be increased to fit the local conditions.
5.2.5.1
Pump Selection
Pumps shall be selected to optimize conditions. Selection shall be made to maximize pumping
efficiency under variable flows and pressures. Where possible, variable speed drives should be used.
Acceptable pumps are horizontal split case pumps and vertical turbine pumps, either wet well or can
type. In very small systems, rotary lobe pumps may be considered.
Actual pump selection for the proposed networks will be made based on system head-capacity curves
under various flow conditions. The following are to be considered in the design of an irrigation
pumping system:
1.
Required range of head and flows – band of operating pressures expected
2.
Net Positive Suction Head Available (NPSHA)
3.
Number of pumps
4.
Operating and control strategy
5.
Efficiency
6.
Power required for pump drive
7.
Potential for upgrading capacity
Adaptability is important because initial flows may be significantly lower than design-year flows.
When this is the case, the selected pump(s) should be in the mid-range of available impeller sizes so
that simple changes in impellers can be made to improve pumping station capacity. Use of variable
speed drives will greatly simplify such considerations.
5.2.5.2
Booster Pumping Stations
The large area of coverage and variable topography of the irrigation system makes it inefficient to
provide all areas adequate pressure under all conditions in a single pressure zone. Therefore,
booster pumping stations may be used at several points in the transmission network to maintain
minimum delivery pressures at higher elevations or at remote locations from the storage sites. The
location of the booster pumping stations will be based on the modeling developed for the TSE
irrigation system.
5.2.5.3
AUGUST 2010
Surge Pressure Limiting Equipment
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-6
Pressure transients or surges can be generated in the pumped supply system following power
failures, pump starting or stopping, and sudden valve closure. If not controlled, these may cause pipe
damage or pipe failure in extreme instances. Consideration shall be given to the need for surge
limiting equipment to protect the supply system due to possible transient pressure variation. The
calculation of surge shall be carried out by appropriate methods and using the relevant general
equations and surge calculation software according to the conditions specified by the designer and
based on the most unfavorable operating conditions. Where surge protection is found to be
necessary, the designer shall size and specify the appropriate surge protection equipment.
5.2.5.4
Pumping Station Facility Building
Aboveground pumping station structures will be located immediately adjacent to storage facilities.
The architectural detail of pumping stations shall blend with the architectural scheme of the
surrounding area. Pumping station structures shall be designed to ensure a safe working
environment for operation and maintenance staff as well as maximizing performance and minimizing
costs.
The pumping station shall be located adjacent to paved public roads for maintenance vehicle access.
For sites that are not located adjacent to a paved public road, a reservation of a 10 meter wide access
way from landlocked lots and to paved public roads shall be provided.
Provisions shall be made to facilitate removal and replacement of major equipment including pumps,
motors, switchgear, and other mechanical and electrical equipment. Lift equipment and adequate
access openings shall be provided for equipment removal and replacement.
5.2.6
Fire Hydrants
The requirement for water for fire-fighting purposes shall be determined in accordance with local
regulations. Where the irrigation distribution network is combined with fire flows, the irrigation network
shall be adequately designed to meet the minimum requirement of fire flows and pressure in
accordance with established standards. Criteria for hydrant assembly spacing shall be as indicated in
Section 1 – Water Design Standard.
Fire hydrant assemblies shall be connected to irrigation distribution mains at various intervals
depending on the type of road. Placement of fire hydrants shall supplement and not overlap or
conflict with the locations of fire hydrants on the water distribution system.
All connections to irrigation systems shall be at hydrant leads located just upstream of the hydrant
isolation valve in the hydrant assembly.
All fire hydrants on irrigation distribution mains shall be clearly identified as “Recycled Water – Do Not
Drink” in Arabic language and with an international symbol.
AUGUST 2010
REVISION NO. 03
W ATER REUSE FOR LANDSCAPE IRRIGATION 5-7
6
Standards for Barrier-Free Design
6.1
Introduction
6.1.1
Purpose
These Standards are intended to inform designers and contractors providing services to the
Government of The Great Socialist People’s Libyan Arab Jamahiriya of the minimum requirements for
barrier-free design.
6.1.2
Application
The Government of The Great Socialist People’s Libyan Arab Jamahiriya shall insure that the design
of buildings, structures and premises, or parts of buildings, structures and premises, that it purchases,
constructs or significantly renovates after these standards come into force complies with the
guidelines before occupation or regular use by its Residents. These Standards will be applied and
implemented on a “go-forward” basis.
‘Significant Renovation’, The Housing and Infrastructure Board are encouraged to apply these
Standards to renovations or changes of smaller spaces and other projects where possible.
The following definitions further clarify application of these Standards:
6.1.3
Definition of Significant Renovation
These Standards will apply to renovations or changes to government owned or occupied spaces of at
least 1000 square meters or where 50% of the floor space is affected.
Significant renovations do not include projects limited only to repairs or restoration to wall finishes.
6.1.4
Maintenance
It is essential that barrier-free paths of travel and facilities be properly maintained in accordance with
other applicable legislation or standard maintenance practices in order to reduce the creation of new
barriers. Some examples of maintenance items include:
6.1.5
1.
Timely repair of uneven surfaces;
2.
Removal of furniture, fixtures and stored items that impede clearance spaces or
corridor widths;
3.
Proper leveling of elevators;
4.
Adjustment of door closers and elevator doors to prescribed limits;
5.
Maintenance of prescribed lighting levels; and
6.
Proper maintenance of non-glare surfaces.
Emergency Evacuation Planning
Facility Emergency Evacuation Planning should address accessibility procedures for persons with
disabilities. Persons with disabilities who regularly occupy a facility should have access to Emergency
Evacuation Plans in a range of formats, including large text and electronic formats. This will help to
improve the understanding of evacuation methods and promote adequate training of persons with
disabilities of the emergency measures.
6.2 Exterior Areas
6.2.1
Parking and Drop-Off Areas
6.2.1.1
AUGUST 2010
Provide a minimum number of barrier-free car parking spaces in each parking area as
follows:
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-1
Table 6-1 Barrier Free Parking Spaces
6.2.1.2
Total parking spaces provided
Minimum barrier-free car spaces
required
1 -20
1
21 -100
2
101 -150
3
151 -200
4
over 200
1 additional for each additional
50 spaces or part thereof
Barrier-free car parking spaces shall have a minimum width of 2400mm plus a 1500mm
wide access aisle. The access aisle must be level. Length of the space shall be
5500mm. Two adjacent spaces may share the same access aisle.
Figure 6-1 Barrier-Free Car Parking Spaces
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-2
Figure 6-2 Symbols
6.2.1.3
AUGUST 2010
In addition to the barrier-free car spaces described in 6.2.1.1, provide a minimum
number of van parking spaces in each parking area as follows:
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-3
Table 6-2 Barrier Free Parking Spaces (Vans)
6.2.1.4
Total Spaces Provided
Minimum van spaces required
1 – 50
1
51 – 3002
2
301 – 700
3
Over 700
4
Barrier-free van parking spaces shall have a minimum width of 3500mm plus a 1500mm
wide access aisle to accommodate vans with built-in wheelchair lifts. The access aisle
must be level. Length of the space shall be as required but at least 6000mm. Two
adjacent spaces may share the same access aisle Figure 6-3.
Figure 6-3 Barrier-Free Van Parking Spaces
6.2.1.5
Barrier-free car and van parking spaces shall be located as close as possible to the
main accessible entrance of the building and shall lead directly to the building entrance
without crossing any drive aisles. Provide a curb ramp (that will not be blocked by a
parked vehicle) directly adjacent to the designated spaces. The accessible route shall
be clearly marked.
6.2.1.6
The surface of all barrier-free parking spaces must be level (maximum slope in any
direction 2%), firm (no gravel) and slip-resistant. Pavement markings must use non-slip
paint. Do not paint the entire surface of the parking space.
6.2.1.7
Provide signage to designate the barrier-free spaces as reserved for permit holders:
1.
A vertical post-mounted sign in front of the space, with the center of the sign between
1500mm and 2000mm above the ground (Figure 6-4); and
2.
A painted pavement marking in the center of the space, in contrasting color to the
pavement, 1000mm in length, with the International Symbol of Access – see Figure 62.
6.2.1.8
Provide an additional sign at van spaces labeled “Van Accessible.”
6.2.1.9
Provide a passenger pick-up area at or near the main accessible entrance. The access
aisle on passenger side shall be minimum 1500mm wide by 6000mm long.
6.2.1.10 Barrier-free parking spaces and passenger pick-up areas shall have a minimum clear
height 2850mm, including along the vehicular access/egress route.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-4
6.2.1.11 Provide a call button or two-way communication system at all underground parking
areas that have accessible parking spaces.
Figure 6-4 Vertical Parking Sign
6.2.2
Walkways and Ramps
6.2.2.1
Provide an accessible route from streets and parking areas to all accessible entrances.
The accessible route shall be minimum 1600mm wide. Surfaces shall be maximum 5%
(1:20) running slope and maximum 2% (1:50) cross slope. Where running slope must
exceed 5% (1:20), provide a ramp in accordance with 6.2.2.6
6.2.2.2
Walkways and ramps shall have an even, firm, slip-resistant surface. Where a level
change is 75 mm or more, a handrail is required and must comply with this section.
6.2.2.3
Where the accessible route is adjacent to a vehicular route, it shall be separated from it
by a cane-detectable curb or railing.
6.2.2.4
Accessible routes must be free from overhead protrusion hazards. Provide a canedetectable railing, planter or bench anywhere that the overhead clearance is less than 2
m (Figure 6-5).
6.2.2.5
Where possible, locate gratings out of the accessible route. Any gratings in accessible
routes walkways must be level and have a maximum 13mm wide opening in the
direction of travel.
6.2.2.6
A sloped walkway shall be designed as a ramp wherever the gradient exceeds 5%
(1:20). Exterior ramps shall have:
1.
Minimum width of 900mm between handrails;
2.
Maximum gradient of 8% (1:12);
3.
Level area of at least 1670mm by 1670mm at the top and bottom of the ramp.
4.
Level area of at least 1670mm long and at least the same width of the ramp at
intervals of not more than 9m along its length, where there is a change in direction of
the ramp and at any intermediate doors along the length of the ramp;
5.
Handrails on both sides
6.
A wall or guard on each side that is not less than 1070mm above the ramp surface;
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-5
7.
Edge protections in the form of curb or rail.
Figure 6-5 Overhead Hazards
Figure 6-6 Cane Detectable Obstructions
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-6
Figure 6-7 Edge Ramp Protection
6.2.2.7
Ramps shall have a color contrasting, textured, detectable warning surface in
accordance with section 6.4.7.2 at the top and bottom a minimum of 920mm from the
start of the slope, extending the entire width of the stair or ramp.
6.2.2.8
Where the location of the ramp is not readily evident from the main access route,
provide a sign incorporating the International Symbol of Accessibility and a directional
arrow indicating the location.
6.2.2.9
Provide curb ramps at all level changes along barrier-free paths of travel. Curb ramps
shall have:
1.
Maximum gradient of 13% (1:7.5);
2.
Minimum width of 1200mm (exclusive of flared sides);
3.
A surface (including flared sides) that is slip-resistant, color and texture contrasted
with adjacent surfaces;
4.
A smooth transition from the curb ramp to the adjacent surfaces; and
5.
Flared sides with a slope of not more than 10% (1:10).
6.2.2.10 Provide a detectable hazard surface wherever a walkway adjoins a hazardous area
such as an unprotected drop-off, edge of a pool or to separate a walkway from a drive
aisle that is at the same level.
6.2.2.11 Provide a level area adjacent to all accessible entrance doors.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-7
Figure 6-8 Curb Ramps
6.2.3
Entrances and Exits
For new buildings, all public entrances shall be barrier-free. For existing buildings, as many as
feasible (but no less than one-half of all public entrances) shall be barrier-free. Provide signage
incorporating the International Symbol of Accessibility to indicate the location of all barrier-free
entrances. The barrier-free entrance must connect the exterior accessible route with the interior
accessible route. Where an entrance consists of multiple doors beside each other, only one door in
each set need be barrier-free.
All required exits from the ground level must be barrier-free. Signage incorporating the International
Symbol of Accessibility shall indicate the location of the barrier-free exits.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-8
6.2.3.1
Clear glass doors and sidelights at the entrances shall have a 100mm wide contrasting
color strip mounted continuously 1350 mm above the floor.
6.2.3.2
Two doors in series (such as in vestibules) shall have minimum 1200mm clear between
the open doors (Figure 6-).
Figure 6-9 Vestibule Clearance
6.2.3.3
Loose floor mats that can cause a tripping hazard or impede wheelchair use are not
permitted in the barrier-free path of travel.
Barrier-free entrance and exit doors shall be a minimum of 915mm wide, such that frame stops, the
door thickness and horizontal hardware such as panic bars shall not reduce the clear width of the
doorway to less than 865mm.
Figure 6-10 Door Clear Width
6.2.3.4
Provide a minimum clear level space on both sides of doors as follows:
1.
1500mm x 1500mm on the pull side;
2.
1200mm x 1200mm on the push side.
6.2.3.5
AUGUST 2010
At least one door in every barrier-free entrance and exit (including doors leading from
parking areas to the building) shall be equipped with an automatic operator. If there are
two doors in series (vestibules), both doors shall have an automatic operator. Doors
shall remain open a minimum of 5 seconds and shall take a minimum of 3 seconds to
close from a 70 degree position. Pushbuttons, key switches, and card readers shall be
located in conformance with 6.4.5. If the automatic door is a swinging door, provide a
cane-detectable guard rail with a horizontal member no more than 680mm above the
ground (Figure 6-11).
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-9
Figure 6-11 Cane Detectable Railing
6.2.3.6
Doors shall have lever hardware, push/pull plates, or exit devices (panic hardware).
Round knobs and thumb-latches are not acceptable.
6.2.3.7
Any exterior door not equipped with an automatic operator shall require a maximum
force of 38N to open. Door closers shall take a minimum of 3 seconds to close from a
70 degree position.
6.2.3.8
Where a revolving door is used, an adjacent barrier-free swinging door shall be
provided.
6.2.4
Exterior Amenities
6.2.4.1
Where exterior amenities such as outdoor seating, terraces, playgrounds etc. are
provided, ensure that they include accessible components. Tables and seating areas
shall have proper clearances.
6.2.4.2
Where picnic tables or outdoor seating are provided, ensure at least some are placed
on a hard surface, and are accessible from the barrier-free walkways. If only some are
barrier-free, provide signage incorporating the International Symbol of Accessibility
indicating the locations.
6.2.4.3
Where kiosks or pay booths are intended to be used by pedestrians, ensure that at least
one window is located at a maximum of 860mm above grade and has an even, level
(maximum 2%) access clearance area of not less than 750mm x 1200mm.
6.3 Interior Areas
6.3.1
Stairs and Ramps
6.3.1.1
Interior stairs shall have:
1.
Closed risers;
2.
Maximum rate of 60%;
3.
Uniform riser height (180mm high maximum) and tread depth (280mm deep
minimum);
4.
Maximum nosing projection of 38mm, with a bevel or radius between 6mm and 10mm
and no abrupt underside;
5.
Color contrasting, slip-resistant nosings 40-60mm deep;
6.
Minimum light level of 100 lux; and
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-10
7.
Detectable warning surfaces as per 6.4.7 at top of the stairway.
6.3.1.2
The underside of all open stairs, escalators and other overhead features must be
protected by cane-detectable railings, planters or benches anywhere the overhead
clearance is less than 2030mm. (Figure 6-5)
6.3.1.3
Handrails shall:
1.
Be provided on both sides of all stairs and ramps;
2.
Be continuous, except where other paths of travel intercept;
3.
Be mounted at a uniform height between 865mm and 920mm above the stair nosing
or ramp level;
4.
Have an extension of 300mm beyond the top riser and 300mm plus the tread depth at
the bottom riser;
5.
Have returns (to a post, wall or floor) at all terminations;
6.
Have a continuous (without interruption by newel posts) graspable profile of 30 43mm, with a minimum clearance of 50mm to the adjacent wall;
7.
Have a minimum of two rails;
8.
Be free of sharp or abrasive elements; and
9.
Be color-contrasted from the adjacent wall surface.
6.3.1.4
Sloped floors shall be designed as a ramp where the gradient exceeds 5% (1:20).
Interior ramps shall have:
1.
Minimum width of 900mm clear between handrails;
2.
Maximum gradient of 8% (1:12);
3.
Level area of at least 1670mm by 1670mm at the top and bottom of the ramp;
6.3.1.5
AUGUST 2010
Except where the location of the ramp is clearly evident, provide signs incorporating the
International Symbol of Accessibility indicating the location of the ramp.
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-11
Figure 6-12 Handrails
6.3.2
Lobbies and Corridors
6.3.2.1
All floor levels above or below the main accessible level that are used by the public shall
be accessible by ramps (section 6.2.2) or elevators (in accordance with section 6.3.3).
6.3.2.2
Interior barrier-free routes shall be minimum 1100mm wide with a 1600mm by 1600mm
turn-around space a minimum of 30m apart.
6.3.2.3
Corridors shall be free from overhead and protrusion hazards. Any overhead
obstruction shall be minimum 2030mm high. Any horizontal projection more than
100mm into the corridor that is less than 2030mm high shall have a cane-detectable
warning no more than 680mm above the floor (Figure 6-5).
6.3.2.4
Wherever a turnstile is used, it shall have a gate directly adjacent with a clear width of at
least 865mm. Where the location of the gate is not readily apparent, a sign shall
indicate its location.
6.3.2.5
All floor surfaces shall be hard, level, slip-resistant, non-glare. Carpets shall be nonstatic and short, dense pile. Floor patterns shall not be visually confusing.
6.3.2.6
Any gratings or drains in floors shall have maximum 13mm openings in either direction.
6.3.2.7
Provide a detectable hazard surface wherever a walkway adjoins a hazardous area
such as an unprotected drop-off or the edge of a pool.
6.3.3
Elevators and Lifts
6.3.3.1
All passenger elevators layouts shall comply with Figure 6-27.
6.3.3.2
Ensure that the emergency communication within the elevator is clearly audible. Do not
permit the playing of any music in elevators.
6.3.3.3
Provide a mirror on the back wall of the elevator to assist people in wheelchairs and
scooters in backing out of the elevator. However, mirrors on sidewalls should not be
permitted due to visual distractions and confusion.
6.3.3.4
Loose mats and loose flooring are not permitted in elevators or lifts.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-12
6.3.3.5
Platform lifts shall be permitted only if the persons using them can independently
operate them. Lifts that require a key or assistance from another person are not
acceptable.
6.3.3.6
Provide an LED-messaging system in each elevator to enable communication in the
event of an emergency with persons who are deaf or hard of hearing.
6.3.3.7
Provide voice-activated speakers in all elevators.
6.3.4
Interior Doors and Doorways
6.3.4.1
Doors shall be a minimum of 915mm wide, such that frame stops, the door thickness
and horizontal hardware such as panic bars shall not reduce the clear width of the
doorway to less than 850mm.
6.3.4.2
All doors shall have lever hardware, push/pull plates, exit devices (panic hardware) or
automatic operators. Knobs and thumb-latches are not acceptable.
6.3.4.3
Unless the door is equipped with an automatic operator, provide clearance beside doors
as follows:
1.
300mm clear beside latch at push side of door
2.
600mm clear beside latch at pull side of door
6.3.4.4
Any interior door not equipped with an automatic operator shall be single hand
operation and require a maximum force of 22N to open. Door closers shall take a
minimum of 3 seconds to close from a 70 degree position.
6.3.4.5
Thresholds shall be maximum 13mm high. Where over 6mm high, shall be beveled at a
slope of not more than 1:2.
6.3.4.6
Doors shall have vision panels, either in the door or in a directly adjacent sidelight,
except where privacy concerns make them unfeasible. Vision panels shall have the
bottom edge no more than 900mm above the floor and no more than 250mm from the
latch side of the door.
6.3.4.7
Clear glass doors and sidelights at the entrances shall have a 100mm wide contrasting
color strip mounted continuously 1350mm above the floor.
6.3.4.8
Two doors in series (such as in vestibules) shall have a minimum 1200mm clear
between the open doors.
6.3.4.9
Provide a minimum clear level space on both sides of doors as follows:
1.
1500mm x 1500mm on the pull side.
2.
1200mm x 1200mm on the push side
6.3.4.10 Where a revolving door is used, an adjacent barrier-free swinging door shall be
provided.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-13
Figure 6-13 Door Clearances
6.4 Facilities
6.4.1
Washrooms/Bathrooms/Toilets
6.4.1.1
Every floor that is served by washrooms shall have either:
a) A barrier-free individual washroom as described in Figure 6-17; or
b) A barrier-free water closet stall, lavatory and accessories
6.4.1.2
For new buildings, or where the extent of renovation includes reconfiguration of
washrooms (i.e., new fixture locations), only section 6.4.1.1a is permissible. For
renovations where this option is unfeasible, section 6.4.1.1b is acceptable.
6.4.1.3
Barrier-free individual washrooms shall have:
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-14
1.
A door that complies with section 6.3.4;
2.
An automatic operator with the ability to be locked from the inside;
3.
A minimum area of 3.5 square meters, with minimum dimension between opposite
walls of 1.7m;
4.
A clear turning radius of 1500mm (does not include space under lavatory)
5.
A water closet that complies with section 6.4.1.5;
6.
A lavatory that complies with section 6.4.1.7;
7.
A shelf or counter at least 200mm x 400mm, mounted not more than 1000mm above
the floor;
8.
A coat hook mounted not more than 1200mm above the floor and projecting not more
than 40mm;
9.
An automatic hand dryer or paper towel dispenser mounted in accordance with 6.4.5;
10.
Washroom accessories (such as soap dispensers, vending machines, waste
receptacles, etc.) that comply with section 6.4.5; and
11.
An emergency call button.
6.4.1.4
Barrier-free facilities within a multi-fixture washroom shall have:
1.
A door that complies with section 6.3.4, with an automatic operator, or be designed
so that no door is necessary;
2.
If there are two doors in series, there shall be at least 1200mm clear between them
when open;
3.
At least 1500mm x 1500mm clear space in front of the barrier-free water closet stall;
4.
At least 750mm x 750mm clear space in front of each barrier-free lavatory;
5.
At least one barrier-free water closet stall;
6.
At least one lavatory that complies with section 6.4.1.7 (in new buildings, all lavatories
shall comply);
7.
If urinals are provided, at least one urinal shall comply with 6.4.1.6;
8.
A shelf or counter at least 200mm x 400mm, mounted not more than 1000mm above
the floor;
9.
Washroom accessories (such as soap dispensers, paper towel dispensers, hand
dryers, vending machines, waste receptacles, etc.) shall comply with section 6.4.5;
and
10.
An emergency call button.
6.4.1.5
Barrier-free water closets shall:
1.
Be located between 460mm and 480mm from the adjacent side wall;
2.
Have a transfer space at least 900mm wide clear on the open side;
3.
Have a back support where there is no seat lid or tank;
4.
Have a seat height of 430mm to 460mm above floor;
5.
Have flush controls that are automatic, or are located on the transfer side of the water
closet;
6.
Have two grab bars:
a. One 600mm long, mounted horizontally, centered on the water closet at a
height of 840mm to 920mm above the floor (or 150mm above the tank where
there is one), and
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-15
b. One L-shaped, 760mm x 760mm, mounted with the horizontal portion at a
height of 750mm to 900mm above the floor, and the vertical component
mounted 150mm in front of the water closet OR one 760mm long, mounted
diagonally, sloping upwards at an angle of 30º to 50º, with the lower end
750mm – 900mm above the floor and 50mm in front of the toilet bowl; and
7.
6.4.1.6
Have a non-regulating toilet tissue dispenser mounted in line with the front of the
water closet, between 600mm to 700mm above the floor.
Barrier-free urinals shall:
1.
Have a clear space of at least 750mm wide by 1200mm deep (including under the
urinal);
2.
The urinal rim no higher than 430mm above the floor;
3.
Flush controls no higher than 1200mm above the floor; and
4.
Vertical grab bars on both sides, minimum 600mm long, mounted with the bottom
between 600mm – 650mm above the floor, maximum 380mm from the centerline of
the urinal.
6.4.1.7
Barrier-free lavatories shall:
1.
Have a centerline located at least 460mm from the adjacent side wall;
2.
Have the top of the counter or lavatory located no more than 840mm above the floor;
3.
Have a clear space of 750mm x 750mm in front of the lavatory;
4.
Have clearance beneath the lavatory of at least:
a. 760mm wide;
b. 735mm high at the front edge;
c.
685mm high at a point 205mm back from the front edge;
d. 230mm high over a distance from a point 280mm back from the front edge to
430mm back from the front edge;
5.
Be equipped with automatic faucets, or faucets with lever handle(s) at least 75mm
long, that are located not more than 485mm from the front of the counter or front
edge of lavatory, that are not spring-loaded;
6.
A mirror mounted with the bottom edge as low as possible, but not more than
1000mm above the floor;
7.
Temperature controlled water to not exceed 55 degrees Celsius; and
8.
A soap dispenser mounted within 500mm of the lavatory, no higher than 1100mm,
operable with one hand.
6.4.1.8
Grab Bars shall be:
1.
Slip-resistant;
2.
Diameter of 30mm-40mm;
3.
Have a clear space of 30mm – 40mm from the wall; and
4.
Be firmly mounted to resist a force of 1.3kN in any direction.
6.4.1.9
Barrier-free water closet stalls shall have:
1.
A clear space inside of at least 1500mm x 1500mm, clear of the door swing;
2.
A door which provides at least 860mm clear width which is capable of being locked
from the inside using one hand, with a large thumb turn, with spring hinges to close
automatically;
3.
A water closet that complies with 6.4.1.5; and
4.
A hook mounted not more than 1200mm above the floor and projecting not more than
40mm.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-16
6.4.1.10 Unless the barrier-free washrooms are directly adjacent to the other washrooms,
provide directional signage incorporating the International Symbol of Accessibility
indicating the location.
6.4.1.11 Provide a motion detector control for lights in all barrier-free washrooms. In a multi-unit
washroom, ensure that the sensor will detect motion within the barrier-free stall.
6.4.1.12 Where toilet partitions are provided a minimum of 230mm toe clearance shall be
provided (Figure 6-17).
6.4.2
Shower and Bath Facilities
6.4.2.1
Wherever shower facilities are provided, provide at least one roll-in shower that has:
1.
An interior clear area of at least 900mm x 900mm;
2.
A clear floor area in front of at least 900mm deep and the same width as the shower;
3.
A roll-in threshold not exceeding 13mm high with a maximum bevel slope of 1:2;
4.
A floor drain located outside the shower stall;
5.
A horizontal grab bar on the side wall at least 600mm long, mounted between 700mm
and 800mm above the floor;
6.
A vertical grab bar on the opposite side wall at least 800mm long, mounted with the
lower end between 600mm and 650mm above the floor and between 35mm and
65mm from the outside edge;
7.
A horizontal grab bar on the back wall at least 900mm long, mounted 850mm above
the floor;
8.
A vertical grab bar on the back wall at least 600mm long, mounted with the lower end
between 750mm and 850mm above the floor and between 400mm and 500mm from
the side wall with the other vertical bar;
9.
A flip-up seat mounted on the side wall with the vertical bar;
10.
A hand-held shower head on an adjustable pole;
11.
Controls mounted no more than 1200mm above the floor; and
12.
A slip-resistant floor.
Figure 6-14 Barrier-Free Showers
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-17
Clear Floor Space Requirement
915mm x 915mm Shower Plan
Control Wall Elevation
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-18
Figure 6-15 Barrier-Free Bathtubs
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-19
Figure 6-16 Water Closet Details
Plan
Elevation
Figure 6-17 Toilet Partition Details
6.4.2.2
6.4.3
Wherever bath facilities are provided, provide:
1.
A clear floor area in front of at least 760mm deep and the same width as the bath;
2.
A floor drain located outside the bath;
3.
A horizontal grab bar on the side wall at least 600mm long, mounted between 700mm
and 800mm above the floor (Figure 6-16);
Drinking Fountains
6.4.3.1
Drinking fountains shall have a spout that:
1.
Is located near the front of the unit;
2.
Is between 750mm and 900mm above the floor;
3.
Directs the water flow parallel to the front on the unit; and
4.
Provides a water flow at least 100mm high.
6.4.3.2
AUGUST 2010
Controls shall be automatic or operable with one hand using a force of not more than
22N.
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-20
6.4.3.3
Drinking fountains shall have a clear floor area of 750mm wide by 1200mm deep. All
drinking fountains must be cane-detectable, recessed or otherwise located out of the
route of travel.
6.4.3.4
Cantilevered fountains shall have:
1.
Knee clearance at least 750mm wide x 200 mm deep x 680 mm high; and
2.
Toe space at least 750mm wide x 230mm deep x 230mm (Figure 6-).
Figure 6-18 Cantilevered Drinking Fountain
6.4.4
Public Pay Telephones
6.4.4.1
6.4.5
All public pay telephones shall have:
1.
All operable parts (including coin slot) not more than 1200mm above the floor;
2.
A clear space of 750mm wide by 1200mm deep;
3.
A minimum of 680mm clear knee space;
4.
Illumination level of at least 200 lux; and
5.
A level shelf 450mm wide by 300mm deep, between 720mm to 800mm above the
floor, with a clear space of 250mm above the shelf
Controls
6.4.5.1
All manual controls (light switches, card readers, thermostats, coin slots, control
handles, fire alarm pulls, vending machines, etc.) must be:
1.
Located between 900mm min. and 1200mm max. above the floor;
2.
Located with a clear floor space of at least 750mm x 1200mm (clear of door swing.).
3.
Operable with one hand, without tight grasping, pinching or twisting of the wrist, with
a force not to exceed 22N; and
4.
Of contrasting color to the background.
6.4.5.2
Push buttons for automatic doors shall have minimum dimensions of 100mm and shall
be located such that the opening door does not block them.
6.4.5.3
Information on visual displays shall be supplemented by tactile and/or auditory
information.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-21
Figure 6-19 Control Locations
6.4.6
Signage
6.4.6.1
Signage indicating room uses, names, or numbers shall:
1.
Be consistently located, to the latch side of a door, 150mm from the frame;
2.
Be mounted at a consistent height, such that all characters and symbols are not less
than 1200mm above the floor and not more than 1500mm above the floor;
3.
Have glare-free surface;
4.
Have color contrasted to background;
5.
Be lit to at least 200 lux; and
6.
Include appropriate pictograms wherever possible (i.e., washrooms, stairs, etc.)
6.4.6.2
Characters on signs shall:
1.
Be sans serif with Arabic numerals;
2.
Have a width to height ratio between 3:5 and 1:1 (using an upper case X for character
measurement);
3.
Have a stroke width to height ratio between 1:5 and 1:10;
4.
Be at least 25mm high (for viewing distance of up to 750mm, higher for signs that are
to read further away); and
5.
Have color contrasted from the background, light colored characters/symbols on a
dark background, or dark colored characters/symbols on a light background.
6.4.6.3
Signs that include tactile raised characters (0.8 – 1.5 mm thickness) and Grade 1 Brail,
or auditory information shall be provided at identification signs (including building
directories, floor designations and room designations), regulatory signs (including
identification of building exits) and warning signs (Figure 6-).
6.4.6.4
Signs incorporating the appropriate symbols for access shall be provided at all barrierfree facilities such as parking spaces, building entrances, washrooms, showers,
elevators, telephones, meeting rooms etc.
6.4.6.5
Provide an audible sign at the main entrance to all buildings to provide information that
will assist in way-finding through the building.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-22
Figure 6-20 Signs
6.4.7
Tactile Warnings
6.4.7.1
Provide tactile warnings (textured surfaces, knurled lever handles etc.) at the following
locations:
1.
Doors to hazardous areas;
2.
Tops of all stairs and ramps (Figure 6- and Figure 6-);
3.
Where a barrier-free walkway crosses a vehicular way;
4.
The edges of flush pools, planters, etc. that are not protected by curbs (Figure 18A);
a. Be composed of truncated domes;
b. Be slip-resistant; and
c.
Have a contrasting color to the surrounding surface.
Figure 6-21 Detectable Warning Indicator Location
6.4.7.2
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-23
Figure 6-22 Tactile Warnings Indicator Location
6.4.7.3
Detectable warning indicators shall be composed of truncated domes and have a
contrasting color to the surrounding surface (Figure 6-).
Figure 6-23 Tactile Warnings & Detectable Warning Indicator
6.4.8
Counters and Line up Guides
6.4.8.1
1.
Clear floor space of 750mm wide by 1200mm deep in front;
2.
Counter height maximum 860mm above the floor; and
3.
Clear knee space 1000mm wide by 680mm high.
6.4.8.2
6.4.9
Provide a section at all service counters (reception, public service, coat checks, etc.)
with:
Where line-up guides are provided, they shall:
1.
Provide a clear width of at least 1100mm;
2.
Have a minimum space of 1670mm x 1670mm at changes in direction;
3.
Be cane-detectable at or below 680mm above the floor; and
4.
Be color-contrasted from the floor.
Places of Assembly
6.4.9.1
AUGUST 2010
For meeting rooms, boardrooms, courtrooms, assembly areas, cafeterias, coffee shops,
etc., provide designated space for seating for persons in wheelchairs or scooters as
follows:
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-24
Table 6-3 Seating Requirements
6.4.9.2
Total seats provided
Minimum designated seating required
Up to 100
2
101 - 200
3
201 -300
4
301 -400
5
401 - 600
6
over 600
1% of seating capacity
Designated spaces shall be on a level surface level (maximum slope in any direction
1%), and at least 840mm wide by 1220 mm deep (front or rear access) or 1525mm
deep (side access). Where the seating is fixed, at least one fixed seat directly adjacent
to each barrier-free seating space shall be signed as reserved for companion seating.
Figure 6-24 Wheel Chair Viewing Space
6.4.9.3
AUGUST 2010
Lines of sight must be comparable to other seating and must not be compromised by
standing members of the audience.
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-25
6.4.9.4
Ensure that tables in areas such as meeting rooms, cafeterias, and libraries are a
maximum of 860mm high, and have a clear knee space of at least 750mm wide,
480mm deep, and 680mm high.
6.4.9.5
Aisles such as cafeteria lines, spaces between tables and aisles between Library stacks
shall be minimum 915mm wide.
6.4.9.6
Anywhere that coat racks are provided, ensure that at least one section has a rod height
not more than 1370mm above the floor.
6.4.10
Assisted Listening Devices
6.4.10.1 Provide an assisted listening device in any auditorium, assembly room, meeting room or
theatre with an area greater than 100 s.m. and an occupant load more than 75 people.
Such rooms shall be signed with the symbol for persons who are hard of hearing.
6.4.10.2 Any television set displaying information for the public shall include closed captioning.
6.4.11
Visual and Audible Alarms
6.4.11.1 All building alert and alarm signals, including fire alarms, building entrance release
hardware and other signals intended for the public to indicate operation of a building
access control system shall provide both an audible and a visual signal.
6.4.11.2 Visual alarms shall:
1.
Have a light intensity of at least 75 Candelas;
2.
Be located so that at least one is visible from any portion of a floor area;
3.
Have a flash rate within the frequency range of 1-3 Hz; and
4.
Be synchronized to flash in unison wherever multiple alarms may be visible at one
time.
6.4.11.3 Where the emergency evacuation planning of a facility necessitates that persons with
disabilities await assistance in order to be evacuated (example: floor level above grade
served by stairs), provide a safe Area of Refuge in a fire-separated room, equipped with
two-way communication, emergency lighting, and separate ventilation. This
requirement is waived for fully sprinkled buildings.
6.4.12
Life Safety
6.4.12.1 Where a building has an emergency power supply, all automatic doors operators will be
provided with emergency power.
6.4.12.2 All facilities shall have an Emergency Policy and Emergency Evacuation Plan that
addresses the needs of people with disabilities.
6.4.12.3 All sleeping and living rooms to be provide with audio and visual smoke/carbon dioxide
detectors which are hardwired and on a separate circuit.
6.4.13
Cooking & Laundry Facilities
6.4.13.1 Where a building has cooking or laundry facilities, all such facilities will be provided with
fixtures and appliances to allow for access for people with disabilities.
6.4.13.2 All laundry facilities shall have a washer and dryer that address the needs of people
with disabilities (Figure 6-25).
6.4.13.3 All separate laundry rooms shall have a clear turning area 1500 mm to allow for the
turning of a wheel chair.
6.4.13.4 All cooking facilities shall have a layout that addresses the needs of people with
disabilities.
6.4.13.5 All kitchens to have a handicap working area which is at least 760 mm wide.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-26
Figure 6-25 Washers & Dryers
Figure 6-26 Kitchen Layouts
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-27
Figure 6-27 Elevator Clearances
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-28
References
ADA Accessibility Guidelines September 2002
Bill 125 - Ontarians with Disabilities Act. December 14, 2001
CAN/CSA B651-04 Accessible Design for the Built Environment. 2004
CNIB, Clearing Our Path. August 1998
GPC Research. Report on Findings: Quantitative Results from On-Line Barrier-Free
Kailes, June Isaacson. Emergency Evacuation Preparedness – A Guide for People with
Disabilities and Other Activity Limitations. 2002
Making Ontario Open for People with Disabilities – A Blueprint for a Strong and Effective
Ontarians with Disabilities Act. April 22, 1998
Management Board Secretariat. Architectural Design Standards for Court Houses. April
1999
Management Board Secretariat. Barrier-Free Design Guide for Ontario Government
Buildings. 1992
Ministry of Community and Social Services website,
http://www.mcss.gov.on.ca/mcss/english/how/howto_buildings.htm, July 14, 2006.
Ministry of Municipal Affairs and Housing Provincial Planning and Environmental Services
Branch. Handbook on Planning for Barrier-Free Municipalities (draft).
Ministry of Municipal Affairs and Housing Technical Advisory Committee. Barrier Free
Requirements in the Ontario Building Code: Recommendations for Change. December 2002
Ministry of Municipal Affairs and Housing, Ontario Building Code 2006, O. Reg. 350/06.
Ministry of Citizenship, Culture and Recreation. Preventing and Removing Barriers for
Ontarians with Disabilities. July 1998
Holten, Shane. Planning a Barrier-Free City of Toronto. July 2001.
Universal Design Institute. Access – A Guide to Accessible Design. 2000.
AUGUST 2010
REVISION NO. 03
STANDARDS FOR BARRIER-F REE DESIGN 6-29
7
Surveying Standards
7.1 Purpose
To provide general reference for surveying procedures performed by and for Libya Housing and
Infrastructure Board (HIB). This publication establishes minimum standards, policies, and procedures
of surveying for HIB. It provides information on the use of surveying technology to perform surveys
for large scale and small scale projects. Accuracy is a prime consideration in surveying and is
stressed in this publication.
7.2
7.2.1
Horizontal Control Surveys
Definition
A horizontal control survey is performed for the purpose of placing geographic coordinates of latitude
and longitude (X and Y coordinates) on permanent monuments for referencing lower levels of
surveys. A projection is used to place the coordinates on a plane of northing and easting values for
simplified measurements. Scale and elevation factors are applied to make the distance
measurements applicable to the exact project location on the working surface. If possible, project
control should be planned so that project control monuments serve for both horizontal and vertical
control. It is important that project control plans consider the need for supplemental control.
7.2.2
Field Methods
Particularly for horizontal control surveys, Global Positioning System (GPS) is quickly replacing the
use of the total station for long distance traversing. The inherent error of each GPS derived baseline
(about 5 mm plus 1 part per 1,000,000) will make accuracy at short distances less attractive but using
baselines of many kilometers suddenly becomes phenomenally accurate and cost effective.
When feasible, horizontal project control shall be established using GPS surveys complying with
second-order accuracy standards (see Attachment 7-3 for tolerances). When GPS survey methods
cannot be used for all or part of a Horizontal Project Control Survey, a Total Station Survey System
(TSSS) traverse network shall be used. The TSSS traverse will comply with second-order accuracy
standards.
Planning the control network so that it will meet the needs of all subsequent project surveys is critical.
Key steps in the control planning process are to:
Ascertain the need for additional corridor control
Develop a survey work schedule that meets the needs of the Project Development
schedule.
Research the existing horizontal and vertical control networks.
Recover and evaluate existing control.
Plan the project control network and select the methods for establishing control.
Plan supplemental control.
New control stations shall be permanently marked in a manner suitable for the terrain, the design of
which shall be agreed with HIB or its representative.
These control stations shall typically be by means of a two centimeter diameter and one meter long
iron rod set into at least a half a cubic meter of concrete.
A station control sheet (survey card) at a scale of 1:100 will be prepared and include a
photograph of the station with a small sign indicating the station number in the
photograph. An overall control map will be prepared at a scale commensurate with the
project size that will indicate the location of all control points for the project.
Significant nearby topographic features shall be recorded and shown on the station
control sheet.
A minimum of three witness/reference points shall be surveyed from the control station
with a bearing and distance to a semi-permanent object such as a building corner, light
standard, sign or other such items.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-1
All monuments set by the surveyor shall be set at sufficient depth to retain a stable and distinctive
location and be of sufficient size to withstand the deteriorating forces of nature and shall be of such
material that in the surveyor’s judgment will best achieve this goal.
When delineating a right-of-way (ROW) or boundary line as an integral portion of a survey the
surveyor shall set, or leave as found, sufficient, stable and reasonably permanent survey markers to
represent or reference the property or boundary corners, angle points, and points of curvature or
tangency. ALL SURVEY MARKERS SHALL BE SHOWN AND DESCRIBED with sufficient evidence
of the location of such markers.
7.2.3
Coordinate Adjustment
Control Points set for design and construction projects will be referenced to the Survey Department of
Libya (SDL) approved map projection of the Libyan Transverse Mercator two-degree (LTM2°) grid,
Libyan Geodetic Datum (LGD) of 2006. The data for this information can be obtained from the SDL
on their published Description Card for Ground Survey Control Point. All Description Cards for
surveys will be obtained from the SDL and will have their official stamp on the card for authentication.
A survey report showing the World Geodetic System of 1984 (WGS 84) geodetic coordinates along
with the LGD 2006 geodetic and LTM 2° grid coordinates shall be submitted. The report will show
Longitude, Latitude (WGS84 and LGD2006), Ellipsoid Height, North, East (LTM2°), Elevation, Scale
Factor, and Surface Adjustment Factor for each point.
The Surface Adjustment Factor (SAF) allows conversion of grid coordinates to surface coordinates
and distances, and vice-versa. For additional information, refer to Attachment 7-2, Survey Report
Guidelines.
7.3 Vertical Control Surveys
7.3.1
Definition
A vertical control survey is performed for accurately determining the orthometric height (elevation) of
permanent monuments to be used as bench marks for lower quality leveling.
Differential leveling is the preferred method of carrying elevations, referring to the use of
compensator-type engineer’s levels and electronic digital/bar code leveling systems. However, GPS
can be used indirectly but with less accuracy. Height measurements from the ellipsoid can be
determined very accurately with GPS. Trigonometric leveling, with a total station, is not acceptable for
vertical control work.
The use of first order leveling is cost prohibitive and unnecessary in most surveying cases.
Discrepancies between originally run level lines in some cases negate the advantages of the
precision of the first order and sometimes second order level runs. In most cases third order leveling
is acceptable for providing control and design surveys if good surveying procedures are adhered to.
At a minimum, the following specifications below are based on using a compensator or electronic level
and the use of wooden or metal rods employed for third order work.
Table 7-1 Third Order Differential Leveling Requirements
Operations/Specification
Compensatory-Level Compensator-Level
Electronic/Digital Bar
Three-Wire
Single-Wire
Code Level
Observation
Observation
Difference in length between fore
and back sites, never to exceed
(m)
10
10
10
Maximum sight lengths (m)
90
90
90
Minimum ground clearance of
sight line (m)
0.5
0.5
0.5
Maximum section and loop
misclosure (mm)
18 v D (see note 1)
18 v D (see note 1)
12 v D (see note 1)
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-2
Operations/Specification
Compensatory-Level Compensator-Level
Electronic/Digital Bar
Three-Wire
Single-Wire
Code Level
Observation
Observation
Collimation (two-peg) test
Daily (see note 2)
Daily (see note 2)
Daily (see note 2)
Minimum number of readings
N/A
N/A
3 (see note 3)
Notes:
1.
vD = Square root of the length of section or loop in kilometers (section is defined as a series of setups between
two permanent control points; loop is defined as a series of setups closing on the starting point).
2.
Control level run: readjust level if 2 mm in 60 m is exceeded.
3.
If the standard error of the mean exceeds 1 mm, continue repeat measurements until the standard error of the
mean is less than 1 mm.
The instrument should be treated with care and a peg test should be performed on a regular basis.
Level rods are equally critical and should be checked periodically. All back-sight and fore-sight shots
should be balanced.
Most digital levels have on-board adjustment programs and/or a memory card that will allow the data
to be transferred to a computer for adjustment. Manual readings can also be hand entered into the
data collector to record the data, warn of out-of-tolerance readings, adjust the point elevations, and
compile reports.
A carefully planned GPS network survey can be used to obtain orthometric heights. Since GPS
measures heights from the imaginary ellipsoid surface, the data must be converted to useable
orthometric heights through a model of interpolated geoid separation measurements. In order to get
the accuracy needed for a vertical control survey, there must be at least 3 or 4 high quality bench
marks surrounding the project area (and in 3 or 4 separate quadrants) to better model the area. In
other words, at least one bench mark should be fixed in each of the four (4) quadrants of the survey
area, such that nearly all of the newly surveyed stations will fall inside a boundary drawn around the
outside benchmarks. Additional benchmarks inside the perimeter will aid in strengthening the
adjustment. This sometimes makes the use of GPS impractical –differential leveling may be just as
cost effective, if the distances are not too great.
7.3.2
GPS Network Design Example:
Roughly locate both new points and existing control on a map showing roads to use in
moving the observers around the project.
From reconnaissance and mission planning software, determine the best times to
observe.
For each session, draw the independent baselines chosen to be observed on map. Move
through the project until all points have been observed.
Observing the rules for time differences, plan the repeated occupations and observations.
Consider redundancy requirements.
Measure and record antenna height in two different units at the beginning and before the
end of each session.
Fill out observation sheet each session. (See Attachment “A”)
Every one moves every session (where practical).
In the scope of these specifications, GPS data processing includes the review and cataloging of
collected data files, processing phase measurements to determine baseline vectors and/or unknown
positions, and performing adjustments and transformations to the processed vectors and positions.
Each step requires quality control analysis, using statistical measures and professional judgment, to
achieve the desired level of confidence. Each of these steps is also very dependent upon the
measurement technique, the GPS receiver, and antenna types; the observables recorded, and the
processing software.
Typically, the elevation basis is either with an existing project (datum specified by project) or by using
Mean Sea Level datum as defined by SDL. A statement of the basis of elevations shall be made in
computer files and placed on all map prints similar to one of the following examples:
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-3
7.3.3
1.
Elevations refer to a BM set near the N. E. corner of the intersection of Al-Shutt Street
and Gurgi Road (Location), an “X” on top of a concrete wall (description). Elevation is
100.00 meters.
2.
Elevations are based upon bench mark A1422, Published elevation—126.042 meters
above Mean Sea Level.
Benchmarks
A benchmark is a relatively permanent material object, natural or artificial, bearing a marked point
(used exclusively for elevation control) whose elevation above or below an adopted datum is known.
Establish benchmarks with physical characteristics and quality commensurate with the order of the
leveling survey. Benchmarks should be of a stable, permanent nature; e.g., galvanized steel pipe;
steel rod driven into a firm soil base; or cast in place concrete. A brass disk epoxied into a drilled hole
in rock or concrete is also acceptable.
Benchmarks should be conveniently located and easily accessible. Whenever possible, benchmarks
should be located outside of construction areas, clear of traffic, and within a public right of way.
Space benchmarks as required by project conditions and convenience of operation, generally not to
exceed 300 meters apart. Prepare a written benchmark/station description for inclusion in the survey
notes and in the project final control report.
A vertical project control survey shall be performed for each specific project that requires elevations to
define topographic data points or positions of fixed works. The establishment of vertical project
control monuments is important because all subsequent project surveys requiring elevations are to be
based on the vertical project control.
Vertical project control surveys shall be based on a single, common vertical datum to ensure that
various phases of a project and contiguous projects are consistent.
When feasible, vertical control for projects should be established at all horizontal control stations.
Additional benchmarks should be set to provide convenient control for photogrammetry, topographic,
and construction purposes.
7.4
7.4.1
Topographic Surveys
Definition
A topographic survey is a survey which has for its major purpose the determination of the
configuration and relief of the surface of the earth (ground), presenting them as contour lines on a
plot, and the location of natural and/or man made features thereon.
A topographic survey is prepared for the purpose of gathering relevant information that will be
represented on either a topographic map or in a Digital Terrain Model (DTM). Topographic surveys
are also referred to as Engineering Surveys, which are associated with engineering design; highway
planning, engineering design, and ROW design are the primary purposes.
Topographic surveys are necessary in order to prepare an accurate topographic map and require the
expert skill of a surveyor well versed in maintaining accuracy and precision in detail mapping. A
planimetric map is a two dimensional (2D) map that represents the horizontal and vertical positions of
the features represented; distinguished from a topographic map by the addition of relief in a
measurable form. A topographic map can also be three dimensional (3D) that represents the same
features as a planimetric map but uses contours or comparable symbols to show mountains, valleys,
and plains. A planimetric map is a map that presents the horizontal positions only for the features
represented; distinguished from a topographic map by the omission of relief in a measurable form.
Contours, being an integral part of a topographic survey in 3D, will have sufficient spot elevations
(ground elevation points) to generate 0.5-m contour intervals for the project. In regions where there is
little variation in surface height (relief), the points may be more widely spaced, whereas in areas of
more variation in height, the point density is increased.
7.4.2
Utility Surveys
Utility surveys are undertaken to locate existing utilities above and below ground for (a) consideration
in engineering design, (b) purposes of utility relocation, and (c) right-of-way acquisition and
negotiation. It is important to locate all significant utility facilities.
As a minimum a Topographic Survey shall include the following facilities and critical points:
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-4
Pipeline intersection point with centerlines and/or right of way lines, with size and depth of
lines.
Pipeline vents and markers, angle points, meter vaults, valve pits, etc.
Water, sanitary and storm sewer line intersection points with size and depths of lines.
Manholes, valve boxes, meter boxes, crosses, tees, bends, etc.
Elevation on waterlines, sewer inverts, and manhole rims
Fire hydrants and valves
Roadways
Curb and gutters and centerline roadway and sidewalks
Utility Poles
Traffic signs and signals
Bridges, headwalls, etc.
Survey control monuments
7.4.3
Digital Terrain Model (DTM)
A Digital Terrain Model (DTM) is a mathematical model of a project surface that becomes a three
dimensional representation (3D) of existing and proposed ground surface features with three
dimensional coordinates. Critical calculations and processes based on the DTM include contouring,
quantities, drainage models, watersheds, hydraulics, water catchment areas, and cross section
sheets.
A DTM is created through the construction of a Triangulated Irregular Network (TIN) and is based on
modeling the terrain surface as a network of triangular facets created by connecting each data point
to its nearest neighboring points. Each data point (having x, y and z coordinates) is the vertex of two
(2) or more triangles. The advantage of the TIN method is its mathematical simplicity- all DTM
calculations are either linear or planar.
The processes and the resulting DTM offer many advantages over a topographic survey. Field data
for a DTM is collected in a way that allows the surveyor to use the latest in automated survey
technology. Traditional data collection (for a topographic survey) involves taking cross sections,
typically every 30 meters, along a horizontal control line or in a grid pattern. This method is still used
along with data points (shots) taken at every break in elevation to create a more accurate DTM. The
emphasis is on identifying all features and changes in elevation within project limits. Data is collected
using an electronic data collector with an electronic total station or with the use of real time kinematic
(RTK GPS). The data points are assigned feature codes, attributes, descriptions, comments, and
connectivity linking codes to add intelligence to a point at the time of data entry into data collector.
The surveyor should have this in mind when performing his data collection: too much is inefficient,
too little does not accurately describe the surface.
7.4.4
Route Survey
A route survey is an application of the above described topographic or DTM survey along a
determined linear ROW route, either existing or proposed, for a utility or roadway.
When this text discusses procedures or standards relating to either a topographic survey or survey for
a DTM, the accuracy, standards, equipment and basic procedural methods employed will be the
same. A topographic survey will be performed and a DTM can be used for most surveying
applications where route design and engineering are required, whereas a topographic map may be
better suited for large area site design and development. This specification is intended for use in
developing a design survey, a DTM, or a topographic survey, with accuracy sufficient to meet design
needs and requirements.
A 3D model or a DTM may be preferred for purposes such as:
Highway/roadway planning, design
ROW design
Drainage studies
Site development, planning
Architectural planning, design
Landscape design.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-5
A significant advantage of a DTM is that it offers the ability to view, inspect, and smoothly navigate
through, over and across a DTM in a 3D environment for the purposes of locating, editing, and
correcting raw field data (points and break-lines/chains) in 3D.
A completed route survey will provide sufficient qualitative information and dimensional data for
indicating the feasible alignment, grades and cross sections.
7.4.5
Considerations - Other Technology
A computer model or a DTM is the ultimate work product of any of these newer methods of data
acquisition. Depending on the critical factors of each project, including type, terrain, accuracy,
precision required, cost, traffic conditions, and safety, such advanced methods may warrant serious
consideration as a complement to conventional data gathering or as a replacement of common or
conventional surveying methods. While conventional aerial photogrammetry may still be viable, as
technology continues to advance, existing methods such as photogrammetry with airborne Global
Positioning System (GPS) control becomes more accurate and even more cost effective. Other,
newer methods of terrain modeling are also available.
Ground based scanning is an automated collection of data by reflector-less laser which involves high
density scanning of an object or location to collect a “point cloud” of data points. The point cloud of
data is further processed into a 3 dimensional computer model image. Typically done from a remote
instrument location or multiple locations, 3D Laser scanning is especially beneficial for sites or objects
that are difficult to access, have high traffic volumes, involve extreme detail or have other extreme
dangers or conditions associated.
This method has also been utilized in place of conventional topographic or digital terrain model (DTM)
surveying with much success, especially where high traffic volumes or lane closure issues (safety)
were critical factors. Presently the accuracy of the scanned data is said to equal or even exceed that
of conventional survey methods, even electronic total station work, with the additional advantage of a
greater number of data points all throughout the structure or project. Other methods or technology
should be discussed with and approved by HIB or its representative.
7.4.6
Work Product
A DTM or Topographic Survey requires:
A control survey network, with horizontal and vertical positions on primary control points
that are monumented, referenced, and placed near or on the project site.
Points of secondary control, which are based upon and which supplement primary control
to facilitate data acquisition within a project.
A description and location sketch of each control point.
7.4.7
Information Required
Information should include the following:
Project or site location shown on a map
ROW maps depicting current ROW width(s) and other land, ownership and survey
information
Ownership information of adjacent tracts if available
Intersecting road ROW information and documentation if available
Construction plans of existing facilities if available
Intended use of the survey and required form of deliverable, files required, etc.
Accuracy required and method of display (contours, spot elevations, etc.)
Horizontal and vertical datum upon which the survey is be based
Existing survey control information and data sheets, if available, for horizontal and vertical
monumentation
7.4.8
Monuments
Reference points and control monuments for a topographic survey may include temporary stakes,
hubs, and nails in pavement, iron rods, or reinforced concrete monuments.
A wooden hub or stake, nail or iron rod is considered as secondary control (temporary bench mark or
control point) which only supplements primary survey control monumentation to facilitate data
acquisition.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-6
Primary control points, whether set by GPS or conventional survey methods, shall be of reasonable
permanence and may include concrete monuments.
Monuments whether set or existing shall be well referenced, numbered or named according to
procedure, indexed in the project data or field notes and identified in the computer file final
deliverable.
Point numbers may be furnished for a monument numbering system. A location sketch and data
sheet for each monument should be furnished.
7.4.9
Field Procedures
DTM or topographic surveys require a reliable horizontal and vertical control system based on
acceptably closed and adjusted traverses and level loops. Attention should be given toward
developing this control system before any detail work is begun.
Field work shall be performed to achieve the specified or intended accuracy and results as stated in
this publication, in accordance with accepted technical methods, and as directed by the manufacturer
of the surveying instrument(s) or equipment used.
Field personnel shall be well trained in the technical aspects of surveying as related to their respective
duties.
Surveying instruments shall be checked and kept in close adjustment according to their
manufacturer’s specifications or in compliance with textbook standards. At a minimum all instruments
should be calibrated yearly by a certified company to the calibration standards required by the
manufacturer or standards traceable to an institute of standards.
Electronic distance measuring devices shall be compared against a standardized
baseline at 6 month intervals, however a comparison check should always be done as
needed, especially if an instrument has been dropped, damaged or is suspect of the
same.
This comparison includes electronic total stations or any other electronic measuring
instrument.
Total stations and theodolites shall be compared against a standard known angle at a 6
month interval; however, a comparison check should always be done as needed,
especially if an instrument has been dropped, damaged or is suspect of the same.
Levels, auto or digital, should be checked by the two-peg test or reading the elevation
difference between two reference points taken from 1.) A middle setup between points
and also 2.) From an end setup. This test provides a fairly accurate check for the
amount of collimation error. A collimation error indicates an out of adjustment condition,
which usually requires a shop cleaning and adjustment.
Auxiliary tapes, cloth or fiberglass, shall only be used for rough measurements where
precision is not important, such as determining the width of ditches, the location of
excavations or other irregular improvements. Tapes of this sort shall not be used to
measure distances in excess of 30 meters.
Field measurements of angles and distances shall be performed in such a manner as to attain the
closures and tolerances as found in these standards.
Where aerial photogrammetry is to be used to compile the topographic map, the surveyor shall
consult with the photogrammetrist as to specific requirements for the photo control and for additional
supplemental information required by conditions of a specific project or location.
Horizontal and vertical photo control (picture points) shall be based on and looped to the
control system.
Identification of photo control (picture points) must be precise and clear since these points
will be used to build the network from which the photogrammetrist must work.
Photo control points, set before the aerial photography is made, shall be located from,
and looped to the control system. The density and pattern for paneled picture points shall
be determined through consultation and coordination with the photogrammetrist.
For these purposes, methods that are more modern are normally used, such as the DTM survey that
incorporate methods described in the section below.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-7
Surveying procedures with electronic total station or with GPS shall incorporate control points that are
tied to a primary control system network of an appropriate level of precision and accuracy for the
project.
Acquisition of field data may require running secondary control and bench marks that begin and end
at points on the primary control system.
The use of open ended legs or “spur” lines should be avoided whenever possible. When such lines
are necessary, appropriate checks shall be made on all field data before leaving the vicinity.
Any field notes written in a field book shall be kept in a neat and orderly manner on all control points,
primary or secondary. Appropriate annotations on location, description of point and reference to
identifying specific features located during the DTM or topographic survey shall be made.
7.4.10
Topographic Features
The perimeter limits of any unique or special features such as historic structures, cemeteries, burial
grounds or gravesites known or found within the project limits, or adjacent to it, and which may be
affected (by the existing or proposed ROW ), shall be shown by actual location.
Features within ROW corridors to include buildings and improvements and 15 meters outside of ROW
need to be surveyed. The project manager may require an extension of this distance.
Items to be located as a minimum are as follows:
Center lines and top of banks of dry creeks, streams or other confined intermittent
watercourses.
Paths, car trails, pasture roads, etc.
Additional data points outside of the ROW, as required and directed by client.
Creeks, streams, rivers and water bodies, shown and identified by name if available.
Water levels shall be determined and displayed by elevation.
Drainage areas - field information on drainage area(s) of a project shall be collected in the
same manner as other information to the extent as directed by the project manager
and/or client.
Utilities as mentioned in Utility Surveys.
7.4.11
Electronic Data
In nearly all cases, field work is automated by the use of computer software and hardware for
collecting, reviewing, editing, and processing field data. A data collector may be connected to the
instrument (total station, GPS receiver, digital level, etc.) to store the raw measurement data and
perform coordinated geometry (COGO) functions while in the field. Original raw data must be saved
as a file for retention, as a matter of record, before any data editing or processing is done.
7.4.12
Data Collection
Field data in electronic form will be collected in addition to standard written notes. Its purpose is to
provide a more flexible and user definable method of recording horizontal angle, vertical angle and
slope distance from most of the total stations and in a standard format recognized by good surveying
methods. A standard Field Book will include written notes of the date, weather, crew, job name and
job number, plus a description of the work being performed. It will also be used to record pertinent
field information in an accurate, clear format.
There are numerous ways to provide connectivity. When performing radial topography surveys for a
DTM, points in the same break-line (survey chains) such as edge of pavement, centerlines and ditch
lines can be linked together. These survey chains can ultimately be imported to mapping files or to
DTM files as DTM break lines.
The contractor will submit their Feature Codes and Cells for use in the field to insure standardization
of line weight, color, levels, and symbology. The feature codes also determine where the points and
survey chains will go, either to a mapping file or a DTM file. Topographic surveys, traverses, and
level runs may be collected in approved software that can then be reduced to coordinates on a
desktop PC.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-8
7.5 Construction Staking
7.5.1
Field Methods
Methods used to establish construction stakes are at the surveyor’s option. These methods may
include any means capable of maintaining the necessary tolerances. The surveyor is responsible to
provide additional control stakes and verification of existing control and to maintain them during the
construction process.
Sufficient independent field checks will be made at the discretion of the surveyor to assure the
integrity of the stakes. The integrity of stakeout set-up points should be verified before use by taking
check shots on other control points. All positions staked in the field should be checked against the
computed positions and the results recorded in electronic stakeout reports and/or on stakeout listings.
Working stakes used by the surveyor in actually performing the work are the surveyor’s responsibility
and are to be set by the surveyor.
7.6 As-Built Surveys
7.6.1
Definition
As-built Surveys (or post construction surveys), show the conditions of the construction project after
the construction is completed.
Features shown on the as-built survey must be surveyed after construction.
7.6.2
Deliverable
As-Built drawings shall include, as a minimum, revisions to alignments and right-of-way, grade
revisions, drainage changes, changes to roadway features and revisions on the location of utility
crossings and irrigation crossovers. All information on the As-Built drawings will be to the Libyan
Transverse Mercator two-degree (LTM2°) grid, Libyan Geodetic Datum (LGD) of 2006.
After construction is complete, the as-built corrections will be placed on a copy of the Cadd files.
Each as-built sheet will be clearly marked as an AS-BUILT SURVEY.
7.7 Survey Map Check List
The following Check List is a minimum amount of information to be placed on a standard map or
maps. It is imperative to have quality maps with pertinent information on them.
Company name, address, telephone number, e-mail address and fax number
Client name, address, telephone number, e-mail address and fax number
Scale and Bar Scale
Date
North arrow
Title Block
Description of survey
Legend
Limits of Survey
Existing and new control
Coordinate basis (datum)
Signature of surveyor (if required)
Notes
Sheet numbers
Control monuments with coordinates and elevations
Border
Vicinity Map
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-9
Attachment 7-1 GPS Log Sheet
GPS LOG SHEET
Project Name
______________________________________________
Operator Name
Observation Date
Station Name
Antenna Height
1st measurement
Meters
2nd measurement
Survey feet
3rd measurement
Average
Measure to:
Bottom of notch
Top of notch
Antenna ref. point
Antenna Type
Actual start time
Actual stop time
4 digit receiver number
NOTES:
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-10
Attachment 7-2 Survey Report Guidelines
The following is a list of minimum items that should be included in a Survey Report.
The SCOPE OF WORK should be detailed enough so that someone unfamiliar with the project would
be able to tell what tasks needed to be done, state the name or names of party performing the survey
and be detailed enough to determine if the contractor has fulfilled their contract obligation. A
discussion of results should be either in the project introduction or in a conclusion section.
There are three map projections approved by the Survey Department of Libya (SDL).
LTM 2° (Libyan Transverse Mercator) with a zone width of 2 degrees
UTM (Universal Transverse Mercator) with a zone width of 6 degrees
LTM 16° with a zone width of 16 degrees
The AECOM Libya Housing and Infrastructure Board Surveying Standards state that surveys will be
referenced to LGD2006 (Libyan Geodetic Datum 2006), LTM2° projection. All of the information on
projections is detailed on the Description Card for Ground Control Point. The description cards can
be obtained from the SDL with their official stamp on the card for authentication. Contact: SDL at
telephone number 021 483 6901. Example: Survey coordinates are provided in LGD2006 datum,
LTM2° Zone 7 projection based on three survey monuments provided by the SDL.
The Equipment Used Section should list the type of equipment used (i.e. Global Positioning System
(GPS) equipment, total stations, and digital levels) and type of hardware and software used for
collection, processing and adjustment. Accompanying equipment certifications or calibration reports
(total stations) should be noted. Also it should be noted that tribrachs and levels were checked and
adjusted prior to each new project.
The technique or combination of techniques used to establish control for projects will need to be
noted (such as a GPS network, Real Time Kinematic (RTK), digital level loops or total station
traverses). Example: 7 GPS points were established and followed with a total station traverse to
establish intermediate control points and collect topographic data with the traverse closure included in
the report. A digital level run was used to check/verify 25% of the GPS derived elevations and the
level run is included in the report.
Problems Encountered with Solutions Section should be explained, including any deviations from the
initial survey plan. Example: The main bench mark in the city is set vertically in a wall, approximately
0.5m above the ground. An auxiliary point was set (2cm rod in concrete) 120m to the north. A digital
level loop was performed to establish the elevation of the new point, which closed within 0.001m. The
new point was then used in the GPS survey adjustment with known elevation.
This section should discuss data processing and methodology used to achieve loop closure. Data
processing/loop closure report should be included in the report; Example: The static GPS network
consisted of 16 points. Each point was connected to a minimum of 4 other points and occupied on at
least 2 separate occasions. A different set-up to catch an HI error was used with a different set of
satellites in the solution. The Loop Closure report should also be included for a comparison of the
GPS vectors; dX, dY and dZ from this point to the next and so on, looping back to the beginning point.
This is a test of the processed GPS baselines before any coordinate adjustments are made. A plot of
the control locations is useful, for example, for being able to see that a point 125km away is being
held fixed as one of the primary horizontal control monuments.
The Network Adjustment/Final Coordinate List Section should show the final coordinate values, with
the adjustments to the primary horizontal and vertical control monuments. Comparison can also be
made with additional control points that were included in the survey but not held fixed in the
adjustment as an additional accuracy check.
SDL description cards of the primary control used and data sheets of newly set control monuments
with all the pertinent data should be included in the report.
If the report is in Arabic, please translate to English. Additionally, the following are items that should
not be included in the survey report:
Catalog cuts from equipment used; Brand, model and serial number is only required
Coordinates and adjustments in other datum’s
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-11
Minimally constrained adjustment of GPS network only in WGS84 and finally in LGD2006
datum
If you have any questions or need clarifications please contact Juan E. Galvan at 092 304 0564 or
juan.galvan@aecom.com.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-12
Attachment 7-3 Tolerances for Conventional Traverse for 2nd and 3rd Order
Item
2nd Order
3rd Order
Remarks
Error of Closure
1:20,000
1:10,000
Loop or between
monuments
Allowable Angular
Closure
Adjusted Mathematical of
Survey Less Than
± 8”
± 15”
1:200,000
1:200,000
N = number of angles
in traverse
Closure No
The above table shows tolerances for conventional horizontal surveys and for GPS horizontal control
surveys. Note that with the use of GPS, there are fewer physical checks and more attention paid to
the number, location and quality of reference monuments due to the nature of GPS static surveying.
No matter which method is used, any printed list, file or map must indicate the appropriate datum,
projection and zone.
AUGUST 2010
REVISION NO. 03
SURVEYING STANDARDS 7-13
8
Roadway
8.1 Highway Systems
8.1.1
Functional Classification
Functional classification is defined as the process by which streets and highways are grouped into
systems according to the character of service they are intended to provide. Each roadway
classification has a distinct function, character, and level of access control.
Table 8-1 Functional System Characteristics
Functional System
General Description
Freeway
Provides the highest level of service at the highest speed for the longest
uninterrupted distance
Full access control using only grade-separated interchanges
Expressway
Provides high speed and long distances traveled by vehicles
Full access control by grade-separated interchanges
Service roads normally provided to serve lands adjacent to the highway,
connected to the expressway mainline by free-flowing ramps
Arterial
Provides moderate distances for traffic and with lower design standards
than expressways
Access generally by means of at-grade intersections (signalized or
roundabout), but may also use grade-separated interchanges
Collector
Collects traffic from locals and channels it into the arterial systems
Provides both land access and traffic circulation with residential
neighborhoods, commercial, and industrial areas
Intended for low speeds and minimal access control
Although used for through traffic, access to adjacent land is very
important
Local
Intended for short distances only with low speed
Provides access to residential and commercial facilities
Provides access to higher systems
The following sections briefly introduce each of the classes:
8.1.2
Freeways
A freeway is a road which is designed to move heavy volumes of high speed traffic under free flowing
conditions. The need for a freeway is generated by high traffic volumes which in turn necessitates
fully controlled access. In rural areas, the freeway connects major cities or industrial areas. In urban
areas, the freeway provides high-standard routes connecting areas of major traffic generation.
8.1.3
Expressways
An expressway is similar to a freeway in its basic function except that it does not require the fully
controlled access. Access may be fully or partially controlled by grade-separated interchanges, and
can have connections to Service Roads that provide access to local roads.
8.1.4
Arterials
Arterial roads are of a lower design standard than freeways and expressways. Their intersections
with other arterials and lower-class roads are generally at grade, and controlled by fixed signing or
traffic signals. Arterials are intended to carry large volumes of traffic moving at medium to high speed,
and are used by a broad range of vehicle types, because they distribute traffic from the higher classes
to the lower classes and vice versa. Arterial roads can also be identified as Service Roads since they
run parallel and are connected to the expressways to provide access to local traffic.
AUGUST 2010
REVISION NO. 03
ROADWAY 8-1
8.1.5
Collectors
The function of these roads is to collect traffic flow from the local roads to the arterial roads and to
distribute traffic flow from arterials back to the local roads. Access to properties is normally allowed
on collector roads. In rural areas, the function of collector is twofold; to provide access to adjacent
land uses and to carry traffic into areas with sparse development.
8.1.6
Local Roads
Local roads are designated to allow vehicles to reach the frontage of properties from a collector road
or arterial road. Their main function is to provide land access, and they generally carry low volumes
of traffic. They serve residential, commercial, or industrial land uses. As this is the lowest class in the
road hierarchy, direct access is permitted to all abutting properties.
8.2
Traffic
8.2.1
Level of Service
The average highway user will tolerate a certain level of congestion and delay before he becomes
frustrated or attempts unsafe driving maneuvers. This level will vary according to the type of facility.
To characterize acceptable degrees of congestion, the level-of-service concept has been developed.
The application of level of service involves choosing the appropriate level for the selected design
year. The Level of Service is graded from A to F, where level A is the highest and level F is the
lowest. Table 8-2 gives general guidelines for use in selecting the level of service. Table 8-3 gives
the general definitions of these levels of service.
Table 8-2 Minimum Level of Service Guidelines
Type of Area and Level of Service
Highway Type
Rural
Level
Rural
Rolling
Rural
Mountainous
Urban and
Suburban
Freeway
B
B
C
C
Expressway
B
B
C
C
Arterial
B
B
C
C
Collector
C
C
D
D
Local
D
D
D
D
Table 8-3 General Definitions of Levels of Service
Level of Service
General Operating Condition
A
Free flow
B
Reasonably free flow
C
Stable flow
D
Approaching unstable flow
E
Unstable flow
F
Forced or breakdown flow
The at-grade intersection should operate at no more than one level of service below the values in
Table 8-2. Capacity of signalized intersections depends on many factors, including:
1.
Intersection geometry including the number and width of lanes, grades, and land use.
2.
Percentage of heavy vehicles
3.
Location of and use of bus stops
4.
Distribution of vehicles by movement (left, thru, right)
AUGUST 2010
REVISION NO. 03
ROADWAY 8-2
8.2.2
5.
Pedestrian-crossing flows
6.
Peak-hour factor
7.
Signal phasing, turning and type of control at each approach
Design Vehicles
The characteristics of vehicles using the highway are important controls in geometric design. These
will vary according to the type of vehicle being considered. When a highway facility or intersection is
under design, the largest design vehicle likely to use that facility with considerable frequency should
be used to determine the selected design values. Typically, trucks have the greater influence on
design. Table 8-4 presents basic information on dimensions for the standard design vehicles.
Table 8-4 Design Vehicle Parameters (meters)
Design Vehicle Type
Symbol*
Height
Width
Length
Min. Design
Turning
Radius
Min.
Inside
Radius
Passenger Car
P
2.0
2.2
5.8
7.3
4.4
Single Unit Truck
SU
4.1
2.6
9.1
12.8
8.6
Single Unit Bus
BUS
4.1
2.6
12.1
12.8
7.5
Articulated Bus
A-Bus
3.4
2.6
18.3
12.1
6.5
Intermediate Semi-Trailer
WB-12
4.1
2.6
15.2
12.2
5.9
Semi-Trailer Combination
Large
WB-15
4.1
2.6
16.7
13.7
5.2
Semi-Trailer Full Trailer
Combination
WB-18
4.1
2.6
19.9
13.7
6.8
Inter-State Semi-Trailer
WB-19
4.1
2.6
21.0
13.7
2.8
Inter-State Semi-Trailer
WB-20
4.1
2.6
22.5
13.7
1.3
Triple Semi-Trailer
WB-29
4.1
2.6
31.0
15.2
6.3
Turnpike Double SemiTrailer
WB-35
4.1
2.6
35.9
18.3
5.2
Motor Home
MH
3.7
2.4
9.2
12.2
7.9
Passenger Car with Trailer
P/T
3.1
2.4
14.9
10.1
5.3
Passenger Car with Boat
Trailer
P/B
-
2.4
12.8
7.3
2.4
Motor Home with Boat
Trailer
MH/B
3.7
2.4
16.2
15.2
10.7
*The designation WB relates to approximate wheelbase; WB-12 denotes a truck whose wheelbase is around
12m.
8.3 Speed
The highway should be designed to accommodate the speed desires of most highway users, within
the limits of safety.
AUGUST 2010
REVISION NO. 03
ROADWAY 8-3
8.3.1
Design Speed
Design speed is the maximum safe speed that can be maintained over a specified section of highway
when conditions are so favorable that the design features of the highway govern. Factors that
influence the design speed include roadway classification, urban and rural areas, economic matters,
and the terrain. Many design elements such as horizontal and vertical curvature, superelevation, and
sight distances, are directly dependent on the design speed. Table 8-5 provides recommended
design speeds for varying conditions.
Table 8-5 Design Speeds
Design Speed (km/h)
Roadway
Classification
Rural Roads
Urban Roads
Absolute Minimum (Only in
Mountainous Terrain)
Min.
Max.
Min.
Max.
Freeway
120
140
100
120
80
Expressway
100
120
80
120
80
Arterial
80
100
60
100
50
Collector
60
80
50
80
50
Local
40
60
30
60
30
8.3.2
Posted Speed
The posted speed provides a factor of safety for those drivers who tend to drive faster than the speed
limit but are still within the design speed. The posted speeds are mandatory to limit the speed of
those fast drivers and provide safe driving condition. Table 8-6 indicates the posted speed which is
appropriate for a given design speed.
Table 8-6 Recommended Posted Speeds
Design Speed (km/h)
Posted Speed (km/h)
30 – 40
30 – 40
50
40
60
50
70
60
80
70
90
80
100
90
120
100
140
120
Local Roads and Streets should have a Posted Speed of 50 km/h or lower as local conditions dictate
such as near school zones.
AUGUST 2010
REVISION NO. 03
ROADWAY 8-4
8.3.3
Ramps
The ramps within a grade-separated interchanges typically have a lower design speed than that of a
mainline. Table 8-7 should be used as the minimum design speed.
Table 8-7 Minimum Design Speed for Connecting Roadways
Mainline Design Speed
(km/h)
Minimum Design Speed for Connecting Roadway (km/h)
Ramps
Loops
50
30
20
60
40
30
70
50
40
80
60
40
90
60
50
100
70
50
120
80
60
140
90
70
8.4 Sight Distance
Sight distance values affect the design of horizontal and vertical alignment, at-grade intersections,
interchanges, and highway crossings. Types of sight distance (stopping, decision, or passing)
depend on the type of highway and potential hazard. On horizontal curves, sight distance is most
critical on the inside of a curve. Roadside objects on the inside of a curve are required to be set back
from the edge of the traveled way by a greater distance than that of a straight line. On vertical
curves, sight distance is typically controlled by the eye and object heights.
8.4.1
Stopping Sight Distance (SSD)
Stopping sight distance is the sum of two distances: the distance traveled during driver
perception/reaction time, and the distance traveled during brake application. The perception/reaction
time is usually 2.5 sec.
Perception/Reaction Distance is calculated by:
PRD = 0.278tV
Where:
PRD = perception/reaction distance (m)
t = perception time + reaction time (sec)
V = initial speed (km/h)
Braking Distance is calculated by:
BD = V²/254(f ± G)
Where:
BD = braking distance (m)
V = initial speed (km/h)
f = coefficient of friction
G = grade (%) divided by 100
When determining stopping sight distances, the following should be applied for eye and object
heights:
AUGUST 2010
REVISION NO. 03
ROADWAY 8-5
Driver’s eye height 1.05m to 2.40m
Object height
0.15m to 2.00m
Figure 8-1 Visibility Envelope for Stopping Sight Distance
Figure 8-1 Visibility Envelope for Stopping Sight Distance
Table 8-8 summarizes the rounded stopping sight distance values for design.
Table 8-8 Stopping Sight Distances
Stopping Sight Distance (m)
Design
Speed
(km/h)
Friction
Coefficient
(f)
Downgrade
Upgrade
Level*
3%
6%
9%
3%
6%
9%
30
0.40
35
32
35
35
31
30
29
40
0.38
50
50
50
53
45
44
43
50
0.35
65
66
70
74
61
59
58
60
0.33
85
87
92
97
80
77
75
70
0.31
105
110
116
124
100
97
93
80
0.30
130
136
144
154
123
118
114
90
0.30
160
164
174
187
148
141
136
100
0.29
185
194
207
223
174
167
160
120
0.28
250
263
281
304
234
223
214
* Values are also included in the Design Controls for Crest and Sag Vertical Curves, Table 8-19.
AUGUST 2010
REVISION NO. 03
ROADWAY 8-6
8.4.2
Passing Sight Distance (PSD)
Passing sight distance applies to undivided two-way, two-lane roads, in which a driver passes another
vehicle without interfering with an oncoming vehicle that appears when the passing vehicle begins its
maneuver. The visibility envelope for the Passing Sight Distance is based on:
Driver’s eye height 1.05m to 2.40m
Object height
1.05m to 2.40m
Table 8-9 provides the passing sight distance for various design speeds.
Table 8-9 Passing Sight Distances
8.4.3
Design Speed (km/h)
Minimum Passing
Sight Distance (m)
30
200
40
270
50
345
60
410
70
485
80
540
90
615
100
670
Decision Sight Distance
Decision sight distance is the distance required for a driver to detect an unexpected or otherwise
difficult-to-perceive information source or hazard in a roadway environment that may be visually
cluttered, recognize the hazard or its threat potential, select an appropriate speed and path, and
initiate and complete the required safety maneuver safely and efficiently.
Decision sight distance, as with stopping sight distance, is the sum of perception/reaction time and
vehicle maneuver time (stopping or a lane change). The application of decision sight distance must
be individually assessed at each location. The visibility envelope for Decision Sight Distance is the
same as for Stopping Sight Distance, namely:
Driver’s eye-height 1.05m to 2.40m
Object height
0.15m to 2.00m
AUGUST 2010
REVISION NO. 03
ROADWAY 8-7
Table 8-10 provides the necessary information to determine the required distance.
Table 8-10 Decision Sight Distance
Design Sight Distance (m)
Design Speed
(km/h)
8.5
8.5.1
Stop Maneuver
All Other Maneuvers
Rural
Urban
Rural
Urban
50
75
160
145
200
60
95
205
175
235
70
125
250
200
275
80
155
300
230
315
90
185
360
275
360
100
225
415
315
405
120
305
505
375
470
Horizontal Alignment
General
Horizontal alignment should be designed to provide a continuous, uniform, and safe driving condition
and speed for vehicles. It should meet the following general considerations:
Horizontal alignment should be as smooth as possible and in harmony with the
topography. Flatter curvature with shorter tangents is generally preferable to sharp
curves connected by long tangents. Angle points should be avoided.
The minimum length of horizontal curves should be:
Lmin = 6V (high speed freeways)
Lmin = 3V (other arterials)
Where V = design speed (km/h)
Broken-back curves (short tangent between two curves in same direction) should be
avoided.
Compound curves should be avoided where possible. Where they are used, the radius of
the flatter curve should not be more than 50% greater than the radius of the sharper
curve. However, this consideration does not necessarily apply at intersections and
roundabouts, where lower speeds pertain.
Reverse circular curves on high-speed roads should include a transition section of
sufficient length to accommodate the reversal of superelevation between the circular
curves.
The horizontal alignment should be in balance with the vertical alignment and consistent
with other design features.
Horizontal curves should be avoided on bridges whenever possible. They cause design,
construction, and operational problems. Where a curve is necessary on a bridge, a
simple curve should be used on the bridge and any curvature or superelevation
transitions placed on the approaching roadway.
Factors that influence the degree of horizontal curvature of a road include:
Safety
Design speed
Topography, adjacent land use and obstructions
AUGUST 2010
REVISION NO. 03
ROADWAY 8-8
Vertical alignment
Maximum allowable superelevation
Roadway classification
Cost
8.5.2
Types of Horizontal Curvature
8.5.2.1
Simple Curves
A simple curve has a constant circular radius which achieves the desired deflection without using an
entering or exiting transition. Because of their simplicity and ease of design, survey, and construction,
this is the most frequently used curve. Figure 8-2 illustrates a simple curve layout.
Figure 8-2 Simple Curve
8.5.2.2
Compound Curves
Compound curves are used to transition into and from a simple curve. Compound curves are
appropriate for intersection curb radii, ramps, and transitions into sharper curves. As the curvature
becomes successively sharper, the radius of the flatter circular curve should not be more than 50%
AUGUST 2010
REVISION NO. 03
ROADWAY 8-9
greater than that of the sharper curve. Figures 8-3 and 8-4 illustrate a typical compound curve layout
and warrants for compound curvature.
Figure 8-3 Compound Curve
AUGUST 2010
REVISION NO. 03
ROADW AY 8-10
Figure 8-4 Compound Curve Transition
8.5.3
Minimum Curvature
There is a direct relationship between the vehicle speed, the radius of the curve, the superelevation,
and the side friction between the tire and the road surface.
Where
R = radius of curve (m)
V = vehicle speed (km/h)
e = superelevation (%) divided by 100
fs = side friction factor
The side friction factor ranges from 0.35 to 0.50 on dry roads and on wet surfaces it may drop to
around 0.2. Table 8-11 provides the minimum radii for varying design speeds and a range of
superelevation rates.
Table 8-11 Minimum Horizontal Curvature
Minimum Radius (m)
Design Speed
(km/h)
Normal Crown
-2%
Maximum Superelevation (e)
2%
4%
6%
8%
30
50
40
35
30
30
40
90
70
60
55
50
50
140
110
100
90
80
60
200
165
150
135
120
70
300
230
215
195
170
80
430
320
280
250
230
90
570
420
375
335
305
100
750
545
490
435
400
120
1220
850
810
755
670
140
1930
1290
1100
965
870
Superelevation is limited to 2%
8.5.4
Spiral Curve Transition
Spiral transition curves improve the appearance of the alignment and assist in the introduction of
superelevation prior to the circular curve. A properly designed transition curve provides a natural,
easy-to-follow path for drivers and minimizes encroachment on adjoining traffic lanes. It provides
flexibility in accomplishing the widening of sharp curves. For the Euler spiral (or clothoid), the degree
of curvature varies directly with the length along the curve. Figure 8-5 shows the layout of a typical
transition curve joining a tangent to a circular curve.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-12
Figure 8-5 Typical Spiral Transition Curve
The length of the transition curve (TS to SC in Figure 8-5) depends on the radius of the circular curve
into which it leads. It is defined by the following formula:
Where
Ls =
length of spiral (m)
V=
design speed (km/h)
q=
rate of change of centripetal acceleration (m/s³)
R=
radius of circular curve (m)
The value of q = 0.3 m/s³ is desirable. Table 8-12 gives rounded values of the computed spiral
lengths of the radii for e = 6% in Table 8-11.
Table 8-12 Spiral Lengths for Minimum Radii at 6% Superelevation
Length of Spiral
Design Speed
Minimum Radius
(km/h)
e = 6%
Desirable
Minimum
60
135
115
60
70
195
130
65
80
250
145
75
90
335
155
80
100
435
170
85
120
755
190
95
140
965
205
100
8.5.5
Horizontal Stopping Sight Distance
Safe sight distance must be provided on the inside of horizontal curves. Obstructions that interfere
with the needed sight distance should be removed, if possible. On horizontal curves, a designer must
provide a “middle ordinate” between the center of the inside lane and the sight obstruction. The basic
equation is:
Where:
M = middle ordinate, or distance from the center of the inside lane to the obstruction (m).
R = radius of curve (m)
S = stopping sight distance (m)
The height of eye is 1080 millimeters and the height of object is 600 millimeters. The line-of-sight
intercept with the view obstruction is at the midpoint of the sight line and 840 millimeters above the
center of the inside lane. See Figure 8-6.
Figure 8-6 Components for Determining Horizontal Sight Distance
8.5.6
Superelevation
Superelevation counterbalances the centrifugal force, or outward pull, of a vehicle traversing a
horizontal curve. This outward pull can be counterbalanced by the roadway being superelevated, the
side friction developed between tires and surface, or some combination of the two. This allows a
vehicle to travel at higher speeds around the horizontal curves.
8.5.6.1
Superelevation Rates
The maximum useable rate for superelevation (emax) is controlled by several factors: Climate
conditions, terrain conditions, type of area, and the frequency of slow moving vehicles. The maximum
rates of superelevation based on roadway classifications are shown in Table 8-13.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-14
Table 8-13 Maximum Superelevation
8.5.6.2
Roadway Classification
Max. Superelevation
(emax)
Local
4%
Collector
4% (urban)
6% (rural)
Arterial
4% (urban)
8% (rural)
Expressway and Freeway
8%
Loops within Interchanges
8%
Superelevation Transition
A length of superelevation transition shall be required to accomplish the change in cross slope from a
normal crown section to a fully superelevated section or vice versa. The length of superelevation
transition shall consist of a tangent runout and a superelevation runoff.
Tangent Runout: is the length of highway needed to accomplish the change in cross slope from a
normal cross section to a section with the adverse crown removed (0%), or vice versa.
Superelevation Runoff: is the length of highway needed to accomplish the change in cross slope
from a section with the adverse crown removed (0%) to a fully superelevated section, or vice versa.
The length for superelevation runoff is dependent on the width of the pavement and the change in
superelevation over the transitional length, and is defined by the following formula:
L=2xW x e
Where
L = superelevation runoff length (m)
W = pavement width (m)
e = algebraic difference in superelevation (%)
Superelevation runoff lengths should be long enough so that the rate of change of the edges of
pavement relative to the centerline does not exceed empirically developed controls. These maximum
relative gradients, which provide a minimum length of runoff, are given in Table 8-14.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-15
Table 8-14 Maximum Relative Gradients
Design Speed
(km/h)
Maximum Relative Gradient
(%)
Equivalent Maximum
Relative Slope
30
0.75
1:133
40
0.70
1:143
50
0.65
1:154
60
0.60
1:167
70
0.55
1:182
80
0.50
1:200
90
0.47
1:213
100
0.44
1:227
120
0.38
1:263
The pavement may be rotated about the centerline or either edge of the travel lanes. Figure 8-7
shows typical methods of developing superelevation by rotating about the edges and about the center
of the road.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-16
Figure 8-7 Development of Superelevation
8.5.6.3
1.
Design Considerations
Superelevation is introduced or removed uniformly over the lengths required for
comfort and safety.
2.
Place approximately two-thirds of the runoff on the tangent section and one-third on
the horizontal curve.
3.
On compound curves, full superelevation for the sharpest curve should be attained at
the PCC.
4.
For compound curves also, if the flatter entering curve is less than or equal to 150 m,
a uniform longitudinal gradient should be used throughout the transition. If the flatter
entering curve is longer than 150 m, it may be preferable to consider the two curves
separately. Superelevation for the entering curve would be developed by the 2/3rd1/3rd distribution method. This rate would be maintained until it is necessary to
develop the remaining superelevation for the sharper curve.
5.
When spiral transitions are used, the adverse crown is completely removed at the
beginning of the spiral. The tangent runout length occurs prior to the beginning of the
spiral transition. The rate of transition used in the tangent runout should be the same
rate used for the superelevation runoff.
6.
For the spiral transitions, the transition for the superelevation runoff will be applied
over the entire length of spiral, with full superelevation developed at the horizontal
curves’ PSC.
7.
The minimum superelevation runoff lengths for roadways wider than two lanes should
be as follows:
a. Three-lane traveled ways; 1.2 times the corresponding length for two-lane
traveled ways.
b. Four-lane undivided traveled ways; 1.5 times the corresponding length for twolane highways.
c.
8.5.6.4
Six-lane undivided traveled ways; 2.0 times the corresponding length for twolane traveled ways.
Shoulder Superelevation
All outside shoulders and median shoulders of 1.25 meter or greater should slope away from the
travel lanes on superelevated curves. The maximum algebraic difference between the travel lanes
slope and shoulder slope is 0.09 m/m. Shoulders less than 1.25 meters should slope in the same
direction as the travel lane; see Figure 8-8.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-18
Figure 8-8 Highway with Paved Shoulders
8.5.7
Minimum Lane Width on Curves
Because the rear wheels of vehicles do not exactly follow the track of the front wheels, it is necessary
to widen the pavement on low radius curves. Widening is dependent on vehicle geometry
(wheelbase), lane width and curve radius. Widening should be applied in both directions of travel to
produce the lane width of the circular curve as shown in Table 8-15.
Table 8-15 Minimum Lane Width on Curves
Radius (m)
Lane Width (m)
125 – 300
4.5
300 – 400
4.0
More than 400
Normal width
8.6 Vertical Alignment
The highway vertical alignment is controlled by: Topography, traffic volumes and operating
characteristics, highway classification, safety, sight distance, design speed, horizontal alignment,
drainage, access to adjacent properties and cost. Where a highway crosses a waterway, the vertical
profile of the highway must be consistent with the design flood frequency.
8.6.1
Grades
Table 8-16 presents the recommended desirable and maximum highway grades. Flatter grades
should be used where possible. On a long ascending grade it is preferable to place the steepest
grade at the bottom and flatten the grade near the top.
Table 8-16 Recommended Maximum Grades
FUNCTIONAL
CLASSIFICATION
FREEWAY/
EXPRESSWAY
Table 8-16 RECOMMENDED MAXIMUM GRADES
DESIGN SPEED (KM/H)
U/R
TERRAIN
30 40 50 60 70 80 90 100 110 120
URBAN
RURAL
ARTERIAL
URBAN
RURAL
COLLECTOR
URBAN
RURAL
LEVEL
..
..
..
..
..
4
4
3
3
3
ROLLI NG
..
..
..
..
..
5
5
5
4
4
MOUNTAINOUS
..
..
..
..
..
6
6
6
5
..
LEVEL
..
..
..
..
..
4
4
3
3
3
ROLLI NG
..
..
..
..
..
5
5
5
4
4
MOUNTAINOUS
..
..
..
..
..
6
6
6
5
..
LEVEL
..
..
8
7
6
6
5
5
..
..
ROLLI NG
..
..
9
8
7
7
6
6
..
..
10
MOUNTAINOUS
..
..
11
LEVEL
..
..
..
9
5
ROLLI NG
..
..
..
6
MOUNTAINOUS
..
..
..
8
9
8
5
4
7
6
6
5
8
..
..
3
3
4
3
4
4
4
6
6
5
5
5
LEVEL
9
9
9
9
8
7
7
7
ROLLI NG
12
12
11
10
9
8
8
8
MOUNTAINOUS
14
13
12
12
11
10
10
10
6
5
..
7
..
6
..
LEVEL
7
7
7
7
7
6
ROLLI NG
10
10
9
8
8
7
MOUNTAINOUS
12
11
10
10
10
9
LEVEL
8
7
7
7
7
6
6
5
..
..
ROLLI NG
11
11
10
10
9
8
7
6
..
..
MOUNTAINOUS
16
15
14
13
12
10
10
..
..
7
9
5
4
..
6
5
..
8
6
..
LEVEL
ROLLI NG
LOCAL
URBAN
RURAL
Notes:
MOUNTAINOUS
SEE NOTE 4
..
1. FOR GRADES OF LENGTH LESS THAN 150 m AND FOR 1-WAY DOWN GRADES, THE MAXIMUM
GRADE MAY BE 1% STEEPER THAN TABLE VALUES. FOR LOW -VOLUME RURAL HIGHWAYS,
GRADES MAY BE 2% STEEPER.
2. IN URBAN AREAS, GRADES 1% STEEPER MAY BE USED FOR EXTREME CASES WHERE (A) EXISTING DEVELOPMENT
PRECLUDES USING FLATTER GRADES, OR (B) 1-WAY DOWN GRADES IN LEVEL OR ROLLING TERRAIN.
3. GRADES SHOWN FOR RURAL AND URBAN CONDITIONS OF SHORT LENGTH, (LESS THAN 150 m), ON 1-WAY
DOWN GRADES AND ON LOW-VOLUME RURAL COLLECTORS MAY BE 2% STEEPER.
4. GRADES SHOULD BE AS FLAT AS IS CONSISTENT WITH THE SORROUNDING TERRAIN AND LAND USE IN THE AREA.
IN RESIDENTIAL AREAS,THE MAXIMUM GRADE SHOULD BE 15% IN COMMERCIAL AND INDUSTRIAL AREAS
WHERE TRUCK USE IS EXPECTED, THE MAXIMUM GRADE SHOULD BE 8% AND DESIRABLY 5%.
At grade-separated interchanges, the maximum grade for the on and off ramps may be up to 2%
greater than the corresponding maximum grade permitted on the mainline.
In addition to the maximum grade, the designer must consider the length of the grade. The gradient
in combination with its length will determine the truck speed reduction on upgrades. The guidelines
given in Table 8-17 for the maximum length of sustained grade are based on a speed reduction for
trucks of 15 km/h.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-20
Table 8-17 Critical Grade Lengths
% Upgrade
Max. Length of Grade
(m)
2
650
3
400
4
280
5
210
6
175
7
150
8 and more
130
Minimum Grade
The minimum longitudinal grades for proper drainage are:
0.3% for Freeways, Expressways and Arterials
0.2% for Collectors and Local Roads
8.6.2
Vertical Curves
Vertical curves are provided at all changes in grade, except as shown in the following Table 8-18:
Table 8-18 Maximum Change in Grade without Vertical Curves
Table 8-17A Maximum Change in Grade Without Vertical Curves
DESIGN SPEED
(KM/H)
50
60
70
80
90
100 110
MAXIMUM CHANGE IN
GRADE IN PERCENT
1.00
0.80
0.70
0.60
0.40 0.30 0.20
The curvature and length of vertical curves shall be such that the required sight distances are met.
Design controls for the vertical curves are generally based on the following formula, where K implies
the rate of curvature and it is a good indication for proper drainage:
K = L/A
Where
L = length of curve (m)
A = algebraic difference in grades (%)
Computations for vertical curves are shown in Figures 8-9(a),(b), and (c).
AUGUST 2010
REVISION NO. 03
ROADW AY 8-21
Figure 8-9(a) Parabolic Vertical Curves
AUGUST 2010
REVISION NO. 03
ROADW AY 8-22
Figure 8-9(b) Parabolic Vertical Curves
Figure 8-9(c) Parabolic Vertical Curves
The primary control for crest vertical curves is providing adequate stopping sight distance. The
primary control for sag vertical curves is the headlight sight distance, where the height of the
headlights is assumed to be 600 millimeters.
Table 8-19 shows the minimum K values for design as required for the range of values of stopping
sight distances for each design speed.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-24
Table 8-19 Design Controls for Crest and Sag Vertical Curves
Design Speed
(km/h)
8.6.3
Stopping Sight
Distance
Rate of Vertical Curvature, K
(m)
Crest Curves
Sag Curves
30
35
2
6
40
50
4
9
50
65
7
13
60
85
11
18
70
105
17
23
80
130
26
30
90
160
39
38
100
185
52
45
120
250
95
63
Combining Horizontal and Vertical Alignments
To obtain an adequate alignment it is important to integrate the vertical and horizontal geometry, and
to consider the road as a three-dimensional unit. A summary of desirable and undesirable
combinations of alignments is provided in Figure 8-10(a)and Figure 8-10(b).
AUGUST 2010
REVISION NO. 03
ROADW AY 8-25
Figure 8-10(a) Summary of Undesirable Alignment Combinations
AUGUST 2010
REVISION NO. 03
ROADW AY 8-26
Figure 8-10(b) Summary of Desirable Alignment Combinations
8.6.4
Vertical Clearances
Minimum vertical clearances are needed at all overhead structures including bridges, overhead signs
and cables, overhead traffic lights and suspended lighting. The minimum clearance for new
construction is 5.5 m. This clearance includes up to 200 mm for pavement overlay, which may be
applied during the road maintenance, resulting in a clearance of 5.3 m that must be maintained at all
times.
Where a road passing underneath the bridge is on a sag curve, the headroom needs to be increased
to allow for the limiting effect of the sag. Table 8-20(a) provides the additional headroom values.
Table 8-20(a) Additional Clearance for Sag Curves
Sag K Value
Additional
Headroom (m)
4 and 5
0.12
6 and 7
0.08
8 and 9
0.06
10 to 12
0.05
13 to 17
0.04
18 to 25
0.03
26 to 50
0.02
51 to 100
0.01
8.7 Cross Section Elements
8.7.1
General
The limits of the road cross section are governed by the width of the right-of-way available, which is
typically determined at the planning stage. Many factors affect and determine the roadway typical
section such as: design speed, roadway classification, right-of-way, traffic volume, environmental
issues, existing or proposed utilities, bikers, and so many others.
The basic elements of a roadway cross section are:
AUGUST 2010
REVISION NO. 03
ROADW AY 8-27
Right-of-way limits
Borders
Drainage Ditches
Side slopes
Sidewalks
Curbing
Shoulders
Travel Lanes
Cross Slopes
Medians
Horizontal Clearances
Others:
- Service Roads
8.7.2
-
Auxiliary Lanes
-
Bridges
-
Tunnels
Travel Lanes
The number of travel lanes is primarily based on a capacity analysis for the selected design year. The
width of the travel lane will vary according to the functional class of the highway, traffic volumes,
design speed, and level of development as presented in Table 8-20(b).
Table 8-20(b) Recommended Roadway Section Widths Freeways/Expressways
Travel Minimum Lane
Width
Right Paved Usable
Shoulder Width
(Min.)
Left Usable Shoulder
w/
4 or More Lanes
Desirable Width
Left Usable Shoulder
Width (Min.)
3.7 m
3.0 m
2.44 m (3.05 m*)
1.22 m
* With truck volumes over 250 vehicles/day
Note:
610 mm added to usable shoulder width for minimum offset to vertical elements over 200 mm high.
Table 8-21(a) Arterials Minimum Lane and Shoulder Widths
Usable Shoulder (m)
Roadway
Classification
Travel Lane (m)
Right
Left
Desirable
Min.
Desirable ²
Min. ³
Min.
Arterial
3.7
3.5
2.44
1.22
1.22 ¹
Collector
3.7
3.3
2.44
1.22
N/A
Local
3.7
3.0
1.22
0.61
N/A
Notes:
1.
Only used when there is a median
2.
Widths are to be determined based on traffic, pedestrian volumes, right-of-way restrictions, and environmental
impacts.
3.
Absolute minimum offset beyond usable shoulder to vertical element over 200 mm, or beyond travel lane if
usable shoulder not provided is 0.50m.
4.
Service roads or single-lane local roads are to be 4.0m in lane width.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-28
8.7.3
5.
At signalized intersections, lane widths may be reduced. The absolute minimum is 3.0m.
6.
For lane widening on curves, see Section 8.5.7 of this manual.
Shoulders
The outer usable shoulders (normally 1.2 to 2.44m on arterial and low-class roads, and 3.0m on
expressways and freeways) serve several functions. They include:
1.
An area for emergency stopping without disruption to traffic flow
2.
An area for evasive action and recovery
3.
Improvements to highway capacity, safety and driver comfort
4.
Lateral support and drainage for the pavement to keep ponding away from travel
lanes
5.
Improvement of horizontal sight distances and increased lateral clearances to
roadside appurtenances and other obstructions.
6.
Providing additional lanes for diversions and space for road maintenance operations
The usable width of shoulder is the actual width that can be used when a driver makes an emergency
stop. A side slope of 1v:6h or flatter can be used as a usable shoulder. The required width of usable
shoulder is provided in Table 8-20(b) and 8-21.
Outer shoulders may not be required on urban undivided or divided roads (other than freeways and
expressways), because structural support is provided by the curbs and channels, and disabled
vehicles can generally find a safe place to stop in driveways and side streets. Nevertheless their
adoption on collectors in industrial areas can be beneficial. At intersections, usable shoulders may be
eliminated in order to better provide turning movements.
8.7.4
Curbing
Curbs are used extensively on urban streets and highways. Generally, they are not used in rural
areas, except with sidewalks where vertical barrier curb is required. Curbs serve to:
Control drainage
Restrict vehicles to the pavement area
Define points of access to abutting properties
Vertical curbs should not be used on highways with design speeds of more than 70 km/h. If a curb is
necessary in this case, a curb clearance of 0.6m should be added to the outside lane adjacent to
curbed edges. Where there is a shoulder, there is no need to provide a curb clearance.
8.7.5
Borders, Buffer Strips and Sidewalks
The border is the area acting as a buffer zone between the edge of pavement and the right-of-way
line. Border areas separate the traffic from properties abutting the road or highway. On some roads,
sidewalks are included within the border limits. In those cases, a minimum 600 mm buffer strip
separating the sidewalk from the curb is desirable, provided sufficient right-of-way is available.
Borders are capable of accommodating road signs and structures, traffic control devices, traffic
signals, utilities, lighting and landscaping features. The preferred location for these appurtenances
(utility poles, fire hydrants, lighting, and traffic control boxes) is beyond the back of the sidewalk,
especially when a travel lane is immediately adjacent to the curb.
Sidewalks are provided where they are justified by pedestrian activity. Sidewalk width varies
according to projected use and available right-of-way, with 2.0 m preferred. In commercially
developed areas, the entire area between the curb and buildings is often used as a paved sidewalk.
8.7.6
Medians
Medians are used to separate opposing traffic lanes on multi-lane roads. A median will provide many
or all of the following benefits:
Separation from opposing traffic reducing the likelihood of accidents and improving the
traffic flow characteristics.
Refuge for emergency stops
Area for control of errant vehicles
AUGUST 2010
REVISION NO. 03
ROADW AY 8-29
Reduction in headlight glare
Area for deceleration and storage of mainline left-turning and U-turning vehicles
Area for storage of vehicles crossing the mainline at intersection.
Area for placement of luminaire supports, traffic signs, traffic signals, guardrail,
landscaping, and bridge piers.
Increased drainage collection area
Refuge area for pedestrians and bicyclists.
Area for future additional lanes
Medians may range in width from as little as 1.2m in an urban area to 20m or more in rural areas.
Median width will depend on the following:
Functional class
Type of median
Right-of-way available
Traffic operations at crossing intersections
Safety
It is recommended that urban medians be curbed. Rural medians should be provided with a 0.60 m
or 1.22 m shoulder and not curbed; a depressed median is preferred to improve drainage. A curbed
median, however, is desirable where there is a need to control left turn movements and when the
median is to be landscaped. If the median is curbed and paved, the median surface should be
designed to have slopes of 2 percent, and should fall away from the center of the median. Non-paved
medians should be depressed and slope towards the inside at 1V:6H for proper drainage, but
consideration should be given to additional storage capacity or outlets for storm conditions. Paved
medians may require incorporating drainage systems such as manholes, culverts, etc. All drainage
inlets in the median should be designed with the top flush with the ground and safety gratings for
culvert ends.
Table 8-21(b) sets out the minimum widths for certain functional requirements of medians.
Table 8-21(b) Minimum Median Widths for Certain Functions (m)
Requirements
At Signalized
Intersections
Elsewhere
Minimum to accommodate signal heads
1.2 to 1.6
-
Minimum curbed to separate traffic
1
1
Minimum to accommodate pedestrians
2.0 to 3.5
3.5
Minimum to provide left-turn lanes
4.2
4.75
Minimum to provide U-turn
n/a
5.0
Minimum for landscaping provision
n/a
8
Table 8-22 provides the typical median widths based on roadway classifications.
Table 8-22 Typical Median Widths (m)
Urban
Rural
Roadway Classification
Min.
Desirable
Min.
Desirable
Freeways and Expressways
6.0
8.0 to 10.0
6.0
8.0 to 10.0
Primary Arterials
6.0
8.0 to 10.0
6.0
8.0 to 10.0*
AUGUST 2010
REVISION NO. 03
ROADW AY 8-30
Urban
Rural
Roadway Classification
Min.
Desirable
Min.
Desirable
Secondary Arterials
4.0
6.0
4.0
12.1*
Collectors
2.0
6.0
4.0
6.0
* Consideration for future lane widening
8.7.7
Cross Slopes
Surface cross slopes are necessary on travel lanes to facilitate drainage. This reduces the hazard of
wet pavements and standing water. On flexible pavements, travel lanes should be designed for a
cross slope of 0.020 m/m. For outside shoulders, the cross slope is typically 0.030 m/m.
8.7.8
Side Slopes
Cut and fill slopes should be designed to ensure the stability of the roadway and be as flat as possible
to enhance the safety of the roadside. It is strongly recommended that an adequate geotechnical
investigation be carried out prior to specifying the angles of side slopes. The engineer should
consider the following when selecting a cut or fill design:
8.7.9
1.
It is desirable for fill slopes on high speed roadways to be 1V:6H or flatter. All soils
(except possibly wetland or much material) are stable at this rate. The angle of the
side slopes must have regard to the nature of the material concerned. Rock cuttings
in mountainous areas, for example, can be stable at relatively steep angles, whereas
embankments built up from granular materials require shallow angles.
2.
The slopes are generally traversable at 1V:6H. For fills greater than 5 m high in
wetlands and in other sensitive areas, 1:2 slopes (with guardrail) are typical. Site
conditions may require slopes up to 1:1. Slope retaining treatments such as geotextiles shall be considered for these situations.
3.
Erosion possibilities must be minimized. Several rutted side slopes can cause
vehicle rollover even on relatively flat slopes. In good soil, turf can be established on
slopes as steep as 1:1. However, flatter slopes reduce the erosion potential and
should be used where feasible. All slopes shall be planted with sufficient vegetation
to stabilize the slope.
4.
Where the highway mainline intersects a driveway, side road, or median crossing, the
intersecting slopes need to be as flat as possible, preferably 1:12 or flatter; 1:6 slopes
are acceptable.
5.
For cut and fill sections, it may be necessary to reduce the required recovery widths
for environmental, cost, right-of-way or aesthetic considerations. Guardrail should be
used on fill slope where recovery area is not available. In cut sections, a ditch of
sufficient width must be provided to maintain drainage flow from the hillside.
6.
Side slopes can exist under the back spans of overhead bridges. It is typical for
these side slopes to be paved. Aesthetics and bridge design normally dictate the
slope. A maximum slope of 1:1½ is typically used.
Ditch Sections
Roadside ditches divert and remove water from the surface and subsurface of the roadway.
Roadside ditches can have several shapes: V, radial, trapezoidal, or parabolic. The trapezoidal ditch
is the preferred shape when considering safety and ease of design, construction, and maintenance.
Figure 8-11 provides the design information for a typical trapezoidal roadside ditch. Roadway ditch
foreslopes steeper than 1:6 are not desirable for safety reasons.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-31
Figure 8-11 Typical Ditch Section
Notes:
8.7.10
1.
The bottom of the ditch should be below the bottom of the subbase.
2.
Width can be wider to meet hydraulic requirements.
Right-of-Way Limits
The right-of-way width should permit the design of a well-balanced cross section, taking into account
the road class, the projected traffic flows, topography, the surrounding land uses, and any other
relevant parameters. The necessary right-of-way width is the summation of all cross section
elements: lanes, shoulders, curbs, medians, sidewalks, buffer strips, clear zones, drainage ditches,
utility accommodations, and frontage roads. Future roadway widening should also be taken into
consideration.
Right-of-way width should be uniform. In urban areas, variable widths may be necessary due to the
existing development; varying side slopes and embankment heights may make it desirable to vary
ROW width; and ROW limits will likely have to be adjusted at intersections and freeway interchanges.
Other special ROW controls are as follow:
At horizontal curves and intersections, additional ROW acquisition may be warranted to
ensure that the necessary sight distance is always available in the future.
In areas where the necessary ROW widths cannot be obtained, the engineer will have to
consider using steeper slopes, revising grades, or using slope retaining treatments.
Right-of-way should be acquired and reserved for future improvements such as roadway
widening and interchange completion.
Temporary slope easements should be considered to minimize public ownership of land.
8.7.11
Horizontal Clearances
It is important that structures and other roadside features be set back adequately from the edge of the
traveled way. Where adequate clearances cannot be achieved, the structure or feature will require
protection by means of a safety barrier.
The width of the necessary “clear zone” is dependent mainly on the design speed and design ADT of
the road, but also varies according to the side slope of the embankment, if any. Table 8-23 shows the
values of the clear zone width for different road conditions. Table 8-24 shows the horizontal curve
adjustments when horizontal curves are present.
Table 8-23 Clear Zone Width (m)
Fill
Design
Speed
(km/h)
60 or less
60 or less
Cut
1V:3H
1V:5H
to
1V:4H
1V:6H
or
flatter
**
2.0-3.0
2.0-3.0
2.0-3.0
**
3.0-3.5
3.0-3.5
3.0-3.5
Design ADT
1V:6H or
flatter
1V:5H to
1V:4H
1V:3H
Under 750
2.0-3.0
2.0-3.0
750 - 1500
3.0-3.5
3.5-4.5
Fill
Design
Speed
(km/h)
Cut
1V:3H
1V:5H
to
1V:4H
1V:6H
or
flatter
**
3.5-4.5
3.5-4.5
3.5-4.5
5.0-5.5
**
4.5-5.0
4.5-5.0
4.5-5.0
3.0-3.5
3.5-4.5
**
2.5-3.0
2.5-3.0
3.0-3.5
750 - 1500
4.5-5.0
5.0-6.0
**
3.0-3.5
3.5-4.5
4.5-5.0
70-80
1500 -6000
5.0-5.5
6.0-8.0
**
3.5-4.5
4.5-5.0
5.0-5.5
70-80
Over 6000
6.0-6.5
7.5-8.5
**
4.5-5.0
5.5-6.0
6.0-6.5
90
Under 750
3.5-4.5
4.5-5.5
**
2.5-3.0
3.0-3.5
3.0-3.5
90
750 - 1500
5.0-5.5
6.0-7.5
**
3.0-3.5
4.5-5.0
5.0-5.5
90
1500 -6000
6.0-6.5
7.5-9.0
**
4.5-5.0
5.0-5.5
6.0-6.5
90
Over 6000
6.5-7.5
8.0-10*
**
5.0-5.5
6.0-6.5
6.5-7.5
100
Under 750
5.0-5.5
6.0-7.5
**
3.0-3.5
3.5-4.5
4.5-5.0
100
750 - 1500
6.0-7.5
8.0-10.0*
**
3.5-4.5
5.0-5.5
6.0-6.5
100
1500 -6000
8.0-9.0
10.0-12.0*
**
4.5-5.5
5.5-6.5
7.5-8.0
100
Over 6000
9.0-10.0*
11.0-13.5*
**
6.0-6.5
7.5-8.0
8.0-8.5
110
Under 750
5.5-6.0
6.0-8.0
**
3.0-3.5
4.5-5.0
4.5-5.0
110
750 - 1500
7.5-8.0
8.5-11.0*
**
3.5-5.0
5.5-6.0
6.0-6.5
110
1500 -6000
8.5-10.0*
10.5-13.0*
**
5.0-6.0
6.5-7.5
8.0-8.5
110
Over 6000
9.0-10.5*
11.5-14.0*
**
6.5-7.5
8.0-9.0
8.5-9.0
Design ADT
1V:6H or
flatter
1V:5H to
1V:4H
1V:3H
1500 -6000
3.5-4.5
4.5-5.0
Over 6000
4.5-5.0
70-80
Under 750
70-80
60 or less
60 or less
3.
* Where a site specific investigation indicates a high probability of continuing crashes, or such occurrences are
indicated by crash history, the designer may provide clear-zone distances greater than the clear-zone shown in
Table 8-23. Clear zones may be limited to 9 m for practicality and to provide a consistent roadway template if
previous experience with similar projects or designs indicates satisfactory performance.
4.
** Since recovery is less likely on the unshielded, traversable 1V:3H slopes, fixed objects should not be present
in the vicinity of the toe of these slopes. Recovery of high-speed vehicles that encroach beyond the edge of the
shoulder may be expected to occur beyond the toe of slope. Determination of the width of the recovery area at
the toe of slope should take into consideration right-of-way availability, environm ental concerns, economic
factors, safety needs, and crash histories. Also, the distance between the edge of the through traveled lane and
the beginning of the 1V:3H slope should influence the recovery area provided at the toe of slope. While the
application may be limited by several factors, the foreslope parameters which may enter into determining a
maximum desirable recovery area are illustrated in Figure 8-12(a).
Table 8-24 Horizontal Curve Adjustments
Kcz (Curve Correction Factor)
AUGUST 2010
Design Speed (km/h)
Radius
(m)
60
70
80
90
100
110
900
1.1
1.1
1.1
1.2
1.2
1.2
700
1.1
1.1
1.2
1.2
1.2
1.3
600
1.1
1.2
1.2
1.2
1.3
1.4
500
1.1
1.2
1.2
1.3
1.3
1.4
450
1.2
1.2
1.3
1.3
1.4
1.5
REVISION NO. 03
ROADW AY 8-33
Design Speed (km/h)
Radius
(m)
60
70
80
90
100
110
400
1.2
1.2
1.3
1.3
1.4
-
350
1.2
1.2
1.3
1.4
1.5
-
300
1.2
1.3
1.4
1.5
1.5
-
250
1.3
1.3
1.4
1.5
-
-
200
1.3
1.4
1.5
-
-
-
150
1.4
1.5
-
-
-
-
100
1.5
-
-
-
-
-
CZ C = (LC) (KCZ)
Where:
CZ C = clear zone on outside of curvature, meters [feet]
LC = clear-zone distance, meters [feet]
KCZ = curve correction factor
Note: The clear-zone correction factor is applied to the outside of curves only. Curves flatter than 900 m [2860
ft] do not require an adjusted clear zone.
Figure 8-12(a) Example of parallel fill slope design
These distances are measured from the nearest edge of the traveled way to the structure. Where this
clear zone cannot be kept completely free from obstructions, safety barriers should be provided to
protect the driver from a collision with a structure or an errant vehicle.
Safety barriers themselves need to be set back from the edge of the traveled way.
8.7.12
Others
8.7.12.1 Service Roads
Service (Frontage) Roads run parallel, and are connected, to the main highway in both rural and
urban areas. They control access to abutting properties, and in urban areas, they remove the
roadside friction and parking from the main arterial. Service roads can be continuous or intermittent;
can be on one or both sides, and can be one-way or two-way. They segregate the higher speed
through traffic from the lower speed local traffic.
Service roads may also provide an alternative route if maintenance is required on the mainline, or in
case of an emergency.
The width of service road is dependent on the type and turning requirements of the traffic expected to
use it. Service road connections to arterials should be designed as at-grade intersections, while
those for higher class roads should be designed as off-ramps and on-ramps.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-34
The “Outer Separation” between the service road and the mainline should be 2.0m in minimum width.
This width should include any signs or street lighting. A wider outer separation that includes
landscaping to enhance the appearance of the road is preferred.
8.7.12.2 Auxiliary Lanes
The purpose of the auxiliary lanes is one or more of the following:
Speed change lane – used for either acceleration or deceleration.
Climbing lane – introduced on steep up-grades.
Turning lane – permit those vehicles not proceeding ahead to undertake the necessary
maneuver clear of the thru lanes.
Additional storage space – required at some at-grade intersections.
A method of maintaining lane balance
Weaving
8.7.12.3 Bridges
Bridges are designed for grade-separated intersections, continuous viaducts and crossing rivers. The
following general guidelines are important during bridge design phase:
The engineer should establish the clearance requirements and the applicable design
speeds, controlling grades and vertical curvature limits before beginning preliminary
design.
For preliminary design purposes, the depth of the bridge deck may be calculated as the
sum of: approximately 1/8 of the longest span, 0.3m, cross-slope difference, and deck
surfacing. As the design progresses, this preliminary estimate should be replaced by the
designed depth of structure, along with the proposed vertical geometry.
Bridges with long spans, large skew angles, tapers or splays, small radius curvature, or
large superelevation should be avoided, as they are likely to be costly and difficult to
construct. They may also require a greater construction depth.
The typical standards of the approaching roadway should be applied across the bridge, if
possible.
The bridge horizontal alignment should be straight. If horizontal curvature is inevitable,
then the bridge should be on a circular curve rather than a transition, and the radius
should be as large as possible.
The skew angle should be less than 45 degrees.
Avoid tapers and flared ends. If this is not possible, aim to start such changes in cross
section at a pier position.
For intermediate and wide medians, consider having two separate structures.
Bridges should be set on straight grades (6% max. and 0.3% min. to permit longitudinal
drainage) rather than on vertical curves. If this is not possible, crest curve should not be
less than K=30.
Avoid sag curves on bridges due to difficulties with drainage.
Bridges should have Symmetrical spans. Abutments should be at the same elevation.
Edge of curb profiles should be the same to avoid warped deck which is difficult to
construct.
The horizontal and vertical geometries of the bridge should be coordinated.
Visibility requirements on a sag curve underneath a bridge should always be checked.
8.7.12.4 Tunnels
Tunnels are expected to be designed and constructed in many locations in Libya. Shorter lengths of
tunnel or underpass are often required and should be designed using the normal parameters. If it
proves uneconomic to do so, each situation should be considered on its own merits. The following
general guidance is given:
The tunnel should be as short and straight as possible.
The mainline typical section should desirably be continued through the tunnel, but in
some circumstances it may not be an economical solution.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-35
Horizontal curvature in tunnels restricts sight distance. Widening on the inside of the
curve is required to maintain proper SSD and design speed.
Desirable vertical clearance should be maintained inside the tunnel. If this is not
possible, special arrangements must be made for the diversion of oversized vehicles prior
to reaching the tunnel.
Sight envelopes given in Section 4 should be considered for the tunnel as vertical
curvature can restrict visibility.
Grades for tunnel should be selected based on values given in Section 6, lighting and
ventilation requirements.
The design should avoid the need for traffic signs to be provided within the tunnel.
Merging, weaving, or diverging movements within a tunnel are undesirable. On-ramps
and off-ramps should not be provided within tunnels, or for 300m outside the ends of the
tunnel.
Emergency and Fire alarm points are to be implemented in the tunnel.
A raised sidewalk (minimum width is 0.7m) needs to be provided for emergencies and
maintenance operations.
8.8
Grade Separations and Interchanges
Interchanges and grade separations physically separate the through traffic movements of two
intersecting highways. They eliminate dangerous crossings and may be used to bypass busy urban
areas. Interchanges, unlike grade separations, provide access between the two highways by ramps.
8.8.1
Warrants
The general warrants for interchange and grade separations include:
8.8.2
1.
Design Designation – if a fully access-controlled facility is provided, each intersecting
highway must be terminated, rerouted, provided a grade separation, or provided an
interchange. An interchange should be provided on the basis of the anticipated
demand for access to the minor road. Interchange spacing is also a factor. In urban
areas, a general rule is a 1.5 km minimum spacing between interchanges to allow the
entrance and exit maneuvers. Closer spacing may require collector-distributor roads
to remove the merging and existing traffic from the mainline. In rural undeveloped
areas, interchanges should be spaced no closer than 5.0 km apart.
2.
Congestion – An interchange may be warranted where the level of service of an atgrade intersection is unacceptable, and the intersection cannot be redesigned to
operate at an acceptable level.
3.
Safety – The accident reduction benefits of an interchange may warrant its selection
at a particularly dangerous at-grade intersection.
4.
Site Topography – At some sites the topography may allow an interchange that would
cost less than that of an at-grade intersection.
5.
Road-User Benefits – Interchanges significantly reduce the travel time and costs
when compared to at-grade intersections. Therefore, if an analysis reveals that roaduser benefits over the service life of the interchange will exceed the costs, then the
interchange will be warranted.
6.
Traffic Volume – Interchanges are desirable at cross streets with heavy traffic
volumes. The elimination of conflicts due to high crossing volume greatly improves
the movement of traffic.
Interchange Types
8.8.2.1
Three-Leg
Three-leg interchanges, also known as T or Y interchanges are provided where major highways begin
or end. Figure 8-12(b) illustrates examples of three-leg interchanges with several methods of
providing turning movements.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-36
Figure 8-12(b) Three-Leg Interchanges
8.8.2.2
Diamond
Diamond interchanges use one-way diagonal ramps in each quadrant with two at-grade intersections
provided on the minor road. The diamond is usually the best choice of interchange where the
intersection road is not access controlled. The advantages of diamond interchanges include:
1.
All traffic can enter and exit the mainline at relatively high speeds. Adequate sight
distance can usually be provided and operational maneuvers are normally simple.
2.
Relatively little right-of-way is required
3.
All exits from the mainline are made before reaching the structure
4.
Left-turning maneuvers require little extra travel distance
5.
The diamond interchange allows modifications to provide greater ramp capacity, if
needed in the future.
Figure 8-13 illustrates a schematic of a typical diamond interchange.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-37
Figure 8-13 Typical Diamond Interchange (Schematic)
8.8.2.3
Cloverleafs
Cloverleaf interchanges are used at four-leg intersections with loop ramps to accommodate left-turn
movements. Full cloverleaf interchanges are those with loops in all four quadrants; all other are
partial cloverleafs.
Where two access-controlled highways intersect, a full cloverleaf is the minimum type design
interchange that will suffice. However, these interchanges introduce several undesirable operational
features such as:
The double exits and entrances from the mainline
The weaving between entering and exiting vehicles with the mainline traffic
The lengthy travel time and distance for left-turning vehicles
Figure 8-14 provides typical examples of full cloverleafs with and without C-D roads.
Figure 8-14 Full Cloverleafs
Partial cloverleafs are appropriate where right-of-way restrictions preclude ramps in one or more
quadrants. Figure 8-15 illustrates six examples of partial cloverleafs. In these examples, the
desirable feature is that no left-turn movements are made onto the major road.
Figure 8-15 Partial Cloverleaf Arrangements
8.8.2.4
Grade-Separated Roundabouts
A grade-separated roundabout involves a conventional layout that would help in managing queues on
off-ramps. Figure 8-16 illustrates two examples of a grade-separated roundabout.
Figure 8-16 Grade-separated Roundabout
Arrangement (A) is the Simple form of intersection, using two bridges and a large rotary pavement.
When traffic volumes increase, there is adequate space to permit the introduction of signals to the
roundabout entries, and to further increase capacity by modest widening on the approaches.
At higher volumes still, arrangement (B) can be adopted. This layout, known as a three-level
roundabout, takes the cross-traffic on a direct ramp, leaving the roundabout to handle only turning
traffic. Such a layout can be introduced incrementally if the median of the cross route is constructed
at the outset with a width sufficient to accommodate the future flyover.
8.8.3
Interchange Analysis
Interchanges are expensive, and it is necessary to develop and study several alternatives in depth.
Each alternative should be evaluated on the basis of its cost, safety, capacity, operation, and
compatibility with the surrounding highway system.
8.8.3.1
Capacity and Level of Service
An interchange must accommodate the anticipated traffic volumes. They are designed using the
Design Hour Volumes (DHV). The capacity and level of service for an interchange will depend upon
the operation of its individual elements along with the interaction and coordination of each of these
elements in the overall design.
1.
Basic freeway section where interchanges are not present.
2.
Freeway-ramp junctions or terminals
3.
Weaving areas
4.
Ramp proper
5.
Ramp/Minor road intersection
It should be noted that the practical capacity of a single-lane loop lies in the range 800 passenger
cars per hour (pc/h) to 1200 pc/h. Loops rarely operate as two-lane pavements, regardless of their
width, and in general, they should not be designed to do so because of the difficulties in designing
proper ramp terminals and for driver discomfort reasons. In general, therefore, then a DHV of around
1000 pc/h applies to the one-way turning movement in one quadrant of an interchange, serious
consideration should be given to the adoption of a form of connection other than a loop.
8.8.3.2
Selection of Interchange Type
Freeway interchanges are of two general types. A “systems” interchange will connect freeway to
freeway; a “service” interchange will connect a freeway to a lesser facility. Once several alternative
interchange designs have been developed, they can be evaluated considering:
1.
Compatibility with the surrounding highway system
2.
Uniformity of exit and entrance patterns
8.8.4
3.
Capacity and level of service
4.
Operational characteristics (single versus double exits, weaving, signing)
5.
Road user impacts (travel distance and time, safety, convenience and comfort)
6.
Construction and maintenance costs
7.
Right-of-way impacts and availability, and
8.
Environmental Impacts
Traffic Lane Principles
8.8.4.1
Basic Number of Lanes and Freeway Lane Drops
The basic number of lanes is the minimum number of lanes needed over a significant length of a
highway based on the overall capacity needs of that section. The number of lanes should remain
constant over short distances.
Freeway lane drops, where the basic number of lanes is decreased, must be fully designed. They
should occur on the freeway mainline away from any other activity, such as interchange exits and
entrances. The following recommendations are important when designing a freeway lane drop:
8.8.5
1.
Location – The lane drop should occur approximately 600-1000 m beyond the
previous interchange. This distance allows adequate signing and adjustments from
the interchange, but yet is not so far downstream that drivers become accustomed to
the number of lanes and are surprised by the lane drop. In addition, a lane should
not be dropped on a horizontal curve or where other signing is required, such as for
an upcoming exit.
2.
Sight Distance – The lane drop should be located so that the surface of the roadway
within the transition remains visible for its entire distance. This favors placing a lane
drop within a sag vertical curve rather than just beyond a crest. Decision sight
distance to the roadway surface is desirable.
3.
Transition – The desirable taper rate is 100:1 for the transition at the lane drop. The
minimum is 70:1.
4.
Right-Side Versus Left-Side Drop – All freeway lane drops must be on the right side,
unless specific site conditions greatly favor a left-side lane reduction.
5.
Signing – Motorists must be warned and guided into the lane reduction. Advance
signing and pavement markings should be implemented.
Lane Balance
To realize efficient traffic operation through and beyond an interchange, there should be a balance in
the number of traffic lanes on the freeway and ramps. Design traffic volumes and a capacity analysis
determine the basic number of lanes to be used on the highway and the minimum number of lanes on
the ramps. Variations in traffic demand should be accommodated by means of auxiliary lanes where
needed.
After the basic number of lanes is determined for each roadway, the balance in the number of lanes
should be checked on the basis of the following principles:
1.
At entrances, the number of lanes beyond the merging of two traffic streams should
not be less than the sum of all traffic lanes on the merging roadways, minus one.
2.
At exits, the number of approach lanes on the highway must be equal to the number
of lanes on the highway beyond the exit plus the number of lanes on the exit, less
one. There is one exception – the short length of auxiliary lane that exists on a
cloverleaf interchange between the on-loop entrance and the off-loop exit. In this
case, the number of upstream lanes may be the same as the sum of the downstream
lanes.
3.
The traveled way of the highway should be reduced by not more than one traffic lane
at a time.
Figure 8-17 illustrates the typical treatment of the four-lane freeway with a two-lane exit followed by a
two-lane entrance.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-42
Figure 8-17 Coordination of Lane Balance and Basic Number of Lanes
8.8.5.2
Auxiliary Lanes
An auxiliary lane is defined as the portion of the roadway adjoining the traveled way for parking,
speed change, turning, storage, weaving, truck climbing, and other supplementary to through-traffic
movement. An auxiliary lane may be provided to comply with the concept of lane balance, to comply
with capacity requirements in the case of adverse grades, or to accommodate speed changes,
weaving, and maneuvering of entering and leaving traffic. Where auxiliary lanes are provided along
freeway main lanes, the adjacent shoulder would desirably be 2.0m to 3.7m in width.
Auxiliary lanes may be added to satisfy capacity and weaving requirements between interchanges
and to accommodate traffic patterns variations at interchanges. The principles of lane balance must
always be applied in the use of auxiliary lanes. Where interchanges are closely spaced in urban
areas, the acceleration lane from an entrance ramp should be extended to the deceleration lane of a
downstream exit ramp.
Figure 8-18 shows alternatives in dropping auxiliary lanes.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-43
Figure 8-18 Alternatives in Dropping Auxiliary Lanes
8.8.6
Freeway/Ramp Junctions
8.8.6.1
Exit Ramps
Exit ramps are one-way roadways that allow traffic to exit from the freeway to provide access to other
crossing highways. They are provided for all highways which intersect a freeway where the warrants
for an interchange are satisfied.
Deceleration Lanes
Sufficient deceleration distance is needed to allow an exiting vehicle to leave the freeway mainline
safely and comfortably. All deceleration should occur within the full width of the deceleration lane.
The length of the deceleration lane will depend upon the design speed of the mainline and the design
speed of the first (or controlling) curve on the exit ramp. In addition, if compound curvature is used,
there should be sufficient deceleration in advance of each successively sharper curve.
Deceleration lanes can be the taper type or the parallel lane type, with the parallel type preferred. It is
necessary for a full deceleration lane to be developed and visibly marked well ahead of the gore area.
Exit ramps diverge from the mainline at an angle between 2º and 5º. The parameters are shown in
Figures 8-19 thru 8-22.
Figure 8-19 Taper Type Exit Ramp (1-Lane)
Figure 8-20 Parallel Type Exit Ramp (1-Lane)
Figure 8-21 Taper Type Exit Ramp (2-Lane with Lane Drop)
Figure 8-22 Parallel Type Exit Ramp (2-Lane without Lane Drop)
Figure 8-23 provides the deceleration distance for various combinations of highway design speeds
and exit curve design speeds. Deceleration lanes are measured from the point where the lane
reaches 3.75 m wide to the painted nose for parallel types and the first controlling curve for taper
types. Greater distances should be provided if practical. If the deceleration lane is on a grade of 3%
or more, the length of the lane should be adjusted according to the criteria in Table 8-25.
Figure 8-23 Minimum Deceleration Lengths for Exit Terminals with Grades of 2% or Less
AUGUST 2010
REVISION NO. 03
ROADW AY 8-49
Superelevation
The superelevation at an exit ramp must be developed to transition the driver properly from the
mainline to the curvature at the exit. The principles of superelevation for open highways should be
applied to the exit design. The following criteria apply:
1.
The maximum superelevation rate is 0.06 meter/mete
2.
Preferably, full superelevation (0.06 m/m) is achieved at the PCC at the gore nose.
However, this is subject to the minimum longitudinal slopes in Section 8.6.1.
3.
The paved part of the gore is normally sloped at a 0.03 m/m rate.
8.8.6.2
Entrance Ramps
Entrance ramps are one-way roadways that allow traffic from crossing highways to enter a freeway.
They are provided for all highways that intersect a freeway where the warrants for an interchange are
satisfied.
Acceleration Lanes
A properly-designed acceleration lane will facilitate driver comfort, traffic operations, and safety. The
length of the acceleration lane will primarily depend upon the design speed of the last (or controlling)
curve on the entrance ramp and the design speed of the mainline. Typical layouts, showing
geometric parameters, are given in Figures 8-24 thru 8-27. Where lane gain is indicated, the auxiliary
lane may be merged with the nearside lane after a further distance of 400 m, using a taper rate of
1:50 for design speeds of 100 km/h and below, or 1:70 for higher speed roads.
Figure 8-24 Taper Type Entrance Ramp (1-Lane)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-50
Figure 8-25 Parallel Type Entrance Ramp (1-Lane)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-51
Figure 8-26 Taper Type Entrance Ramp (2-Lane with Lane Gain)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-52
Figure 8-27 Parallel Type Entrance Ramp (2-Lane with Lane Gain)
Figure 8-28 provides the data for minimum lengths of acceleration lanes. These lengths are for the
full width of the acceleration lane, and are measured from the end of the painted nose for parallel
types, and from the end of the last controlling curve on taper types, to a point where the full 3.75
meter lane width is achieved. Taper lengths, typically 100 meters, are in addition to the table lengths.
Where grades of 3% or more occur on the acceleration lane, adjustments should be made in its
length according to Table 8-26.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-53
Figure 8-28 Minimum Acceleration Lengths for Entrance Terminals With Grades of 2% or Less
AUGUST 2010
REVISION NO. 03
ROADW AY 8-54
Table 8-25 Speed Change Lane Adjustment Factors as a Function of Grade
Deceleration Lanes
Design
Speed of
Highway
(km/h)
Ratio of Length on Grade to Length for
Design Speed of Turning Curve (km/h)
All Speeds
All Speeds
3 to 4% Upgrade
3 to 4% Downgrade
0.9
1.2
5 to 6% Upgrade
5 to 6% Upgrade
0.8
1.35
Acceleration Lanes
Design
Speed of
Highway
(km/h)
Ratio of Length on Grade to Length for
Design Speed of Turning Curve (km/h)
40
50
60
70
80
3 to 4% Upgrade
All Speeds
3 to 4% Downgrade
60
1.3
1.4
1.4
--
--
0.7
70
1.3
1.4
1.4
1.5
--
0.65
80
1.4
1.5
1.5
1.5
1.6
0.65
90
1.4
1.5
1.5
1.5
1.6
0.6
100
1.5
1.6
1.7
1.7
1.8
0.6
110
1.5
1.6
1.7
1.7
1.8
0.6
120
1.5
1.6
1.7
1.7
1.8
0.6
5 to 6% Upgrade
5 to 6% Downgrade
60
1.5
1.5
--
--
--
0.6
70
1.5
1.6
1.7
--
--
0.6
80
1.5
1.7
1.9
1.8
--
0.55
90
1.6
1.8
2.0
2.1
2.2
0.55
100
1.7
1.9
2.2
2.4
2.5
0.5
110
2.0
2.2
2.6
2.8
3.0
0.5
120
2.3
2.5
3.0
3.2
3.5
0.5
Superelevation
The ramp superelevation should be gradually transitioned to meet the normal cross slope of the
mainline. The principles of superelevation for open highways, as discussed in Section 8.5, should be
applied to the entrance design. The following criteria should be used:
1.
AUGUST 2010
The maximum superelevation rate is 0.06.
REVISION NO. 03
ROADW AY 8-55
2.
Preferably, the cross slope of the acceleration lane will equal the cross slope of the
through land (0.02 m/m) at the PT of the flat horizontal curve near the entrance gore.
3.
The superelevation transition should not exceed the minimum longitudinal slopes in
Table 8-16.
8.8.6.3
Weaving Areas
Weaving occurs where one-way traffic streams cross by merging and diverging maneuvers. This
frequently occurs within an interchange or between two closely-spaced interchanges. Figure 8-29
illustrates a simple weave diagram and the length over which a weaving distance is measured.
Figure 8-29 Weaving Sections
If the weave area is on a freeway, including weaving at cloverleaf interchanges, or if the site
conditions will not allow the necessary distance, a collector-distributor road should be provided.
8.8.6.4
Collector-Distributor Roads
Collector-Distributor (C-D) Roads are provided as a means of eliminating weaving on the mainline.
They are normally found within an interchange, but may be considered for use between interchanges
if weaving difficulties are anticipated. C-D roads are at least two lanes in width, and generally adopt a
design speed 10 km/h to 20 km/h less than that of the mainline.
C-D roads should be considered for all cloverleaf interchanges, which inherently generate significant
weaving movements. When design weaving volumes exceed 1000 pc/h, C-D roads should always be
provided.
8.8.7
Capacity and Level of Service
Factors that will affect the traffic operation conditions at freeway/ramp junctions are:
1.
Acceleration and deceleration distances
2.
Sight distance
3.
Horizontal and vertical curvature at the junction
4.
Merge and diverge volumes
5.
Freeway volumes
Figure 8-30 illustrates several ramp configurations with a table showing the volumes which can be
accommodated at a ramp junction for a given level of service.
Figure 8-30 Capacity of Ramp Configurations
8.8.7.2
Major Forks and Branch Connections
Major forks are where a freeway or expressway separates into two freeways or expressways.
Figure 8-31 illustrates three schematics for a major fork. It is important that one interior lane has an
option to go in either direction. This interior lane should be widened over a distance of about 300550 m.
Branch connections are where two freeways converge into one freeway. Figure 8-32 illustrates two
schematics for a branch connection. When a lane is dropped, as in “B,” this should be designed as a
freeway lane drop.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-57
Figure 8-31 Major Forks
Figure 8-32 Branch Connections
AUGUST 2010
REVISION NO. 03
ROADW AY 8-58
8.8.8
Ramp Design
8.8.8.1
Design Speed
Ideally, the ramp design speed will approximate the low-volume running speed on the intersecting
highways. Where this is not practical, the values in Table 8-26 should be used as the minimum
design speed. These design speeds apply to the ramp proper and not to the freeway/ramp junction.
If the two intersecting mainlines have different design speeds, the higher of the two should control at
the entrance to the ramp. However, the ramp design speed should vary; the portion of the ramp
nearer the lower-speed highway is designed for the lower speed. There are 3 connection types:
Free-flow links - connect the two alignments directly, turning through generally small
angles.
Ramps - connect from a ramp terminal on one alignment to an at-grade intersection on
the other, and vice versa.
Loops - are also free-flow between the two alignments, but typically turn through an
angle of around 270 degrees.
Table 8-26 Design Speeds for Connecting Roadways
Mainline Design Speed
(km/h)
Design Speed for Connecting Roadway (km/h)
Free-flow Links
Ramps
Loops
50
n/a
50
30
60
n/a
50
40
70
n/a
50
40
80
70
60
50
90
70
60
50
100
80
70
50*
120
100
80
50*
140
120
90
**
5.
* Higher Design Speeds may be appropriate in rural areas.
6.
**Loops on a 140 km/h design speed road should always be accessed via a C-D road with a lower design
speed.
8.8.8.2
Cross Section
The following will apply to the ramp cross section:
1.
Ramp Width – Ramps with a design speed of more than 60 km/h should have a right
shoulder of 2.4 to 3.0 m and 3.0 to 1.8m left shoulder. For the other ramps, the sum
of the right and left shoulder widths should not exceed 3.6 m, with a shoulder width of
0.6 to 1.2m on the left and the remainder as the right shoulder. The minimum width is
7 m for one lane ramps and 9 m for two lane ramps.
2.
Cross Slope – Tangent sections of ramps should be uniformly sloped at
0.02 meter/meter from the median edge to the opposite edge. The maximum
superelevation is 0.06 m/m.
3.
Side Slopes – Fill and cut slopes should be as flat as possible. If feasible, they
should be 1:6 or flatter thus eliminating the need for guardrail.
4.
Bridges and Underpasses – The full width of the ramp or loop should be carried over
a bridge or beneath an underpass.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-59
5.
Lateral Clearances to Obstructions – Best practice calls for the lateral clearance from
the edge of the travel lane to be equal to its clear zone, as determined from the
criteria in Section 7.
6.
Exit Ramps – Where the through lane and exit ramp diverge, the typical width will be
7.75 m. This will be maintained until the gore nose is reached and transitioned to the
standard 7 meter width at approximately a 12:1 rate.
7.
Entrance Ramps – The standard 7 meter width will be transitioned to 5 m width at the
convergence with the through lane.
8.8.8.3
Horizontal Alignment
Horizontal alignment will largely be determined by the design speed and type of ramp. The following
should be considered:
1.
Table 8-27 shows the minimum ramp radii required for the ramp design speed.
Ramps should be designed for 50 km/h or greater unless restricted by site conditions.
Table 8-27 Minimum Radii for Intersection Curves
Design (Turning) Speed V (km/h)
15
20
30
40
50
60
Side Friction Factor, f
0.40
0.35
0.28
0.23
0.19
0.17
Assumed Minimum e
0.00
0.00
0.02
0.04
0.06
0.08
Total e + f
0.40
0.35
0.30
0.27
0.25
0.25
Calculated Min. Radius (m)
5
9
24
47
79
113
Suggested Min. Radius
Curve for Design (m)
7
10
25
50
80
115
Average Running Speed (km/h)
15
20
28
35
42
51
Note: For design speeds of more than 60 km/h, use values for open highway conditions.
2.
Outer Connection – The outer connection at cloverleaf interchanges should be as
directional as possible. However, if site conditions are restrictive, it may be allowed
to follow a reverse path alignment around the inner loop.
3.
Loops – Loop ramps should be on a continuously curved alignment in a spiral or
compound curve arrangement.
4.
Two-Lane Ramps – The minimum radius is 100 m.
8.8.8.4
Vertical Alignment
The minimum grade is 0.50%. General values of limiting gradient for upgrades are shown in Table 828, but for any one ramp the selected gradient is dependent upon a number of factors. These factors
include the following:
1.
The flatter the gradient on the ramp, the longer it will be.
2.
The steepest gradients should be designed for the center part of the ramp. Landing
areas or storage platforms at at-grade intersections with ramps should be as flat as
possible.
3.
Downgrades on ramps should follow the same guidelines as upgrades. They may,
however, safely exceed these values by 2% with 8% considered the desired
maximum grade.
4.
K values and desirable stopping sight distance should be the minimum design for
vertical curves.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-60
Table 8-28 Ramp Gradient Guidelines
Ramp Design Speed (km/h)
Maximum Desirable Grade Range (%)
8.8.8.5
30 to 40
40 to 50
60
70 to 80
6-8
5-7
4-6
3-5
Capacity
Table 8-29 provides the volumes for a given ramp design speed and level of service. 1500 pc/h
should be used as a threshold to warrant a two-lane ramp. The minimum radius of a two-lane ramp
should be 100 m. The capacity of a loop ramp is about 1250 pc/h; however, two-lane ramps are
undesirable because of their restrictive geometry. Therefore, if a left-turn movement will exceed
1250, a directional or semi-directional connection may be needed. Ramps must be designed with
sufficient capacity to avoid backups on the mainline.
Table 8-29 Service Volumes for Single-Lane Ramps
(Peak Hour Factor = 1.00; Values in Passenger Cars per Hour)
Ramp Design Speed (km/h)
Level of
Service
30
30-50
50-70
70-80
80
A
**
**
**
**
700
B
**
**
**
1000
1050
C
**
**
1125
1250
1300
D
**
1025
1200
1325
1500
E
1250
1450
1600*
1650*
1700*
F
- Widely Variable -
* For 2-lane ramps, multiply above values by
1.7 for
30 km/h
1.8 For 30-50, 70-80 km/h
1.9 For 50-70 km/h
2.0 For
80 km/h
** Level of service not achievable due to restricted design speed
8.8.9
Spacing of Ramp Terminals
8.8.9.1
Possible Arrangements
There are four possibilities when considering two adjacent ramp terminals:
1.
Both are exits
2.
Both are entries
3.
The first is an exit, the second an entry
4.
The first is an entry, the second an exit
8.8.9.2
Exit/Exit
Table 8-30 shows minimum distances, measured from one painted nose to the next.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-61
Table 8-30 Minimum Spacing between Successive Exits
Minimum Distance From
Preceding Exit Nose (m)
Along the main lane
On a ramp or
connecting roadway
8.8.9.3
Freeways/
Expressways
Arterials/
Collectors/
C-D Roads
300
250
In a free-flow
interchange
250
in other
interchange
180
Entry/Entry
When two traffic streams join, this generally produces an area of "turbulence" for a distance
downstream. A subsequent entry therefore needs to be located far enough downstream to avoid this
unstable area. Table 8-31 shows the recommended spacing.
Table 8-31 Minimum Spacing between Successive Entries
Minimum Distance From
Preceding Exit Nose (m)
Along the main lane
On a ramp or
connecting roadway
8.8.9.4
Freeways/
Expressways
Arterials/
Collectors/
C-D Roads
300
250
In a free-flow
interchange
250
in other
interchange
180
Exit/Entry
This is the safest of the four layouts, and this is reflected in the shorter distances shown in Table 8-32.
Table 8-32 Minimum Spacing between an Exit and an Entry
Minimum Distance From Preceding Exit Nose (m)
8.8.9.5
Freeway Expressway
Arterials/Collectors/
C-D Roads
150
120
Entry/Exit
This is the most complex of the four layouts, as weaving of traffic streams generally occurs. Three
considerations apply:
1.
There is a minimum distance between noses to ensure safe operation even under
very light flow conditions - this is the minimum spacing.
2.
There is a minimum distance between noses to permit the traffic streams in the
design year to cross each other safety - this is the weaving length.
3.
There is a spacing beyond which weaving is considered not to be a relevant factor this is the upper bound for weaving.
Considerations 1 and 3 are purely geometric and the relevant values are given in Table 8-33.
Consideration 2 is determined by the volumes of weaving traffic, and is dealt with in Section 8.8.6.
Table 8-33 Spacing Criteria for Entry/Exit
Distance from Preceding Entry Nose (m)
Minimum Spacing
Freeways/
Expressways
Arterials/
Collectors/
C-D Roads
Leading to, or leading
from, free-flow
interchange
600
480
Between two
other
interchange
480
300
8.8.10
Upper bound
For Clover
Leaf Loops
The minimum is
dependent on
the geometric
design of the
clover-leaf loops
All Types
3000
2000
Appendices
Standard Designs for Freeway/Minor Road Interchanges (Cloverleaf and Diamond), Figure 8-33
through Figure 8-41.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-63
Figure 8-33 Freeway Exit at Interchange
(Via Outer Connection of Cloverleaf Type Ramp)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-64
Figure 8-34 Freeway Exit at Interchange (From Inner Loop Cloverleaf Type Ramp)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-65
Figure 8-35 Freeway Exit at Diamond Interchange
AUGUST 2010
REVISION NO. 03
ROADW AY 8-66
Figure 8-36 Freeway Entrance at Interchange (from outer)
(Cloverleaf Type Ramp)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-67
Figure 8-37 Freeway Entrance at Interchange (from Inner)
(Cloverleaf Type Ramp)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-68
Figure 8-38 Freeway Entrance at Interchange (Diamond Type Ramps)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-69
Figure 8-39 Freeway Entrance – Exit at Interchange
(Inner Loop Entrance – Inner Loop Exit of Cloverleaf Type Ramp)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-70
Figure 8-40 Exit at Interchange
(Partial Cloverleaf Type Ramp)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-71
Figure 8-41 Diamond Ramps (Minor Roadway Exits and Entrances)
8.9 Summary of Design Parameters
The following sections summarize the key geometric parameters relating to preferred design speeds
for all roadway classifications.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-72
8.9.1
Local Roads and Streets
Table 8-34 Summary of Geometric Parameters for Local Roads and Streets
Urban
Geometric Parameter
Rural
Local Road
Preferred Design Speed (km/h)
Major Local
Street
Minor Local
Street
Traffic
Calmed
Layout
60
50
40
30
85
65
50
35
150
110
70
40*
(e=4%)
(e=2%)
(e=2%)
(e=2%)
Maximum Superelevation (%)
4
2
2
2
Maximum Longitudinal Grade (%)
8
8
10
10
Minimum Longitudinal Grade (%)
0.2
0.2
0.2
0.2
Minimum Sag Curve K value
18
13
9
6
Minimum Crest Curve K value
11
7
4
2
Minimum Vertical Clearance (m)
5.5
5.5
5.5
5.5
Stopping Sight Distance (m) (level road)
Minimum Horizontal Radius (m)
* Lower radii are permissible for speed-limiting bends
8.9.2
Collectors
Table 8-35 Summary of Geometric Parameters for Collectors
Geometric Parameter
Rural
Urban
Preferred Design Speed (km/h)
80
60
Stopping Sight Distance (m) (level road)
130
85
Safe Passing Sight Distance (m) (level road)
540
410*
Minimum Horizontal Radius (m) (for e=4%)
280
150
Maximum Superelevation (%)
6
4
Maximum Longitudinal Grade (%)
6
6
Minimum Longitudinal Grade (%)
0.2
0.2
Minimum Sag Curve K value
30
18
Minimum Crest Curve K value
26
11
Minimum Vertical Clearance (m)
5.5
5.5
* It is rarely necessary to provide safe passing sight distance on an urban collector.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-73
8.9.3
Arterials
Table 8-36 Summary of Geometric Parameters for Arterials
Urban
Geometric Parameter
Rural
Generally
In CBD*
100
100
80
Stopping Sight Distance (m) (level road)
185
185
130
Decision Sight Distance (m) (level road)
400
400
305
Minimum Horizontal Radius (m) (for e=4%)
490
490
280
Maximum Superelevation (%)
8
4
4
Maximum Longitudinal Grade (%)
6
6
6
Minimum Longitudinal Grade (%)
0.3
0.3
0.3
Minimum Sag Curve K value
45
45
30
Minimum Crest Curve K value
52
52
26
Minimum Vertical Clearance (m)
5.5
5.5
5.5
Preferred Design Speed (km/h)
* CBD = Central Business District
8.9.4
Freeways/Expressways
Table 8-37 Summary of Geometric Parameters for Freeways/Expressways
Geometric Parameter
Rural
Urban
Preferred Design Speed (km/h)
120
100
Stopping Sight Distance (m) (level road)
250
185
Safe Passing Sight Distance (m) (level road)
470
400
Minimum Horizontal Radius (m) (for e=4%)
670
400
Maximum Superelevation (%)
8
8
Maximum Longitudinal Grade (%)
4
4
Minimum Longitudinal Grade (%)
0.3
0.3
Minimum Sag Curve K value
63
45
Minimum Crest Curve K value
95
52
Minimum Vertical Clearance (m)
5.5
5.5
AUGUST 2010
REVISION NO. 03
ROADW AY 8-74
8.10
8.10.1
Highway Facilities
General
This section discusses the following facilities and roadway features, and provides guidance on their
design and provision:
Pedestrian Facilities
Public Transport Facilities
Parking Facilities
Safety Barriers
Impact Attenuator Systems
Traffic calming
Pedestrian Facilities
8.10.1.1 Safety
Most pedestrian accidents occur in urban areas and most of these occur at at-grade intersections, but
pedestrian safety is a concern in every highway design. The designer can then develop safety
countermeasures. School locations and areas of high pedestrian volumes deserve particular
attention. Following are examples of pedestrian safety measures:
1.
Crosswalks should be provided at every intersection where pedestrians cross.
2.
Sidewalks and other walkways which are designed to accommodate projected
pedestrian volumes limit the use of streets and shoulders as walkways.
3.
Signal phases which favor the pedestrian are desirable. These include pedestrianactuated signals and an exclusive pedestrian signal phase.
4.
Where severe pedestrian safety problems exist or where there is a need to cross a
free-flow high-speed highway, a pedestrian overpass would be required.
5.
Other pedestrian safety measures include lighting, barriers and parking restrictions.
8.10.1.2 Sidewalks
Sidewalks are provided where they are justified by pedestrian activity. Sidewalk width varies
according to projected use and available right-of-way. In commercially-developed and downtown
areas, the entire area between the curb and buildings is often used as a paved sidewalk.
All urban roads should allow space for sidewalks, unless they are being specifically designed to
prohibit walking. In areas with high volumes of pedestrian traffic, sidewalks should be provided on
both sides of the road. Most service roads, however, require a sidewalk on one side only. Sidewalks
should be continuous over the full pedestrian route.
It is desirable to have a sidewalk that is 3.0 m in width which would accommodate high pedestrian
volumes or to accommodate both pedestrians and bicyclists in busy commercial areas. However, the
recommended minimum sidewalk width is 1.8 m. It is also desirable to provide a 1.2m or more buffer
strip between the curb and sidewalk for pedestrian safety from walking close to traffic.
8.10.1.3 Pedestrian Crossings
Crossings are designated safety paths for pedestrians crossing at intersections or across a roadway
for the continuity of pedestrian walkways/sidewalks. The choice of crossing facilities is as follow:
Uncontrolled Marked Crossing. This type of crossing is marked with stripes on the
pavement. It should only be provided on roads with a posted speed of 60 km/h or less, or
on unsignalized right-turning roadways within a signalized intersection where adequate
Safe Crossing Sight Distance is available.
Controlled Marked Crossing. Signals are used to bring traffic to a halt and to indicate
to pedestrians that they may cross with care. This type of crossing exists most frequently
within a signalized intersection, but can be provided on a free-standing basis on roads
with a posted speed of 80km/h or lower.
Grade Separated Crossing. This is the form of crossing which is invariably required on
freeways and expressways, and which may also be justified on arterials, depending on
traffic volume and speed, and the number and nature of pedestrians crossing the road. It
AUGUST 2010
REVISION NO. 03
ROADW AY 8-75
is provided by means of a pedestrian overpass or by a sidewalk on a grade-separated
road crossing.
The width of the pedestrian crossing should generally range from 2.0m min. to 3.0m max. for a 2-way
crossing.
8.10.1.4 Pedestrian Overpasses
Pedestrian overpasses should be considered where a combination of pedestrian volumes, traffic
volumes, and pedestrian accidents indicates their use. The following are general guidelines:
1.
Freeways may divide areas where pedestrian crossings would otherwise be high. If
highway crossings are spaced relatively far apart, a pedestrian overpass may be
justified.
2.
Pedestrian overpasses may be warranted where a significant safety hazard exists.
3.
The vertical clearance for the overpass shall be a minimum of 5.5m.
4.
The overpass must be able to accommodate handicap pedestrians by providing
ramps with grades range from 1:16 (6%) to 1:12 (8%) maximum. The maximum
horizontal run shall vary from 12m to 15m with a landing area of at least 1.5m in
length and 2% slope. See Figure 8-42
Figure 8-42 Handicap Ramp with Landing Area
8.10.2
Public Transport Facilities
The location of bus stops is primarily the concern of the transportation authority in Libya, who will seek
to provide stops within reasonable walking distance of trip generators and attractors. The bus stop
spacing is normally 3 to 4 stops per kilometer in urban areas. The engineer should consult with the
transportation authority to determine whether the road is to be used as a bus route, and, if so, to
establish the desired general location of stops. Buses should be able to stop without obstructing the
flow of traffic. Therefore, it is recommended to provide bus bays, which would allow the buses to stop
without obstructing the flow of traffic. A preferred arrangement for a bus bay is shown in Figure 8-43.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-76
Figure 8-43 Preferred Bus Bay Layout
On secondary arterials and collectors (and on local roads and streets if they are used by buses), it
may be acceptable to permit buses to stop by the curb, provided that:
The bus stop area is kept free from parked vehicles
The bus stop is not located close to a major/minor intersection, and
The presence of a stationary bus would not obstruct any relevant sight lines, and
On an undivided road, the available forward visibility is at least half of the Safe Passing
Sight Distance.
In addition, parking should be prohibited over a distance of 12m before and 8m beyond the bus stop
area. Bus stops on undivided roads should be staggered, beyond each other, so that the view of
crossing pedestrians from one bus is not obstructed by the presence of the bus traveling in the
opposite direction. This arrangement also ensures that where two buses are dropping off passengers
simultaneously, they do not have to set off through the crossing pedestrians dropped off by the other
bus. When providing bus stopping points in the vicinity of intersections, the following points should be
considered:
In general, it is preferable to locate bus stops on the exit side of the intersection. A
distance of at least 10m beyond the limit of the intersection would generally be required.
If a bus stop is to be provided on the approach side, then it must be positioned sufficiently
far in advance that the bus can move off safely and join the relevant traffic lane without
undue interference to other vehicles. A minimum distance of 20m from the end of the bay
to the start of any right-turning maneuver or auxiliary lane should generally be adequate,
but the bay should be located such that a stationary bus is clear of the intersection sight
triangles.
Where a bus route turns right at an intersection, it may be possible to locate the stop on
the approach side of the intersection, with the bus bay being located at the start of an
extended right-turning auxiliary lane.
If a bus stop is located on the approach to a roundabout or signalized intersection, it
should normally be located clear of any queuing vehicles, so that there is no loss of
capacity at the intersection.
Figure 8-44 Bus Stops at Intersections
8.10.3
Parking Facilities
8.10.3.1 General
Where possible, parking should be provided remote from the road, in conveniently located parking
lots designed for the purpose. On service roads and some collectors and local streets, it is however
beneficial to include curbside parking where the adjoining land use warrants it.
Curbside parking should not be provided:
within sight triangles at intersections, in order that visibility can be maintained, and
pedestrians can cross unmasked;
opposite access points to properties, unless there is adequate width for vehicles to enter
and leave the property without impinging on the parking space;
on bends, in order that adequate forward visibility can be maintained and that any
encroachment into the path of oncoming vehicles is eliminated (note that parking on the
outside of bends on local streets may be acceptable);
at pedestrian crossing points, to minimize the width to be crossed by pedestrians;
in advance of pedestrian crossing points, so that pedestrians can clearly see and be seen
(note that an absolute minimum of 5 m free of parking should be provided, and ideally
Safe Crossing Sight Distance, as set out in Section 8.11, should be provided at
unsignalized crossings);
at hydrants;
on local roads, within 6m of the tangent point of any intersection;
at any other location where it would create unsafe conditions
8.10.3.2 Curbside – Parallel Parking
Parallel parking may be provided adjacent to the outer lane of the road. It is recommended that
parallel parking should be provided only on roads of secondary arterial or lower class, or on service
roads running adjacent to primary arterials and expressways.
The standard width required for a parallel parking lane is 2.5 m, each bay being nominally 6.5 m in
length. If the majority of vehicles expected to use the facility are shorter than average, the bay length
may be reduced to an absolute minimum length of 6.0 m. Where residential development is dense
and the requirement for additional on-street parking is great, it is possible in exceptional
circumstances to use a narrower bay width, but the absolute minimum is 2.2 m.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-78
8.10.3.3 Curbside – Angled Parking
If the width of available right-of-way permits, consideration should be given to angled parking layout.
These could be perpendicular to the road or at an angle in order to ensure that vehicles drive
forwards into the bay and reverse out. Parking bay size for angled parking is 2.5 m wide by 5.0 m in
length, but if desired and if space permits, the size may be increased to 2.7 m by 5.5 m (by increasing
width and length dimensions by 10%) in order to provide a more generous layout which is easier to
use. (Intermediate values of width and/or length may also be used.)
The amount of space which the bays occupy within the cross section of the road depends on their
angle relative to the road, as shown in Table 8-38 below.
Table 8-38 Curbside Angled Parking – Width Occupied
within Cross Section of the Road (for a 5.0m x 2.5m bay)
Parking Angle
Width occupied (m)
allowing bumper
overhang at curb
45°
4.70
60°
4.90
75°
4.75
90°
4.25
There is a need for adequate space to maneuver into an angled bay, and this usually requires the
adjacent through lane to be wider than normal. If space permits, it is also good practice to provide a
buffer lane between the edge of the traveled way and the nearest part of the parking bay. This is
particularly beneficial on Service Roads, Collectors, and Secondary Arterials. Table 8-39 shows
these values.
Table 8-39 Curbside Angled Parking Minimum Width
for Adjacent Through Lane
Parking Angle
Minimum width for
through lane (m)
45°
3.75
60°
4.5
75°
6.5
Buffer lane width
(m)
Total Width
(m)
3.75 – 6.25
2.5
(desirable)
1.0
(minimum)
4.50 – 7.00
6.50 – 9.00
OR NONE
90°
7.0
7.00 – 9.50
8.10.3.4 Parking Lots
Parking lots are generally designed on the basis of angled parking, as this provides the most spaceefficient layout. The groups of bays are served by aisles, which generally operate one-way. In the
case of 90º angled bays, two-way circulation is also possible without any increase in aisle width being
required. Buffer lanes are not normally provided in parking lots.
When laying out a parking lot, it is generally found most efficient to align the aisles with the long axis
of the plot, and to seek to maximize the number of bays located at the outer periphery of the available
land, if it is regular in shape. Figure 8-45 shows a parking lot laid out on these principles, and
adopting a 90-degree angle.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-79
Figure 8-45 Parking Lot Laid-out with a 90-Degree Angle
Figure 8-46 Parking Bay Dimensions
Table 8-40 Parking Lot Dimensions (m)
Dimensions
(for a bay size of
2.5m x 5.0m)
Angle
DIM
30°
45°
60°
75°
90°
Bay width
A1
2.50
2.50
2.50
2.50
2.50
Bay width, parallel to aisle
A2
5.60
3.50
2.80
2.70
2.50
Bay length
B1
5.00
5.00
5.00
5.00
5.00
Length of line between bays
B2
10.00
7.50
6.25
5.65
5.00
Bay depth to wall
C1
4.50
5.30
5.60
5.50
5.00
Bay depth to curb
C2
4.15
4.70
4.90
4.75
4.25
Bay depth to interlock
C3
3.40
4.40
5.05
5.15
5.00
Aisle width between bay lines
D
3.50
3.75
4.50
6.00
7.00
Bumper overhang (typical)
E
0.35
0.60
0.70
0.75
0.75
Module, wall to interlock
F1
11.40
13.45
15.65
17.75
18.00
Module, curb to interlock
F2
11.05
12.85
14.95
17.00
17.25
Module, interlock to interlock
F3
10.30
12.55
14.80
17.40
18.00
For trucks and other large vehicles
Bay dimensions are dictated by the size of the design vehicle, as set out in Table 8-4, and the
relevant templates need to be applied to determine the optimum layout. It is normal to provide a bay
which is 1m wider than the width of the vehicle, with no addition to vehicle length, so a sports utility
(SU) vehicle would require a bay of 3.6m by 9.1m. Shallow parking angles of 30 to 45 degrees are
generally appropriate, with aisle widths being dependent on the design vehicle, but typically around
15 to 20m.
8.10.4
Safety Barriers
8.10.4.1 General
A safety barrier is used to protect errant vehicles from impacting roadside objects and structures; and
protects pedestrians and bicyclists from an out-of-control vehicle. Safety barrier can be located
outside of the roadway or in the median, depending on the proximity of the hazard to the clear zone
area. Single-faced longitudinal barrier installed either in the median or on the outside of the roadway
is a “Roadside Barrier.” Double-faced longitudinal barrier which is designed to redirect vehicles
striking either side of the barrier is “Median Barrier.”
Roadside barriers are usually categorized as flexible, semi-rigid, or rigid, depending on their deflection
characteristics on impact. Flexible systems are generally more forgiving than the other categories
since much of the impact energy is dissipated by the deflection of the barrier and lower impact forces
are imposed upon the vehicle. Rigid systems are generally more effective in performance and
relatively low in cost when considering their maintenance-free characteristics.
8.10.4.2 Warrants for Use of Safety Barriers
The decision on whether or not to provide a safety barrier can often be simplified using the following
analysis, with costs and likelihoods being considered where the decision is marginal.
Option 1: Remove or reduce the hazard so that it no longer requires to be protected.
Option 2: install an appropriate safety barrier.
Option 3: Leave the hazard unprotected.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-81
Medians
Head-on impact with an opposing vehicle often leads to fatalities, and so a continuous safety barrier is
often provided in the median of a divided road to separate opposing traffic. Such a barrier should
always be provided on freeways and expressways, and should be considered on other roads carrying
large traffic volumes at high speeds or where there is a fall across the median.
Embankments
Embankment height and side slope are the basic factors considered in determining barrier need as
shown in Figure 8-46. These criteria are based on studies of the relative severity of encroachments on
embankments versus impacts with roadside barriers. Embankments with slope and height
combinations on or below the curve do not warrant shielding unless they contain obstacles within the
clear zone.
Cut Areas
Safety barriers are seldom required in cut areas. Exceptions are where there is a steep rock face or
where large boulders of other obstacles are located in the cutting slope.
Roadside Obstacles
Roadside obstacles include both non-traversable terrain and fixed objects, and may be either manmade (such as culvert inlets) or natural (such as trees). Together, these highway conditions account
for over thirty percent of all highway fatalities each year. Barrier warrants for roadside obstacles are a
function of the obstacle itself and the likelihood that it will be hit. However, a barrier should be
installed only if it is clear that the result of a vehicle striking the barrier will be less severe than the
crash resulting from hitting the unshielded object. Non-traversable terrain and roadside obstacles that
normally warrant shielding are listed in Table 8-42. While roadside obstacles immediately adjacent to
the traveled way are usually removed, relocated, modified, or shielded, the optimal solution becomes
less evident as the distance between the obstruction and the traveled way increases. Table 8-23,
Clear-Zone Distances, is intended as a guide to aid the designer in determining whether the
obstruction constitutes a threat to an errant motorist that is significant enough to warrant action. Most
man-made objects incorporated into a highway project can be designed to minimize or eliminate the
danger they present to a motorist and thus make shielding unnecessary. This is particularly true of
drainage features such as small culverts and ditches.
Protection of bystanders
Although roadside barriers are not particularly installed to protect bystanders or pedestrians but to
protect vehicles from hitting roadside hazards, they provide protection and safety for pedestrians and
bystanders from out-of-control vehicles.
Once it has been decided that a roadside barrier is warranted, the engineer must chose the
appropriate type of barrier. This choice is based on a number of factors including performance
criteria, cost (construction and maintenance), and aesthetics. Table 8-41 summarizes the factors that
should be considered.
Table 8-41 Selection Criteria for Roadside Barriers
Criteria
Comments
Barrier must be structurally able to contain and redirect design
vehicle.
1.
Performance Capability
2.
Deflection
3.
Site Conditions
Slope approaching the barrier, and distance from traveled way, may
preclude use of some barrier types.
4.
Compatibility
Barrier must be compatible with planned end anchor and capable of
transition to other barrier systems (such as bridge railing)
5.
Cost
Standard barrier systems are relatively consistent in cost, but highperformance railings can cost significantly more.
AUGUST 2010
Deflection of barrier should not exceed available room to deflect
REVISION NO. 03
ROADW AY 8-82
Criteria
6.
Comments
Maintenance
A. Routine
Few systems require a significant amount of routine maintenance
B. Collision
Generally, flexible or semi-rigid systems require
Significantly more maintenance after a collision than rigid
Or high performance railings.
C. Materials Storage
D. Simplicity
7.
Aesthetics
8.
Field Experience
AUGUST 2010
The fewer different systems used, the fewer inventory
items/storage space required.
Simpler designs, besides costing less, are more likely to be
Reconstructed properly by field personnel
Occasionally, barrier aesthetics is an important consideration in its
selection.
The performance and maintenance requirements of existing
systems should be monitored to identify problems that
could be lessened of eliminated by using a different barrier type.
REVISION NO. 03
ROADW AY 8-83
Figure 8-47 Comparative Risk Warrants for Embankments
Table 8-42 Barrier Warrants for Non-Traversable Terrain and Roadside Obstacles
Obstacle
Warrants
Bridge piers, abutments, and railing ends
Shielding generally required
Boulders
Judgment decision based on nature of fixed
object and likelihood of impact
Culvert, pipes, headwalls
Judgment decision based on size, shape, and
location of obstacle
Cut and Fill slopes (smooth)
Shielding not generally required
Cut and Fill slopes (rough)
Judgment decision based on likelihood of impact
Ditches (parallel)
Shielding generally required if likelihood of head
on impact is high
Ditches (transverse)
Shielding generally required if likelihood of head
on impact is high
Obstacle
Warrants
Embankment
Judgment decision based on fill height and slope
Retaining Walls
Judgment decision based on relative smoothness
of wall and anticipated maximum angle of support
Sign Luminare supports
Shielding generally required for non-breakaway
supports
Traffic Signal Supports
Isolated traffic signals within clear zone on highspeed rural facilities may warrant shielding
Trees
Judgment decision based on site specific
circumstances
Utility Poles
Shielding may be warranted on a case-by-case
basis.
Permanent bodies of water
Judgment decision based on location and depth
of water and likelihood of encroachment
Notes:
1.
1 Shielding
non-traversable terrain or a roadside obstacle is usually warranted only when it is within the clear
zone and cannot practically or economically be removed, relocated, or made breakaway, and it is determined
that the barrier provides a safety improvem ent over the unshielded condition.
2.
Marginal situations, with respect to placement or omission of a barrier, will usually be decided by crash
experience, either at the site or at a comparable site.
3.
Where feasible, all sign and luminaire supports should be a breakaway design regardless of their distance from
the roadway if there is reasonable likelihood of their being hit by an errant motorist. The placement and locations
for breakaway supports should also consider the safety of pedestrians from potential debris resulting from
impacted systems.
4.
In practice, relatively few traffic signal supports, including flashing light signals and gates used at railroad
crossings, are shielded. If shielding is deemed necessary, however, crash cushions are sometimes used in lieu
of a longitudinal barrier installation.
8.10.4.3 Flexible Barriers
Flexible barriers are generally more forgiving than the other categories since much of the impact
energy is dissipated by the deflection of the barrier and lower impact forces are imposed upon the
vehicle. There are two basic types of flexible system:
1.
Cable Fence - normally comprising 4 strands of tensioned cable. Cable fences
redirect impacting vehicles after sufficient tension is developed in the cable, with the
posts in the impact area providing only slight resistance. The closer the post spacing,
however, the less the barrier can deflect. An important feature of the cable fence is
that, after most impacts, it returns to its original position, and damaged posts are
easily replaced.
2.
Steel Beam - the second type utilizes a standard steel beam section mounted on
relatively weak posts. This system acts in a similar manner to the cable fence. It
retains same degree of effectiveness after minor collisions due to the rigidity of the
beam rail element. However, after major collisions it requires full repair to remain
effective. As with the cable system, lateral deflection can be reduced to some extent
by closer post spacing. This system, as with all barriers having a relatively narrow
retraining width, is vulnerable to vaulting or vehicle under-ride caused by incorrect
mounting height or irregularities in the approach terrain.
8.10.4.4 Semi-Rigid Barriers
Semi-rigid systems work on the principle that resistance is achieved through the combined flexure and
stiffness of the rail. Posts near the point of impact are designed to break or tear away, distributing the
impact force to adjacent posts. Lateral deflection of a semi-rigid barrier may typically be as much as
1.5m.
Semi-rigid barriers usually remain functional after moderate collisions, thereby eliminating the need for
immediate repair. There are different types of systems with each having its own performance
requirements and capabilities. A few examples are listed below.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-85
Box Beam
Open Box Beam
W-Beam (corrugated type of barrier)
Blocked Out W-Beam
Self-restoring Safety Barrier
The self-restoring safety barrier is a high performance barrier designed to be maintenance-free for
most impacts and capable of containing and redirecting large vehicles. The combination of high initial
cost and high performance makes this barrier more suited for use at high accident frequency
locations.
When traffic speeds are expected to be greater than 50 km/h the semi-rigid system should be
tensioned. Tensioned systems usually require a minimum length and radius to be effective (typically
50 m minimum length and 150 m minimum radius). Individual barrier manufacturers’ specifications
should be adhered to.
8.10.4.5 Rigid Barriers
Rigid systems offer no deflection when hit by a vehicle. The impact energy is entirely absorbed by the
vehicle. For this reason, rigid barrier systems are not generally recommended for use on roads with
design speeds over 100 km/h, and their proposed adoption on higher speed roads should be carefully
evaluated by the designer. Commonly used rigid systems are the New Jersey shape and F-shape
Barriers in the USA, and the British Concrete Barrier in the UK. F-shape barrier is preferred because
of its better performance with small vehicle impact with respect to vertical roll and redirection.
Typically the system is relatively low cost, has generally effective performance for passenger-sized
vehicles, and has maintenance-free characteristics. The details for this system are shown in the
Construction Standards.
8.10.4.6 Placement
Lateral offset from the road:
As a rule, safety barriers should be placed as far from the traveled way as conditions permit. This
gives the errant driver the best chance of regaining control of the vehicle without having an accident.
It also provides better sight distance. Table 8-43 gives suggested lateral offsets related to the design
speed, and it should be noted that these are from the edge of traveled way, not the pavement.
Table 8-43 Suggested Setback from Edge of Traveled Way
AUGUST 2010
Design Speed
Setback from
Edge of Traveled
Way (m)
50
1
60
1.5
70
1.7
80
2
90
2.2
100
2.5
120
3
140
3.7
REVISION NO. 03
ROADW AY 8-86
Clearance between barrier and object being protected:
The desirable minimum distance between back of barrier and rigid hazards should not be less than
the dynamic deflection of the safety barrier based on a vehicle impact condition of approximately 25
degrees and 100 km/h.
Manufacturers’ specific requirements must be followed. However, as a guide, the clearances set out
in Table 8-44 are typical.
On embankments care should be taken to ensure that at full deflection of the barrier the wheels of the
vehicle do not overhang the edge of the slope.
The use of curbs with semi-rigid or rigid safety barriers should generally be avoided, as impact with
the curb causes instability in the vehicle’s progress prior to impact with the barrier. However, if the
face of the safety barrier is laterally within 225 mm of the curb face a vehicle is not likely to vault the
barrier, and the performance of the barrier should be within normal tolerances.
Table 8-44 Clearance between Barrier and Object Being Protected
Barrier Type
Clearance from Back
of Barrier to Hazard
(m)
Tensioned wire rope
2
Tensioned beam
1.2
Box beam
1.2
Rigid
0
Length of Need:
The barrier must be long enough to sufficiently shield the hazard from errant vehicles. Figure 8-48
illustrates the typical guardrail layout for protection of a hazard. The minimum length of need for full
height guardrail for 60 km/h, 100 km/h, and 110 km/h is 60 m, 90 m, and 100 m respectively. Barrier
end treatment is in addition to the length of need. See Construction Standards for typical installation
details of guardrail and concrete barrier.
On an undivided highway, the minimum guardrail length on the downstream end of the run to protect
the opposing traffic from the hazard for 60 km/h, 80 km/h, 100 km/h and 110 km/h is 50 m, 60 m,
70 m and 70 m respectively.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-87
Figure 8-48 Barrier Length of Need
End Treatments:
The untreated end of any safety barrier is extremely hazardous if hit, as the beam element can
penetrate the passenger compartment and will generally stop rather than redirect the vehicle. A
crashworthy end treatment is therefore considered essential if the safety barrier terminates within 10m
of the traveled way or in an area where it is likely to be hit end-on by an errant vehicle.
The termination of the safety barrier should not spear, vault or roll a vehicle for end-on or angled
impacts. For impacts anywhere within the length of need, the performance of the barrier depends on
that of the lengths adjacent to the point of impact. For potential impacts close to the end treatment
zone it is therefore essential that the end treatment should have the same redirectional characteristics
as the standard section. This means that the end must be properly anchored.
A number of different end treatments are available, working on a range of principles. Some of these
are listed below.
Breakaway Terminals
Turned Down Terminals
Energy Absorption Systems
Special Anchorage for Cable Fence
Anchorage into Embankment
Further reference is essential to select the most appropriate system for each particular situation.
Placement on Slopes and Behind Curbs
If guardrail is improperly located on slopes or behind curbs, an errant vehicle could impact the barrier
too high or too low, with undesirable results. Therefore, these criteria apply:
1.
Guardrail height is measured from the ground or pavement surface at the guardrail
face. For W-beam and Thrie beam this dimension is typically 550 mm from the
surface to the center post bolt.
2.
Berm and curb must be located to minimize vaulting potential. See the Construction
Standards for details.
3.
Where guardrail is required to be offset from the edge of pavement, it should not be
placed on a slope steeper than 1V:12H.
Transitions
Transition sections of safety barrier act as a link between lengths of different strength or rigidity, and
are necessary:
to provide continuity of protection when two different barriers join; or
where a barrier joins another barrier system such as a bridge rail; or
where a roadside barrier is attached to a rigid object such as a bridge pier
The transition section should be at least as strong as the stronger of the two sections which it links.
It should be long enough so that significant changes in deflection characteristics do not occur within a
short distance. Generally the transition length should be 10 to 12 times the difference in the lateral
deflection of the two systems in question, for example in a transition between a beam with a design
deflection of 1.5m and a rigid barrier or abutment, the transition length should be around 15 to 18 m.
Drainage features such as ditches should be avoided at transition positions as they may initiate
vehicle instability.
The stiffness of the transition should increase smoothly and continuously from the less rigid to the
more rigid system. This can be achieved by decreasing the post spacing, increasing post size or
strengthening the rail element.
8.10.5
Impact Attenuator Systems
Energy absorbing barriers, also known as crash cushions or impact attenuator systems, are protective
devices to prevent errant vehicles from impacting fixed object hazards. This is achieved by rapidly
slowing down a vehicle, if possible, bringing it to a safe stop before the point of impact with the
hazard. If stopping is not achievable, slowing it down would be to such an extent that the severity of
the impact with the object is kept within sustainable limits. Some designs of impact attenuators also
have the capability to deflect and redirect a shallow-angle impact.
Impact attenuator systems are therefore designed specifically for use at locations where fixed objects
cannot be removed, relocated or made to break away, and cannot be adequately protected by a
normal safety barrier. They primarily serve to lessen the severity of an impact with a fixed object,
unlike safety barriers which attempt to redirect the vehicle away from the object.
Impact attenuators work on one of two principles, namely absorption of kinetic energy or transfer of
momentum.
In the first case, the kinetic energy of a moving vehicle is absorbed by hydraulic energy absorbers or
crushable materials. This can be achieved by the use of water filled containers from which the water
will be expelled in a collision, or by a progressively crushable mechanical array of elements. Crash
cushions of this type require a rigid back stop to resist the impact force of the vehicle.
The second concept involves the transfer of momentum of a moving vehicle to an expendable mass
of material or weights. This mass is often provided by a series of free-standing sand filled containers.
Devices of this type require no rigid back stop.
Energy absorbing barriers are generally appropriate for cars traveling at speeds of up to 100 km/h,
but the system could be designed for trucks and buses too with various configurations.
The most common application of energy absorbing barriers is at an off-ramp in a depressed or
elevated structure, where a bridge pier or gore parapet requires protection and there is insufficient
space for a conventional safety barrier lead-in. Figure 8-49 shows an energy absorbing barrier
protecting an obstruction located in the gore area of an off-ramp terminal.
Delineation:
Crash cushions and barrier end treatments are not intended to reduce the frequency of crashes but to
lessen their severity. Nevertheless, if a particular installation is struck frequently, it is important to
determine why the crashes are occurring. Frequently, improved signing, pavement markings, or
delineation may result in fewer crashes. In this regard, conspicuous, well-delineated crash cushions
and end terminals are significantly less likely to be hit night or during inclement weather. If a system is
AUGUST 2010
REVISION NO. 03
ROADW AY 8-89
not reflective, standard object markers make it more conspicuous at night and under conditions of
reduced visibility.
Figure 8-49 Impact Attenuator Protection to Obstruction Located in the Gore Area
For optimum performance, the barrier should ideally be on a relatively level surface. Curbs should not
be provided as they may cause the vehicle to become airborne, thus coming into contact only partially
with the crash cushion.
There are many different designs of impact attenuator systems, each of which has its own particular
merits and applications. In the selection process, the road designer must consider the site
characteristics, cost, maintenance requirements, and structural and safety characteristics of the
different systems.
Further general reference on this subject is given in the American Association of State Highway and
Transportation Officials’ publication, Roadside Design Guide. For details of any specific impact
attenuator systems, the manufacturer’s technical literature should be referred to.
8.10.6
Traffic Calming
8.10.6.1 General
Excessive vehicle speed is a significant factor in the majority of accidents in urban areas. Although
the vehicles concerned may not have exceeded the posted speed, they have traveled faster than the
prevailing conditions required. This is frequently due to the driver being "given the wrong signals"
from the road infrastructure - being unaware that he is driving at a speed much greater for the
circumstances in which he finds himself (either associated with the road layout or related to other road
users and those living in the area).
Traffic calming is a generic name for techniques of speed reduction through road design. The
objective is to alter the driver’s perception of the road so that he drives at a speed which is
appropriate. On roads of arterial standard and above, traffic calming is never appropriate because
they require higher design speeds. On urban collector roads, some elements of traffic calming may
be appropriate, but the place where calming techniques are particularly relevant is in the design of
local streets.
8.10.6.2 Objectives of Traffic Calming
The main objectives are:
to improve road safety
to improve the quality of life for residents of the area
Secondary objectives are:
to smooth the flow of traffic;
to reduce the volume of traffic;
to improve the environmental quality of roads;
to discourage the use of unsuitable routes by heavy vehicles or streams of unnecessary
through traffic;
to limit vehicular atmospheric pollution; and
to reduce traffic noise levels
The introduction of an area speed limit can assist in achieving these objectives, but unless the road is
designed properly, the posted speeds are likely to be disregarded by many drivers.
There are four generic types of calming techniques: traffic engineering measures, visual features,
horizontal alignment features and vertical alignment features.
8.10.6.3 Traffic Engineering Measures
Intersection priority change
This can be introduced to break up a length of road which has priority through a series of
intersections. Care needs to be taken in the signing of such a measure.
One-way streets
The introduction of short lengths of one-way operation can create a "maze"-like road system, thus
discouraging through traffic. The technique can also be used to limit traffic speeds by breaking up
straight lengths of road into short sections, and can also permit the transfer of space from pavement
to sidewalk or landscape use.
Shared surfaces
In appropriate circumstances it may be possible to provide an area to be used by both pedestrians
and motorized traffic. It is essential in such areas to ensure that only very low vehicle speeds are
achievable.
8.10.6.4 Visual Features
Bar markings
These are colored road markings which can be laid across the road, particularly to draw attention to a
change in speed limits. They may also be perceived by changes in tire noise.
Entry treatment
Where drivers enter a calmed road or area, it is usually helpful to draw this to their attention by use of
different visual signals - paving color, texture, or material being the usual method. Alignment features
are often provided in association with entry treatments.
Gate ways
Gateways are a form of entry treatment, but with added vertical features such as walls or fences at
right angles to the road, relatively close to the edge of the traveled way, to give a visual effect of
narrowness.
Planting
The presence of tong sight lines can be a contributory factor to high speeds. Planting serves two
purposes; first, to provide an enhanced environmental appearance, and second, to assist in keeping
sight lines as short as possible, compatible with the very low design speeds which traffic calming
adopts.
Rumble devices
These are textured areas of pavement which cause tire noise to be distinct, thus raising driver’s
awareness.
8.10.6.5 Horizontal Alignment Features
AUGUST 2010
REVISION NO. 03
ROADW AY 8-91
Speed Limiting Bends
These are tight curves, with inner curb radii in the range 10 m to 15 m. They should only be used
where the other elements of the roadscape make it evident to drivers that traffic calmed behavior is
expected. Drivers should be able to see the bend clearly on approach, but sight distances around the
bend should deliberately be reduced by the provision of planting or hard landscaping. A stopping
distance of 30m should be provided.
Build-outs
These are local protrusions of the sidewalk into the pavement area, effectively narrowing the vehicular
traveled way. They are often provided in combination with vertical features.
Chicanes
These consist of a pair of build-outs on alternate sides of the road but not opposite each other, thus
creating horizontal deflections which can only be negotiated by vehicles traveling at low speeds.
Medians
The introduction of a median (which may be raised or flush with the traveled way) on an undivided
road has the effect of reducing lane widths and achieving effective visual narrowing. If space permits,
the median can be planted, and apart from improving the amenity of the road this prevents excessive
forward visibility. Figure 8-50(a) shows this layout.
Figure 8-50(a) Traffic Calming Layout Using Planted Median
Pinch points
These are locations where the road is deliberately made too narrow to permit two-way operation, and
vehicles have to operate in "shuttle" fashion, one direction at a time. On busier roads it may be
necessary to give priority by signing to one direction of travel. Figure 8-50(b) shows such an
arrangement.
Figure 8-50(b) Traffic Calming Layout Using Pinch Point
Sidewalk widening
Reallocation of space within the right of way can sometimes be achieved by widening sidewalks and
reducing traffic space accordingly.
8.10.6.6 Vertical Alignment Features
Sidewalk crosswalks
These allow pedestrians to continue at sidewalk level across an intersection, with the road being
ramped up to sidewalk level and down again. In these installations, drivers are expected to give way
to pedestrians.
Road humps
Humps are locally raised areas of pavement, typically 100 to 200 mm high and 4 m long (parallel to
traffic direction), which can only be crossed comfortably by vehicles traveling at very low speeds.
Speed cushions
These are a form of flat-topped road hump which extends across only part of the traveled way,
allowing buses (with wider wheelbase) to pass on the level, but requiring cars to run one or both
wheels over the cushion.
Speed tables
These are raised areas of pavement flush with the sidewalk, and are often provided over the whole
area of an intersection.
Speed bumps
These are small road humps, typically up to 75 mm high. They are normally 0.3 m long (parallel to
traffic direction) and laid in threes, at 1.3 m centers.
8.11 Intersections
8.11.1
General Design Considerations
An intersection is the area where two or more roads join or cross at-grade. It can be a major or minor
intersection or a roundabout, which will be covered in Section 8.12. The intersection should be
designed to accommodate an acceptable level of service. The values in Table 8-2 should be met,
when feasible, so that the highway facility will operate at a consistent level of service. At a minimum,
the at-grade intersection should operate at no more than one level below the values in the table.
Key issues to be addressed in the design of intersections include:
Visibility
Driver perception
Signing and road marking
Traffic control
Design vehicle and geometric implications
Pedestrian safety
8.11.1.1 Intersection Spacing
The location of main intersections is generally dictated by the geographical position of the roads
within the network, and intermediate intersections are usually a function of the surrounding area and
its current or future development. The spacing of intermediate intersections is a balance between the
needs of through traffic on the road and the requirement to access adjacent development.
Factors which should be taken into account when determining the need for an intersection (and hence
the spacing of intersections) include:
Roadway classification
The general intersection spacing which applies to such a road class
The potential traffic demand for access to/from the main road
The length of the alternative route if no intersection is provided
The design speed and posted speed of the road
AUGUST 2010
REVISION NO. 03
ROADW AY 8-93
The lengths required for any weaving to occur safely
Decision sight distances
The physical dimensions of the intersection itself
Measures that can be used to reduce the number of intersections along a route include:
Service roads for collecting local traffic movements together
The closure of minor roads at the main road providing alternative access.
The information shown in Table 8-45 should only be used as broad guidance when considering the
minimum spacing of intersections.
Table 8-45 Minimum Intersection Spacing (Measured center-to-center)
Intersection Spacing (m)
Roadway Classification
Urban Areas
Rural Areas
Freeway
1500
2000
Expressway
1000
2000
Primary Arterial
400
1500
Secondary Arterial
200
1000
Collector
100
100
Local Road
No minimum specified
100
8.11.1.2 Capacity and Level of Service
A capacity analysis must be performed during the design of any at-grade intersection. A future design
year, typically 20 years from the date the facility is completed, should be used. Often, the analysis will
dictate several geometric design features such as approach width, channelization, exit width, and
number of approach and exit lanes. As was mentioned before, the intersection should be designed to
accommodate an acceptable level of service. Refer to Section 8.11.1.1.
8.11.1.3 Vehicle Considerations
Vehicle turning paths yield minimum turning radii which are used in the design of intersections.
Computer programs utilize turning movement analysis for the P, SU, BUS, A-BUS, WB-12, WB-15,
and WB-18 vehicles. Normally, WB-18 vehicle is not used for intersection design but generally
restricted for freeways/expressways and their access roads. A vehicle must be able to negotiate the
vertical profile at an intersection without dragging its underside or front and rear edges. This vehicle
characteristic most often presents problems at driveway entrances and exits.
8.11.1.4 Alignment
At-grade intersections should occur on tangent sections of highway. Where a minor road intersects a
major road on a horizontal curve, this complicates the geometric design of the intersection particularly
sight distance, channelization, and superelevation. Preferably, the intersection should be relocated to
a tangent section of the major road. Another possibility is to realign the minor road to intersect the
major road perpendicular to a tangent at a point on the horizontal curve. However, this arrangement
would still result in difficult turning movements if the superelevation is high.
At-grade intersections should be as close to 90 degrees as possible. Skewed intersections increase
the travel distance across the major highway, adversely affect sight distance, and complicate the
design for turning movements. Intersection angles of more than 30 degrees from the perpendicular
cause particular problems. Skewed intersections should be realigned to 90 degrees, if possible,
particularly for those which deviate by more than 30 degrees. Realignment shall be considered when
accident data or traffic volumes indicate a need to do so.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-94
8.11.1.5 Profile
The vertical profile of an at-grade intersection should be as level as possible, subject to drainage
requirements. This also applies to the distance along any intersection leg, called the storage
platform, where vehicles stop and wait to pass through the intersection. The storage platform typically
should accommodate 3 vehicles with a gradient of 2%.
Grades approaching or leaving the intersection will affect vehicle deceleration distances (and
therefore stopping sight distance) and vehicle acceleration distances. Where the grades exceed 3%,
the stopping sight distance must be adjusted according to the criteria in Section 8.4.
In general, the profile and cross section of the major road will be carried through the intersection, and
the minor road will be adjusted to fit the major road. This will require transitioning the crown of the
minor road to an inclined section sloped to fit the longitudinal gradient of the major highway. The
transition should be gradual and comparable to the transition rates for superelevation as discussed in
Section 5.6. Intersections of two major roadways should be graded to meet drainage and comfort
considerations.
8.11.1.6 Vehicular Safety
At-grade intersections contribute significantly to the number of highway accidents. Many pedestrian
accidents occur at urban intersections. In rural areas, there is normally a large speed differential
between through vehicles and turning/entering vehicles. All at-grade intersection safety problems can
be minimized by proper design of its geometric elements: sight distance, roadway width, turning
lanes, alignment and profile, channelization, and turning radii.
When redesigning an existing at-grade intersection, the designer should review the accident history
and/or analyze the accident patterns at that intersection. The designer should then include
countermeasures to correct the problem. For example, several angle or rear-end accidents involving
left-turning vehicles at an unsignalized intersection may indicate the need for an exclusive left-turn
lane.
The type and level of sophistication of traffic control will affect the safety and geometric design of the
intersection. Following are examples of how geometric design and traffic control are related at an
intersection:
1.
At intersections with no signal control, the full pavement widths, including lane
alignments, should be continued through.
2.
Stop control may sufficiently reduce capacity to warrant additional approach lanes.
3.
Stop and signalization control require the consideration of stopping or decision sight
distance for the approaching vehicles.
4.
Signalization will impact the length and width of storage areas, location, and position
of turning roadways, and channelization. The number and type of lanes for signalized
intersections will be significantly different than for unsignalized intersections.
5.
The intersection must be designed to allow for physical placement of the traffic
control devices in the safest location. Traffic control devices configuration must be
coordinated with the local authority.
8.11.1.7 Control
Signs and signals are employed to convey control information to the driver. Traffic signals have
definite disadvantages and advantages and should be installed only after other less restrictive means
of control, such as STOP and YIELD signs, have been employed without success.
Traffic control signals control vehicular and pedestrian traffic by assigning the right-of-way to various
movements for certain pre-timed or traffic-actuated intervals of time. They are one of the key
elements in the function of many intersections. Careful consideration should be given in plan
development to intersection and access locations, horizontal and vertical curvature with respect to
signal visibility, pedestrian requirements, and geometric schematics to ensure the best possible signal
operation (individual signal phasing and traffic coordination between signals).
Traffic control signals should not be installed unless one or more of the signal warrants are met.
Information should be obtained by means of engineering studies and compared with the requirements
set forth in the warrants. If these requirements are not met, a traffic signal should neither be put into
operation nor continued in operation (if already installed).
AUGUST 2010
REVISION NO. 03
ROADW AY 8-95
An investigation of the need for traffic signal control should include where applicable, at least an
analysis of the factors contained in the following warrants:
Warrant 1 - Minimum vehicular volume.
Warrant 2 - Interruption of continuous traffic
Warrant 3 - Minimum pedestrian volume
Warrant 4 - School crossings
Warrant
Warrant
Warrant
Warrant
5 - Progressive movement
6 - Accident experience
7 - Systems
8 - Combination of warrants
Warrant 9 - Four Hour Volumes
Warrant 10 - Peak Hour Delay
Warrant 11 - Peak Hour Volume
When traffic control signals are not warranted but some control of the intersection is required,
consideration may be given to the installation of STOP or YIELD signs.
A number of techniques are available for evaluating the operation of a signalized intersection,
determining appropriate signal timing, and considering design alternatives. Among these techniques,
the most important are:
1.
The “critical movement” based technique of the 2000 Highway Capacity Manual
(HCM), latest edition.
2.
Computer software packages based on the HCM including: Highway Capacity
Software (HCS), SIDRA (Signalized and Unsignalized Intersection Design and
Research Aid), 94’ CINCH, and EzSignals.
3.
The signal-optimization techniques incorporated in the latest versions of the following
software packages: Synchro, 94’ CINCH and SIG/Cinema.
4.
Vehicle queue lengths using the following software packages: SIDRA, 94’ CINCH,
and EzSignals.
The latest version of any of the above programs is acceptable for signal design and evaluation at
isolated intersections.
For problems involving signal progression or coordination, the use of one of the following programs is
encouraged:
The latest versions of PASSER, Transyt, or Synchro are useful for designing or
evaluating signal systems along an arterial or in a network.
For simulation of signal operations on an arterial or in a network, the latest version
CORSIM (Traf-NETSIM) is recommended.
8.11.1.8 Other Considerations
1.
Expectancy. Intersections are points of conflict between vehicles, pedestrians,
bicycles, and other users. Intersection design should permit users to discern and
perform readily the maneuvers necessary to pass through the intersection safely and
with a minimum of interference.
2.
Pedestrians. Intersections are the most significant point where vehicles and
pedestrians share roadways. When pedestrians approach an intersection, there is a
major interruption. The sidewalk should provide sufficient storage area for those
wanting to cross plus area for cross traffic to pass. The storage area (SA) necessary
for pedestrians at a signalized intersection can be computed by the following formula:
SA = R(C – Gw) Ap
Where:
R = rate of flow of pedestrians for design period, number/sec
C = cycle length of signal, sec
Gw = length of walk indication on the pedestrian signal, sec
AUGUST 2010
REVISION NO. 03
ROADW AY 8-96
Ap = storage area per person in queue (generally 0.5 square meter per
person).
The designer should provide for the critical design period such as that containing the
peak pedestrian flow, a period of heavy pedestrian cross-traffic, or frequent interference
from turning motor vehicles.
Once pedestrians are given the walk indication, the crosswalk width becomes important.
The crosswalk must be wide enough to accommodate the pedestrian flow in both
directions within the duration of pedestrian signal phase. The necessary crosswalk
width Xw can be estimated by the following equation:
Xw = (RC/P) (C/Gw)
Or the level of service at which an existing crosswalk is operating can be computed
from:
P = (RC/Xw) (C/Gw)
When:
R = Rate of flow of pedestrians for design period, number/sec
C = cycle length of signal, seconds
Gw = length of walk indication on the pedestrian signal, seconds
Xw = crosswalk width, m; and
P = pedestrian-crossing volume in number/meter/minute.
From a pedestrian perspective, short crosswalks are desirable. If the intersection is not
signalized or if stop signs do not prohibit conflict with vehicular traffic, pedestrians must
wait for sufficient gaps in the traffic to cross. It is desirable for the pedestrian to cross the
entire roadway in a single cycle and not be caught in the median. The clear area on the
sidewalk free of obstructions should have a minimum 1.5 meter clearance between
objects (poles, control boxes etc.).
8.11.2
3.
The Handicapped. Design considerations for the handicapped should be included at
intersections. The intersection plan should be evaluated for the convenient and safe
locations of the ramps for the handicapped. Drainage inlets should be located on the
upstream side of all crosswalks and sidewalk ramps. This design operation will
govern the pedestrian crosswalk patterns, stop bar locations, regulatory signs, and in
the case of new construction, establish the most desirable location of signal supports.
4.
Bus Stops and Turnouts. The location of bus stops and turnouts can have a
considerable impact on traffic flow, turning movements, sight distance, and
pedestrian safety.
5.
Bicycles. Intersections frequently present hazards for bicyclists. Pedestrian
crosswalks at intersections can be utilized by bicyclists to cross over.
6.
Access to Abutting Property. Intersection design elements, such as channelization,
can eliminate access to abutting property. While such access control contributes to
safety, it may upset the desired balance between access and mobility. Each
intersection must be evaluated independently to assure that design features are
consistent with safety and the functional class of the roadways.
Intersection Sight Distance
Two sight distance criteria must be met at intersections. First, the driver must be able to see the
intersection itself. At a minimum, stopping sight distance must be provided to the intersection.
However, decision sight distance is often the desirable treatment at inter-sections because:
1.
Many at-grade intersections present roadway conditions that are too complex for the
2.5 second perception/reaction time factored into the stopping sight distances.
2.
Decision sight distance allows time to conduct an evasive maneuver, which is
desirable at intersections where slower moving, stopped, or crossing vehicles may be
in the through lane.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-97
Intersections often have high numbers of accidents. Therefore, the additional visibility proved by
decision sight distance may be warranted.
When measuring for sight distance, the intersection surface should be used as a 0.0 meter height of
object. Decision sight distance and its values are discussed in Section 8.4.3.
The second sight distance criterion which must be met is the corner sight distance along the legs of
the intersecting highway. One of five sight distance conditions (or a combination) may apply at the
intersection; these cases are discussed in the following sections. For each case, the criteria will
determine what minimum sight triangle must be free of obstructions to allow the intended maneuver.
In addition, for Case IIIA the applicable design vehicle must be selected based on the type and
frequency of vehicles using the intersection.
No rigid criteria can be established for case selection. The designer must decide which of the five
cases will be the design control based on an assessment of the functional classes of the intersecting
highways, traffic control, traffic volumes, traffic composition, and highway design speed. Accident
patterns may indicate where a critical problem exists and therefore which sight distance case should
be selected.
8.11.2.2 Case I – No Control: Enabling Either Vehicle to Adjust Speed
At intersections without traffic control, drivers should at a minimum be able to adjust their speed to
avoid a collision. Figure 8-51 provides the minimum sight distances along each intersecting leg
assuming 3 seconds of perception/reaction time. Distances da and db can be extracted from the table
for the sight triangle.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-98
Figure 8-51 Sight Distance at Intersections Minimum Sight Triangle
No Control or Yield Control on Minor Road
The Case I distances are considerably less than the lower stopping sight distances. Therefore, the
use of the Case I criteria should be limited to low-volume, low-speed intersections where attaining
greater sight distance would be too costly. They typically apply to intersections in residential areas
and between minor rural roads.
8.11.2.3 Case II – No Control: Enabling Either Vehicle to Stop
At intersections without traffic controls, it is desirable to provide enough sight distance along the
intersecting legs to allow either vehicle to stop. The Case II sight distances are provided in Figure 851, which are the greater stopping sight distances. At restricted sites, the lower stopping sight
distances may be used.
Where it is too costly to remove an obstruction which blocks the needed sight triangle, the Case II
criteria can be used to determine the safe speed through the intersection. Advance warning signs
should then be used to notify approaching drivers of the hazard
8.11.2.4 Case IIIA - Stop Control: Enabling Vehicles to Cross a Major Highway
At an intersection with stop control on the minor road, the driver of a stopped vehicle must have
sufficient sight distance in both directions to cross a major road without interfering with oncoming
vehicles. Figure 8-52 provides an illustration of the Case IIIA layout and the necessary equations for
computation of "d,” the sight distance needed in either direction. The following steps are necessary in
the calculation:
1.
Select the design vehicle. This should be the vehicle which will be making the
crossing maneuver with considerable frequency to justify the sight distance provided.
2.
Calculate the distance “S” the crossing vehicle must traverse. As shown in Figure 852, this will depend upon the length of the vehicle, the width of the major highway,
and the typical setback distance (usually 3 m).
3.
Find ta the time needed to travel distance "S,” from Figure 8-53. This will depend
upon the selected design vehicle. The values from the figure are valid for relatively
flat conditions.
4.
Select a value "J,” the perception/reaction time for a driver to begin moving the
vehicle. Normally, J is assumed to be 2.0 seconds. However, a somewhat lower
value may be justified in urban areas where drivers use many intersections with stop
control.
5.
Calculate "d", the minimum sight distance along the major highway, from the equation
in Figure 8-52.
d = 0.28 V (J+ ta)
When testing for adequate sight distance, use a height of eye of 1070 mm and height of object of
1300 mm.
Figure 8-52 Sight Distance at Intersections
(Vehicle Crossing Major Highway from Stop – Case IIIA)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-100
Figure 8-53 Sight Distance at Intersections, Case III
Acceleration from Stop
Example (Case IIIA)
Given:
Design speed of major highway - 100 km/hr
W = 13 m
Problem:
Determine required distance "d" for a passenger vehicle to cross the highway safely.
Solution:
Step 1:
Use a passenger vehicle.
Step 2:
D = 3 m; W = 13 m; and L = 6 m; Therefore:
S = 3 + 13 + 6 = 22 m
Step 3:
From Figure 11.3 for "assumed P” ta = 5.7 sec,
Step 4:
J = 2.0 sec.
Step 5:
d = 0.28 x 100 (2.0 + 5.7)
d = 216 m
8.11.2.5 Case IIIB (Left Turn) and IIIC (Right Turn) - Stop Control
If a vehicle operator intends to turn left or right onto a highway from a stopped position, additional
sight distance is needed. Figure 8-54 illustrates Case IIIB and Case IIIC. Figure 8-55 provides the
design criteria for the sight distance needed along the major highway. Preferably, the criteria for
design speed should be used; the criteria for average running speed are acceptable as a minimum.
Normally, sight distances for Case IIIB and IIIC should be satisfied. (Note: Criteria for buses and
trucks have not been established. The corner sight distances for these vehicles would obviously be
much greater.)
Cases IIIB and IIIC should be used at an intersection where the frequency of left-turning and/or rightturning vehicles justifies the additional costs of providing the sight distance. A review of the
intersection accident history may indicate the extent of any sight distance problems.
Figure 8-54 Intersection Sight Distance at At-Grade Intersections
Figure 8-55 Intersection Sight Distances
at At-Grade Intersection (Case IIIB and Case IIIC)
8.11.2.6 Case IV – Signal Control
Due to a variety of operational characteristics associated with all intersections, sight distance based
on the Case III procedures must be available to the driver. This principle is based on the increased
driver workload at intersections and the problems involved when vehicles turn onto or cross the major
highway. The problems associated with unanticipated vehicle conflicts at signalized intersections,
such as, violation of the signal, right turns on red, malfunction of the signal, or use of flashing
red/yellow mode, further substantiate the need for incorporation of Case III sight distance even at
signal-controlled intersections.
A basic requirement for all controlled intersections is that drivers must be able to see the control
device soon enough to perform the action it indicates. At intersections where right turns on red are
permitted, the departure sight line for right turning vehicles should be determined by the methods
discussed in "Case IIIC, Turning Right into a Major Highway."
In addition, when determining sight lines for the design maneuver, the designer should consider the
effects of roadside appurtenances, parked cars, or any other restriction to the sight line.
8.11.2.7 Effect of Skew
Sight distance calculations must be adjusted when the angle of intersection is less than 60 degrees.
Figure 8-56 shows the adjusted sight triangles of oblique angle intersections. The following
alterations are necessary in the analysis:
Because of the difficulty of looking for approaching traffic, the intersection should never be treated as
Case I, even where traffic is light.
Treatments by Case II or Case III, whichever is larger, should be used at oblique angle intersections.
The d distance along the highway can be computed from the equation d = 0.28v (J-ta) by reading ta
from Table 8-46.
Figure 8-56 Sight Distance at Skewed Intersections
Table 8-46 Acceleration Rates for Passenger Vehicles
AUGUST 2010
Speed
(km/h)
Distance
(m)
ta
(s)
30
25
5.7
40
40
7.3
50
70
9.8
60
110
12.3
70
160
15.2
80
235
18.8
90
325
22.4
100
455
27.4
110
650
33.9
REVISION NO. 03
ROADW AY 8-104
8.11.2.8 Effect of Vertical Profile
A vehicle descending a grade requires a somewhat greater distance to stop than does one on level
grade: also, a vehicle ascending a grade requires less distance in which to stop. The effect of grade
on acceleration can be expressed as a multiplicand to be applied to t a as determined for level
conditions for a given distance. See Table 8-47.
Table 8-47 Effect of Gradient on Accelerating Time (ta) at Intersections
Ratio, Accelerating Time on Grade To Accelerating Time on Level Section
Design Vehicle
8.11.3
Crossroad Grade (%)
-4
-2
0
+2
+4
P
0.7
0.9
1.0
1.1
1.3
SU
0.8
0.9
1.0
1.1
1.3
WB-15
0.8
0.9
1.0
1.2
1.7
Intersection Turns
8.11.3.1 Design of Right Turns
The following steps apply when designing an at-grade intersection to accommodate right-turning
vehicles:
1.
Select the design vehicle based on the largest vehicle likely to make the turn, unless
this would be a relatively infrequent occurrence. (Typically use the Semi-tractor
combination or SU design vehicle where applicable).
2.
Select the design speed at which the vehicle should be allowed to make the turn.
The turning radii designs discussed in Section 8.11.3.1.1 are negotiable at speeds of
15 km/h or less. If higher turning speeds are desired, then a turning roadway should
be used (Section 8.11.3.1.2).
3.
Determine the tolerable encroachment onto other lanes. This will vary with traffic
volumes, lane width, and one-way or two-way operation.
4.
Determine the need for auxiliary turn lanes.
5.
Determine the availability of right of way.
6.
Consider the effects of parking on turning movements.
7.
Evaluate the need to accommodate pedestrian movements.
8.
Select the appropriate channelization treatment.
Turning Radii
Turning radii allow vehicles to negotiate a right turn. A curve radius with or without modification is
used. The edge of pavement or curb line for a right turn can be designed by these methods.
1.
Simple radius,
2.
Simple radius with taper offsets,
3.
3-centered symmetric compound curve,
4.
3-centered asymmetric compound curve, or
5.
Spiral curve
The simple radius with taper offset provides a good transition for the turning vehicle. Therefore, they
should be used where practical. Table 8-48 & Table 8-49 provide the data for the two methods for
various design vehicles and turning angles. These designs will allow the design vehicle to turn at
speeds up to 15 km/h. Figure 8-57 illustrates minimum designs for simple curves for passenger and
AUGUST 2010
REVISION NO. 03
ROADW AY 8-105
single-unit vehicles. Figures 8-58 to 8-61 provide the design details and examples for simple curve
radii with taper offsets for 90 degrees, less than 90 degrees, and greater than 90 degrees angle of
turns.
Table 8-48 Minimum Edge of Traveled Way Designs for Turns at Intersection
Simple Curve Radius with Taper
Angle
of Turn
(degrees)
Design
Vehicle
Simple
Curve
Radius (m)
Radius
(m)
Offset
(m)
Taper
(m:m)
P
18
-
-
-
SU
30
-
-
-
WB-12
45
-
-
-
Ws-15
60
-
-
-
WB-19
110
67
1.0
15:1
WB-20
116
67
1.0
15:1
we-29
77
37
1.0
15:1
WB-35
145
77
1.1
20:1
P
15
-
-
-
SU
23
-
-
-
WB-12
36
-
-
-
WB-15
53
36
0.6
15:1
WB-19
70
43
1.2
15:1
WB-20
76
43
1.3
15:1
WB-29
61
35
0.8
15:1
WB-35
-
61
1.3
20:1
P
12
-
-
-
SU
18
-
-
-
WB-12
28
-
-
-
WB-15
45
29
1.0
15:1
WB-19
50
43
1.2
15:1
WB-20
60
43
1.3
15:1
WB-29
46
29
0.8
15:1
30
45
60
AUGUST 2010
REVISION NO. 03
ROADW AY 8-106
Simple Curve Radius with Taper
Angle
of Turn
(degrees)
Design
Vehicle
Simple
Curve
Radius (m)
Radius
(m)
Offset
(m)
Taper
(m:m)
WB-35
-
54
1.3
20:1
P
11
8
0.6
10:1
SU
17
14
0.6
10:1
WB-12
-
18
0.6
15:1
WB-15
-
20
1.0
15:1
WB-19
-
43
1.2
20:1
WB-20
-
43
1.3
20:1
WB-29
-
26
1.0
15:1
WB-35
-
42
1.7
20:1
P
9
6
0.8
10:1
SU
15
12
0.6
10:1
WB-12
-
14
1.2
10:1
WB-15
-
18
1.2
15:1
WB-19
-
36
1.2
30:1
WB-20
-
37
1.3
30:1
WB-29
-
25
0.8
15:1
WB-35
-
35
0.9
15:1
P
-
6
0.8
8:1
SU
-
11
1.0
10:1
WB-12
-
12
1.2
10:1
Ws-15
-
17
1.2
15:1
WB-19
-
35
1.0
30:1
WB-20
-
35
1.0
30:1
WB-29
-
22
1.0
15:1
WB-35
-
28
2.8
15:1
P
-
6
0.6
10:1
75
90
105
120
AUGUST 2010
REVISION NO. 03
ROADW AY 8-107
Simple Curve Radius with Taper
Angle
of Turn
(degrees)
Design
Vehicle
Simple
Curve
Radius (m)
Radius
(m)
Offset
(m)
Taper
(m:m)
SU
-
9
1.0
10:1
WB-12
-
11
1.5
8:1
WB-15
-
14
1.2
15:1
WB-19
-
30
1.5
25:1
WB-20
-
31
1.6
25:1
WB-29
-
20
1.1
15:1
WB-35
-
26
2.8
15:1
P
-
6
0.5
15:1
SU
-
9
1.2
8:1
WB-12
-
9
2.5
6:1
WB-15
-
12
2.0
10:1
WB-19
-
24
1.5
20:1
WB-20
-
25
1.6
20:1
WB-29
-
19
1.7
15:1
WB-35
-
25
2.6
15:1
P
-
6
0.6
10:1
SU
-
9
1.2
8:1
WB-12
-
9
2.0
8:1
WB-15
-
11
2.1
6:1
WB-19
-
18
3.0
10:1
WB-20
-
19
3.1
10:1
WB-29
-
19
2.2
10:1
WB-35
-
20
4.6
10:1
P
-
5
0.2
20:1
SU
-
9
0.5
10:1
WB-12
-
6
3.0
5:1
135
150
180
AUGUST 2010
REVISION NO. 03
ROADW AY 8-108
Simple Curve Radius with Taper
Angle
of Turn
(degrees)
AUGUST 2010
Design
Vehicle
Simple
Curve
Radius (m)
Radius
(m)
Offset
(m)
Taper
(m:m)
WB-15
-
8
3.0
5:1
WB-19
-
17
3.0
15:1
WB-20
-
16
4.2
10:1
WB-29
-
17
3.1
10:1
WB-35
-
17
6.1
10:1
REVISION NO. 03
ROADW AY 8-109
Table 8-49 Cross Street Width Occupied by Turning Vehicle
Various Angles of Intersection and Curb Radii
AUGUST 2010
REVISION NO. 03
ROADW AY 8-110
Figure 8-57 Minimum Designs for Simple Curves
Figure 8-58 Detailed Layout of Simple Curve Radius, Taper Offset (90 Degree)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-112
Figure 8-59 Detailed Layout of Simple Curve Radius, Taper Offset ( ‹ 90 Degrees)
Figure 8-60 Detailed Layout of Simple Curve Radius, Taper Offset ( › 90 Degrees)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-114
Figure 8-61 Effect of Curb Radii on Turning Paths
of Various Design Vehicles
Turning Roadways
Turning roadways are channelized areas which allow a right turn to be made away from the
intersection area. They should be considered where:
it is desirable to allow right turns at 25 km/h or more
intersections are skewed; or
buses or semi-trailers must be accommodated
Table 8-50 provides the design data for the horizontal alignment, width, and superelevation for
various design speeds. Figure 8-62 illustrates a typical design for a turning roadway. These criteria
apply to the design of a turning roadway.
Curvature - 3 centered compound curves should be used. Table 8-51 and Figure 8-63
show the minimum design criteria.
Spirals - May also be used for smoother transitions. See Table 8-52 for minimum spiral
lengths.
Superelevation - Superelevation on turning roadways does not need to be developed to
the strict criteria of open highways. A flexible approach may be used where
superelevation is provided as site conditions allow. The maximum superelevation is 0.04
m/m. If possible, the superelevation should be developed in the same manner as
described in Section 5 for deceleration lanes at freeway exits.
Speed-Change Lanes - For large differences between the design speeds of mainline and
turning roadway, the designer should consider deceleration and acceleration lanes. The
decision to use a speed-change lane will depend upon the functional classification of the
two highways, traffic volumes, accident history, design speed, and the speed differential
between the mainline and turning roadway. Speed-change lanes should be provided
from high-volume, high-speed urban and rural arterials. Acceleration lanes are normally
provided when the turning roadway is merging with these facilities. A 15:1 taper is
sufficient for deceleration lanes, and a 25:1 taper is preferred for the acceleration lane.
Preferably, the length of the speed change lane should be determined from the criteria in Section 8.8
for interchanges.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-115
Table 8-50 Designs for Turning Roadways
Design1
Speed
(km/h)
Side
Friction
(f)
Assumed2
Superelevation
(e)
e+ f
30
.27
.02
40
.23
50
.20
4
Minimum3
Radius
(m)
A
B
C
.29
28
4.50
5.0
5.5
.04
.27
46
4.25
5.0
5.25
.04
.26
70
4.0
5.0
5.0
1.
For design speeds greater than 50 km/h use open highway conditions
2.
Superelevation is typically between .02 and .04
Width (m)
A flatter curve, no more than twice the minimum radius, should be used to transition into and out of
the sharper radius. The minimum length of the flatter transition curve will be:
Radius (m)
30
45
60
75
90
120
150+
Minimum Length
(m)
12
15
18
24
30
36
43
Desirable Length
(m)
18
20
27
36
42
41
60
3.
Add a minimum of 0.5 m and desirable 1.25 m on each side of a barrier curb.
Traffic conditions are:
A – Predominantly P vehicles, but some consideration for SU trucks;
B – Predominantly SU vehicles, but some considerations for semitrailers;
C – Sufficient bus and semitrailer vehicles to govern design (>10%)
AUGUST 2010
REVISION NO. 03
ROADW AY 8-116
Figure 8-62 Typical Design for Turning Roadway
AUGUST 2010
REVISION NO. 03
ROADW AY 8-117
Table 8-51 Minimum Designs for Turning Roadways
3-Centered
Compound Curve
Angle
of Turn
(degrees)
75
90*
105
120
135
150
Design
Classification
Radii
(m)
Offset
(m)
Width
of Lane
(m)
Approx.
Island
Size (m2)
A
45-23-45
1.0
4.2
5.5
B
45-23-45
1.5
5.4
5.0
C
55-28-55
1.0
6.0
5.0
A
45-15-45
1.0
4.2
5.0
B
45-15-45
1.5
5.4
7.5
C
55-20-55
2.0
6.0
11.5
A
36-12-36
0.6
4.5
6.5
B
30-11-30
1.5
6.6
5.0
C
55-14-55
2.4
9.0
5.5
A
30-9-30
0.8
4.8
11.0
B
30-9-30
1.5
7.2
8.5
C
55-12-55
2.5
10.2
20.0
A
30-9-30
0.8
4.8
43.0
B
30-9-30
1.5
7.8
35.0
C
48-11-48
2.7
10.5
60.0
A
30-9-30
0.8
4.8
130.0
B
30-9-30
2.0
9.0
110.0
C
45-11-48
2.1
11.4
160.0
NOTES: Asymmetric three-centered compound curve and straight tapers with a simple curve can also be used
without significantly altering the width of roadway or corner island size.
2
Painted island delineation is recommended for islands less than 7 m in size
Design Classification:
A - Primarily passenger vehicles; permits occasional design single-unit truck to turn with restricted clearances.
B - Provides adequately for SU; permits occasional WB-15 to turn with slight encroachment on adjacent traffic
lanes.
C - Provides fully for WB-15.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-118
Table 8-52 Minimum Lengths of Spirals for Intersection Curves
Design (turning) speed (km/h)
30
40
50
60
70
Minimum radius
25
50
80
125
160
Assumed C
1.2
1.1
1.0
0.9
0.8
Calculated Length of Spiral (m)
19
25
33
41
57
Suggested Minimum Length Of Spiral
20
25
35
45
60
Corresponding Circular Curve
Offset From Tangent (m)
0.7
0.7
0.7
0.8
0.9
AUGUST 2010
REVISION NO. 03
ROADW AY 8-119
Figure 8-63 Designs for Turning Roadways with Minimum Corner Islands
AUGUST 2010
REVISION NO. 03
ROADW AY 8-120
8.11.3.2 Auxiliary Turning and Storage Lanes
Warrants for Right-Turn Lanes
Exclusive right-turn lanes should be considered for at-grade intersections, as follows:
1.
at intersections with high-speed and/or high-volume turning movements;
2.
at unsignalized intersections on two-lane urban or rural highways which satisfy the
criteria in Figure 8-64.
3.
at intersections where the accident experience, existing traffic operation, or
engineering judgment indicate a significant hazard or capacity problem related to right
turning vehicles
Figure 8-64 Right-Turn Warrants at Unsignalized Intersections on 2-Lane Highways
AUGUST 2010
REVISION NO. 03
ROADW AY 8-121
Warrants for Left-Turn Lanes
Exclusive left-turn lanes should be considered for at-grade intersections, as follows:
1.
at intersections with major roads on urban and rural arterials;
2.
at unsignalized intersections on two-lane urban or rural highways which meet the
criteria; Refer to Table 8-53.
3.
at intersections where the accident experience, existing traffic operations, or
engineering judgment indicate a significant hazard or capacity problem related to leftturning vehicles
Length of Auxiliary Turn and Storage Lanes
The length of the turning lane is the sum of its taper, deceleration, and storage lengths:
1.
Taper - A taper of 15: 1 should be used. Short curves should be used at the
beginning and end of the taper.
2.
Deceleration - It is desirable for the lengths for deceleration to be the same as those
given for deceleration lanes at freeway exits in Chapter 8, and for all deceleration to
occur within the full width of the turn lane. Figure 8-65 provides the minimum criteria
for the length of turn lanes.
3.
Storage Length - The storage length should be long enough to store the number of
vehicles likely to accumulate in the design period. The following minimum criteria will
apply:
a. At unsignalized intersections the storage length should accommodate the
number of turning vehicles likely to arrive in an average two-minute period
within the peak hour. As a minimum, 15 m should be allowed; if the turning
traffic is over 10% trucks, a minimum of 25 m should be provided.
b. At signalized intersections, the storage length should be based on 1.5 or 2.0
times the average number of vehicles that would store per cycle.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-122
Table 8-53 Guide for Left-Turn Lanes on Two-Lane Highways
Advancing Volume/Hour
Opposing
Volume/Hour
Left Turns
5%
10%
20%
30%
60 km/h Operating Speed
800
330
240
180
160
600
410
305
225
200
400
510
380
275
245
200
640
470
350
305
100
720
515
390
340
80 km/h Operating Speed
800
800
280
210
135
600
600
350
260
170
400
400
430
320
210
200
200
550
400
270
100
100
615
445
295
100 km/h Operating Speed
800
230
170
125
115
600
290
210
160
140
400
365
270
200
175
200
450
330
250
215
100
505
370
275
240
Right and left-turn lanes should be designed as follows:
1.
Figure 8-65 illustrates a typical right-turn lane and a typical left-turn lane (on a divided
highway). Minimum distances for deceleration are provided.
2.
Figure 8-66 illustrates the typical treatment for developing a left-turn lane on an
undivided highway.
3.
Figure 8-67 illustrates the typical design for a by-pass lane on low speed facilities in
developed areas. This is a relatively inexpensive design to provide for through and
left-turn movements at unsignalized intersections. It is appropriate for T-intersections
where left-turning volumes are light to moderate, where right of way is restricted, and
accident history is negligible.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-123
Figure 8-65 Typical Right and Left Turn Lanes on Divided Highway
TYPICAL RIGHT TURN LANE
TYPICAL LEFT TURN L ANE
NOTES:
1.
Widths must be increased for curb offsets or shoulders, where applicable.
2.
As shown in the figure, all deceleration will desirably occur after the full width of the turning lane begins. If
possible, the criteria in Table 8-53 should be used. However, in areas of restricted right-of-way, this may not be
practical. Use the following minimum distances for deceleration:
Design Speed
(km/h)
Length (m)
(Deceleration and Taper – Grades 2% or Less)
50
70 m
60
100 m
80
130 m
AUGUST 2010
REVISION NO. 03
ROADW AY 8-124
Figure 8-66 Typical Left-Turn Lane on an Undivided Highway
NOTES:
1.
Tables are based on:
Curve radii are minimum radii for open highway conditions for given design speed and a normal crown of
0.02 m/m, which is the typical cross slope.
Tangent Distance Assumes A Taper Of: L=Ws²/100
2.
See Figure 8-65 for details of turning lane taper.
3.
See Figure 8-65 for details of turning lane length.
4.
Island may be raised, painted, or scored concrete.
Figure 8-67 By-Pass Lane in Highly Developed Areas
on an Undivided Highway at Less than 60 km/h
NOTES:
1.
2.
3.
L = Length, m
W = By-Pass Lane Width, m
S = Design Speed, km/h
Increase Length If Storage Requirements Exceed 30 m.
May be used as an alternative to Figure 8-66 in highly developed areas, where right-of-way is restricted.
Other Considerations
When designing an auxiliary turning and storage lane, these factors should also be considered:
1.
Where the proper length of a turn lane cannot be provided or becomes prohibitive,
the designer may consider a dual-turn lane. Generally, a dual-turn lane
approximately 60% as long as a single-turn lane will operate comparably. However,
double left turns require a protected turn phase to operate properly.
2.
A right-turn lane in an urban area will often require parking restrictions beyond the
usual restricted distances from the intersection. Also, it may require relocating nearside bus stops to the far side of the intersection.
3.
With sufficiently wide medians, a left-turn lane may be offset 0.5 m or more from the
inside through lane to provide a striped island between the two.
4.
Medians must be designed to accommodate the turning radii of the design vehicle.
5.
Pavement markings for lanes must line up from one side of the intersection to the
other.
6.
The width of the turn lane should be 3.0m minimum.
7.
Median openings should be designed according to the criteria in Section 8.11.3.4.
8.11.3.3 Two-Way Left-Turn Lanes
A continuous or two-way left-turn lane (2WLTL) is a paved, flush, traversable median which can be
used for left-turn storage in either direction. A 2WLTL may be considered in developed areas with
frequent commercial roadside access and with no more than two through lanes in each direction.
Although the 2WLTL offers advantages, they are hazardous unless there is sufficient sight distance
and adequate delineation. The following should be used as guidance in selecting and designing a
2WLTL:
1.
A 2WLTL is limited to arterials with operating speeds of 70 km/hr or less.
2.
The preferred lane width is 4.5 m with a minimum lane width of 3.75 m.
3.
At minor intersections, the 2WLTL should be extended up to the intersection. At
major and/or signalized intersections, the 2WLTL should be terminated in advance of
the intersection. An exclusive left-turn lane of the proper length should be provided.
4.
Any 2WLTL must be clearly marked and adequately delineated to prevent possible
use as a passing lane. Overhead signing should be used.
5.
A 2WLTL may be used where average daily traffic through volumes are 10,000 to
20,000 (4 lane) and 5,000 to 12,000 (2 lane) and left turns consist of at least 70 midblock turns per 300 m during peak hour and/or 20% or more of the total volume. High
left-turning volumes combined with high average daily traffic (ADT) could possibly
lead to operational and safety problems. Restricting all left turns except at public
road intersections and indirect (jug handle) U-turns, or providing a raised median,
with left turn and/or U-turn lanes should also be considered. Each site requires
careful evaluation of the suitability of the 2WLTL.
8.11.3.4 Median Openings
Median openings should be provided primarily at public road intersections and to allow left turns to
and from the main highway.
In order to provide coordinated signal progression for mainline traffic, median openings should not be
closely spaced. On major arterials, signalized intersections with median openings should be spaced
no closer together than 500 m to 600 m. On minor arterials, signalized intersections with median
openings should be spaced no closer together than 400 m to 500 m.
Median openings must be designed to accommodate left-turning vehicles properly. Left-turning
vehicles trace essentially the same path as right-turning vehicles. Figures 8-68 and 8-69 illustrate the
design vehicle paths and provide the criteria for intersections with control radii 15 m and 23 m. The
following criteria apply:
1.
AUGUST 2010
The nose should be designed to accommodate the traffic movement at the
intersection.
REVISION NO. 03
ROADW AY 8-126
2.
The minimum lengths of median openings are 12 m and are shown on Table 8-450 to
Table 8-453. Intersections on a skew may require larger openings.
3.
The acceptable encroachment is the primary factor in selecting the design vehicle.
The median opening figures illustrate how much the larger vehicles encroach on the
adjacent lanes for a given design. The decision to use the SU or WB-15 design is
based on truck volumes, through traffic volumes, design speed, accident history,
costs, signalization, and judgment.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-127
Figure 8-68 Minimum Design of Median Openings (SU Design Vehicle)
Control Radius of 15 m
AUGUST 2010
REVISION NO. 03
ROADW AY 8-128
Figure 8-69 Minimum Design of Median Openings (WB-12 Design Vehicle)
Control Radius of 23 m
AUGUST 2010
REVISION NO. 03
ROADW AY 8-129
Table 8-54 Minimum Design of Median Openings (SU Design Vehicle)
Control Radius of 15 m
Width L=Minimum Length of Median Opening (m)
Median
Semicircular
Bullet Nose
(m)
1.2
28.8
28.8
1.8
28.2
22.8
24
27.6
20.4
3.0
27.0
1&6
3.6
26.4
17.4
4.2
25.8
15.9
4.8
212
15.0
&0
24.0
13.2
7.2
22.8
12.0 MIN
8.4
21.6
12.0 MIN
46
20.4
12.0 MIN
10.8
19.2
12.0 MIN
12.0
18.0
12.0 MIN
15.0
15.0
12.0 MIN
18.0
12.0 MIN
12.0 MIN
21.0
12.0 MIN
12.0 MIN
Table 8-55 Minimum Design of Median Openings (WB-12 Design Vehicle)
Control Radius of 23 m
Width L=Minimum Length of Median Opening (m)
Median
Semicircular
Bullet Nose
(m)
AUGUST 2010
1.2
43.8
35.6
1.8
43.2
34.5
2.4
42.6
33.0
3.0
42.0
31.5
3.6
41.4
30.0
REVISION NO. 03
ROADW AY 8-130
Width L=Minimum Length of Median Opening (m)
Median
Semicircular
Bullet Nose
(m)
4.2
40.8
28.8
4.8
40.2
27.6
6.0
39.0
2T5
7.2
37.8
23.4
8.4
36.6
21.9
9.6
35.4
20.1
10.8
34.2
18.6
12.0
30.0
17.1
18.0
27.0
12.0 MIN
24.0
21.0
12.0 MIN
30.0
15.0
12.0 MIN
33.0
12.0 MIN
12.0 MIN
36.0
12.0 MIN
12.0 MIN
Table 8-56 Effect of Skew on Minimum Design for Median Openings
Typical Values Based on Control Radius of 15 m
Length of Median Opening Measured
Normal to the Crossroad (m)
Bullet Nose
Skew
Angle
(degree)
Width of
Median
(m)
SemiCircular
A
Symmetrical
B
3
27
19
6
24
13
9
21
12 MIN.
12
18
12 MIN.
15
15
12 MIN.
18
13
12 MIN.
3
32
24
23
6
28
17
16
9
25
14
12 MIN.
12
21
12 MIN.
12 MIN.
15
18
12 MIN.
12 MIN.
Asymmetrical
B
R For
Design C
(m)
0
10
AUGUST 2010
REVISION NO. 03
ROADW AY 8-131
Length of Median Opening Measured
Normal to the Crossroad (m)
Bullet Nose
Skew
Angle
(degree)
Width of
Median
(m)
SemiCircular
A
Symmetrical
B
Asymmetrical
B
R For
Design C
(m)
18
14
12 MIN.
12 MIN.
3
36
29
27
29
6
32
22
20
28
9
28
18
14
26
12
24
14
12 MIN.
25
15
20
12 MIN.
12 MIN.
23
18
16
12 MIN.
12 MIN.
21
3
41
34
32
42
6
36
27
23
39
9
31
23
17
36
12
27
19
13
33
15
23
15
12 MIN.
30
18
18
12
12 MIN.
27
3
44
38
35
63
6
39
32
27
58
9
35
27
20
53
12
29
23
15
47
15
24
19
12 MIN.
42
18
19
15
12 MIN.
36
20
30
40
AUGUST 2010
REVISION NO. 03
ROADW AY 8-132
Table 8-57 Design Controls for Minimum Median Openings
Design Vehicles Accommodated
Control Radius (m)
12
15
23
Predominant
P
SU
WB-12
Occasional
SU
WB-12
WB-15
8.12
Roundabouts
8.12.1
General
Roundabouts are circular intersections with specific design and traffic control features. These
features include yield control of all entering traffic, channelized approaches, and appropriate
geometric curvature to ensure that travel speeds on the circulatory roadway are typically less than 50
km/h. Thus, roundabouts are a subset of a wide range of circular intersection forms.
A roundabout can be provided on any class of road where at-grade intersections are permissible, and
so is an appropriate form of intersection on all roads, except for freeways and expressways where atgrade intersections are not to be used.
It is reasonable to assume that roundabouts on Local Roads will operate within capacity, and it is
likely that roundabouts on Collectors can be designed to do so too. On Arterials, adequate capacity
may often be difficult to achieve while maintaining a safe layout.
8.12.2
Design Principles
The principal objective of roundabout design is to secure the safe interaction of traffic between
crossing traffic streams with minimum delay. This is achieved by a combination of geometric layout
features that should be matched to the volumes of traffic in the various streams, to vehicle speeds,
and to any location constraints that apply. Roundabouts are defined by two basic operational and
design principles:
Yield-at-Entry: Also known as off-side priority or the yield-to-left rule, yield-at-entry
requires that vehicles on the circulatory roadway of the roundabout have the right-of-way
and all entering vehicles on the approaches have to wait for a gap in the circulating flow.
To maintain free flow and high capacity, yield signs are used as the entry control.
Deflection of Entering Traffic: Entrance roadways that intersect the roundabout along
a tangent to the circulatory roadway are not permitted. Instead, entering traffic is
deflected to the right by the central island of the roundabout and by channelization at the
entrance into an appropriate curved path along the circulating roadway.
From a safety viewpoint, the roundabout should be designed to limit through speeds by means of
adequate deflection angles and entry path curvature, and this may constrain pavement widths and
thus limit the available capacity. See Figure 8-70.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-133
Figure 8-70 Deflection of Entering Traffic
8.12.3
General Features of a Roundabout
8.12.3.1 Layout
A roundabout has a one-way circulating pavement around a central island which is 4m or more in
diameter. The entries are generally designed to permit more than one vehicle to enter the roundabout
side-by-side, and the approaches may be "flared" to achieve adequate entry width. Figures 8-71 and
8-72 depict basic design and geometric elements of a roundabout. Entries from undivided roads
should be provided with medians of divided roads should be widened in a similar manner. The
minimum diameter for a central island is 4m. Flush paving should be considered for roundabouts with
island diameters in the range 4m to 12m.
Figure 8-71 Typical Roundabout Design
Figure 8-72 Basic Geometric Elements of a Roundabout
8.12.3.2 Number of Entries
The number of entries recommended is either three or four. Roundabouts perform particularly well
with three legs, being more efficient than signals, provided that the traffic demand is evenly balanced
between the legs. If the number of entries is greater than four, driver comprehension can be
adversely affected. The roundabout also becomes target, and it is likely that higher circulating speeds
will occur. Six legs should be considered as the absolute maximum.
8.12.4
Speeds through the Roundabout
Because it has profound impacts on safety, achieving appropriate vehicular speeds through the
roundabout is the most critical design objective. A well-designed roundabout reduces the relative
speeds between conflicting traffic streams by requiring vehicles to negotiate the roundabout along a
curved path.
8.12.4.1 Speed profiles
Figure 8-73 shows the operating speeds of typical vehicles approaching and negotiating a
roundabout. Approach speeds of 40, 55, and 70 km/h about 100 m from the center of the roundabout
are shown. Deceleration begins before this time, with circulating drivers operating at approximately
the same speed on the roundabout. The relatively uniform negotiation speed of all drivers on the
roundabout means that drivers are able to more easily choose their desired paths in a safe and
efficient manner.
8.12.4.2 Design speed
International studies have shown that increasing the vehicle path curvature decreases the relative
speed between entering and circulating vehicles and thus usually results in decreases in the enteringcirculating and exiting-circulating vehicle crash rates. However, at multilane roundabouts, increasing
vehicle path curvature creates greater side friction between adjacent traffic streams and can result in
more vehicles cutting across lanes and higher potential for sideswipe crashes. Thus, for each
roundabout, there exists an optimum design speed to minimize crashes.
Figure 8-73 Sample Theoretical Speed Profile (Urban Compact Roundabout)
Recommended maximum entry design speeds for roundabouts at various intersection site categories
are provided in Table 8-58.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-136
Table 8-58 Recommended Maximum Entry Design Speeds
8.12.4.3 Vehicle Paths
To determine the speed of a roundabout, the fastest path allowed by the geometry is drawn. This is
the smoothest, flattest path possible for a single vehicle, in the absence of other traffic and ignoring all
lane markings, traversing through the entry, around the central island, and out the exit. Usually the
fastest possible path is the through movement, but in some cases it may be a right turn movement.
A vehicle is assumed to be 2m wide and to maintain a minimum clearance of 0.5m from a roadway
centerline or concrete curb and flush with a painted edge line. Thus the centerline of the vehicle path
is drawn with the following distances to the particular geometric features:
1.5 m from a concrete curb,
1.5 m from a roadway centerline, and
1.0 m from a painted edge line
Figure 8-74 and 8-75 illustrate the construction of the fastest vehicle paths at a single-lane
roundabout and at a double-lane roundabout, respectively. Figure 8-76 provides an example of an
approach at which the right-turn path is more critical than the through movement.
Figure 8-74 Fastest Vehicle Path through Single-lane Roundabout
Figure 8-75 Fastest Vehicle Path through Double-lane Roundabout
Figure 8-76 Example of Critical Right-turn Movement
The design speed of the roundabout is determined from the smallest radius along the fastest
allowable path. The smallest radius usually occurs on the circulatory roadway as the vehicle curves
to the left around the central island. However, it is important when designing the roundabout
geometry that the radius of the entry path (i.e., as the vehicle curves to the right through entry
geometry) not be significantly larger than the circulatory path radius.
8.12.5
Design Vehicle
An important factor determining a roundabout’s layout is the need to accommodate the largest
motorized vehicle likely to use the intersection. The turning path requirements of this design vehicle
will dictate many of the roundabout’s dimensions. Before beginning the design process, the designer
AUGUST 2010
REVISION NO. 03
ROADW AY 8-138
must be conscious of the design vehicle and possess the appropriate vehicle turning templates or a
CAD-based vehicle turning path program to determine the vehicle’s swept path.
The choice of design vehicle will vary depending upon the approaching roadway types and the
surrounding land use characteristics. Commonly, WB-15 vehicles are the largest vehicles along
collectors and arterials. Smaller design vehicles may often be chosen for local street intersections.
In general, larger roundabouts need to be used to accommodate large vehicles while maintaining low
speeds for passenger vehicles. However, in some cases, land constraints may limit the ability to
accommodate large semi-trailer combinations while achieving adequate deflection for small vehicles.
At such times, a truck apron may be used to provide additional traversable area around the central
island for large semi-trailers (Figure 8-77). Truck aprons, though, provide a lower level of operation
than standard non-mountable islands and should be used only when there is no other means of
providing adequate deflection while accommodating the design vehicle.
Figure 8-77 Design Vehicle with the Use of an Apron
8.12.6
Inscribed Circle Diameter
The inscribed circle diameter is the distance across the circle inscribed by the outer curb (or edge) of
the circulatory roadway. As illustrated in Figure 8-89, it is the sum of the central island diameter
(which includes the apron, if present) and twice the circulatory roadway. The inscribed circle diameter
(ICD) is determined by a number of design objectives. In general, the ICD should be a minimum of
30 m to accommodate a WB-15 design vehicle. Smaller roundabouts can be used for some local
street or collector street intersections, where the design vehicle may be a bus or single-unit truck.
At double-lane roundabouts, accommodating the design vehicle is usually not a constraint. The size
of the roundabout is usually determined either by the need to achieve deflection or by the need to fit
the entries and exits around the circumference with reasonable entry and exit radii between them.
Generally, the inscribed circle diameter of a double-lane roundabout should be a minimum of 45 m.
The size of the smallest acceptable ICD is determined by the selected design vehicle. It is good
practice to allow a tolerance of 1.5m from both inner and outer curbs, and so typical minimum lCDs
are as set out in Table 8-59.
Table 8-59 Recommended Inscribed Circle Diameters
Site Category
Typical
Design Vehicle
Inscribed Circle
Diameter Range*
Mini-Roundabout
Single-Unit Truck
13 – 25m
Urban Compact
Single-Unit Truck/Bus
25 – 30m
Urban Single Lane
WB-15
30 – 40m
Urban Double Lane
WB-15
45 – 55m
Rural Single Lane
WB-20
35 – 40m
Rural Double Lane
WB-20
55 – 60m
* Assumes 90-degree angles between entries and no more than 4 legs.
In general, smaller inscribed diameters are better for overall safety because they help to maintain
lower speeds. It should be noted, however, that if roundabouts are below 40m ICD it can prove
difficult to achieve adequate deflections. In such cases consideration could be given to the use of a
larger, low-profile central island which would provide adequate deflection for standard vehicles but
allow overrun of all or part of the island by the rear wheels of articulated vehicles and trailers.
In high-speed environments, however, the design of the approach geometry is more critical than in
low-speed environments. Larger inscribed diameters generally allow for the provision of better
approach geometry, which leads to a decrease in vehicle approach speeds. Larger inscribed
diameters also reduce the angle formed between entering and circulating vehicle paths, thereby
reducing the relative speed between these vehicles and leading to reduced entering-circulating crash
rates.
8.12.7
Circulating Roadway Width
The circulating roadway pavement width should, if possible, be circular in plan, and its width should
generally not exceed 15m. However, flush block-paved 'collars' around the central island can be used
to provide additional width if long vehicle turning movements need to be catered for on smaller
roundabouts.
The width of the circulating pavement should be constant and should be between 1.0 and 1.2 times
the width of the widest entry. It may be necessary to exceed 1.2 on smaller ICD roundabouts, but
care should be taken to ensure that the wider pavement does not permit vehicle paths with less than
adequate deflection.
It is normal practice to avoid short lengths of reverse curve between an entry and the subsequent exit
by joining those curves with tangents between the entry and exit curves. One method is to increase
the exit radius. However, where there is a considerable distance between the entry and the next exit,
as with three-leg layouts, reverse curvature may be unavoidable. The circulating pavement must be
wide enough to allow those vehicles which have entered the roundabout side-by-side to continue
side-by-side. Allowance should be made for increased width because of the curve, as set out in
Table 8-60. For island diameters less than 30m, the width requirements should always be checked
using a relevant software package or swept path templates.
Table 8-60 Minimum Width of Circulating Pavement
Island Diameter
(m)
30
AUGUST 2010
Circulation
2-Lane
3-Lane
12.6
Check
REVISION NO. 03
ROADW AY 8-140
Island Diameter
(m)
8.12.8
Circulation
2-Lane
3-Lane
50
11.1
using
Template
75
10.3
15.0
100
9.9
14.7
150
9.3
13.8
200
9.0
13.2
250
8.7
12.6
Entry Width
Entry width is the largest determinant of a roundabout’s capacity. The capacity of an approach is not
dependent merely on the number of entering lanes, but on the total width of the entry. In other words,
the entry capacity increases steadily with incremental increases to the entry width. Therefore, the
basic sizes of entries and circulatory roadways are generally described in terms of width, not number
of lanes. Entries that are of sufficient width to accommodate multiple traffic streams (at least 6.0m)
are striped to designate separate lanes. However, the circulatory roadway is usually not striped, even
when more than one lane of traffic is expected to circulate. The practical range for entry width is 6.0m
to 15.0m, but for undivided roads, the upper limit should be 10.5m.
Entry width is measured from the point where the yield line intersects the left edge of the traveled-way
to the right edge of the traveled way, along a line perpendicular to the right curb line. The width of
each entry is dictated by the needs of the entering traffic stream. It is based on design traffic volumes
and can be determined in terms of the number of entry lanes. The circulatory roadway must be at
least as wide as the widest entry and must maintain a constant width throughout.
To maximize the roundabout’s safety, entry widths should be kept to a minimum. The design should
provide the minimum width necessary for capacity and accommodation of the design vehicle in order
to maintain the highest level of safety. Typical entry widths for single-lane entrances range from 4.3
to 4.9m; however, a minimum entry width should not be less than 4m for the accommodation of trucks
and buses.
When the capacity requirements can only be met by increasing the entry width, this can be done in
two ways:
By adding a full lane upstream of the roundabout and maintaining parallel lanes through the entry
geometry; or
By widening the approach gradually (flaring) through the entry geometry.
Figures 8-78 and 8-79 illustrate these two widening options.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-141
Figure 8-78 Approach Widening by Adding Full Lane
Figure 8-79 Approach Widening by Entry Flaring
Flaring is an effective means of increasing capacity without requiring as much right-of-way as a full
lane addition. While increasing the length of flare increases capacity, it does not increase crash
frequency. Entry widths should therefore be minimized and flare lengths maximized to achieve the
desired capacity with minimal effect on crashes. Generally, flare lengths should be a minimum of 25m
in urban areas and 40m in rural areas. However, if right-of-way is constrained, shorter lengths can be
used with noticeable effects on capacity.
8.12.9
Entry Curves
The entry radius is an important factor in determining the operation of a roundabout as it has
significant impacts on both capacity and safety. The entry radius, in conjunction with the entry width,
the circulatory roadway width, and the central island geometry, controls the amount of deflection
imposed on a vehicle’s entry path. Larger entry radii produce faster entry speeds and generally result
in higher crash rates between entering and circulating vehicles. In contrast, the operational
performance of roundabouts benefits from larger entry radii.
The entry curve is designed curvilinearly tangential to the outside edge of the circulatory roadway.
Likewise, the projection of the inside (left) edge of the entry roadway should be curvilinearly tangential
to the central island. Figure 8-80 shows typical roundabout entrance geometry.
Figure 8-80 Typical Roundabout Entrance Geometry
8.12.9.1 Entry Curves at Single-lane Roundabouts
For single-lane roundabouts, it is relatively simple to achieve the entry speed objectives. With a
single traffic stream entering and circulating, there is no conflict between traffic in adjacent lanes.
Thus, the entry radius can be reduced or increased as necessary to produce the desired entry path
radius. Provided sufficient clearance is given for the design vehicle, approaching vehicles will adjust
their path accordingly and negotiate through the entry geometry into the circulatory roadway.
Entry radii at urban single-lane roundabouts typically range from 10 to 30m. Larger radii may be
used, but it is important that the radii not be so large as to result in excessive entry speeds. At local
street roundabouts, entry radii may be below 10m if the design vehicle is small.
At rural and suburban locations, consideration should be given to the speed differential between the
approaches and entries. If the difference is greater than 20 km/h, it is desirable to introduce approach
curves or some other speed reduction measures to reduce the speed of approaching traffic prior to
the entry curvature.
8.12.9.2 Entry Curves at Double-lane Roundabouts
At double-lane roundabouts, the design of the entry curvature is more complicated. Overly small
entry radii can result in conflicts between adjacent traffic streams. This conflict usually results in poor
lane utilization of one or more lanes and significantly reduces the capacity of the approach. It can
also degrade the safety performance as sideswipe crashes may increase.
8.12.10 Exit Curves
Exit curves usually have larger radii than entry curves to minimize the likelihood of congestion at the
exits. This, however, is balanced by the need to maintain low speeds at the pedestrian crossing on
exit. The exit curve should produce an exit path radius (R3 in Figure 8-81) no smaller than the
circulating path radius (R2). If the exit path radius is smaller than the circulating path radius, vehicles
will be traveling too fast to negotiate the exit geometry and may crash into the splitter island or into
oncoming traffic in the adjacent approach lane. Likewise, the exit path radius should not be
significantly greater than the circulating path radius to ensure low speeds at the downstream
pedestrian crossing.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-143
The exit curve is designed to be curvilinearly tangential to the outside edge of the circulatory roadway.
Likewise, the projection of the inside (left) edge of the exit roadway should be curvilinearly tangential
to the central island. Figure 8-82 shows a typical exit layout for a single-lane roundabout.
Figure 8-81 Vehicle Path Radii
Figure 8-82 Typical Roundabout Exit Geometry
8.12.10.1 Exit Curves at Single-lane Roundabouts
At single-lane roundabouts in urban environments, exits should be designed to enforce a curved exit
path with a design speed below 40 km/h in order to maximize safety for pedestrians crossing the
exiting traffic stream. Generally, exit radii should be no less than 15m.
In rural locations where there are few pedestrians, exit curvature may be designed with large radii,
allowing vehicles to exit quickly and accelerate back to traveling speed. This, however, should not
result in a straight path tangential to the central island because many locations that are rural today
become urban in the future. Therefore, it is recommended that pedestrian activity be considered at all
exits except where separate pedestrian facilities (paths, etc.) or other restrictions eliminate the
likelihood of pedestrian activity in the foreseeable future.
8.12.10.2 Exit Curves at Double-lane Roundabouts
As with the entries, the design of the exit curvature at double-lane roundabouts is more complicated
than at single-lane roundabouts.
8.12.11 Vertical Considerations
Elements of vertical alignment design for roundabouts include profiles, superelevation, approach
grades, and drainage.
8.12.11.1 Profiles
The vertical design of a roundabout begins with the development of approach roadway and central
island profiles. The development of each profile is an iterative process that involves tying the
elevations of the approach roadway profiles into a smooth profile around the central island.
Generally, each approach profile should be designed to the point where the approach baseline
intersects with the central island. A profile for the central island is then developed which passes
through these four points (in the case of a four-legged roundabout). The approach roadway profiles
are then readjusted as necessary to meet the central island profile. The shape of the central island
profile is generally in the form of a sine curve. Examples of how the profile is developed can be found
in Figures 8-83, 8-84 and 8-85 which consist of a sample plan, profiles on each approach, and a
profile along the central island, respectively. Note that the four points where the approach roadway
baseline intersects the central island baseline are identified on the central island profile.
Figure 8-83 Sample Plan View
AUGUST 2010
REVISION NO. 03
ROADW AY 8-145
Figure 8-84 Sample Approach Profile
Figure 8-85 Sample Central Island Profile
8.12.11.2 Superelevation
As a general practice, a cross slope of 2% away from the central island should be used for the
circulatory roadway. This technique of sloping outward is recommended for four main reasons:
It promotes safety by raising the elevation of the central island and improving its visibility;
It promotes lower circulating speeds;
It minimizes breaks in the cross slopes of the entrance and exit lanes; and
It helps drain surface water to the outside of the roundabout.
The outward cross slope design means vehicles making through and left-turn movements must
negotiate the roundabout at negative superelevation. Excessive negative superelevation can result in
AUGUST 2010
REVISION NO. 03
ROADW AY 8-146
an increase in single-vehicle crashes and loss-of-load incidents for trucks, particularly if speeds are
high. However, in the intersection environment, drivers will generally expect to travel at slower
speeds and will accept the higher side force caused by reasonable adverse superelevation.
Figure 8-86 provides a typical section across the circulatory roadway of a roundabout without a truck
apron. Figure 8-87 provides a typical section for a roundabout with a truck apron. Where truck
aprons are used, the slope of the apron should be 3 to 4 percent; greater slopes may increase the
likelihood of loss-of-load incidents.
Figure 8-86 Typical Circulatory Roadway Section
Figure 8-87 Typical Section with a Truck Apron
8.12.11.3 Locating Roundabouts on Grades
It is generally not desirable to locate roundabouts in locations where grades through the intersection
are greater than four percent. The installation of roundabouts on roadways with grades lower than
three percent is generally not problematic. At locations where a constant grade must be maintained
through the intersection, the circulatory roadway may be constructed on a constant-slope plane. This
means, for instance, that the cross slope may vary from +3 percent on the high side of the roundabout
(sloped toward the central island) to -3 percent on the low side (sloped outward). Note that central
island cross slopes will pass through level at a minimum of two locations for roundabouts constructed
on a constant grade.
Care must be taken when designing roundabouts on steep grades. On approach roadways with
grades steeper than -4 percent, it is more difficult for entering drivers to slow or stop on the approach.
At roundabouts on crest vertical curves with steep approaches, a driver’s sight lines will be
compromised, and the roundabout may violate driver expectancy. However, under the same
conditions, other types of at-grade intersections often will not provide better solutions. Therefore, the
roundabout should not necessarily be eliminated from consideration at such a location. Rather, the
intersection should be relocated or the vertical profile modified, if possible.
8.12.11.4 Drainage
With the circulatory roadway sloping away from the central island, inlets will generally be placed on
the outer curb line of the roundabout. However, inlets may be required along the central island for a
roundabout designed on a constant grade through an intersection. As with any intersection, care
should be taken to ensure that low points and inlets are not placed in crosswalks. If the central island
is large enough, the designer may consider placing inlets in the central island.
Normal cross slopes for drainage on roundabouts should not exceed 2%. To avoid ponding,
longitudinal edge profiles should be graded at not less than 0.5%.
8.12.12 Visibility
8.12.12.1 Eye and Object Heights
Visibility to the left and across the central island of a roundabout should be obtainable from a driver's
eye height of 1.05m to an object height of 1.05m, and the envelope of visibility should extend to 2.4m
above the road surface. It is therefore the same envelope as for Passing Sight Distance. All other
visibilities should be assessed in accordance with the envelope for Stopping Sight Distance set out in
Figure 8-88.
Where signs are to be erected on a median, verge or deflection island within the envelope of visibility,
including to the left, the mounting height should not be less than 2.4m above the pavement surface,
and the envelope needs to be carefully checked on sites where there are significant changes of
grade.
8.12.12.2 Visibility on the Approach
On the approach to a roundabout, normal Stopping Sight Distance (SSD) applies, in accordance with
the appropriate design speed. The SSD is measured to the "Give Way" line as shown in Figure 8-89.
Figure 8-88 Stopping Sight Distance on Approach to Roundabout
8.12.12.3 Visibility to the Left
Drivers of all vehicles at the "Give Way" line should be able to see the full width of the circulating
pavement to their left, from the "Give Way" line for an adequate distance "a" (measured along the
centerline of the circulating pavement as indicated in Table 8-61, and shown in Figure 8-89.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-148
Table 8-61 Visibility at Roundabouts
Inscribed Circle
Diameter
(m)
Visibility Distance “a”
(m)
Less than 40
Whole Intersection
40 to 60
40
More than 60 to 100
50
More than 100
70
The area which should be able to be seen from the centerline of the inner approach lane for a
distance of 15m back from the "Give Way" line is as shown in Figure 8-90.
These requirements apply to all roundabouts, including those with parapets on either side of the
circulating pavement. A check should also be made to ensure that the combination of cross slopes
and longitudinal grades does not restrict visibility.
Figure 8-89 Visibility to the Left from the “Give Way” Line
AUGUST 2010
REVISION NO. 03
ROADW AY 8-149
Figure 8-90 Visibility to the Left over the 15m before the Give Way Line
8.12.13 Entry Curbing
On uncurbed approach roads with or without shoulders, care should be taken when introducing the
curbs at the roundabout. Normally, the curb should be introduced at the back of the shoulder, with
the shoulder running out as a smooth curved length at an average rate not exceeding 1:10. Figure 891 and 8-92 show typical arrangements for undivided and divided roads.
Figure 8-91 Shoulder Run-out on an Undivided Road
AUGUST 2010
REVISION NO. 03
ROADW AY 8-150
Figure 8-92 Shoulder Run-out on a Divided Road
8.12.14 Safety at Roundabouts
Roundabouts generally have a lower accidents rate than signalized intersections handling similar
traffic flows. The severity of accidents at roundabouts is also considerably lower than at other types
of intersection.
The factor which has the greatest influence on safety at roundabouts is vehicle speed, at the entry or
within the roundabout. Geometric features that can have a major contributor effect in causing
excessive entry and circulating speeds are:
Inadequate entry deflection
A very small entry angle which encourages fast merging maneuvers with circulating traffic
Poor visibility to the "Give Way" line
More than four entries, necessitating a large roundabout configuration
Additional safety aspects to be considered when designing a roundabout layout include:
Visibility to the left at entry: This has comparatively little influence upon accident risk;
there is nothing to be gained by increasing visibility above the recommended level.
Crest Curves: Roundabouts should not be sited on crest curves, as this impairs forward
visibility and driver comprehension.
Speeds: A design which encourages entry to the roundabout at low speed and which
enables drivers to accelerate steadily on exit contributes significantly to safety, allowing
the intersection to be left clear for following road users. This can be achieved by adopting
smaller curb radii on entry and larger curb radii on exit.
In urban areas, when approach speeds are low, a ring of contrasting paving can be laid in a chevron
pattern inside the central island perimeter at a gentle slope, to aid roundabout visibility.
The provision of yellow Rumble Strips, in association with the advance signing for a roundabout may
be beneficial on fast approaches. In other countries, accident reductions of more than 50% have
been reported from similar markings.
AUGUST 2010
REVISION NO. 03
ROADW AY 8-151
9
Flexible Pavement Design Manual
9.1 Purpose
The objective of this manual is to provide the Engineer or Designer with sufficient information so that
the necessary input data can be developed and proper engineering principles applied to design a new
flexible pavement, or develop a properly engineered rehabilitation project. This design manual
addresses methods to properly develop a rehabilitation project, pavement milling, and the
computations necessary for the pavement design process.
The standards in this manual represent minimum requirements, which must be met for flexible
pavement design for new construction and pavement rehabilitation of HIB projects. Any variances
should be documented in project files.
Pavement design is primarily a matter of sound application of acceptable engineering criteria and
standards. While the standards contained in this manual provide a basis for uniform design practice
for typical pavement design situations, the Designer must also apply sound engineering judgment. It
is the responsibility of the Designer to insure that the designs produced conform to HIB policies,
procedures, standards, guidelines, and good engineering practices.
9.2 General
Effective pavement design is one of the more important aspects of project design. The pavement is
the portion of the highway which is most obvious to the motorist. The condition and adequacy of the
highway is often judged by the smoothness or roughness of the pavement. Deficient pavement
conditions can result in increased user costs and travel delays, braking and fuel consumption, vehicle
maintenance repairs and probability of increased crashes.
The pavement life is substantially affected by the number of heavy load repetitions applied, such as
single, tandem, tridem and quad axle trucks, buses, tractor trailers and equipment. A properly
designed pavement structure will take into account the applied loading. To select the appropriate
pavement type/treatment and properly design a pavement structure, the Designer must obtain
information from field investigations and input from HIB Engineer.
9.3 Design Process
To design a pavement structure properly, the designer must rely on his own expertise as well as that
of soils and planning engineers. Design process includes:
1.
Review Pavement Management Data to determine the appropriate scope of work
and treatment type (i.e. new pavement, reconstruction, reclamation, resurfacing, or
pavement preservation);
2.
Evaluate existing pavement to confirm the scope of work and determine preliminary
design and appropriate construction strategy. Research roadway history and traffic
data; verify existing pavement materials and structure. Perform field trips to make
site inspections, prepare a pavement condition checklist, communicate with
engineering and maintenance forces for history of roadway performance,
groundwater problems and other background information;
3.
Evaluate sub-base and sub-grade for drainage characteristics and bearing
capacity;
4.
Make structural calculations. The traffic, soils, and existing pavement data is used
to calculate specific pavement course requirements;
5.
Set specifications. The pavement materials, construction methods, and finished
project requirements must be both practical to attain and clearly defined. The
Designer must ensure that the plans, specifications, and estimate clearly and
unambiguously define the requirements.
9.4 References
The pavement design procedures contained in this manual are based on the 1972 AASHTO Interim
Guide as revised in 1981. These are the standard procedures to be followed for the design of all
pavement structures subject to this manual.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-1
For HMA structural resurfacing on expressways and other controlled access highways, the design
procedures contained in the 1993 AASHTO Guide for Design of Pavement Structures may be utilized.
The 1993 AASHTO Guide features the following:
Use of statistical reliability instead of the factor of safety design; and
Use of resilient modulus tests for soil support (a dynamic test) vs. CBR (a static test).
9.5
Pavement Types, Definitions and Abbreviations
Different types of pavement are commonly used in the construction of roadways. There are three
different types of pavement. These are:
Flexible Pavement
Rigid Pavement
Composite Pavement
Since Libya roadways are primarily asphalt pavement, the design for rigid and composite pavements
are not detailed in this manual.
9.5.1
Flexible Pavement
This manual outlines the design methods for flexible pavement (Hot Mix Asphalt (HMA) and also
known as bituminous concrete). A flexible pavement structure consists of the following layers – the
sub-base, base course, intermediate course, surface course, and where determined necessary, a
friction course.
The sub-base consists of granular material - gravel, crushed stone, reclaimed material or
a combination of these materials.
The base course is a granular layer placed upon the compacted sub-base (suitable for
warm weather). A Hot Mix Asphalt (HMA) base course can also be used depending upon
weather temperature. A gravel base course can be designed and specified for low
volume roadways (<2,000 vehicles per day) depending upon loading and other design
considerations.
The intermediate (binder) course is an HMA pavement layer placed upon the base
course.
The surface (wearing) course is the top HMA pavement layer and is placed upon the
intermediate course.
A friction course is a specialized thin-lift wearing course which, when specified, is
placed over the surface course. Friction courses provide improved vehicle skid
resistance, but do not provide any structural value to the pavement. Typically friction
courses are placed on high volume limited access roadways.
Typical cross-sections illustrating the pavement courses for low traffic volume pavements and high
traffic volume pavements are shown in Figure 9-1.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-2
Figure 9-1 Pavement Courses for Flexible Pavement Structure
9.5.2
Pavement Design Terms and Definitions
The following terms and abbreviations are commonly used in pavement design.
Binder – The liquid asphalt material in an HMA mixture that bonds the aggregate
together.
Equivalent Single Axel Load (ESAL) – The conversion of mixed vehicular traffic into its
equivalent single-axle, 80 kN Load. The equivalence is based on the relative amount of
pavement damage.
Daily ESAL (T80) – The average number of equivalent 80 kN loads which will be applied
to the pavement structure in one day. Normally, a 20-year design period is used to
determine the daily load.
ESAL Applications per 1000 Trucks and Combinations – A factor which reflects the
relative mix of sizes and weights of trucks on various classes of highways (e.g., freeways,
arterials, collectors, and local streets). Truck percentages typically exclude two-axle, fourtire pickup trucks, the effect of which may be ignored.
Pavement Serviceability Index (PSI) – A measure of a pavement's ability to serve traffic
on a scale of 0 to 5. It reflects the extent of pavement condition.
Terminal Serviceability Index (Pt) – A pavement design factor which indicates the
acceptable pavement serviceability index at the end of the selected design period (usually
20 years).
Sub-grade – The undisturbed virgin substrate or embankment material which the
pavement structure is placed upon.
Bearing Ratio – The load required to produce a certain penetration using a standard
piston in a soil, expressed as a percentage of the load required to force the piston the
same depth in a selected crushed stone. Bearing Ratio values are normally determined
using the California Bearing Ratio (CBR) text method.
Design Bearing Ratio (DBR) – The selected bearing ratio used to design the pavement.
It is based on a statistical evaluation of the CBR test results on the soil samples.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-3
Soil Support Value (SSV) – An index of the relative ability of a soil or stone to support
the applied traffic loads. It is specifically used for the pavement design method in the
AASHTO Interim Guide for Design of Pavement Structures. The soil support value of the
sub-grade is related to its CBR (DBR).
Structural Number (SN) – A measure of the structural strength of the pavement section
based on the type and thickness of each layer within the pavement structure.
Layer Coefficient – The relative structural value of each pavement layer per millimeter of
thickness. It is multiplied by the layer thickness to provide the contributing SN for each
pavement layer.
Skid Resistance – A measure of the coefficient of friction between an automobile tire
and the roadway surface.
Designer – The consultant under contract to HIB or the municipality.
Table 9-1 Equivalent 80 kN axle applications per 1000 trucks flexible pavements (ESAL)
Highway Class
ESAL
Freeways/Expressways
1100
Major Arterial
880
Minor Arterial (Urban and Suburban)
880
Minor Arterial (Rural)
660
Collector (Urban and Suburban)
880
Collector (Rural)
660
Local Roads
660
9.6 Typical Pavement Design Procedures For 30% Submittal
Figure 9-2 illustrates the pavement design steps associated with the 30% submittal. All pavement
designs are determined by the Designer with the HIB Engineer responsible for reviewing and
approving all pavement designs. The major tasks in the design process are presented in the following
figure.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-4
Figure 9-2 30% Design Activities
9.6.1
Step 1 – Determine Scope of Work
The Designer will determine the appropriate scope of work for the pavement design. This can be a
new pavement, reconstruction, reclamation, resurfacing, pavement preservation, pedestrian/bicycle
facility, or a combination of work. The scope of work may or may not include widening or corrective
work to the existing pavement. To determine the scope of work for existing pavements (i.e. all work
other than new pavement) the Designer shall review existing pavement data and/or perform
pavement sampling. Pavement reports will identify the apparent scope of pavement treatment
required.
9.6.1.1
New Pavement
New pavement is a pavement structure placed on a prepared sub-grade. It applies to new highway
construction, to a relocated highway, or to the new part of a widened highway.
9.6.1.2
Pavement Reconstruction
Reconstructed pavement or full depth reconstruction results when an existing pavement structure is
completely removed to the sub-grade and replaced with a new pavement structure. This type of work
is needed when the existing pavement has deteriorated to such a weakened condition that it cannot
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-5
be salvaged with corrective action. The type and extent of pavement distress will determine when
pavement reconstruction is necessary.
9.6.1.3
Pavement Reclamation
Reclaimed pavement reuses an existing pavement structure through the pulverizing and mixing of the
existing pavement and granular sub- base into a gravel base material to be overlaid with new HMA
layers. The reclamation method is usually performed on site.
9.6.1.4
Pavement Resurfacing
Pavement resurfacing consists of placing the needed thickness of hot mix asphalt on an existing
pavement. The resurfacing will return the pavement to a high level of serviceability and provide the
necessary structural strength for the pavement design period.
9.6.1.5
Pavement Preservation
Pavement Preservation involves the application of properly timed surface treatments to ensure that
pavements in good condition will remain in good condition. Preservation treatments extend the
pavement service life, but generally provide no structural strength.
9.6.2
Step 2 – Collect Basic Project Data
The designer must collect the basic project data listed in the Pavement Design Checklist included in
Attachment 9-1 at the end of this manual along with a Field Inspection Report, as described below.
9.6.2.1
Project Identification
Provide the project location information and project design engineer.
9.6.2.2
Traffic Data
At a minimum, the following traffic data is required:
Current ADT, (ADT for year of proposed opening to traffic);
Projected ADT (20 years);
ADT truck percentage;
Number of lanes;
Divided/undivided; and
Source of traffic data.
9.6.2.3
Existing Pavement Information
The thickness and type of each pavement layer (i.e., surface course, intermediate course, base
course, sub-base) and sub-grade information shall be recorded. This data is necessary for proper
design and analysis of the pavement structure for all types of projects. Base plans and profiles should
also be obtained for purpose of pavement design.
9.6.2.4
Field Inspection Report
A field inspection report must also be prepared which includes the general condition of the roadway.
The field report should note pavement deficiencies including type of distress, extent of distress and
severity of distress (See Attachment 9-1). The report should also include other field observations such
as; adequacy of drainage, presence of curbing, edging, berm or shoulder condition, sidewalks, curb
cuts and driveways, and any other characteristic that may be pertinent to the analysis of the existing
pavement and scope of work. The Designer should also research and document known problems with
the existing pavement through discussion with field maintenance personnel.
9.6.3
Step 3 – Determine Design Bearing Ratio (DBR)
Table 9-2 summarizes the recommended action to determine the Design Bearing Ratio based on the
Daily ESAL (T80). Projects having T80 values less than 15 should use the minimum design for the
roadway’s classification (refer to Table 9-6). Projects having T80 values between 15 and 120 should
use DBR values based on AASHTO soils classification as shown in Table 9-3. Projects having T80
values greater than 120 will require AASHTO soils classifications and CBR testing. Soil classification
data and CBR test data should be used for DBR determination.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-6
Table 9-2 Design Bearing Ratio Determination
Value From Line (h) of
Data Sheet 1 (T80)
Action
T80 < 15
Use Minimum Design (See Table 9-6)
15 < T80 < 120
Assume DBR based on Soil
Classifications from Table 9-3
T80 > 120
AASHTO soils classification and CBR
test results to be used for DBR
determination
Table 9-3 DBR Based on AASHTO Soils Classification
9.6.4
Step 4 – HIB Reviews Scope of Work and DBR Determination
9.6.4.1
HIB Engineer Reviews Scope of Work
The HIB Engineer will review the Designer's recommendation, scope of pavement work, the
preliminary pavement design, traffic data and the pavement checklist documenting the engineered
design solution. The HIB Engineer will provide comments on the scope of work and the preliminary
pavement design.
9.6.4.2
HIB Engineer Approves DBR as Submitted
The HIB Engineer will approve the Design Bearing Ratio used for the design. He will approve, reject,
modify or request additional sampling and testing.
9.6.4.3
Use DBR from Previous Work
If it is available and still applicable, the Designer will use the DBR used for the original pavement
design or any previous pavement resurfacings before submittal to HIB.
9.6.4.4
Subsurface Exploration for New Pavements
For new pavements, the Designer must perform a subsurface exploration to determine the soil
gradation, properties and stratification data. The Designer will prepare soil exploration method and
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-7
plan which will include test pit, pavement cores, etc. the required number and their locations. This
information is to be in written form and shown on project base plans.
9.6.5
Step 5 - HIB Reviews/Comments on the 30% Design
The HIB will review and comment on the 30% Design recommendation from the Design Engineer.
9.7 New and Reconstructed Pavement
This section specifies the HIB procedure for determining the detailed design of a new or reconstructed
pavement. This procedure applies to HMA pavements only. HIB uses the AASHTO Interim Guide for
Design of Pavement Structures as the basic design methodology. However, HIB has incorporated
some modifications to the Guidelines procedures to reflect specific conditions in Libya and to simplify
the procedure.
The Pavement Design Form – New or Reconstructed Pavements (cover sheet and data sheets 1
through 3) are included in Attachment 9-2. This form must be completed by the Designer and
submitted to the HIB at the 30% Submittal.
9.7.1
Pavement Design Cover Sheet
The following information must be recorded on the cover sheet:
Enter the project identification data at the top of the cover sheet.
Summarize the recommended pavement design by documenting the surface, base, and
sub-base data. List the depths, type of layer, and recommended lifts.
Describe the special borrow, if required for the project. Special borrow may be necessary
where the existing sub-grade is susceptible to frost penetration within the typical frost
penetration depth. If this subsurface condition exists, subsurface exploration and soil
analysis may be warranted. The Designer will recommend the type and depth of special
borrow to be used for frost control. Special Borrow is generally placed on freeways and
arterial routes. Consideration for placement on other roads will depend on functional
classification, traffic volumes, presence of utilities, construction methods, etc.
9.7.2
Data Sheet 1: Pavement Structural Design Data
Data Sheet 1 includes the following information:
Line (a): Enter the anticipated (current) ADT for date of opening.
Line (b): Enter the future ADT. Generally the design period for pavements is 20 years;
however there may be occasions when the traffic information submitted does not cover
the design period. In these cases the future ADT is to be estimated by approved
methods. Under certain circumstances, pavements may be designed for periods of less
than 20 years.
Line (c): Calculate the average ADT during the design period.
Line (d): Calculate the average ADT in one direction.
Line (e): Enter the truck percentage for the ADT.
Line (f): Calculate the average daily truck volume in one direction.
Line (g): Enter the equivalent 80 kN axle application per 1,000 trucks and combinations.
(See Table 9-1)
Line (h): Calculate the number of 80 kN axle loads per day in one direction (T80).
9.7.3
Design Bearing Ratio (DBR) Determination
Use the value on Line (h) (T80) and Table 9-2 to determine the sub-grade or Sub-base DBR. The
Designers make a general computation of the sub-grade or sub-base DBR for reviews by the HIB
Engineer.
9.7.4
Data Sheet 2: Determining Structural Number (SN)
The following steps are required to determine the structural number (SN):
Step 1: Determine the design lane equivalent daily 80 kN applications based on the
number of lanes.
Step 2: Determine the DBR for the sub-grade from Table 9-2 and 9-3. The sub-base DBR
is 40 for the typical sub-base on new or reconstructed pavements (gravel).
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-8
Step 3: Determine the soil support value (SSV). Figure 9-3 illustrates the relationship
between the DBR and SSV.
Step 4: Determine the required structural number (SN) above the sub-base and above
the sub-grade. Figure 9-4 should be used. Use the design-lane T80 from Step 1 for the
daily equivalent 80 kN single axle load. Use the SSV from Step 3 for the soil support
value.
Step 5: Increase the SN by 15% to determine the design SN to adjust for climatic and
other environmental conditions.
Figure 9-3 DBR vs. SSV
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-9
Figure 9-4 Structural Number (SN) Nomograph (For Flexible Pavement P = 2.5)
Source: Interim Guide for Pavement Structures. AASHTO, 1972
9.7.5
Data Sheet 3: Pavements Structural Number (SN)
By trial and error, the designer will select the most cost-effective design that provides the required SN
for the highway conditions. The designer should also consider minimum and maximum lift thicknesses
and the logistics of construction procedures when designing the pavement design combinations using
this procedure.
Step 1: Select each pavement layer component and the thickness of each layer.
Step 2: From Table 9-5 select the layer coefficient for each pavement layer.
Step 3: Determine the contributing SN for each pavement layer by multiplying the layer
coefficient by its thickness.
Step 4: The minimum thicknesses of each layer are noted on Table 9-6.
Step 5: Check to ensure that the required SN is provided above the sub-base and the
sub-grade. If not, increase the layer thickness as necessary. If the trial design exceeds
the required SN, reduce the layer thicknesses.
Step 6: Determine several alternate pavement designs which satisfy the SN
requirements. The selected design will be based on economics.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-10
Step 7: Regardless of the calculations from the pavement design analysis, the minimum
design thickness should not be less than those shown in Table 9-6.
Table 9-4 Pavement Thickness
Table 9-5 Layer Coefficients for New and Reconstructed Pavements
AUGUST 2010
Placement Component
Layer Coefficient (per mm)
Surface Course:
Hot Mix Asphalt Riding Surface and Binder
1.73 x 10-2
Base Course:
Crushed Stone (Dense Graded), or
Hot Mix Asphalt
0.55 x 10
-2
1.34 x 10
Subbase:
Crushed Stone (Dense Graded)
Gravel
0.55 x 10-2
-2
0.43 x 10
REVISION NO. 03
-2
FLEXIBLE PAVEMENT DESIGN MANUAL 9-11
Table 9-6 Minimum Pavement Thickness (New and Reconstructed Flexible Pavements)
Highway Type and Pavement
Course
Thickness
Layer
(mm)
Coefficient
SN
Expressway
50
0.0173
0.86
Arterial
45
0.0173
0.78
Collector & Local
45
0.0173
0.78
50
0.0173
0.86
Expressway
50
0.0173
0.86
Arterial
50
0.0173
0.86
Collector & Local
50
0.0173
0.86
Expressway
70
0.0134
0.94
Arterial
50
0.0134
0.67
Collector & Local
-
-
-
Low volume
70
0.0134
0.94
Expressway
200
0.0055
1.10
Arterial
200
0.0055
1.10
Collector & Local
200
0.0055
1.10
Expressway
200
0.0043
0.86
Arterial
200
0.0043
0.86
Collector & Local
250
0.0043
1.08
Low volume
250
0.0043
1.08
HMA Surface Course (Wearing)
Low volume
1
HMA Intermediate Course
(Binder)
HMA - Base 1 *
Crushed Stones - Base 2 *
Gravel Sub-base **
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-12
Highway Type and Pavement
Course
Thickness
Layer
(mm)
Coefficient
SN
Expressway
-
-
4.62
Arterial
-
-
4.27
Collector & Local
-
-
3.82
Low volume
-
-
2.88
Total Structural Number
1 Low volume design can be used on residential roads and parking lots in housing projects.
* Thicknesses for Base 1 and Base 2 can simultaneously be changed to produce the same overall SN.
** Subbase may not be used if soil conditions show an adequate subgrade that provides the required SN.
The above table is only valid when the conventional design calculations indicate a required pavement
structure less than the above. All pavement thicknesses shall be designed as detailed here. The use
of crushed stone as part of the base course makes a firmer base for the paving machines and
reduces the amount of gravel required. Gravel gives a structural support (though it is weaker than
crushed stone), and provides better drainage.
9.8 Reclamation
For reclaimed pavements, the Designer will determine the depth of reclamation required. A minimum
300 mm granular base or sub-base course must be provided beneath the HMA pavement courses.
The detailed procedure is as outlined in the HIB Master Specifications. The Designer must complete
the Pavement Design Form – New and Reconstructed Pavements in accordance with Section 9.6
above.
9.9 Pavement Resurfacing
A pavement resurfacing can be used if the Designer determines that an existing pavement is in
reasonably good condition. A pavement resurfacing may be in conjunction with roadway widening
and/or corrective work to the existing pavement. The Pavement Resurfacing Design Form and a
completed example (cover sheet and data sheets 1 to 3) are included in Attachment 9-3. The depth of
HMA resurfacing will be determined by the following procedure.
9.9.1
Pavement Resurfacing Design Cover Sheet
The following must be recorded on the Pavement Resurfacing Design Coversheet:
Enter the project identification data at the top of the cover sheet.
Document the existing pavement structure before resurfacing.
Record the recommended pavement resurfacing thickness.
9.9.2
Data Sheet 1: Pavement Structural Design Data
Data Sheet 1 should be completed using the following procedure:
Line (a): Enter the current ADT.
Line (b): Enter the future ADT, usually for 20 years beyond the current. Note that the
traffic data available may not correspond to the dates in Lines (a) and (b). If not, the
designer should assume a uniform straight-line increase between the data. This
assumption can then be used to determine the traffic volumes in Lines (a) and (b).
Line (c): Calculate the average ADT during the design period.
Line (d): Calculate the average ADT in one direction.
Line (e): Enter the truck percentage for the ADT.
Line (f): Calculate the average daily truck volume in one direction.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-13
Line (g): Enter the equivalent 80 kN axle application per 1,000 trucks and combinations
(See Table 9-1).
Line (h): Calculate the number of 80 kN axle loads per day in one direction (T80).
Line (i): Calculate the design lane equivalent daily 80 kN applications based on number
of lanes.
Line (j): Enter the sub-grade DBR and SSV.
Line (k): Determine the required SN above the sub-grade from Figure 9-4.
Line (l): Determine the design SN by increasing the SN by 15%.
Table 9-7 Layer Coefficients for Existing Pavements
Table 9-8 Reduction Factors for Existing Pavement
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-14
9.9.3
Data Sheet 2: Actual SN of Existing Pavement
The following steps are required to complete Data Sheet 2:
Line (a): Enter the SSV of the existing pavement elements. The SSV for the penetrated
crushed stone base, the sand bound crushed stone base, and the gravel sub-base are
usually assumed as shown. However, if laboratory-determined DBR results are available,
these values should be used. Enter the SSV for the sub-grade from Line (j) of Data Sheet
1.
Line (b): Determine the SN of the existing pavement. Follow these steps:
i
Table 9-5 provides the layer coefficient for each layer component for a new
pavement.
ii The coefficients in Table 9-7 should be multiplied by a reduction factor (RF)
from Table 9-8. The RF will be based on a visual survey of the type and extent
of distress in the existing pavement. The RF will apply even if corrective work is
performed on the existing pavement.
iii The contributing SN for each layer is calculated by multiplying its depth by the
layer coefficient and RF.
iv The total SN is found by summing the SN of each pavement layer.
Line (c): Determine the actual SN above each layer of the existing pavement. The SN for
each layer is entered in the appropriate column. The "Total SN" reflects the cumulative
SN above each pavement layer.
9.9.4
Data Sheet 3: Determination of Resurfacing Thickness
The following steps are needed to complete Data Sheet 3:
Line (a): Determine the required SN above each layer of the existing pavement using
Figure 9-4. The values from Line (i) on Data Sheet 1 and from Line (a) of Data Sheet 2
are used in the figure. The SN values from Figure 9-4 are increased by 15% to determine
the design SN.
Line (b): Determine the SN deficiency for each layer for the existing pavement. The
required SN from Line (a) of Data Sheet 3 is entered in the first column. Enter the value
from Line (c) of Data Sheet 2 in the second column. The first column SN minus the
second column SN yields the SN difference, which is entered in the third column. (Note: A
negative value indicates there is no SN deficiency for that pavement layer.)
Line (c): The largest SN deficiency from the table in Line (b) is used to determine the
thickness of the pavement resurfacing. The SN per mm is 0.0173 for the Hot Mix Asphalt
surface course. Regardless of the calculation, the minimum overlay thickness is 50 mm
for modified top course.
9.10 Limited Access Highway Pavement Resurfacing Design
When designing structural resurfacings on limited access highways, the Designer may elect to use
non-destructive testing to determine the appropriate resurfacing. The following general parameters
are considered the minimum standards for these roadways:
9.10.1
Design Method
Both a layered component analysis and non-destructive testing analysis should be reviewed to
calculate the effective existing SN.
9.10.2
Serviceability
An initial serviceability no greater than 4.5 should be assumed. A terminal serviceability no greater
than 2.75 should be selected.
9.10.3
Reliability
Traffic disruption and congestion associated with construction operations result in significant user
costs. Increased design reliability helps reduce these user costs. Thus, reliability levels approaching
99.9 percent are used to design structural resurfacings on the Highway System. Reliability levels
approaching 99.5 percent should be used to design structural resurfacings on other limited access
highway.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-15
9.10.4
Back-Calculation
Non-destructive testing must be analyzed to determine the resilient modulus of the soil. Because
differing stress states occur between field conditions and lab conditions, a correction factor must be
used to convert field-determined modulus values to lab values for design calculations. For granular
soils, a resilient modulus correction factor (C) of 0.33 shall be used. Depending upon the project, the
back-calculated resilient modulus values of the sub-grade could vary significantly. Extremely high
modulus values could be indicative of subsurface irregularities such as shallow bedrock or
groundwater. To minimize the possibility of such erroneous modulus values, only modulus values
within one standard deviation of the mean should be used to calculate the average resilient modulus
for design purposes.
9.10.5
1993 AASHTO Pavement Resurfacing Design
Once the non-destructive testing has been analyzed and the future traffic loadings have been
determined, the Designer will determine the required future structural number.
9.11 Typical Pavement Design for Low Volume Roads
In this revision of the Guidelines, the minimum pavement cross section has been reduced for low
volume roads (2,000 AADT maximum). This new minimum cross section reduces the thickness of
HMA base course and provides for the placement of Gravel base course in its place. These revisions
are reflected in Table 9-6 Minimum Pavement Thickness (New and Reconstructed Flexible
Pavements).
9.11.1
Design Procedures
For the purpose of designing pavements on low volume roadways, the Designer should begin with the
minimum low volume roadway cross section. This design should be adequate for virtually all
roadways less than 1,000 AADT and most roadways less than 2,000 AADT and 3% truck traffic. If the
design calculations indicate that a greater thickness is required, then the Designer should adjust the
pavement layer thickness accordingly.
9.12 For Further Information
Interim Guide for Design of Pavement Structures, AASHTO, 1972 (Revised 1993).
Layered Pavement Design Method for Massachusetts, Massachusetts Department of
Public Works and Massachusetts Institute of Technology (MIT), January, 1965.
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-16
Attachment 9-1 Pavement Design Checklist
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-17
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-18
Attachment 9-2 New or Reconstructed Pavement Form
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-19
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-20
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-21
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-22
Attachment 9-3 Overlay Design Form
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-23
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-24
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-25
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-26
Attachment 9-4 Sample Problems and Completed Forms
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-27
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-28
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-29
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-30
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-31
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-32
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-33
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-34
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-35
AUGUST 2010
REVISION NO. 03
FLEXIBLE PAVEMENT DESIGN MANUAL 9-36
10 Uniform Traffic Control Devices
All traffic control devices shall be in accordance with the Traffic and Licensing Department of Libya.
The Traffic and Licensing Department adopted the requirements of “Manual on Uniform Traffic Control
Devices” by Kingdom of Saudi Arabia, Ministry of Communications. This manual should be used for
traffic signs, pavement markings, traffic signals, traffic control for work areas, traffic control for school
areas, and traffic control for railroad grade crossings. The following additional requirements should
be used in traffic control for work areas.
10.1 Traffic Control for Work Area (Supplements)
The safety of road users, which include drivers, pedestrians and bicyclists, as well as personnel in
work zones, should be an integral and high priority element of every project in the planning, design,
construction, and maintenance phases. All projects and works on highways, roads, and streets shall
have a traffic management plan. All work shall be executed under HIB approved procedures and
shall require approval by CM/CS. This document contains supplemental information to Part 5 of the
“Manual on Uniform Traffic Control Devices” by Kingdom of Saudi Arabia (MUTCD) and contains
guidelines and standards for the preparation of traffic management plans and for the execution of
traffic control in work zones, for construction and maintenance operations and utility work on
highways, roads, and streets in all regions of Libya. Typical applications for various situations are
provided at the end of this document. Modification can be made to these details as long as the
changes comply with design standards set forth in the MUTCD and as required by HIB and the
CM/CS. The sign spacing shown on the details is typical (recommended) distances. These distances
may be increased or decreased based on field conditions, in order to avoid conflicts or to improve site
specific traffic controls.
10.2 ROADWAY CONSTRUCTION
10.2.1
Corridor and Network-wide Constructions
Roadway construction can range from a site-specific construction to corridor construction, and even to
an overall network construction program. As work activities are developed at the construction site,
they affect the overall corridor construction staging, traffic movements, number of lanes used, utilities,
and pedestrian access. To determine the number of lanes to be maintained within the construction
zone, it would depend on the existing level of service of the roadway and how that affects the whole
corridor function. Also to maintain traffic mobility, alternative roadways or detours can be used to
bypass the construction sites. Based on local conditions, the local authority can sacrifice mobility in
order to expedite the construction. See Figures 10a – 10d at the end of this document for examples
of construction layout plans.
For a network-wide construction program, various construction projects must be coordinated
concurrently and on schedule, as the case here with the ongoing construction projects in all regions of
Libya. A key tool for this coordination is the development and implementation of a traffic monitoring
system which would include traffic sensors, cameras, variable message signs, and other traffic
monitoring tools that can be integrated into a local traffic management system, See Figure 10-1. The
purpose of the traffic monitoring system is to track the traffic conditions and evaluate the impacts of
construction throughout the network which will in turn be used in the scheduling and coordinating of
other projects to minimize conflicts and maintain a reasonable level of service for both the travelling
public and the pedestrians. A traffic model is essential for simulating traffic conditions in the network
construction program based on different scenarios of lane or road closures and their impacts.
10.2.2
Authority
A traffic management plan that would address traffic mobility, safety, local and pedestrian access
must be enforced by local authorities with jurisdiction over the regulations of the roadway to make
sure that the plan is implemented properly. There shall be adequate statutory authority for the
implementation and enforcement of needed road user regulations, parking controls, speed zoning,
and the management of traffic incidents. Such statutes shall provide sufficient flexibility in the
application of Temporary Traffic Control (TTC) to meet the needs of changing conditions in the TTC
zone.
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-1
Figure 10-1 Network Traffic Management Program
10.3 Traffic Control Zones
The primary function of Temporary Traffic Control is to provide for the reasonably safe and efficient
movement of road users through or around traffic control zones during project construction while
reasonably protecting workers, responders to traffic incidents, and equipment.
Of equal importance to the public traveling through the traffic control zone is the safety of workers,
performing the many varied tasks within the work space. Traffic control zones present constantly
changing conditions that are unexpected by the road user. This creates an even higher degree of
vulnerability for the workers and incident management responders on or near the roadway. At the
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-2
same time, the traffic control zone provides for the efficient completion of whatever activity interrupted
the normal use of the roadway.
The following principles must be applied to temporary traffic control zones:
Traffic movement should be disrupted as little as possible, with the proper closure,
transition, and speed reduction configurations.
Road users should be guided in a clear and positive manner while approaching and
within construction, maintenance, and utility work areas.
Routine inspection and maintenance of traffic control elements should be performed both
day and night.
Both the Contractor and CM/CS should assign at least one person on each project to
have day-to-day responsibility for assuring that the traffic control elements are operating
effectively and any needed operational changes are brought to the attention of their
supervisors.
The Contractor shall comply with all local police regulations and authorities in Libya for
traffic management and traffic control configuration in work zones.
Special plans preparation and coordination with transit, other highway agencies, law
enforcement and other emergency units, utilities, and schools might be needed to reduce
unexpected and unusual road user operation situations.
Contractors of adjacent constructions shall coordinate construction staging, lane closures,
and traffic shifting.
During TTC activities, commercial vehicles might need to follow a different route from
passenger vehicles because of bridge, weight, clearance, or geometric restrictions. Also,
vehicles carrying hazardous materials might need to follow a different route from other
vehicles.
Traffic management in temporary traffic control zones should be designed on the
assumption that road users will only reduce their speeds if they clearly perceive a need to
do so, and then only in small increments of speed.
TTC zones should not present a surprise to the road user. Frequent and/or abrupt
changes in geometrics and other features should be avoided. Transitions should be well
delineated and long enough to accommodate driving conditions at the speeds vehicles
are realistically expected to travel.
A Traffic Management Plan (TMP) should be used for a temporary traffic control zone to
specify particular traffic control devices and features, or to reference typical drawings
such as those contained in this manual. The TMP should start in the planning phase and
continue through the design, construction, and restoration phases.
Applications of speed reduction countermeasures and enforcement can be effective in
reducing traffic speeds in temporary traffic control zones.
10.3.1
Application
Planned work phasing and sequencing should be the basis for the use of traffic control devices for
temporary traffic control zones. This manual should be consulted for specific traffic control
requirements and examples where construction or maintenance work is planned.
10.3.2
Guideline
General plans or guidelines should be developed to provide safety for motorists, bicyclists,
pedestrians, workers, enforcement/emergency officials, and equipment, with the following factors
being considered:
The basic safety principles governing the design of permanent roadways and roadsides
should also govern the design of TTC zones. The goal should be to route road users
through such zones using roadway geometrics, roadside features, and TTC devices as
nearly as possible comparable to those for normal highway situations.
A TMP, in detail appropriate to the complexity of the work project or incident, should be
prepared and understood by all responsible parties before the site is occupied. Any
changes in the TMP should be approved by an official knowledgeable (for example,
trained and/or certified) in proper TTC practices.
Road user movement should be inhibited as little as practical, based on the following considerations:
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-3
TTC at work and incident sites should be designed on the assumption that drivers will
only reduce their speeds if they clearly perceive a need to do so.
Frequent and abrupt changes in geometrics such as lane narrowing, dropped lanes, or
main roadway transitions that require rapid maneuvers, should be avoided.
Provisions should be made for the reasonably safe operation of work, particularly on highspeed, high-volume roadways.
Road users should be encouraged to use alternative routes that do not include TTC
zones.
Bicyclists and pedestrians, including those with disabilities, should be provided with
access and reasonably safe passage through the TTC zone.
Roadway occupancy should be scheduled during off-peak hours and, if necessary, night
work should be considered.
Early coordination with officials having jurisdiction over the affected cross streets and
providing emergency services should occur before roadway or ramp closings.
Motorists, bicyclists, and pedestrians should be guided in a clear and positive manner while
approaching and traversing TTC zones and incident sites. The following principles should be applied:
Adequate warning, delineation, and channelization should be provided to assist in guiding
road users in advance of and through the TTC zone or incident site by using proper
pavement marking, signing, or other devices that are effective under varying conditions.
Providing information that is in usable formats by pedestrians with visual disabilities
should also be considered.
TTC devices inconsistent with intended travel paths through TTC zones should be
removed or covered. However, in intermediate-term stationary, short-term, and mobile
operations, where visible permanent devices are inconsistent with intended travel paths,
devices that highlight or emphasize the appropriate path should be used. Providing traffic
control devices that are accessible to and usable by pedestrians with disabilities should
be considered.
Flagging procedures, when used, should provide positive guidance to road users
traversing the TTC zone.
To provide acceptable levels of operations, routine day and night inspections of TTC elements should
be performed as follows:
Individuals who are knowledgeable (for example, trained and/or certified) in the principles
of proper
TTC should be assigned responsibility for safety in TTC zones. The most important duty
of these individuals should be to check that all TTC devices of the project are reasonably
consistent with the TMP and are effective in providing reasonably safe conditions for
motorists, bicyclists, pedestrians, and workers.
As the work progresses, temporary traffic controls and/or working conditions should be
modified in order to provide reasonably safe and efficient road user movement and to
provide worker safety. The individual responsible for TTC should have the authority to
halt work until applicable or remedial safety measures are taken.
TTC zones should be carefully monitored under varying conditions of road user volumes,
light, and weather to check that applicable TTC devices are effective, clearly visible,
clean, and in compliance with the TMP.
When warranted, an engineering study should be made (in cooperation with law
enforcement officials) of reported crashes occurring within the TTC zone. Crash records
in TTC zones should be monitored to identify the need for changes in the TTC zone.
Attention should be given to the maintenance of roadside safety during the life of the TTC zone by
applying the following principles:
To accommodate run-off-the-road incidents, disabled vehicles, or emergency situations,
unencumbered roadside recovery areas or clear zones should be provided where
practical.
Channelization of road users should be accomplished by the use of pavement markings,
signing, and crashworthy, detectable channelizing devices.
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-4
Work equipment, workers' private vehicles, materials, and debris should be stored in such
a manner to reduce the probability of being impacted by run-off-the-road vehicles.
10.3.3
Traffic Management Plans
A TMP describes traffic control measures to be used for facilitating road users through a work zone or
an incident area. Traffic management plans play a vital role in providing continuity of reasonably safe
and efficient road user flow when a work zone, incident, or other event temporarily disrupts normal
road user flow.
TMPs range in scope from being very detailed to simply referencing typical drawings, as shown in this
document, and standard approved highway agency drawings and manuals, or specific drawings
contained in the contract documents. The degree of detail in the TMP depends entirely on the nature
and complexity of the situation. The TMP components would typically include the following:
General Layout – overall construction sequencing of the project.
Legends and Abbreviations – To identify the symbols and abbreviations shown on the
plans.
Construction Phasing Plans – detailed construction staging showing work zones, traffic
movements, channelizing devices and staging notes.
Staging Sections – sections showing the work staging and sequencing with emphasis
on buffer width, vertical difference, treatment of temporary conditions and safety
measures. Staging notes can be shown with the sections or on the phasing plans.
Temporary Profiles – In some cases, a temporary profile is necessary to meet an interim
condition of roadway construction. The profile must be shown with all its geometric
values.
Detour Plans – location plans showing the detours to where traffic is diverted to bypass
construction area. The plans include all necessary detour, street names, and arrow
signs.
Miscellaneous Details – details of temporary treatments, special details, and traffic
control devices, which can be referenced to in this manual.
Factors that must be considered in the TMP planning and preparation:
TMPs should be prepared by persons knowledgeable about the fundamental principles of
TTC and work activities to be performed. The design, selection, and placement of TTC
devices for a TMP should be based on engineering judgment.
Coordination should be made between adjacent or overlapping projects to check that
duplicate signing is not used and to check compatibility of traffic control between adjacent
or overlapping projects in terms of lane closure, transition, and traffic shifting.
Traffic control planning should be completed for all highway construction, utility work,
maintenance operations, and incident management including minor maintenance and
utility projects prior to occupying the TTC zone. Planning for all road users should be
included in the process.
Provisions for effective continuity of accessible circulation paths for pedestrians should be
incorporated into the TTC process. Where existing pedestrian routes are blocked or
detoured, information should be provided about alternative routes that are usable by
pedestrians with disabilities, particularly those who have visual disabilities.
Access to temporary bus stops, reasonably safe travel across intersections with
accessible pedestrian signals, and other routing issues should be considered where
temporary pedestrian routes are channelized. Barriers and channelizing devices that are
detectable by people with visual disabilities should be provided.
Provisions may be incorporated into the project bid documents that enable contractors to
develop an alternate TMP.
Modifications of TMPs may be necessary because of changed conditions or a
determination of better methods of safely and efficiently handling road users.
This alternate or modified plan should have the approval of the responsible highway agency prior to
implementation.
Provisions for effective continuity of transit service should be incorporated into the TTC planning
process because often public transit buses cannot efficiently be detoured in the same manner as
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-5
other vehicles (particularly for short-term maintenance projects). Where applicable, the TMP should
provide for features such as accessible temporary bus stops, pull-outs, and satisfactory waiting areas
for transit patrons, including persons with disabilities, if applicable.
Reduced speed limits should be used only in the specific portion of the TTC zone where conditions or
restrictive features are present. However, frequent changes in the speed limit should be avoided. A
TMP should be designed so that vehicles can reasonably safely travel through the TTC zone with a
speed limit reduction of no more than 16 km/h.
A reduction of more than 16 km/h in the speed limit should be used only when required by restrictive
features in the TTC zone. Where restrictive features justify a speed reduction of more than 16 km/h,
additional driver notification should be provided. The speed limit should be stepped down in advance
of the location requiring the lowest speed, and additional TTC warning devices should be used.
Reduced speed zoning (lowering the regulatory speed limit) should be avoided as much as practical
because drivers will reduce their speeds only if they clearly perceive a need to do so.
10.3.4
Components of Temporary Traffic Control Zones
Most TTC zones are divided into four areas: the Advance Warning Area, the Transition Area, the
Activity Area, and the Termination Area. Figure 10-2 illustrates these four areas. These four areas
are described in the following sections.
10.3.4.1 Advance Warning Area
The advance warning area is the section of highway where road users are informed about the
upcoming work zone or incident area.
The advance warning area may vary from a single sign or high-intensity rotating, flashing, oscillating,
or strobe lights on a vehicle to a series of signs in advance of the TTC zone activity area.
Typical distances for placement of advance warning signs on freeways and expressways should be
longer because drivers are conditioned to uninterrupted flow. Therefore, the advance warning sign
placement should extend on these facilities as far as 800 m or more.
On urban streets, the effective placement of the first warning sign in meters should range from 0.75 to
1.5 times the speed limit in km/h, with the high end of the range being used when speeds are
relatively high. When a single advance warning sign is used (in cases such as low-speed residential
streets), the advance warning area can be as short as 30 m. When two or more advance warning
signs are used on higher-speed streets, such as major arterials, the advance warning area should
extend a greater distance.
Since rural highways are normally characterized by higher speeds, the effective placement of the first
warning sign in meters should be substantially longer—from 1.5 to 2.25 times the speed limit in km/h.
Since two or more advance warning signs are normally used for these conditions, the advance
warning area should extend 450 m or more for open highway conditions.
Advance warning may be eliminated when the activity area is sufficiently removed from the road
users’ path so that it does not interfere with the normal flow.
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-6
Figure 10-2 Component Parts of a Temporary Traffic Control Zone
10.3.4.2 Transition Area
The transition area is that section of highway where road users are redirected out of their normal path.
Transition areas usually involve strategic use of tapers, which because of their importance are
discussed separately in detail.
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-7
When redirection of the road users’ normal path is required, they shall be channelized from the normal
path to a new path.
In mobile operations, the transition area moves with the work space.
10.3.4.3 Activity Area
The activity area is the section of the highway where the work activity takes place. It is comprised of
the work space, the traffic space, and the buffer space.
The work space is that portion of the highway closed to road users and set aside for workers,
equipment, and material, and a shadow vehicle if one is used upstream. Work spaces are usually
delineated for road users by channelizing devices or, to exclude vehicles and pedestrians, by
temporary barriers.
The work space may be stationary or may move as work progresses.
Since there might be several work spaces (some even separated by several kilometers or miles)
within the project limits, each work space should be adequately signed to inform road users and
reduce confusion.
The traffic space is the portion of the highway in which road users are routed through the activity area.
The buffer space is a lateral and/or longitudinal area that separates road user flow from the work
space or an unsafe area, and might provide some recovery space for an errant vehicle. Neither work
activity nor storage of equipment, vehicles, or material should occur within a buffer space.
Buffer spaces may be positioned either longitudinally or laterally with respect to the direction of road
user flow. The activity area may contain one or more lateral or longitudinal buffer spaces. A
longitudinal buffer space may be placed in advance of a work space.
The longitudinal buffer space may also be used to separate opposing road user flows that use
portions of the same traffic lane, as shown in Figure 3.
Typically, the buffer space is formed as a traffic island and defined by channelizing devices.
When a shadow vehicle, arrow panel, or changeable message sign is placed in a closed lane in
advance of a work space, only the area upstream of the vehicle, arrow panel, or changeable message
sign constitutes the buffer space.
The lateral buffer space may be used to separate the traffic space from the work space, as shown in
Figures 2 and 3, or such areas as excavations or pavement-edge drop-offs. A lateral buffer space
also may be used between two travel lanes, especially those carrying opposing flows.
The width of a lateral buffer space should be determined by engineering judgment.
10.3.4.4 Termination Area
The termination area shall be used to return road users to their normal path. The termination area
shall extend from the downstream end of the work area to the last TTC device such as END ROAD
WORK signs, if posted.
An END ROAD WORK sign, a Speed Limit sign, or other signs may be used to inform road users that
they can resume normal operations.
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-8
Attachment 10-1 Traffic Management Plan (Sample) No. 1
96th Street Station Construction of Second Avenue Subway in NYC
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-9
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-10
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-11
Attachment 10-2 : Traffic Management Plan (Sample) No. 2
Construction Work
AUGUST 2010
REVISION NO. 03
UNIFORM TRAFFIC CONTROL DEVICES 10-12
11 Landscape Design Criteria
This section presents standard design criteria for landscape. It has been developed as a way of
establishing a baseline, or minimum, for the standard of implementation sought in new developments.
Where appropriate proposals may be presented that provide additional detail, or standards. These
will be considered on their merit, but must improve on the criteria herein and meet recognized
international standards. Where alternatives are put forward and explanation must accompany the
reasons why they are being proposed.
The criteria presented have been developed to reflect typical conditions. It is understood that certain
situations, climatic conditions, and locations may require modification or interpretation of the criteria
herein.
11.1 Landscape Design Criteria
The Developer shall be responsible for landscaping within the project’s site boundaries, including
open spaces and for pedestrian (footpath/sidewalk) planting areas up to roadside curb with street
according to the landscape design criteria described herein.
There will be a presumption that all plants should be directly sourced and grown from in-country
nurseries. Developers should therefore consider and build-in the necessary lead times. Details to the
contrary should be outlined and the reasons for sources elsewhere specified.
11.1.1
Landscape and Planting
11.1.1.1 General Guidelines
The landscape design must be carefully planned and take into account the intended purpose of the
project and enhance the functionality of the community. Landscaping should reinforce design
concepts and not obstruct or interfere with street signs, lights, or road/walkway visibility. The choice
of species in all locations should be primarily indigenous and must meet and reflect local growing
conditions with the size and scale of the tree appropriate to the location. Species should be chosen
which require low maintenance.
11.1.1.2 Planting
Provide planting at low levels to reinforce routes, mark focal points, and add to the visual
environment. Planting should be varied with a variety of colors and sizes of plants utilized. Species
which flower at different times in the year should be used to ensure that spaces are attractive all year
round.
In public squares, plant beds should be raised in order to reinforce routes, add visual interest, and
prevent from being walked over.
Selection of plants should be based on climatic, geologic, and topographical conditions of the site.
Annual color plantings should be used only in areas of high visual impact close to where people can
appreciate them. Otherwise, drip irrigated, perennial plantings should be the primary source of color.
Selection of water-efficient and low-maintenance plant material is recommended.
AUGUST 2010
REVISION NO. 03
LANDSCAPE DESIGN CRITERIA 11-1
Figure 11-1 Use of Raised Beds
Good use of raised beds to add interest to a public square and to prevent people walking on plants. Wall also serves as
somewhere people can sit.
All planted areas must be a minimum of 25 mm below adjacent hardscape to reduce runoff and
overflow.
Plants having similar water use shall be grouped together in distinct hydrozones.
Planter islands in parking lots with canopy trees to meet local jurisdiction's shading requirements
should have planter beds sized roughly by the expected canopy area in square meters equaling the
square meter of planter bed.
Native desert plants shall be specified to be:
Planted in a shallow, wide, rough hole three to five times the root ball width.
The root ball will be set on either undisturbed native soil or a firmed native soil.
The root ball top will be set even with surface grade or above grade if the soil is poorly
drained.
The hole will be backfilled with native soil.
Extra soil may be brought in to mound up around plants where the soil is poorly drained.
Any organic material will be applied only as surface mulch over the planting hole.
Figure 11-2 Use of Colorful Flowers
Figure 11-3 Tree Grate in Paved Area
11.1.1.3 Grassy Areas
Provide grass in all unpaved areas within parks and public spaces. The addition of grass in these
areas will help prevent the spread of dust and sand. These ‘islands of green’ should provide visual,
as well as facility, focal points for the local community. They should therefore be strategically placed,
sensitive to the potential for leisure and recreational uses such as picnicking and informal play.
11.1.1.4 Trees
A cluster of trees should be established within landscaped areas, providing a contrast to the built form
or acting as a focal point. Trees will provide significant shading for all outdoor activities and should be
located adjacent to pathways and hard paved areas. Tree pits and grates should be provided around
all existing and newly planted trees in paved areas.
Use trees and bushes to provide wind screens and to visually separate car parking from the outdoor
green space. In important areas designers may choose to use a more exotic selection of plants to
emphasize the importance of the location if designers can be confident that the resources exist to
maintain these plants and put in place management and maintenance schemes.
11.1.1.5 Turf Areas
Large turf areas shall be found only in areas of maximum human contact. These areas include
recreational areas such as that found in city parks and school yards. Large, nonfunctional turf areas
shall be minimized and reviewed to see if the same effect can be obtained with other plant material.
Avoid designing long, narrow or irregularly shaped turf areas because of the difficulty in irrigating
uniformly without overspray onto hardscape and/or structures. Areas with less than 2.5 m in width
and areas between sidewalks and curbs shall be planted to drip irrigated groundcovers and lowgrowing shrubs. No turfgrass will be allowed in these areas unless subsurface drip irrigated.
The use of a soil covering mulch or a mineral groundcover of a minimum 50 mm depth to reduce soil
surface evaporation is encouraged around trees, shrubs and on non-irrigated areas.
The use of boulders and creek stones should be considered to reduce the total vegetation area; make
sure these areas have enough shade to avoid reflected or retained heat.
Screening may be provided by walls, berms, or plantings.
11.1.2
Planting on Private Development Parcels
1.
Existing trees of calipers above 100 mm shall be encouraged to remain where use
and grading requirements allow.
2.
All trees within residential and commercial parcels shall be nursery grown, container
grown or ball and burlapped. All trees shall have a 75 mm to 100 mm caliper with 3.5
m to 4 m minimum height at time of planting. These trees shall grow to a minimum
125 mm to 150 mm caliper with a 5.5 m to 6 m height and shall be limb up (clear
trunk) a minimum of 2.5 m above ground. There shall be at least one tree of the
species listed, planted every 4 meters along project boundaries.
3.
In parking areas, there shall be at least one tree of the species listed, planted for
every 3 consecutive parking spaces (every 6 when they are back to back). The use
of berms and additional trees along the perimeters of parking is encouraged to screen
the parking area from public view.
4.
All areas not occupied by buildings, pedestrian (sidewalk) or parking areas shall be
landscaped. The use of native species of trees, shrubs, vines, groundcovers and
perennials is required as standard.
5.
Full maintenance and management regimes will be detailed for a minimum of five
years. Use of native species will reduce these long term costs.
6.
Shrubs of like species, except those used as specimens, shall be planted in groups
rather than as individuals. Shrubs shall be planted a minimum of 1.0 m on center
unless otherwise indicated.
7.
Planting clusters of fruit trees in groups of four or more (regularly spaced) is
encouraged to create small orchards. Areas for small herb and vegetable gardens are
encouraged.
8.
Hedges shall be a minimum height of 1.0 m with a spacing of 0.5 m on center.
Permitted plants for use in hedge fences are provided in species list in this section.
9.
Vines of listed species shall be planted along boundary walls and fences at a
minimum of 2.0 m on center intervals to insure continuous coverage and soften hard
surfaces. One vine species shall be selected per boundary line.
10.
Slopes greater than 3:1 shall be densely planted with masses of trees, shrubs, vines
or groundcovers in combinations of 9 or more of each, to achieve a lush effect.
11.
The ground surface in rights-of-way and drainage easements is to be planted with
grass species capable of tolerating the shade created by canopy trees. Grass may
be seeded and mulched, or planted by plugs or sodded.
12.
As a minimum requirement, each development parcel is to be provided with one
canopy or flowering tree for every apartment. In addition, a minimum of 20% of the
yard area is to be planted in groundcovers or grasses. For single detached villas and
units shall be provided with one tree for every 150 square meter of building plot (lot
area).
13.
Planting areas are to be designed so that rainwater leaving the roof either long and
edge or via a gutter downspout, does not erode the planting. To this end drainage
devices are to be installed in any area where concentrated water run-off strikes the
ground. Splash blocks of concrete, dry well, or connections to storm sewers are all
acceptable means of preventing erosion on lots. Particular emphasis is placed on the
need to cater for the dispersal and storage of storm water runoff.
AUGUST 2010
REVISION NO. 03
LANDSCAPE DESIGN CRITERIA 11-4
Figure 11-4(a) Landscaping around the home (1)
Figure 11-4(b) Landscaping around the home (2)
14.
11.1.3
Slopes and surroundings around retention ponds shall be landscaped with
appropriate plant materials. Basins of retention ponds shall be mown and kept free
from rubbish (garbage) and regularly maintained.
Planting on Public Streets and Streets within Private Developments
1.
All trees in public streets shall be nursery grown, container grown or ball and
burlapped. All trees shall have a 75 mm to 100 mm caliper with 3.5 m to 4.0 m
minimum height at time of planting. These trees shall grow to a minimum 125 mm to
150 mm caliper with a 5.5 m to 6.0 m height and shall be limb up (clear trunk) a
minimum of 2.5 m above ground.
2.
All palms in public streets shall be nursery grown, container or ball and burlapped. All
palms shall have a minimum height of 6 m.
3.
There shall be at least 1 tree of the species listed planted every 6.0 meters along
both pedestrian pathways (sidewalks) of public streets, streets within private
developments and public spaces.
11.1.4
4.
In parking areas, there shall be at least one tree of the species listed planted for
every 3 consecutive parking spaces (every 6 when are back to back). The use of
berms and additional trees along the perimeters of parking is encouraged to screen
the parking area from public view.
5.
Trees and palms planted in rows or series shall be selected to insure uniformity of
height, caliper, and appearance between them.
6.
Continuous hedges of one species shall be planted in front of parking spaces along
each parcel frontage. Hedges shall be a minimum height of 1 meter planted at a
spacing of 0.75 meter on center. Hedges also form an important part in ‘softening’
hard landscaping, the general streetscape, and as ecological havens for birds and
wildlife. Their inclusion is encouraged wherever possible and appropriate.
Planting on Public Parks and Landscaped Open Areas
Outdoor spaces are extremely important to any development. They are used as pedestrian routes
and as places where people can relax and socialize. A large amount of resident’s time is spent
outside and as such these spaces will have a very large impact on the quality of life of residents.
Landscaping add visual interest to an area, makes pedestrian routes more enjoyable to use, and
provide shading and wind protection to pedestrians where necessary.
This sub-section covers parks, public squares, courtyards, and public gardens. Designers should
make decisions based on strong concepts to ensure that the function of a space is clearly defined.
Outdoor areas are most successful when they have a clear function and a unifying theme to aesthetic
design decisions. Full information on design concepts should be submitted in accordance with
specified requirements below.
In addition to the criteria specifications outlined above, designs must comply with the following
guidelines when delivering criteria:
1.
On common landscaped open areas, provide common outdoor areas that are usable
in all seasons, including shaded areas for outdoor use in warmer months.
2.
Consider the special needs of each group of the expected residents.
3.
When located on ground level, open areas should be screened from public view by
landscaping, courtyard walls, or privacy fences.
4.
On sloping sites, landscaped open areas should be sensitively terraced or provided in
decks or balconies.
5.
The requirements for private usable open areas could be reduced if a project
provides some common usable open areas on the site.
6.
Private open areas should be oriented to receive good sun penetration and provide
shaded areas for outdoor use in the warmest months.
7.
Variety and Identity - Designers must provide outdoor spaces which are interesting
and add to the aesthetic environment. Outdoor space designs must be varied and
should be an individual response to the area in which they are located. Outdoor
spaces should be designed in conjunction with buildings to reinforce architectural
themes and ideas.
11.2 Landscaping Plans Submittals Requirements
The landscape design plan shall be drawn on project base sheets at a scale that accurately and
clearly identifies the following:
1.
Show tract name, tract number or parcel map number on cover sheet.
2.
Show proposed planting areas.
3.
Show plant material location and size.
4.
Show plant botanical and common names.
5.
Where applicable, plant spacing shall be identified.
6.
Natural features including but not limited to rock outcroppings, existing trees and
shrubs that will remain incorporated into the new landscape.
AUGUST 2010
REVISION NO. 03
LANDSCAPE DESIGN CRITERIA 11-6
7.
Show a vicinity map showing site location on top sheet or on cover sheet.
8.
Show a title block on each sheet with the name of the project, city, name, and
address of the professional design company with its signed professional stamp if
applicable.
9.
Reserve a 75 mm by 150 mm space for a district signature block on lower right corner
of the cover page and on all of the landscape, irrigation design/detail/specification
sheets.
10.
Show plan scale and north arrow on design sheets.
11.
Show graphic scaling on all design sheets.
12.
Show all property lines and street names.
13.
Show all paved areas such as driveways, walkways, and streets.
14.
Show all pools, ponds, lakes, fountains, water features, fences and retaining walls.
15.
Show locations of all overhead and underground utilities.
16.
Show total landscaped area in square meters. Separate area by hydrozone. Show
the total percentage area of each hydrozone. Include total area of all water features
as separate hydrozones of still or moving water. Show Estimated Annual Applied
Water Use, for each major plant group hydrozone and water feature hydrozone
expressed in either seasonal (turfgrass) or annual (trees, shrubs, groundcovers, and
water features) billing units.
17.
Show Total Estimated Annual Applied Water Use for each major plant group
hydrozone and water feature hydrozone expressed in either seasonal (turfgrass) or
annual (trees, shrubs, groundcovers and water features) billing units.
18.
Show Total Estimated Annual Applied Water Use for the entire project.
19.
Show Total Maximum Annual Applied Water Allowance for the proposed project.
20.
Designate recreational areas and recreational turf areas.
21.
When model homes are included, show the Maximum Annual Applied Water
Allowance and Estimated Annual Applied Water Use (by hydrozone with totals) for
each model unit.
11.3 Landscape Grading Plan
1.
The grading plan design shall indicate finished configurations and elevations of the
landscaped areas, including the height of graded slopes, drainage patterns, pad
elevations, and finish grade.
2.
Turfgrass plantings are prohibited on slopes greater than three-to-one. Slopes
steeper than three-to-one shall be planted to permanent ground covering plants
adequate for proper slope protection.
3.
All grading must retain normal storm water runoff and, as much as possible, provide
for an area of containment. All irrigation water must be retained within property lines
and not allowed to flow into public streets or public rights-of-way. Where appropriate,
a simulated dry creek bed may be used to convey storm drainage into retention
areas. A drywell should be installed if the retention basin is to be used as a
recreational area.
4.
Avoid mounded or sloped planting areas that contribute to runoff onto hardscape.
Sloped planting areas above a hardscaped area shall be avoided unless there is a
drainage swale at toe of slope to direct runoff away from hardscape. The swale
areas may be planted to turf, ground cover, or low shrubbery and shall be watered
separately.
AUGUST 2010
REVISION NO. 03
LANDSCAPE DESIGN CRITERIA 11-7
Figure 11-5 Shrub and Tree Planting Details (1)
Figure 11-6 Shrub and Tree Planting Details (2)
Figure 11-7 Planting Details – Tree on Pavement
Figure 11-8 Hedge Planting Detail
Figure 11-9 Planting Details – Palm on Pavement
11.3.2
11.3.3
Tree and Plant Maintenance
1.
All landscaping should be provided with; (1) a planting regime plan; and (2) shall be
accompanied with a long term management and maintenance programme.
2.
Trees shall be planted utilizing guy wires as shown in details to insure proper growth.
All palm trees shall be braced according to specifications.
3.
Plants shall be watered, mulched, weeded, pruned, sprayed, fertilized, cultivated, and
otherwise protected and maintained in a healthy condition. Irrigation of landscaped
areas is required and these systems shall be maintained in working order.
4.
Prior to establishment, settled plants shall be reset to proper grade position, planting
saucer restore, and dead material removed. Guys shall be tightened and repaired to
restore tree to intended position.
5.
Sod areas shall be mowed and edged regularly where they meet structures of
pavement at bed areas.
6.
Debris, including fallen branches, leaves, fronds, seedpods, and any foreign materials
will be removed from the site on a weekly basis.
7.
Hedges shall be pruned and maintained regularly to insure a uniform and continuous
height of a minimum of 50 mm and a maximum of 1.2 m above ground.
8.
Pesticides shall be applied only in accordance to label instructions. Where possible,
environmentally-friendly solutions to pest control should be applied. No pesticides
shall be allowed to contact water surface.
9.
All planting along public streets, streets within private developments and public
spaces shall have irrigation systems.
Indigenous Species
The planting of indigenous species is encouraged and preferred wherever possible and practical.
Where alternatives are proposed, these should be appropriate to the conditions and should not put
undue pressure on limited resources to sustain their life above and beyond what is practical.
Contractors will therefore be required to propose detailed planting regimes that meet these, and those
requirements outlined above. The following plant species provide an indicative list, examples of the
primary sources for planting regimes in Libya. Contractors are encouraged to use this listing as a
base rather than as an exhaustive listing.
Key
Botanical Name
Common Name
Shrubs
Cymbopogon proximus
Solenostemma arghel
Agave Americana
Atriplex halimus
Calotropis procera (Faftan Calotrope)
Cleodendron inerme
Hemerocallis
Kochia scopara
Leucophyllum frutescens
Nerium Oleander
Pennisetum setaceum
Senecio cineraria
(TBD)
(TBD)
(TBD)
(TBD)
solitary buske
Wild jasmine
Day Lily
Summer Cypress
Texas sage
Oleander
Fountain Grass
Dusty Miller
Groundcovers and
Climbers
Mesembryanthemum edule
Catharanthus rosea
Bougainvillaea spectabilis
Acacia ongerop
Ajuga reptans
Festuca ovina glauca
Delasperum alba
Malephora crocea
Ipomoea biloba
Porulaca grandiflora
Thymus serphyllum
Hottentot Fig
Vinca rosea
(TBD)
(TBD)
Carpet Bugle
Blue Fescue
White Ice plant
Red Ice plant
Goat´s Foot Creeper
Rose Moss
Creeping Thyme
Grasses
Cynodon Dactylon
(TBD)
Palms and Trees
Acacia Farnesia
Acacia raddiana
Phoenix dactylifera
Washingtonia robusta
Albizia lebbeck
Albizzia Julbrissin
Melia azederach
Parkinsonia aculeta
Prosopis juliflora
Sweet acacia
(TBD)
Date Palm
Fan Palm
Mothers tounge
(TBD)
China Berry
Jerusalem Thorn
Mesquite
Wind Screen Plants
Tamarix aphylla
Casuarina equistifolia
Eucalyptus camalduensis
Eleagnus pungens
Athel tree
Beefwood
Red Gum
Silverberry
AUGUST 2010
REVISION NO. 03
LANDSCAPE DESIGN CRITERIA 11-11
12 Streetscape
This section presents standard design criteria for streetscape. It has been developed for sources of
best practice as a way of establishing a baseline, or minimum, for the standard of implementation
sought in new developments.
Where appropriate proposals may be presented that provide additional detail, or standards. These
will be considered on their merit, but must improve on the criteria herein and meet recognized
international standards. Where alternatives are put forward and explanation must accompany the
reasons why they are being proposed. In most, if not all instances, the use of appropriate qualified
designers, engineers, technicians and other specialists is required as standard.
12.1 Introduction
‘Streets’ form the core of the transport network; whether paved, with formal demarcation, as in many
towns, or unpaved forming an informal thoroughfare through a rural settlement, streets are also the
building blocks of the urban area, fulfilling a wide range of roles.
They need to be managed to support all the objectives for any settlement however large or small. The
functions of streets include:
Streets as movement corridors
Streets as the focus of activities
Streets as city identity
All of these functions work together towards ‘place making’ and are influenced by the design of the
street and the landscaping that contribute to the streetscape.
A key component of ‘place making’ is the creation of public spaces, with footways that are sufficiently
safe, attractive and comfortable to use so that people are encouraged to walk in the settlement they
live for pleasure and function in a safe way.
Footways should be sufficiently spacious for their purpose and be uncluttered. People see a scene in
its totality. The space between buildings, usually the roadways and footways, is seen as part of a
wider townscape made up of buildings and streets. Cherished views of important monuments and
groups of buildings are appreciated far more when not detracted by unnecessary foreground clutter.
Within this context there are opportunities for more exciting designs which have a place in the wider
public realm and key spaces of the settlements in Libya. However, throughout Libya, it is essential
that the design of streets should be clear and simple.
12.2 Good Design
An essential element of a settlement’s visual character is the relationship between the buildings and
the roadways and footways. There should be a presumption to maintain this relationship. Footways
should be plain and simple, and generally uniform as a suitable setting for a settlement’s buildings.
Traffic equipment and signs, together with their posts, supports, boxes and guard railings should be
kept to the practical minimum. Roadway markings, applied colors, traffic lines and signs, etc. should
also be minimized while ensuring the aims of national transport standards of road safety. A street
environment must also welcome pedestrians.
The objectives of creating a public realm of real quality, with road safety issues central, can be
achieved by attention to design detail. While it is not always possible to undertake comprehensive
public realm improvements, in the same way that a series of poor changes can result in a degradation
of the public realm so positive changes can, over a period of time, help to regain the standards of
public realm quality that Libyan cities deserve. This embraces the following practices:
Roadways – how curbs/edging, footpaths and drainage channels are laid out, mounting
stones and lighting plinths set and to what standards and specifications.
Footpaths – securing the key elements of a footway - curb, drainage, channel and
roadway. Considering how slabs are aligned, odd sizes cut (on the inside of the footway
and shaped to the profile of the building or boundary), sizing and quality specifications.
AUGUST 2010
REVISION NO. 03
STREETSCAPE 12-1
Features – monitoring and regulating the numerous additional features that have
appeared as part of the street scene. These include spur stones, bollards, railings and
gateposts.
Street relationship - The critical relationship between the roadway, pavement width and
alignment and the building property boundaries. The growth in car ownership has led,
often forced, the adaptation of our streets for a variety of reasons, including
accommodating increased levels of traffic. Retaining and reinforcing these relationships is
a key objective. This does not mean that curb lines cannot change. However, the manner
in which the changes are made must maintain the relationship.
Street pattern – New streets are being created all across Libya. It is important that these
new streets and new public spaces use a design language that is derived from existing
streets and spaces, providing positive connections back to existing parts of a settlement
or area. It is also important that these new development areas utilize a recognizable
range and ‘palette’ of materials.
12.3 Objective
The guidelines have been developed to help redefine those elements of street design that make up
its character and to ensure new proposals that impact the streetscape are designed, as far as
practicable, to improve and at the very least reinforce the existing character. An over reaching
objective is therefore:
… to facilitate the delivery of a streetscape that provides an enhanced environment for
pedestrians that is designed to respond to its built context and, at the same time,
meets the requirements of traffic movement… .
12.4 Principles
The following ‘eight-principle’ approach is advocated for adoption:
Principle 1 – Preservation and enhancement of settlements historic form and ‘grain’, particularly in
locations with a high heritage and archaeological value (e.g. world heritage status medina), both
during and after construction phases.
Principle 2 – For renovation and rehabilitation areas, respecting and enhancing local character.
Ensure that when new street works are proposed they take the local character of the area as a
reference point for the design of layout and overall design arrangement and detailing.
Principle 3 – New streets to contribute to formation of recognizable street pattern. They should be
designed as part of a recognizable ‘townscape’ that picks up on street characteristics specific to the
settlement. They should form a part of a coherent relationship between building, footway, roads and
other features.
Principle 4 – Contributing to Place Making, creating streets that people would wish to use. Streets are
the arena where the public interface takes place and, as such, should be designed so that they are
not dominated by traffic or with over complicated instruction and segregation. Instead they should
reflect human scale and be simply designed in a manner that is easily understood and attractive to
pedestrians.
Principle 5 – Best Practice. If there is a real desire to create streets that people wish to use, it will be
necessary to draw upon and experiment with international best practice. For example, consider a
reduction in traffic related signage and markings without putting people at risk.
Principle 6 – Achieving Quality of the public realm can be achieved through the careful consideration
of a number of measures. Taken together these will have a significant impact on the appearance of
the streets. These include a reduction in clutter, using natural materials, drawing on a minimum
number palette of materials, simple, clean designs and a coordination of design and color.
Principle 7 – Maintenance. A well-cared for public realm is the result of good design and effective ongoing maintenance. The type of simple clean design to which a settlement should aspire would
make maintenance easier. Maintaining and managing an uncluttered, simple street design requires all
those involved in the public realm to share in a philosophy of care.
Principle 8 – A Coordinated Approach across a settlement will only be achieved if the appropriate
processes and protocols are in place. Adherence to these is the key to consistency and ensuring that
AUGUST 2010
REVISION NO. 03
STREETSCAPE 12-2
high standards of design are maintained through the life of any scheme.
12.5 Design Guidelines and Criteria
12.5.1
Planting Regimes
Planting regimes, on-street trees and landscaping provide an attractive and healthier urban
environment- contributing to a sense of place and improving air quality and linkages in habitat
networks. Correctly positioned, street trees can provide an important contribution to the urban
structure of any settlement or city, providing accents and space in contact with the urban built form,
with many public squares or meeting places enjoying the setting of significant trees.
In the ‘suburban’ development areas trees are focused on gardens, where they complement the
streetscape, predominantly from behind a boundary walls. New development offers the opportunity to
increase tree cover and general landscaping. In any development trees should be used to reflect
varying approaches, introduce ‘color’ and ‘texture’ into the development. The following guidelines
should be considered:
Trees should be planted into designated soft landscaped areas where possible, in
preference to hard surfaces.
In general public street arrangements/through streets, etc, preference will be for trees to
be located within gardens and frontages, where appropriate and not in the footway.
Groups of trees should be established within landscaped areas, providing a contrast to
the built form in a street layout, acting as a focal point to a view and providing shade.
Where existing trees are to be retained, the general arrangement of the street and public
realm should be designed to take account of the trees requirements.
Consideration should be given to the impact of underground services on proposals.
Tree grids should be porous resin bonded gravel or a more solid concrete/metal cover
flush with the surrounding paving (unless an ‘up stand’ is more suitable).
Tree guards should not be used.
Generally trees in paving should be planted to a minimum of an extra -heavy standard
size (to ensure they have a proper chance of surviving and prospering)
Street trees planted into landscaped areas should be standard or smaller size.
The choice of species in all locations must meet and reflect local growing conditions and
the size and scale of the tree appropriate. Wherever possible they should be locally
sourced and grown.
Clearly planting regimes will differ greatly across Libya, based on their geography (coastal, desert or
mountain) and location (city or rural area). It is proposed that individual fact sheets on preferred
planting schemes, making recommendations on the type, size and age of species, should be
prepared by the relevant specialists in due course.
Planting regimes should also have a wider reference to supporting wildlife. Where appropriate plants
should be selected that increase the instances of attracting and supporting the local fauna.
12.5.2
Footway layout
Footway layouts should be designed for the use and enjoyment of pedestrians. They should provide
sufficient space for the user, provide a setting to the adjoining buildings and be as clear and clutter
free as possible. The layout of footways should be simple. Public footways should not be used to
take up differences in level when new entrances to buildings are being created.
Respect the proportional relationship between the footway, buildings and the roadway
(with a presumption against reducing footway widths).
Ensure footways avoid awkward or abrupt changes in level and access or frontages with
developments are clear and uninterrupted.
Vehicle run-ins and crossovers (for access to buildings and parking for example) should
not normally interrupt the footway layout. Dropped curbs and reinforced surfaces are
recommended.
Retain existing access where it would provide reference to the character of the area.
AUGUST 2010
REVISION NO. 03
STREETSCAPE 12-3
Protect, strengthen or increase heights of curbs where appropriate in new schemes or
high use areas where extensive maintenance proposals may be required.
Materials should be consistent to make maintenance and replacement easier.
12.5.3
Paving
Paved pathways should be provided from the car parking to the entrance of the building. Provide
paved areas for pedestrian pathways, seating areas, child play areas, and other features. Provide
adequate dedicated bicycle lanes throughout the development.
Paving should be modular, a minimum of 500mm x 500mm and be constructed from stone, precast
concrete or grass-crete. A variety of paving types should be used throughout the development to add
identity to different areas.
Paving is an integral part of the footway streetscape. Some simple applications should be promoted.
For example:
Small module paving (below say 450mm by 600mm) should be avoided for footways,
preferring larger unit paving or simple flexible surface treatments. (500mm by 500mm
should be the smallest unit used).
Use precast concrete, grass-crete or asphalt.
Include the use of colored tactile (blister and hazard) paving at crossings and hazards as
a warning at steps. The resulting contrast provides the necessary signal for those who
are visually impaired. Consider the need of specific users who may live in or near the
area, such as the elderly or visually impaired.
In areas outside or adjoining the public street, such as squares and public spaces, there are
opportunities to introduce a wider variety of materials and paving styles that respond to modern
design proposals. However these should relate clearly to adjoining street footway paved areas in
their general arrangement and there will be a presumption for the use of natural paving materials in
key public spaces.
Roadway curb lines and in most streets curb ‘up stands’ are an essential part of the design and layout
of the street.
Curb lines should be used at all times to define a footway and should run parallel with the
building line.
Newly laid curb ‘up-stands’ shall normally be set to a minimum of 125mm. In many urban
settlements across Libya, consider higher up-stands to prevent parking and provide a
suitable alternative to bollards to protect the footway.
Pedestrian crossings and associated refuge islands should be designed as complete entities and to
consistent details. Designs should seek to introduce the minimum requirements to avoid unnecessary
clutter (e.g. guard rails should be avoided) and should ensure that the surrounding footway and
roadway designs are consistent in detail, material and proportion to their surroundings.
The scale and proportion of the roadway means that it can have a marked impact on the appearance
of the street. The choice of materials and infrastructure used affect this appearance.
The maintenance of the roadway is important and an excessive use of different materials and features
can be a burden to upkeep. Simplifying the design and layout of these features and thinking about the
requirements in a particular location rather than just applying the standard can help ease such a
burden. Materials should therefore be consistent to make replacement and maintenance easier.
Awareness of emerging best practice for standardized solutions should also be considered at the start
of the project where there is scope for improving the overall design of proposals. This recognizes
design philosophies are changing and new approaches are being tried. It is essential that safety is
maintained in the design and application of any approach at all times.
Roadway, parking and loading restriction lines and markings - should be applied (in the narrow 50mm
wide format), replacing original lines and with careful consideration to how they are applied to local
features.
Raise entry treatments and speed tables enhance conditions for pedestrians on busy footways. Entry
treatments are a common way to persuade drivers to give way to pedestrians. ‘Movement and
Development’ requires that raised crossings, as far as possible, send a visual message to motorists
and pedestrians that the footway continues across the side street. The area of raised roadway should
AUGUST 2010
REVISION NO. 03
STREETSCAPE 12-4
have a tactile surface at its footway edge at the crossing point. They should be tall enough to
discourage unauthorized access without restriction visibility lines.
At junctions and at crossing points in the street, the curb should be dropped to improve crossing
facilities. The dropped curb should be on the direct pedestrian ‘desire’ line, so that pedestrians are
able to cross the road conveniently and preferably at right angles to the direction of pedestrian travel.
A minimum width of 3 meters should be specified, dependant on site conditions. Exceptional numbers
of pedestrians, in locations normally within Libya’s larger cities, may require the width to be increased
to 10 meters.
12.5.4
Street Furniture and Features
Street Furniture and Features are often provided in the context of the street in addition to signage.
These features also have an effect on the setting of the surrounding urban form as well as the overall
function of the street. All street furniture and features should be located with this in mind. The
presumption will be to co-ordinate and in some cases minimize furniture and features, taking into
account the requirements for signage outlined above.
Sitting is an important aspect of ensuring unobstructed footways. A desired minimum of
1200mm unobstructed footway is required which will generally extend from the building
line towards the front of the footway.
The use of guardrails and bollards to protect vehicle overrun should be limited.
Simple contemporary standard furniture and features will be used consistently in general
street arrangements.
Key or unique public spaces (such as new squares, local shopping centers, look-outs or
waterfront locations) could be considered for alternative solutions (feature sites).
Whilst the styles and designs of many items of street furniture will be standardized, there are,
however, opportunities to introduce elements of public art to add interest or texture to streets and
spaces. This can range from the use of carved stone and metalwork features to the location of major
pieces of public art. Opportunities for public art will best be highlighted through development briefs
and master plans. Any art proposed will consider the maintenance implications, resources for upkeep
and local characteristics.
12.5.5
Lighting
Provide and install lighting to illuminate pathways, seating areas, playgrounds, landscaping, important
features and buildings. Lighting is important for security and safety and allows people to use outdoor
spaces after sunset.
Lighting detailing, style and the type of light source should be considered with consistency, long term
maintenance as key considerations. Positioning should be considered in the context of the street
scene.
The choice of light source is important as it will determine the night time appearance of the area in
which new lighting is installed as will the position of the lighting units in order to achieve the required
lighting standard.
Consideration and adaptation to best practice is vital. The current lamp sources being specified are
mainly high pressure sodium (SON), metal halide and compact fluorescent (CDM, PL). There is an
ever increasing range of lamp sources and only the most efficient available should be used wherever
possible to help reduce future maintenance and energy costs.
Specific detailing can be provided for additional street features, including bollards, railings and
gateposts, traffic lights, CCTV cameras, seating, tables and chairs, trade, domestic and recycling
bins, control, power and telecom panels.
12.5.6
Benches
Designers should provide benches for outdoor seating in the green space and near the buildings.
Locate benches in shaded places. Benches can be placed individually to create private spaces for
individuals or in groupings to create a public place. Benches should be very durable and attached to
paving or otherwise anchored. At any point within an open space people should not have to walk far
to get to somewhere where they can sit down.
Benches should be incorporated into the overriding themes of patterns. A variety of materials,
textures and lightings can be used to provide variety in the types of benches provided.
AUGUST 2010
REVISION NO. 03
STREETSCAPE 12-5
Benches should be made from very durable weather resistant materials and should be designed to
require as little maintenance as possible.
12.5.7
Planters
In public squares raised beds should be used in areas to bring plantings closer to eye levels and to
stop people from walking on the plants and flowers.
Provide planting beds filled with plants sensitive to the local environment. The form of planting should
create a layering of textures, colors and plant forms, creating geometric pattern and texture derived
from Islamic culture.
12.5.8
Playground Equipment
Provide playground equipment in the outdoor spaces for each cluster of buildings in line with national
and international guidance.
Playgrounds should be located in an open, visible area which can be seen from building windows for
supervision. They must provide an appropriate ground surface to prevent injuries. Use only high
quality equipment which can be easily maintained and has appropriate international safety
specifications. Fence off play areas providing a single access point to increase security and to enable
parents to monitor children more easily. Provide benches for parents to rest on while children are
playing.
12.5.9
Water Features in Public Open Spaces
Water features should be used in significant public spaces to provide focal points and landmarks. In
hot climates providing cooling fountains which children can play in may be popular.
Only water features which use water sparingly and reuse water should be used due to the scarcity of
water in Libya. Consideration should be given to what maintenance a water feature will require and
only fountains with commonly available parts should be chosen.
12.5.10 Shading Strategies
Shade structures may incorporate lighting, ventilation fans, misting, plants, retail signage and seating.
Canopies and trellises can also be used in a variety of ways to provide shade and reduce heat
affects. They will be used for public gathering locations as well as playgrounds.
Canopies and trellises should be made of heat reflective materials (e.g. light wood, tensile fabric,
metal, etc.) Shading structures should varied be used to reinforce themes within areas.
Provide at least one pavilion or shading structure for each cluster of buildings constructed using
durable, permanent materials. Use trees to provide shade to important pathways.
12.5.11 Signage
The street with its footways and roadways form the setting to the surrounding buildings and urban
form. All signage should be located with this in mind, adopting national standard specifications at all
times. The presumption will be to minimize signage. This can be achieved in some cases through
consideration of alternative locations as well as combined use and operation.
In general signage should be considered on a street/site specific basis, but proposing a consistent
approach for the entire street or area where possible and should consider the following approach.
This should embrace:
Locate signage onto buildings, walls and street furniture, where possible and reduce the
use of poles to minimize clutter.
Poles for signs will be positioned to the rear of the footway or 450mm from the curb edge
in both cases ensuring that the middle of a footway is not obstructed.
12.6 Delivering the Principles
A structured program of steps to aid in the delivery of these principles is advocated. This will ensure
the broad principles are applied sustainably and reflect local characteristics and conditions whilst
maintaining good design practice. The objectives of sustainability, low maintenance and long term
enjoyment will drive this implementation process and in so doing encourage wider training and
development for the adoption of best practice methods and simple solutions.
AUGUST 2010
REVISION NO. 03
STREETSCAPE 12-6
13 Bridge Inspection
13.1 Introduction
This provides guidance for bridge inspection personnel, provides a reference for consultants, and
helps to ensure consistency in bridge inspection, rating, and evaluation. This section contains:
Introduction; Qualifications, Responsibilities, and Duties of Bridge Inspection Personnel; Field
Inspection Requirements; Ratings and Load Posting; Routing and Permits; Bridge Programming;
Bridge Records and an Appendix.
13.1.1
References
The publications related to bridge inspection with their issue dates are:
1.
AASHTO Movable Bridge Inspection, Evaluation, and Maintenance Manual, 1st
Edition, 1998
2.
AASHTO Manual for Bridge Evaluation, 1st Edition, 2008
3.
FHWA Bridge Inspector's Reference Manual, 1 Edition (December 2006)
4.
NCHRP Maintenance and Inspection of Fracture Critical Bridges, 2005
5.
AASHTO Manual for Maintenance Inspection of Bridges (1993)
6.
AASHTO Manual for Condition Evaluation of Bridges (1994)
7.
AASHTO Guide Specifications for Fracture Critical Non-redundant Steel Bridge
Members, 1986
8.
AASHTO Interim Specifications for Bridges, 1990
9.
AASHTO Standard Specifications for Highway Bridges, 17th Edition 2002
10.
AASHTO Guide for Selecting, Locating, and Designing Traffic Barriers, 1977
11.
AASHTO Load and Resistance Factor Design Specifications, 2004
12.
ASTM Standard Terminology Relating to Fatigue and Fracture Testing, ASTM 182396e1
13.
ASTM Specification for Carbon Structural Steel A36/A36M -97 Volume 01.04, 1997
14.
FHWA National Bridge Inspection Standards (1988)
15.
FHWA Recording and Coding Guide for the Structure Inventory and Appraisal of the
Nation’s Bridges (1972, 1979, 1988, 1991, and 1995)
16.
FHWA The Bridge Inspector’s Manual for Movable Bridges (1977)
17.
FHWA Culvert Inspection Manual (about 1979)
18.
FHWA Inspection of Fracture Critical Bridge Members (1986)
19.
FHWA Scour at Bridges, a technical advisory (1988)
20.
FHWA Hydraulic Engineering Circular No. 18 (about 1988)
21.
FHWA Bridge Inspector’s Training Manual 90 (1991)
22.
FHWA Scour at Bridges, Technical Advisory, 1988
23.
TxDOT Administrative Circular No. 60-75,1975TxDOT Construction Specifications,
1962
24.
TxDOT Memo from C.W.Heald,P.E. Closing of Weak Bridges, February 1999
25.
TxDOT Memo from Robert L. Wilson, P.E Texas Transportation Code, Title 7, Chapter
621 Closing and Posting Recommendations for Off-System Structures, October 1997
AUGUST 2010
st
REVISION NO. 03
BRIDGE INSPECTION 13-1
13.1.2
26.
NHI (National Highway Institute) Safety Inspection of In-Service Bridges
27.
Texas Bridge Load Rating Program of 1988
28.
National Society of Professional Engineer’s program for National Certification in
Engineering Technologies, National Institute for Certification in Engineering
Technologies (NICET)
29.
Traffic Management Section, HIB Design Criteria
AASHTO Inspection Manuals
13.1.2.1 1974 AASHTO Manual
(The small “green book”) described the minimum information considered necessary for inspection,
records, rating, and check of bridge load capacities. Primary subjects with their major items were:
Inspections
Frequency of two years
Waterway, debris, and channel profile to be observed
Investigate evidence of scour and undercutting
Deterioration of main structural members, deck, superstructure, and bents
Fatigue details of steel girders to be considered (little guidance given)
Abnormal cracking in concrete members
Bridge railings to have only visual inspection, no strength requirements
Trusses inspected for damage, bracing, condition of paint
Records
Written Structural Inventory and Appraisal (SI&A) sheet
Condition Ratings given as 9 to 0 as now, but little guidance on selection of ratings
At least two photos to be taken
All normal identifications, widths, clearances, etc. to be recorded
Painting record to be kept
Stress calculations to be kept
All spans should be listed by length.
Ratings
Calculations in accordance with current AASHTO bridge specifications
Operating and Inventory Ratings to be H- or HS-equivalents
Higher safety factor allowed for heavily traveled routes
Dimensions from as-built or field measurements if necessary
Pictorial posting signs recommended.
Load Capacity of Bridges
Consider two lanes loaded with rating trucks if bridge is 5.50 M clear or wider
Allow fewer lanes if warranted by judgment of Engineer
“Train” of lighter-weight trucks to be considered, spaced at 9.10 M headway when at H12
or less
Load distribution and allowable stresses as given by AASHTO Bridge Specifications
Sample calculations given in Appendix B of AASHTO Manual
Load Factor Rating introduced as an acceptable method
13.1.2.2 1978 AASHTO Manual
The third AASHTO Manual was issued in 1978 (the small “yellow book”) and included all the same
information and requirements as the first two AASHTO Manuals, with some reordering of contents. In
addition, the following major additions and modifications were made as compared to the 1974
AASHTO Manual:
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-2
Records
Recommendations modified for repair, maintenance, and posting
Ratings
Definition of Inventory Rating changed to omit the equivalency to the original design load
Typical load and speed posting signs omitted and reference made to Traffic Management
Section, HIB Design Criteria.
Load Capacity of Bridges
The “Secant Formula” was added for steel column strength calculations (this formula is
believed to be out-of-date and should not be used by a rater)
Allowable Inventory Rating stresses listed for A36, A572, A441, and other steel types
Increased allowable bearing stresses on rivets and bolts
13.1.2.3 1983 AASHTO Manual
th
The 4 AASHTO Manual was issued in 1983 in loose-leaf form (the large “yellow book”) and
contained essentially the same requirements as the first three AASHTO Manuals. The Records and
Ratings requirements were essentially unchanged from the 1978 AASHTO Manual. The following list
summarizes the major additions and modifications since the 1978 AASHTO Manual:
Load Capacity of Bridges
Allowable Inventory of Rating stresses became more detailed
Allowable bearing stresses on rivets and bolts for Operating Ratings was again increased
to be consistent with the increases made in 1974 for Inventory Rating
Allowable Inventory stresses for A7 bolts and rivets clarified
Allowable Operating Rating stresses for high-strength bolts detailed for all conditions
Comparative chart for fastener bearing stresses added
Maximum Operating Rating concrete stresses in bending clarified
13.1.2.4 AASHTO Interim Specifications
The AASHTO Interim Specifications of 1984 through 1990 included some re-ordering and editing of
various sections of the 1983 AASHTO Manual. In addition, there were significant changes and
additions made in certain sections. These changes are summarized as follows:
In 1984 the inspection frequency could be increased to more than two years for certain
types of bridges if properly documented. An example is reinforced concrete box culverts.
In 1984 the two lanes of live loading for roadways between 5.5 M to 6.0 M was clarified.
For roadways over 6.0 M in width, the spacing between trucks became 1.20 M, which is
the same as the AASHTO bridge specifications. This corrected a long-time disparity
between the bridge specifications and the AASHTO Manual.
In 1986 there was a major change in the qualification of inspection personnel which
required that the individual in charge must be a Registered Professional Engineer. Prior
to this time, the individual in charge could be qualified by experience.
In 1986 scour was specifically identified as an item requiring more intense inspection.
In 1986 non-redundant structures were identified as requiring the initiation of special
inspection procedures.
In 1986 concrete bridges with no plans were allowed to be rated by simple physical
inspection and evaluation by a qualified engineer.
In 1987 underwater inspection was identified as an important inspection requirement.
In 1987 hangers and pins were identified as features to be properly inspected.
In 1987 new sections entitled Evaluation and Limiting Vehicle Weights were added.
Higher safety factors could be considered for structures with large volumes of traffic. In
addition, the agency responsible for maintenance of a structure could use stress levels
higher than Inventory Ratings to post a bridge if inspection levels exceeded the minimum.
In 1987 speed postings were allowed in certain cases to reduce impact loads and thus
reduce the need for lowering weight limits.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-3
In 1988 the requirement that all inspections be done by a Registered Professional
Engineer was re-interpreted to allow an inspection team leader to be qualified by
experience. However, the person in responsible charge must be an Engineer.
In 1988 emphasis was placed on underwater inspection of pilings, particularly those
exposed to salt water or salt spray, and any foundation member in contact with brackish
or chemically contaminated waters.
In 1989 the minimum weight limit for posting was clarified to be three tons at the
Operating Rating stress level.
In 1989 a new Appendix B was added that described the five basic Inspection Types:
Inventory
Routine
Damage
In-Depth
Interim
The categories and description of each Inspection Type were relatively broad. However,
clarifications were made that the first Inventory Inspection was to determine all the
Structure Inventory and Appraisal data required by FHWA and that Routine Inspections
were defined as those done at regularly scheduled intervals.
In 1990 only minor editorial changes were made.
13.1.2.5 AASHTO Manual, 2000
AASHTO adopted the 2nd Edition (148 pages, loose-leaf) Manual for Condition Evaluation of Bridges
and is considered current at this time June 2009.
Major additions and changes since the 1983 AASHTO Manual are:
Records
Total bridge width is to be recorded. Prior to this time, the total was implied by the
summation of the deck width, sidewalk or curb width, and railing type.
Critical features such as special details, scour susceptibility, fatigue-prone details, etc. are
now to be recorded.
Flood records are to be kept if known. This information is not entered in the Coding
guide, but should be kept in the Bridge Folder described in Subsection 13.7.
Inspections
Qualifications of the Inspection Program Manager are changed again to allow the person
to be qualified by experience. Qualifications for Inspection Team Leader are modified to
allow training to be based on a National Institute for Certification in Engineering
Technologies (NICET) Level III or IV certification in Bridge Safety Inspection.
The five basic Inspection Types are now called:
Initial
Routine
Damage
In-Depth
Special
The categories and description of each Inspection Type are essentially the same as described for the
1983 AASHTO Manual as modified by the 1989 Interim.
Detailed sections are added on methods of inspection including equipment, safety,
advance planning, and preparation for inspections.
Sections are added to describe inspection procedures, including organized and
systematic field notes and procedures.
Emphasis is placed on obtaining uniformity in condition ratings by different field inspection
teams by developing an objective system of evaluation and training.
New emphasis is placed on inspection of substructures including susceptibility to
earthquake damage.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-4
More emphasis is placed on various types of substructure inspection.
Detailed inspection recommendations are given for each of the various types of bridge
superstructure including new superstructure types such as cable-stayed and pre-stressed
concrete segmental bridges and new component types such as pre-stressed deck panels.
Fracture-critical members are to be properly identified.
More detail is required on description of timber components.
Greater detail is added on inspection of trusses.
Material Testing
Extensive new material is added on field testing of materials for concrete, steel, and
timber including reference to the various newer methods such as acoustic emission for
steel and pull-off and thermographic tests for concrete.
Sampling techniques are described in detail.
Interpretation and evaluation of field and laboratory material tests is discussed.
Non-Destructive Load Testing
This is a new section in the AASHTO Manual. However, very little useful information on
actual load testing procedures is given.
Methods of determining equivalent standard ratings from load tests are complex and
costly, and are seldom used.
Ratings
The rating section of the AASHTO Manual is much more extensive than corresponding
sections in previous editions.
The description of the safety factors for the Load Factor Rating method is similar to the
factors in the new AASHTO Load and Resistance Factor Design (LRFD) Specification.
The AASHTO Manual now states when a redundant bridge has details not available from
plans, then a physical inspection and evaluation may be sufficient to approximate the
ratings. An interpretation on applying this criterion to redundant bridges will be presented
in Chapter 5, Ratings and Load Posting.
Structural grade of reinforcing steel is listed separately in the Load Factor Method of
rating but is combined with all the older unknown grades for the Allowable Stress Rating
Methods.
The AASHTO Manual now contains detailed examples of allowable stress, load factor,
and load and resistance factor (LRFR) ratings for a simple-span, I-beam structure and for
a simple-span, concrete structure.
13.1.3
Inspection Procedures
The FHWA Bridge Inspector’s Training Manual 90 was published in July 1991 and is the basic current
reference for all field inspectors. Hereinafter it will be referred to as Manual 90.
Manual 90 presents the basic information needed by all bridge inspectors and rating personnel. It
includes an excellent history of the National Bridge Inspection Program. It also includes a description
of all the common types of bridges, materials, and details used in bridge construction. Recommended
procedures are presented in detail along with many diagrams and photos. Manual 90 also presents a
fair description of basic structural mechanics for bridge members.
The purposes of bridge inspection are:
Primarily for preventive maintenance
To ensure public safety and confidence in bridge structural capacity
To protect public investment and allow efficient allocation of resources
To effectively schedule maintenance and rehabilitation operations
To provide a basis for repair, replacement, or other improvements such as retrofit railings
Bridges are inspected every two years, but the frequency may be increased depending on the
condition of the bridge. More detail will be given in Chapter 4, Field Inspection Requirements.
There are five basic types of inspection, each of which will be described in greater detail in Chapter 4,
Field Inspection Requirements:
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-5
Initial Inspection. Performed on new bridges or when bridge is first recorded.
Routine Inspections. Those regularly scheduled, usually every two years for most normal
bridges
Damage Inspections. Those performed as a result of collision, fire, flood, significant
environmental changes, loss of support, etc. These inspections are also called
Emergency Inspections and are performed on an as-needed basis.
In-Depth Inspections. Performed usually as a follow-up inspection to better identify
deficiencies found in any of the above three types of inspection. Detailed Underwater
Inspections are considered a type of In-Depth Inspection. Fracture-critical Inspections
are another type of In-Depth Inspection.
Special Inspections. Performed to monitor a particular deficiency or changing condition.
Unusual bridge designs or features such as external, grouted, post-tensioned tendons
may require a Special Inspection.
13.2 Bridge Inspection Personnel
13.2.1
Requirements
13.2.1.1 General Requirements
Personnel involved in the various bridge inspection activities must be qualified for their specialized
jobs. In general, depending on the level of responsibility, they must be knowledgeable in the various
aspects of bridge engineering including design, load rating, construction, rehabilitation, and
maintenance.
HIB Requirements
These are summarized as:
The individual in charge of the Bridge Inspection of the RBD, or the contract consultant
firm) must:
be a Licensed Professional Engineer, or
be qualified for licensing, or
have a minimum of ten years experience in bridge inspection assignments and have
completed a comprehensive training course based on the Bridge Inspector’s Training
Manual 90.
The individual in charge of a bridge inspection team must have the same qualifications as
above, or
have a minimum of five years experience in bridge inspection assignments and have
completed a comprehensive training course based on the Bridge Inspector’s Training
Manual 90.
13.2.1.2 AASHTO Requirements
These are described in the current AASHTO Manual for Condition Evaluation of Bridges.
HIB Requirements
At a minimum, all bridge inspection activities performed by Contractors must comply with HIB
requirements. HIB requirements for bridge inspection personnel are also the same as those in
AASHTO requirements, and in addition, some jobs may require more specific job-related knowledge
and skills such as:
The use of breathing apparatus for underwater inspection
The various applicable requirements for inspection safety including applicable
Occupational, Safety, and Health Administration (OSHA) requirements
Advanced computer skills related to bridge analysis
Geotechnical and hydrological knowledge
Familiarity with HIB bridge construction specifications and with current and old HIB bridge
designs
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-6
HIB also has special requirements for Contractors retained to perform bridge inspection tasks. All
firms must be pre-qualified. Further information on Contractor requirements is presented later in this
chapter in the section titled “Bridge Inspection by Contractor”.
13.2.2
Bridge Inspection Personnel
13.2.2.1 General Position Requirements
Certain knowledge, skills, or abilities are general in nature to most bridge inspection engineeringrelated positions. The level of knowledge, skill, or ability in these general areas increases in
relationship to the level of the position and will not be specifically described for each of the positions.
Some of the particular areas of necessary skill and knowledge for bridge inspection personnel are:
Ability to perform engineering calculations
Knowledge of bridge engineering fundamentals and application of engineering theory
Ability to analyze, interpret, and review technical data
Ability to use a personal computer along with applicable software
Knowledge of all types of bridge construction methods in North Africa and the Gulf
Region
Knowledge of AASHTO specifications, HIB design procedures, bridge standards, and
details
Ability to exercise initiative and independent engineering judgment
Ability to schedule and lead the work of others when appropriate to the position
Ability to communicate effectively and maintain proper working relationships
Various special skills and knowledge are also necessary for some of the positions, some of which are
unique to the bridge inspection operations such as:
Knowledge of applicable local laws and regulations
Knowledge of bridge inspection methods and procedures
Familiarity with associated inspection safety requirements
Skill in use of scuba or other underwater inspection equipment
Ability to make bridge inspection-related technical and training presentations and to
represent the department in public meetings and conferences
13.2.3
Bridge Inspections by Contractors
13.2.3.1 General Requirements
All firms contracted by HIB to perform routine bridge inspections must be pre-certified in accordance
with the requirements of all applicable codes. All bridge inspections shall also be performed in
accordance with this Manual.
Routine Bridge Inspections
For routine bridge inspections, the firm must employ an individual to serve as Project Manager who
meets the following qualifications.
Is a Licensed Professional Engineer, or
Has a minimum of ten years experience in bridge inspection assignments in a responsible
capacity.
The bridge inspection Team Leaders employed by the firm must also be qualified and have:
The same qualifications as above for the Project Manager, or
Has a minimum of five years experience in bridge inspection assignments
Complex Bridge Inspections
For complex bridge inspections, such as those requiring fracture-critical inspections, the firm must
employ a minimum of one Licensed Professional Engineer, to serve as Project Manager, who has
seven (7) years of bridge inspection or design experience, including one year of inspection or design
of bridges considered as complex.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-7
The firm must also employ as a complex bridge inspection Team Leader, an individual who has a
minimum of six years of bridge inspection or design experience, including one year of inspection or
design of bridges considered as complex.
Pre-certification Procedures for Contractors
Bridge inspection contracts are developed and monitored by RBD personnel. Contractors must be
able to demonstrate the required minimum amount of experience in bridge inspection, rating, and
evaluation.
Consultant personnel must have completed the required training in bridge inspection.
Familiarity with HIB Master Specifications is necessary. Strong knowledge of HIB Bridge Construction
Specifications and Bridge Design is also necessary.
13.2.4
Use of the Contractor Pool
Contractor firms who are pre-certified to perform bridge inspections are to be made available to HIB.
The list of certified firms is updated by the RBD every two years. The necessary procedures that
must be followed to utilize these Contractors is described below.
13.2.4.1 Request for Contractor Inspection
The RBD with a lead time of at least two to three months shall initiate the following:
A request in writing
An estimate of the total numbers of bridges to be inspected
An identification of the bridges as being on- and/ or off-system and shall forward to RBD
Head for approval citing reasons why Contractors are to be engaged
Work Authorization Issuance
The RBD will send the Contractor a Work Authorization along with a fee schedule.
The work authorization shall include the following
Description of where the bridge inspections will take place
Number of bridges to be inspected by type
Total Libyan Dinar amount on the Work Authorization
Termination date for the completion of the inspections
Once the work authorization has been accepted by the Contractor, they may begin bridge inspections.
13.2.4.2 Managing the Contractor Bridge Inspection
To ensure that bridge inspections are being performed in a competent and timely fashion, the RBD
will perform continuing oversight of the work by following these steps:
Verify the Contractor’s bridge inspection Project Engineer and the individual Team
Leaders against the list provided by the RBD.
Periodically visit the Contractor’s inspection teams in the field to verify team composition
and to observe actual inspections.
When completed inspections are submitted by the Contractor, the RBD should review at
least 10 percent of the office work and 7 percent of the field work.
RBD should monitor the amount of completed Contractor bridge inspections to ensure
that additional structures that might be added as the work progresses will be noted and
adjusted in the Work Authorization.
If additional funds or time is needed to complete the Work Authorization, a request for a
Supplemental Agreement must be made to the RBD.
A Supplemental Agreement request should be made to the RBD at least 2 weeks before
the termination of the initial Work Authorization.
13.2.4.3 Completion of Work Authorization
When the bridge inspections covered by the Work Authorization are finished, The RBD should
complete an HIB evaluation form. This aids in ensuring the overall quality of the work provided by the
Contractor, and also aids in the Contractor pool selection for the next two-year cycle.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-8
13.3 Field Inspection Requirements
13.3.1
Types of Bridge Inspection
There are five basic types of bridge inspection:
Initial Inspections
Routine Inspections
Damage Inspections
In-Depth Inspections
Underwater Inspections and Fracture-Critical Inspections are two types of In-Depth
Inspection
Special Inspections
Inspection of post-tensioned, grouted, external tendons is an example of a Special
Inspection.
13.3.2
Initial Inspections
Initial Inspections are performed on new bridges or when existing bridges are first entered into the
database. This inspection provides a basis for all future inspections or modifications to the bridge.
Initial deficiencies are noted which might not have been present at the time of construction. Changes
in the condition of the site should also be noted such as:
Erosion
Scour
Re-grading of slopes
The final new bridge completion checklist should include the notification of HIB R&B Department
Engineer when the bridge is opened to traffic and available for use by permit vehicles.
The opening of a new bridge, particularly an off-system bridge, is a good time to ensure that a set of
copies of the bridge plans are included with the Bridge Records. RBD require all Contractors to
submit a copy of the final structural plans to RBD within 31 days after construction or rehabilitation is
completed.
The initial Bridge Folder is prepared as a result of the Initial Inspection. A detailed description of the
Bridge Folder contents is given in Chapter 7, Bridge Records. The arrangement of the folder shall be
maintained and must include the recommended series of photos.
13.3.3
Routine Inspections
Routine inspections are those regularly scheduled, performed, and recorded in accordance with all
the procedures described in subsection 13.7, Bridge Records, and the instructions for the coding
guide. These are usually done every two years for most bridges and every four years for culverts.
13.3.3.1 Inspection Equipment
The equipment needed for routine bridge inspections usually includes the following:
Cleaning tools including wire brushes, screwdrivers, brushes, scrapers, etc.
Inspection tools including pocket knife, ice pick, hand brace, bit, chipping hammer, etc.
Visual aid tools including binoculars, flashlight, magnifying glass, dye penetrant, mirror,
etc.
Basic measuring equipment including thermometer, center punch, simple surveying
equipment, etc.
Recording materials such as appropriate forms, field books, cameras, etc.
Safety equipment including rigging, harnesses, scaffolds, ladders, bosun chairs, first-aid
kit, etc.
Miscellaneous equipment should include C-clamps, penetrating oil, insect repellant, wasp
and hornet killer, stakes, flagging, markers, etc.
Specialized measuring tools such as paint film gage, calipers, optical crack gage,
tiltmeter, SHIFLO, etc. The SHIFLO is a device used to measure the depth of scour
during flood flows with a depth finder. It is not used during Routine Inspections.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-9
Underwater Inspections may require the use of Scuba gear.
Inspections which may significantly interfere with normal traffic movement and which might affect the
safety of the inspectors must be coordinated with Traffic Authorities in order that appropriate traffic
control measures may be undertaken. Inspections of the underside of bridges that cannot be reached
by conventional ladders may be performed by the use of vehicles with under-bridge platforms.
13.3.3.2 Interim Inspections
Brief inspections are also performed by Bridge Inspection Engineers approximately every six months
on most structures to identify unusual conditions or changes. These inspections do not review all the
points of interest done in a normal Routine Inspection. No formal records are kept of these brief
inspections. However, unusual conditions or changes will often result in a follow-up In-Depth,
Damage, or Special Inspection.
13.3.4
Damage Inspections
Damage Inspections are those performed as a result of collision, fire, flood, significant environmental
changes, loss of support, etc. These inspections are also sometimes called Emergency Inspections
and are performed on an as-needed basis.
13.3.5
In-Depth Inspections
13.3.5.1 Reasons for In-Depth Inspections
In-Depth Inspections are usually performed as a follow-up inspection to an Initial, Routine, or Damage
Inspection to better identify any deficiencies found.
Underwater Inspections and Fracture-Critical Inspections are both types of In-Depth Inspection.
These are described in more detail below.
Load testing may also sometimes be performed as part of an In-Depth Inspection. However, load
testing for determining bridge load capacity is costly and interpretation of the results are sometimes
open to question.
13.3.5.2 Underwater Inspections
Underwater Inspections are a type of In-Depth Inspection. These are regularly performed every five
years. The frequency can be less than five years if conditions warrant.
A master list of bridges needing underwater inspections is compiled and updated during routine
inspections. Once a bridge is added to the master list, it will remain there until it is no longer in use.
Some bridges must be inspected at intervals more frequent than the required five years due to the
susceptibility to scour or other factors such as the age of the bridge, configuration of the substructure,
environment, adjacent features, or existing damage. The frequency, type, and level of inspection are
left up to the owner.
13.3.5.3 Underwater Inspection Methods
There are currently three methods used to conduct Underwater Inspections. These are:
Wading -- The most basic of the three methods, wading requires only a probing rod and
wading boots to be effective.
Scuba diving -- A method that allows a more detailed examination of substructure
conditions at the Mud-line. The diver has freedom of movement and may carry a variety
of small tools with which to probe or measure.
Hardhat diving-- Involves the use of sophisticated diving equipment and a surface
supplied air system. This inspection method is well suited when adverse conditions will
be encountered, such as high water velocity, pollution, and unusual depth or duration
requirements.
The choice of which method to employ depends largely on accessibility and the required inspection
detail.
13.3.5.4 Levels of Underwater Inspection
Standard levels of inspection are:
Level I -- Consists of a simple visual or tactile (by feel) inspection, without the aid of tools
or measuring devices. It is usually employed to gain an overview of the structure and will
precede or verify the need for a more detailed Level II or III inspection.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-10
Level II -- A detailed inspection which involves physically cleaning or removing growth
from portions of the structure. In this way, hidden damage may be detected and
assessed for severity. This level is usually performed on at least a portion of a structure,
supplementing a Level I.
Level III -- A highly detailed inspection of an important structure which is warranted if
extensive repair or replacement is being considered. This level requires extensive
cleaning, detailed measurements, and testing techniques that may be destructive or nondestructive in nature.
13.3.5.5 Underwater Structural Elements
The elements of a bridge structure that may be located below the water line are abutments, bents,
piers, and protection systems. Bents are distinguished from piers in that they carry the loads directly
to the foundation, rather than using a footing.
Abutments normally do not require an Underwater Inspection, but in rare instances may be
continuously submerged. Although usually founded on piles or drilled shafts, abutments occasionally
rest on spread footings in rock. Scour is almost always the primary consideration when an
underwater abutment inspection is being conducted. Local scour is often detectable during diving
inspections, although sediment will eventually refill a scour hole between the events that cause the
scour. More general scour, or channel degradation, will usually be undetectable to the diver and must
be determined from known channel cross sections or historical data.
13.3.5.6 Underwater Inspection Devices
There are several types of sounding or sensing devices available for use by divers in underwater
investigations. Most common is the black and white fathometer, which uses sound waves reflected
from the channel bottom and records the depths continuously on a strip chart. It provides an
inexpensive, effective means of recording channel depths but will not detect a refilled scour hole.
Other methods are color fathometers, which use different colors to record different densities and in
this way can often detect scour refill; ground penetrating radar, which works well for shallow water but
has limited usefulness in murky water; and fixed instrumentation, which is reliable but requires
periodic monitoring and resetting to be effective.
13.3.5.7 Underwater Structural Materials
Piers and bents, if located in a navigable waterway area, are often subject to material defects or
collision damage as well as scour. Concrete is the most common type of material encountered in
underwater inspections. Common defects in concrete substructures include cracking, spalling,
laitance, and honeycombing. Minor or even moderate damage to concrete can be tolerated if it does
not endanger the reinforcement. Corrosion of the reinforcement can lead to serious difficulties.
Steel substructures are very susceptible to corrosion near the waterline or between the high and low
water levels. In this area, the presence of oxygen and frequent wet/dry cycles promote deterioration
at an accelerated rate and steel should be measured to determine the possibility of section loss.
13.3.5.8 Fracture-Critical Inspections
Fracture-Critical Inspections are a type of Special Inspection. These inspections are usually limited to
non-redundant tensile stress areas. They are regularly performed every five years. The frequency
can be less than five years if conditions warrant. Methods of inspection may include dye penetrant,
magnetic particle, or ultrasonic techniques.
13.3.5.9 History of Fracture Critical Considerations
Early development of modern steel design focused on stress and strain; little was known or
recognized about the potential adverse effects of multiple stress cycles. Early materials such as
wrought iron were not capable of great unit strength. Early designs lacked the sophistication that
would require a designer to closely address details. Even after the introduction of electric arc welding
in the 1880s, most steel bridges were simple-span, composed of built-up and riveted members.
Design of continuous beam highway bridges began after welding technology was improved. The
result of the use of continuity was more flexible structures that were more subject to deflections and
rotations. The result of the use of welding, was simpler bridges and more consistent construction
quality.
As steel production and availability improved, along with higher strength steels, design engineers
were quick to accept the obvious benefits. However, no material is perfectly homogenous, and the
fact that steel could have hidden flaws was essentially ignored by designers. After World War II, there
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-11
was a massive expansion of highway bridge construction. The popularity of personal motor vehicles
increased as a result of more highways and thus more highways and bridges were needed. The
construction material of choice was initially steel throughout much of the country. Many designed
smaller structures with concrete, which is still serving well in many cases. Steel bridges, particularly
trusses, were used for longer crossings, usually for streams and rivers.
13.3.5.10 Fatigue Failures
The Truss Silver Bridge at Point Pleasant, West Virginia , USA collapsed suddenly in 1967 due to the
brittle fracture of an eye bar link, resulting in the loss of 46 lives and closure of a major route. After
the failure, significant additional research efforts were initiated in fracture mechanics. As a result, the
effects of multiple stresses at less than yield of the materials were understood more thoroughly.
th
The first recognition of redundant and non-redundant members was presented in the 12 edition of
the AASHTO Bridge Specifications in 1977. The first guide specifications for fracture critical bridge
members were issued by AASHTO in 1978.
13.3.5.11 Fracture-Critical Members
After design engineers began to recognize the problems associated with multiple stresses at less than
allowable values, further information was developed to assist in the design process and in evaluation
of existing structures. After notable failures, it was recognized that many existing bridges may be
nearing failure due to fatigue. Fracture-Critical (FC) members were recognized and defined as a
member or component whose failure in tension would result in the collapse of a bridge. These are
commonly referred to as non-redundant members. Methods were developed to help determine which
structures must be further evaluated by designers for susceptibility to fatigue problems. Designers
began to include Fracture Control Plans (FCP) in bridge design details.
Most common types of FC members are tension flanges and sometimes parts of webs of flexural
members such as beams and girders. Tension members of trusses, particularly eye bars, which
commonly make up the lower chords of old trusses, can also be FC. Other tension members of
trusses, such as diagonals, are also FC. Concrete members are not often used in tension. The
design of flexural concrete members with multiple reinforcing bars precludes possibility of abrupt
failure due to their internal redundancy.
The following rules-of-thumb usually determine FC members:
Two-girder bridges are defined as FC. Fracture of lower flanges in positive moment
areas (mid spans) and upper flanges in negative moment areas (over supports) can be
expected to lead to collapse of the structure. However, cracks over interior supports
sometimes lead to subsequent higher positive stresses in the spans with no catastrophic
collapse. Therefore, these FC components receive more frequent periodic In-Depth
Inspections.
All steel caps are defined as FC. While this statement is bold, an exception is difficult to
imagine.
Lower chords of trusses are FC. This determination is based on the fact that most truss
bridges employ only two trusses and most are simple span.
Secondary members such as diaphragms and stiffeners are not FC. They are rarely
used in a manner where failure would lead to structure collapse. However, caution must
be observed in evaluating certain truss members that may appear to be secondary when
in fact their attachment to main FC members can provide a starting place for the main
member failure.
13.3.5.12 Redundancy
The concept of structural redundancy is well known. Any statically indeterminate structure may be
said to be redundant, to varying degrees, depending upon its supports. A two-span straight girder is
redundant. However, a two-span curved girder is also redundant, but the support reactions are
determinate. These definitions of redundancy are of little value to the field inspector who must make
a determination of FC potential for various members in a bridge. There are two types of redundancy
that concern the FC inspector:
1.
AUGUST 2010
Load Path Redundancy. Superimposed traffic loads are supported directly by the
deck, which in turn is supported by longitudinal stringers or beams. A bridge with a
single box girder would therefore be non-redundant since a failure in the box would
collapse the bridge. Likewise, a two-girder bridge is non-redundant since one girder
cannot assume all of the load for which two are designed. However, it can be argued
REVISION NO. 03
BRIDGE INSPECTION 13-12
that a continuous two-girder bridge is structurally redundant since a girder failure
would not cause collapse, but the structure would sag excessively. Three or more
girders will usually have enough load capacity due to inherent design factors of safety
to avoid collapse. The failure of one girder will immediately cause the loads to be
shared by the other girders. However, the FHWA considers three-girder bridges with
more than 4.60 M girder spacing to be FC. The strength of the deck system should
be considered for this case. Some deck systems for wide beam spacings are twoway slabs and others have stringer and floor beam systems with one-way slabs.
Those with two-way slabs will still have a load-path redundancy, while those with
stringers and floor beams will be more unstable after failure of one girder in a threegirder system.
2.
Internal Redundancy. This term refers primarily to built-up members, such as riveted
plate girders. A single plate or shape in the built-up member might fail without
causing collapse. However, even members such as this must sometimes be
considered non-redundant, since like two-girder structures, failure of one portion of
the member can overload the remaining portions such that there is not sufficient
remaining capacity to prevent total failure. Usually, if the cross-sectional area of the
largest shape or plate in a built-up member is less than about 30 to 40 percent of the
total member area, then the member may be considered to have internal redundancy.
13.3.5.13 Inspection Procedures for FC Members
Inspection procedures begin with proper advance planning. The more important planning aspects,
usually based on an office review of the structural plans, are:
Identify possible FC members.
Note the particular members in the structure that may require special field attention, such
as built-up tension members composed of few individual pieces.
Pre-plan necessary access to the members, including special equipment needs such as
ladders, bucket truck, or climbing gear.
Many FC members are a result of structures designed for urban situations with necessary
complex alignment geometries. Proper inspection of these bridges may require closing a
traffic lane. Safe traffic control must be coordinated in advance with RBD and the Traffic
Authorities.
If the structure involves a railroad, a railroad flagger must be coordinated with the proper
railroad company.
Identify and make available any necessary special tools and equipment that may be
required in addition to the normal inspection gear. A high-pressure washer is often useful
in cleaning areas where a large accumulation of debris might obscure view of FC areas.
Non-destructive test equipment such as ultra-sonic devices may be advantageous in
some areas, particularly inspection of box-type bent caps and pin-and-hanger
connections.
The actual field inspection of all FC members consists of several steps. The most important step is a
visual inspection. The inspector notes any:
Visual cracks and their direction and location
Evidence of rust, which may form at a working crack
Weld terminations in a tension area
Interrupted back-up-bars used for built-up-member fabrication
Arc strikes, scars from assembly cables or chains, or other physical damage
Cross-section changes which may cause a sudden increase in the stress pattern
13.3.5.14 Fatigue and Fatigue Fracture
Members subjected to continued reversal of stress, or repeated loading such that a range of change
in stress occurs, are subject to a behavior called fatigue. Members that have a relatively constant,
steady stress are not subject to fatigue. The term has been in use for almost a century and is
currently defined by the American Society of Testing Materials (ASTM 1823-96e1) as “the process of
progressive localized permanent structural change occurring in a material subjected to conditions that
produce fluctuating stresses and strains at some point or points and that may culminate in cracks or
complete fracture after a sufficient number of fluctuations.” Fatigue can result in:
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-13
Loss of strength
Loss of ductility
Reduced service life
Fatigue fractures are the most difficult to predict since conditions producing them are often not clearly
recognizable. Fatigue occurs at stress levels well within the elastic range, that is, less than the yield
point of the steel, and is greatly influenced by minor imperfections in the structural material and by
fabrication techniques.
Fatigue fracture occurs in three distinct stages:
Local changes in atomic structure, accompanied by sub-microscopic cracking
Crack growth
Sudden fracture
13.3.5.15 Fatigue-Prone Details
Fatigue fracture almost always begins at a visible discontinuity, which acts as a stress-raiser. Typical
examples are:
Design details such as holes, notches, or section changes
Flaws in the material such as inclusions or fabrication cracks
Poor welding procedures such as arc strikes
Weld terminations
Certain structural details have been long recognized as stress-raisers and are classified as to their
potential for damage. These details appear in the current AASHTO Bridge Specifications, HIB Bridge
Manual and other technical publications. Most of these common details should be familiar to the
fracture critical bridge inspector.
Proper consideration of member detail and sizing during design will help control stress level and thus
control crack growth. The stress range, or algebraic difference in the maximum and minimum stress,
also becomes important. The most effective way to control cracking and eventual fracture is sensible
detailing. Details such as out-of-plane bending in girder webs and certain weld configurations can
cause crack propagation and fracture.
Design for fatigue also includes observing a fracture control plan (FCP). The FCP identifies the
person responsible for assigning fracture-critical designations. It establishes minimum qualification
standards for welding personnel and fabrication plants. It also sets forth material toughness and
testing procedures. The specific members and affected sections are also identified in the FCP.
During fabrication, these members are subject to special requirements.
Fatigue failure is always an abrupt fracture, called a brittle fracture. A brittle fracture is distinguished
from a ductile fracture by absence of plastic deformation and by the direction of failure plane, which
occurs normal to the direction of applied stress. Other failure surfaces due to high stress are usually
at an angle to the direction of the stress and are often accompanied by a narrowing or necking of the
material. Brittle fracture failures have no narrowing or necking present.
The three main contributing factors to brittle fracture are:
Stress level
Crack size
Material toughness, sometimes called fracture toughness
Small, even microscopic cracks can form as a result of various manufacturing and fabrication
processes. Rate of propagation, or growth, of cracks also depends on the stress level and the
material toughness. Material toughness is the ability of a material to resist brittle fracture. This
resistance is primarily determined by chemical composition and to some extent by the manufacturing
processes.
Usually, higher strength steels are more susceptible to brittle fracture and have lower toughness.
Toughness can be improved by techniques such as heat treatment or by quenching and tempering.
13.3.5.16 Weld Details
Inspectors concerned with FC inspections must acquaint themselves with the characteristics of good
and poor structural details and be able to identify those details in the field. Welding creates the
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-14
details most susceptible to fatigue and fracture. Therefore, it is imperative to recognize features
prone to FC failure.
Major FC problem areas are at weld discontinuities or changes in geometry such as:
Toes of fillet welds
Weld termination points
Welds to girder tension flanges from other connections such as stiffeners or diaphragms
Ends of welded cover plates
Welded cover plates on rolled beams were a very common detail until fatigue failures began to be
recognized by bridge engineers. Whether the weld is terminated or continued around the end of the
cover plate, the condition is at best Category E.
Weld attachments to a girder web or flange can reduce fatigue strength as the length of the
attachment increases. Welds two inches or less fall in Category C and those greater than four inches
in length reduce to Category E. Such details are commonly used to attach diaphragms and wind
bracing to maintain structural members, either at the flange or web. Details such as run-off tabs and
back-up bars may also provide possible stress riser discontinuities if not smoothed by grinding after
removal.
Inspectors should familiarize themselves with acceptable and unacceptable fillet weld profiles in order
to recognize potential problem areas in the field.
13.3.5.17 Fatigue in Secondary Members
Secondary members may also have fatigue problems. For instance, main girder stress reversal may
induce vibrations in lateral bracing or diaphragms. In many cases the number of stress reversals in
the secondary member is a magnification of those stresses in the main member. The attachment of
plates to a girder web may cause out-of-plane bending in the web, a situation not usually considered
by the designer.
In general, secondary members themselves are not subject to a FC inspection. However, some
secondary members, even though designed only as secondary members, such as lateral wind
bracing in the lower plane of a girder system, will act as primary members. These cases generally
occur in curved or heavily skewed structures. A curved bridge will have twisting or torsional effects
due to the live loads that are partially resisted by the diagonal lateral wind bracing. These braces,
particularly those near supports, should be inspected for possible fatigue cracks.
13.3.5.18 Proper Welding and Repair Techniques
Proper welding of structural steel members is a tedious process under the very best of conditions,
which are usually found in the fabrication shop. Any field welding, whether it is a welded girder splice,
retrofit detail, or repair, should be closely examined for visible problems. Many shop splices are
accomplished by automatic welding machines under controlled conditions and can be smoothly
ground to eliminate surface discontinuities. Field splicing operations are subject to exposure to the
elements and difficulties in stabilizing the pieces to be joined. In addition, the welding is usually done
by hand and therefore subject to human error. Welded field splices for bridges should be subject to
careful inspection and must be done by certified welders. The welded field splices for these bridge
are usually of the same quality as shop splices and are often further inspected by radiographic (X-ray)
techniques.
The inspector should also be aware of problems that may arise from the use of improper field repair
processes. Often a well-intentioned repair can actually make a member even more susceptible to
brittle fracture.
13.3.5.19 FC Inspection Techniques
FC inspection techniques may include non-destructive testing to determine the condition of a
structural member. There are several types available, including radiographic, ultrasonic, dye
penetrant, and magnetic particle inspection. All are acceptable methods, but each has limitations and
may not be suitable for a particular situation. One single technique may not be sufficient to assess
damage and a combination of more than one may be advisable. Usually these types of inspection are
best left to personnel who have undergone the proper training.
The selection of the type of non-destructive testing method for a particular location is usually a
function of the detail. For instance, potential cracks at the ends of welded cover plates are often
inspected by the use of radiographic methods. Cracks in pins are best inspected by ultrasonic
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-15
techniques. Subsurface defects such as inclusions may be found by magnetic field irregularities, and
cracks adjacent to fillet welds at tee-joints are usually inspected by dye penetrant.
13.3.6
Special Inspections
Special Inspections are performed to monitor new types of structures, structure details, or materials. A
Special Inspection may also be used to help develop an information database.
An example of a Special Inspection is the inspection of the grouted ducts in externally post-tensioned
members of pre-cast segmental type bridges.
13.4 Ratings and Load Posting
13.4.1
Overview
This Section includes discussion of the following topics:
Condition Ratings
Appraisal Ratings
Load Ratings
Legal Loads
13.4.2
Condition Ratings
13.4.2.1 Definition of Condition Ratings
Condition Ratings based on the field inspections can be considered as “snapshots in time” and cannot
be used to predict future conditions or behavior of the structure. However, the Condition Ratings
based on the inspections along with the written comments by the field inspector act as the major
source of information on the status of the bridge. The Condition Ratings also help in planning for any
necessary repairs or modifications. In addition, the Condition Ratings are used as flags when
performing overweight permit evaluations.
Condition Ratings are one-digit numbers given by the field inspector to the various components of a
bridge. They are intended to be objective and not distorted by personal beliefs or opinions. There is
significant emphasis to have the Condition Ratings be more consistent between inspectors given the
same deficiency of structural component.
Condition Ratings are a measure of the deterioration or damage and are not a measure of design
deficiency. For instance, an old bridge designed to lower load capacity but with little or no
deterioration may have excellent Condition Ratings while a newer bridge designed to modern loads
but with deterioration will have lower Condition Ratings.
The channel, waterway, riprap, and other channel protection components under and directly upstream
and downstream of the bridge are often inter-related to one another in assigning the Condition Rating
for the channel.
13.4.2.2 Recording Condition Ratings
Condition Ratings are entered on the Bridge Inspection Record, BIR. There are six component items
covered on the form, each of which lists four to 11 elements. The Item Numbers relate to the entry of
the data in the electronic Bridge Inventory Files, the detailed instructions for which are contained in
the instructions for coding guide. The six component items plus a miscellaneous item are:
Deck (Item 58)
Superstructure (Item 59)
Substructure (Item 60)
Channel (Item 61)
Culverts (Item 62)
Approaches (Item 65)
Miscellaneous (used for information, but not entered in the Bridge Inventory file. Still
important as part of the Bridge Folder).
The elements for each component have minimum values (shown to the left of the element description
on the BIR Form that the rating must equal or exceed. Each element is rated based on independent
consideration. For instance, poor or deficient secondary members (bracing, diaphragms, etc.) in a
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-16
superstructure may cause the Superstructure (Item 59) component to have a poor rating even though
there is no significant deterioration of the main members. The summary Component Rating must be
the least of the element ratings comprising that component.
However, it should be noted that Deck (Item 58) component is independent of its associated element
ratings such as joints, railings, wearing surface, etc.
The known presence of chlorides in the deck, superstructure, or substructure concrete or low
compressive strengths from cores should not influence Condition Ratings. The Condition Rating
should be determined solely on the observed, materials-related, physical condition of the component
at the time of the inspection.
The BIR Form has page/s for fully supportive written comments for each of the above features. These
comments are required for any Condition Rating of 7 or less. The form includes a brief summary of
the description of each level of rating. More detail on the Condition Rating for each Item Number is
given in the instructions for coding guide.
13.4.2.3 Assigning Condition Ratings
The general considerations for assignment of the ten levels of Condition Ratings require that each
element be evaluated separately. However, other deficiencies may affect the condition if they are
directly related. For instance, instability of an approach embankment may reduce the abutment
Condition Rating but not reduce the Superstructure Condition Rating.
Only permanently installed repairs are to be considered when assigning Condition Ratings.
Permanent implies that the repair has returned the damaged or deteriorated element to a condition as
good as or better than the remainder of the bridge. For instance, a steel beam damaged by an overheight load that reduced the load capacity of the beam is considered permanently repaired when a
section is replaced or a bent section is straightened by proper techniques and no residual cracks can
be found. The strength of the repaired member is the primary concern. Modifications and repairs that
simply improve the appearance of a damaged member should not be considered to improve the
Condition Rating.
Components with temporary repairs, even though functioning, should not be considered for Condition
Rating. For instance, a support or brace to a partially undermined column could be susceptible to
damage from another flood; therefore, the Condition Rating must be made on the basis that the
support is not present. Temporary repairs must not be considered in determining Condition Ratings
because they directly affect the calculations of the Sufficiency Ratings.
Condition Ratings are still a matter of judgment, which should be made based on experience,
knowledge, and consistency with other structures with the same deterioration.
13.4.3
Appraisal Ratings
13.4.3.1 Definition of Appraisal Ratings
Appraisal Ratings consider the field condition, waterway adequacy, geometric and safety
configurations, structural evaluation, and safe load capacity of the bridge. As for Condition Ratings,
they should be as objective as possible. Given the same field information, project plans, materials,
geometric, and waterway data, the same Appraisal Ratings should result independent of the
appraiser.
Seven features are evaluated for their effect on the safety and serviceability of the bridge and its
approaches. The intent is to compare the bridge to a new structure built to current standards.
Appraisal Ratings are usually done in the office where access to all necessary information and
specifications is available. However, an experienced Bridge Appraiser may make some appraisals in
the field while performing the duties of a Bridge Inspector.
13.4.3.2 Recording Appraisal Ratings
As an aid in recording the features, instructions are given on the Bridge Appraisal Worksheet, (BAW).
The Item Numbers are related to the entry of the data in the bridge inspection database. The detailed
instructions for entering data are contained in the instructions for coding guide. The seven features
are:
Traffic Safety Features (Item 36)
Structural Evaluation (Item 67)
Deck Geometry (Item 68)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-17
Under-clearances (Item 69)
Bridge Posting (Item 70)
Waterway Adequacy (Item 71)
Approach Roadway Alignment (Item 72)
The Bridge Appraisal Worksheet has space for fully supportive written comments for each of the
above features. These comments are required even for features with no deficiency. The following
paragraphs summarize instructions for coding the above seven features.
13.4.3.3 Traffic Safety Features (Item 36)
This feature applies only to bridges carrying vehicle traffic. It is a measure of the adequacy of traffic
safety features in meeting current acceptable standards, which reflect modern design criteria. Four
digits are assigned that approximately measure the adequacy the traffic safety feature. The first digit
is for the Bridge Railings, the second digit is for the Guardrail to Bridge Railing Transitions, the third
digit is for Approach Guardrails, and the fourth digit is for Guardrail Terminals. Each of these four
parts to Item 36 is assigned a value of 1 if it meets currently acceptable standards, a value of 0 if it
does not, or a value of N if not applicable. Note that these values do not give a true measure of the
comparative strength or crash test level for the traffic safety feature.
Collision damage or deterioration is not considered when assessing traffic safety acceptability. It must
be assumed that damage to traffic safety features will be repaired in the near future.
Bridge class culverts do not require coding of traffic safety features if the headwall of the culvert is 9.0
M or more from a traveled lane. If there is zero to 1.0 M of fill over a culvert, and acceptable guard
fence is installed over the culvert and along the approaches, then bridge railings and transitions are
not required. Culverts with less than 1-meter of fill may also have guard fence instead of bridge railing
if the steel posts are properly attached to the culvert.
Acceptable traffic safety standards have been developed using the current AASHTO Standard
Specifications for Highway Bridges and the AASHTO Guide for Selecting, Locating, and Designing
Traffic Barriers. Current acceptable bridge railing details are shown in the HIB Bridge Manual.
13.4.3.4 Structural Evaluation (Item 67)
This feature considers major structural deficiencies and is based on the Condition Ratings of the
Superstructure (Item 59), the Substructure (Item 60), and the Inventory Rating (Item 66) as related to
the Average Daily Traffic (Item 29). Items 66 and 29 are correlated in a table included with the
detailed instructions for Item 67 in the instructions for coding guide.
The Structural Evaluation Appraisal Rating should generally be no higher than the lowest of the
Superstructure or Substructure Condition Ratings or the Inventory Rating - ADT correlation.
13.4.3.5 Deck Geometry (Item 68)
This feature applies only to bridges that carry vehicle traffic. Roadway widths are measured
perpendicular to traffic direction and between faces of railings, curbs, and median barriers. Mountable
curbs are ignored if 100mm or less in height.
The Deck Geometry Appraisal Rating is determined from a four-part table included with the detailed
instructions for Item 68 in the “Instructions for Coding Guide”. This table relates the ADT (Item 29),
Bridge Roadway Width (Item 51), and Number of Lanes (Item 28).
This Appraisal Rating is further controlled by another table in the instructions for Item 68 in the
“Instructions for Coding Guide” that relates the Minimum Vertical Clearance (Item 53) and the
Functional Classification (Item 26) of the bridge.
The Deck Geometry Appraisal Rating is taken as the lowest number based on width, lanes, or vertical
clearance and Functional Classification of the highway on which the bridge is located.
13.4.3.6 Under-clearances (Item 69)
This feature is a measure of both vertical and lateral clearances for any roadway or railroad passing
under the bridge being rated. The vertical clearance is measured down from the lowest part of the
bridge to the lower traveled roadway surface (excluding paved shoulders) or top of railroad rails.
The Under-clearances Appraisal Rating is determined from two tables included with the detailed
instructions for Item 69 in the “Instructions for Coding Guide.” These tables relate the Vertical Underclearance (Item 54) and the Functional Classification (Item 26) of the lower roadway or railroad, and
the Lateral.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-18
Under-clearances Right and Left (Items 55 and 56) of the lower roadway or railroad.
The Under-clearances Appraisal Rating is taken as the lowest number based on the vertical and
lateral clearances and the Functional Classification of the lower roadway or railroad.
13.4.3.7 Bridge Posting (Item 70)
This feature compares the load capacity of the bridge to the State Legal Load. At this time, the term
“Legal Load” is assumed to be a load equivalent to the conventional HS-20 load pattern. Therefore,
any Inventory Rating less than HS-20 requires further evaluation of the bridge. Bridges are normally
not load restricted unless the capacity is less than an HS-20 Operating Rating. The need for load
restriction will be explained in more detail in the section of this chapter titled Legal Loads and Load
Posting.
Specific criteria for coding this Appraisal Rating are included with the detailed instructions for Item 70
in the “Instructions for Coding Guide,” which has five posting levels. The Bridge Posting Appraisal
Rating is 5 if the Operating Rating (Item 64) is more than HS-20. The Bridge Posting Appraisal Rating
has a value of 0 to 4 depending on the percentage the Operating Rating is below the State Legal
Load, which for this item is taken as HS-20 loading.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-19
Figure 13-1 AASHTO Design Loads
13.4.3.8 Waterway Adequacy (Item 71)
This appraisal feature applies to all bridges carrying vehicle traffic over any type of waterway. It
represents the capacity of the waterway opening to carry peak water flows and is based on the criteria
included with the detailed instructions for Item 71 in the “Instructions for Coding guide” which has
eight values range from 2, meaning the bridge is frequently overtopped by flood waters, to 9, meaning
that chance of overtopping is remote.
The estimated potential for traffic delays from flood overtopping is also considered when assigning a
value to waterway adequacy. The design flood is the maximum water flow that can pass under bridge
for a given recurrence frequency, usually expressed in years.
When hydraulic information is unavailable, the design flood is assumed to be equal to the frequency
of overtopping the bridge. Local officials and residents can often provide information on the frequency
of overtopping.
13.4.3.9 Approach Roadway Alignment (Item 72)
This feature applies to adequacy of the approach roadway to safely carry vehicle traffic considering
both horizontal and vertical alignments.
Specific criteria are included with the detailed instructions for Item 72 in the instructions for coding
guide. Approach curvature, lane and shoulder widths, surface roughness, and sight distances all
enter into the evaluation of this Appraisal Rating. For bridges on crest or sag vertical curves,
consideration must also be given to headlight and stopping sight distances.
When approach alignment is questionable, the inspector should drive the alignment on the
approaches to the bridge in order to estimate an advisory safe speed with due consideration given to
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-20
minimum sight distances. Advisory speed on approach curves is the speed above which more than
usual concentration and effort on the part of a normal driver would be required to remain safely in the
proper lane. Advisory speed limit should be taken as the posted advisory speed if one exists.
13.4.4
Load Ratings
13.4.4.1 Definition of Load Ratings
The Load Rating is a measure of bridge live load capacity and has two commonly used categories:
Inventory Rating, as defined by the current AASHTO Manual for Condition Evaluation of
Bridges, is that load, including loads in multiple lanes, that can safely utilize the bridge for
an indefinite period of time.
Operating Rating, defined by the same manual, is the maximum permissible live load that
can be placed on the bridge. This load rating also includes the same load in multiple
lanes. Allowing unlimited usage at the Operating Rating level will reduce the life of the
bridge.
13.4.4.2 Determination of Load Ratings
Currently, all Inventory and Operating Ratings are expressed in terms of an equivalent HS-truck as
shown in the AASHTO Manual for Condition Evaluation of Bridges. Prior to about 1995, many ratings
were for an equivalent H-truck, shown in AASHTO Manual for Condition Evaluation of Bridges. The Htruck directly corresponds to single-unit trucks, which used to be common on rural highways. Today,
even rural Farm- or Ranch-to-Market highways and many off-system highways are exposed to much
larger semi-trucks; therefore, the HS-truck is more realistic.
Inventory or Operating Ratings are usually determined using either Load Factor (LF) or Allowable
Stress (AS) methods. Since 2000, LF is to be used for all on-system bridges. Either AS or LF may be
used for all off-system bridges.
13.4.4.3 Inventory Rating and Design Load Considerations
The Inventory Rating (Item 66) can usually be initially estimated to be at least equal to the design
loading if no damage or deterioration exists and the original design was made using an HS load
pattern. Many old plans have a design loading shown as H-20 S-16 which some raters have
misinterpreted as meaning H-20. AASHTO replaced the H-20 S-16 designation in 1965 with the HS20 designation. Re-rating these bridges using LF procedures will usually increase the Inventory
Rating above HS-20. Some newer bridges have been designed on a case-by-case basis for higher
design loads, but HIB bridge design practice is still to design to the HS-20 loading.
13.4.4.4 Design Supplement
The primary subjects of the supplement that affected bridge design can be summarized as follows:
1.
Crown Width Bridges. The 1944 AASHTO Bridge Specifications required curbs on
all bridges. Bridge curbs may be omitted provided the guard fence or an equivalent
member is carried continuously through the structure.” The 1949 AASHTO Bridge
Specifications allowed the condition of no curbs with certain additional width
limitations.
2.
Design Overload. The 1944 AASHTO Bridge Specifications required an overload to
be considered for all bridges designed for less than an H-20 (18.20T) or H-20 S-16
(32.70T) loading, now called HS-20 loading. The overload was to be the design truck
(usually H-15) increased by 100 percent, but without concurrent loading of adjacent
lanes, thus allowing single-lane load distribution. The allowable stress was to also be
increased to 150 percent of the basic allowable. This provision can be modified
specifically to apply the same overload to truss counter members for all design
loadings. Truss counters are those members that, for some positions of live load, will
change from tension to compression. If a truss was designed H-15, H-20, or H-20 S16, the overload was applied in determining the size of counter member.
3.
Lane Load Negative Moments. The 1944 AASHTO Bridge Specifications required
for H-10, H-15, or H-20 lane loads an additional concentrated load in one other span
in a continuous unit positioned to produce maximum positive and negative moments.
The distance between the concentrated loads for the lane load is limited to a
maximum of 9.20M. This is probably based on the fact that the AASHTO 1944 Bridge
Specifications did not require an additional concentrated load for H-20 S-16 lane
loadings. The H-20 S-16 truck loadings have a second axle spaced from 4.30 M to
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-21
9.20 M from the first heavy axle. The 1949 AASHTO Bridge Specifications made the
lane loading negative moment requirement the same for HS-trucks. The provision for
continuous spans subjected to lane load can be modified by limiting the spacing
between the additional concentrated load to 9.20 M. This limit had the effect of
reducing the lane load negative moment maximums for some continuous spans. The
9.20 M limit may also have been in recognition that the second large axle for an HSload pattern is spaced at a maximum of 9.20 M from the first large axle, or it might
have been because the lane load approximately represents a train of trucks with a
headway distance of 9.20 M between trucks. It would have been more logical for the
second concentrated load to be placed a minimum of 9.20 M from the first instead of
a maximum of 9.20 M. Current specifications do not limit the distance between the
two loads for negative moment lane loadings.
4.
Impact Load Provision. The 1944 AASHTO Bridge Specifications required that the
shortest length of adjacent spans in a continuous unit be used for the negative
moment impact value. In 1949, AASHTO changed this to the current provision of
using the average length of the adjacent spans. Both versions of the impact provision
for continuous units or other structures where discontinuous lane loadings are applied
to be the loaded length as indicated by the influence line for the section of member
considered had the effect of slightly increasing the impact value.
5.
Special Axle Loads. The AASHTO Bridge Specifications further limited the 11.00 T
axle to slab spans under 5.50 M and the two 7.30 T axles for slab spans over 5.50 M.
This provision had the effect of reducing the design load for many slab spans
designed during that time. Some beams have been designed using the single 11.00 T
axle. It is believed to be an error for beams to have been designed this way. For this
reason, any plans prepared with a design load of H20 or H20 S-16 should be
carefully evaluated.
13.4.4.5 Customary Rating Procedures
The initial load rating should always be re-calculated; the design loading should not be used as the
final Inventory Rating. When a bridge was originally designed, the designer often had to select the
next size of reinforcing bar, size of steel beam, or thickness of cover plate to meet the design stress
criteria. Sizes that were larger than the theoretically perfect size of member result in Inventory
Ratings significantly higher than the design loading. However, the design loading and date of original
construction is an important part of the bridge data since they often provide a basis for determining
initial routing of overload permits.
If the original design was made using an H-load, such as H-15, or H-20, then the equivalent HS
Inventory Rating will usually be significantly less numerically. For example, an H-15 design might rate
at HS-12. However, this difference means that the total inventory HS-load capacity is 19.60 Tons (two
8.70 T axles and one 2.20 T axle totaling 21.80 Tons) as compared to the H-15 design of 13.60 T.
Bridge designs made using AS procedures with an allowable of 5 percent overstress for some
components are to be re-analyzed using LF procedures.
AS rating procedures are usually set at 55 percent of the material yield stress for steel structures and
50 percent of the material yield stress for Grade 40 reinforcing steel in concrete structures. When
AASHTO first introduced the use of Grade 60 reinforcing steel in the 1970 Interim Bridge Design
Specifications, the allowable of 165.40 MPa for Grade 60 was assigned based approximately on the
ratio of the Grade 60 ultimate strength to that of Grade 40. Thus the AS procedures were still
compatible in factor of safety for concrete members.
LF rating procedures usually assign a dead load factor of 1.3 and live load factors of 2.17 (when
computing Inventory Ratings) and 1.3 (when computing Operating Ratings). The resulting stresses or
bending moments are compared to the yield of steel members or the ultimate capacity of concrete
members also considering appropriate phi strength reduction factors.
Note that the value of 2.17 is the dead load value of 1.3 times 1.67. The load factor of 1.3 accounts
for a 30 percent increase in all loadings, either dead or live, so as to provide a uniform safety factor.
The factor of 1.67 accounts for the variability of live load configurations other than a standard HS-load
pattern, and further provides for potential overloads. See Subsection 13.4, Legal Loads.
Specific analysis of structures for overweight loads, particularly super-heavy permits over about
127.30 Tons, is usually done with a load multiplier consistent with the restricted speed of the vehicle.
Commonly this factor is about 1.1, with total stresses compared to an allowable of 75 percent of the
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-22
yield for steel bridges or 75 percent of the ultimate capacity for concrete bridges including prestressed beam bridges. This procedure is explained more fully in subsection 13.6, Routing and
Permits.
Temporary repairs must not be considered for Inventory or Operating Ratings. However, temporary
repairs are taken into account when assigning the operational status code of Item 41 to the structure.
Temporary repairs are to be considered for the operational status code only until a more permanent
repair is made and should not be used for more than four years. The Inventory Rating directly affects
the Sufficiency Rating, and therefore temporary repairs must not be assigned any weight in the Load
Rating calculations.
When the design loading is unknown or deterioration exists, load rating calculations must use all field
information and conventional analysis techniques. Even when the design loading is known, the only
acceptable method for accurate load rating is to do calculations based on the plans and known field
measurements.
13.4.4.6 Rating Concrete Bridges with No Plans
A concrete bridge with unknown reinforcing details (no plans) can be rated for AASHTO Load (HS-20)
at the Operating Level, which is currently defined for load rating purposes as an HS-20 design load,
provided that the following two considerations are met:
It has been carrying unrestricted traffic for many years.
There are no signs of significant distress.
Notation that the ratings are assumed must be inserted in the permanent Bridge Record described in
Chapter 8, and the bridge should be inspected at more frequent intervals, usually each year, until an
inspection history of at least four years is developed. This procedure is summarized in detail by
Figure 5-2
Three additional considerations for rating concrete bridges with unknown reinforcing are:
Bridge must exhibit proper span-to-depth ratios of the main members, which indicates
that the original design was by competent engineers. In general, this consideration means
that for simple span structures the span-to-depth ratio of main members should not
exceed approximately 20. Span-to-depth ratios exceeding this ratio may indicate that the
designer did not properly consider reasonable design truck loadings.
Construction details, such as slab thickness and reinforcement cover over any exposed
reinforcing, should conform to specifications current at the time of the estimated
construction date.
Appearance should show that construction was done by a competent builder.
A comparative original design rating can be used to estimate the amount of reinforcing in the main
members. Normally, if the design was done prior to about 1950 and the above five considerations
exist, then the amount of reinforcing can be estimated based on a percentage of the gross concrete
area of the main beams (if tee-beam construction), or depth of slab (if slab construction). Two of the
examples below describe this method, and a third example describes a method that can be used for
pre-stressed beam bridges with no plans or other documentation.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-23
Figure 13-2 Load Ratings for Concrete Bridges without Plans
*Permit Trucks with gross or axle weights that exceed the state legal load limits will not be allowed to use these
bridges.
I.F. – Inspection Frequency.
Refer to AASHTO Manual for Condition Evaluation of Bridges, Chapter 7, Section 7.4.
13.4.4.7 Examples of Rating Concrete Bridges with No Plans
1.
Example 1. A flat-slab bridge designed between about 1930 and 1960 can be
assumed to have approximately 0.7 percent tension steel based on the total slab
depth. Calculations with this amount of steel using AS procedures with stresses,
materials, covers, and live load distribution appropriate to the AASHTO Bridge
Specifications for the estimated date of construction should give at or very near an H10, H-15, or perhaps an H-20 theoretical rating. Any other value would make the
assumptions suspect. After this analysis is made, an analysis using LF procedures,
HS loading, and current load distributions should give an acceptable rating. Flat-slab
bridges constructed off-system can also often be rated by this procedure providing
the above five considerations are also met. This method is not suitable for evaluation
of FS slabs, which may be recognized as those with narrow roadways and tall integral
curbs.
2.
Example 2. A multi-beam concrete bridge built between about 1940 and 1965 can be
estimated to have approximately 0.3 percent tension steel based on beam spacing
and an estimated depth to the center of the steel group of 0.9 D where D is the total
depth of the tee-beam. As in Example 1, an “old” AS rating can first be calculated for
comparison. If reasonable, then a modern LF rating can be made with HS loading
and the estimated amount of reinforcing steel. The amount of steel can be adjusted
slightly so the AS design exactly matches an H-rating of H-10, H-15, or H-20.
3.
Example 3. Some bridges are composed of pre-stressed beams but no plans exist.
This condition is often found for off-system bridges. The ratings should be done
using conservative assumptions and good engineering judgment. One procedure
would be to assume that the beams were designed to an H-15 loading in
conformance with the estimated date of specifications. Using this assumption, an AS
calculation can be made to estimate the even number of 12 mm 114 T strands. An
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-24
LF rating using the HS-loading can then be performed based on this number and size
of strand. In some countries, pre-stressed beams were probably never designed to
less than H-15. Most beams have been designed to H-20 or HS-20. Pre-stressed
beam fabricators keep good records of their products, and identification of the design
loading may sometimes be tracked down.
All three of these examples should give H-ratings using AS procedures that are close to a realistic
design load. For instance, a calculated value of H-14.4 could reasonably be assumed to verify that
the original design was H-15. A calculated AS value of H-13 would be suspect, and further
investigation will be required.
13.4.4.8 Ratings for Unusual Bridges
Unusual bridges, such as those composed of old railroad flat cars, can be rated, but care must be
taken to ensure that the critical rating component is considered. For instance, flat cars were originally
designed for a maximum point load combined with a uniform load over the whole car. When used for
traffic loadings, even though the main two-girder members may give a good equivalent HS load
rating, the transverse stiffening members and floor beams often control the live load capacity.
Another type of unusual bridge is the continuous cast-in-place (CIP) flat slab. Most of these bridges
were designed in the 1940s and 1950s to an H-15 or H-20 load pattern. Unfortunately, the design
negative moments were from the single truck load in one span. Current design procedures use a lane
load with two concentrated loads in adjacent spans for the controlling negative moment case for
longer continuous bridges or with two heavy axles of the HS-20 load pattern at variable spacing in
adjacent spans for shorter continuous bridges. These bridges are thus under designed for HSloadings and as a consequence many should actually be load posted. However, the current AASHTO
Bridge Specifications do not differentiate between single-and multiple-lane distribution factors for slab
bridges. As a result, this type of bridge has greater strength for multiple trucks positioned in the
middle of the bridge span. Some structural evaluators will make live load distribution adjustments
based on the number of lanes loaded for flat slab bridges. However, this must be done with care and
properly correlated to two- or three-dimensional methods of analysis.
13.4.4.9 HS and HS Load Ratings
Previously, all ratings were done with the equivalent H-truck, shown in Figure 13-1, or the HS-truck
shown in Figure 13-1. Currently all ratings are only with the HS-truck. A moment equivalency
conversion from H- to HS-ratings is not recommended since this process would assume that the
structure was exactly designed for the given H-loading. In addition, continuous spans cannot be
converted by this process. Most structures have a degree of capacity past the design H-load,
particularly since load distribution assumptions of the AASHTO Bridge Specifications have been made
more liberal since the time many structures were commonly designed using H-loads. However, as
previously explained, some bridges were intentionally designed with AS methods to a 5 percent
overstress for some components.
It is not acceptable to ratio the design live load moments for an H-truck to the same moment for an
equivalent HS-truck. For instance, if a 14.634 M simple-span bridge has a design load of H-15, the
design load for moment equivalency would be HS-10.8. However, due to the above reasons, the
actual rating based on LF methods might easily be HS-9 or HS-13. A LF rating must be made.
13.4.5
Legal Loads and Load Posting
13.4.5.1 Definition of Legal Loads
Legal Loads are those that may safely use any of our highways and bridges. Some routes and many
bridges must be load-posted to protect them from possible damage. At this time, a load capacity of
HS-20 is considered to best represent the Legal Load for evaluation of the need for load posting.
Truck loads are considered “legal” if the gross load, axle load, axle configuration, length, and width
are within the current size and weight laws or rules.
In general, the maximum gross load on any truck cannot exceed 36.40 T, the maximum load on any
pair of tandem axles cannot exceed 15.50 T, and the maximum load on any single axle cannot
exceed 9.10 T. Total length must not exceed 19.80 M and total width must not exceed 2.44 M.
Legal Loads do not have a greater effect on bridges than the current HS-20 design total gross load of
32.70 T even though they may have a total “legal” weight of 38.20 T. This apparent contradiction is
due to the different axle load configurations and numbers of axles.
13.4.5.2 Load Posting
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-25
Load posting is often required for structures that, due to their original design or condition, do not have
the structural capacity to safely carry the Legal Loads. Posting may be at Operating Rating levels
provided that the Condition Ratings exceed those defined in Figure 5-3 and Figure 5-4 and other
requirements are met. Otherwise, if the Condition Ratings are less than those defined, the Posting
must be at Inventory Rating levels.
All load postings of a given truck size actually mean that two trucks of the posted capacity can safely
pass on the bridge. This concept is often misinterpreted by those doing load ratings and making load
posting recommendations. It is recognized that a bridge posted for an HS-5 (8.20 T gross load) can
safely carry a single truck of significantly more than 8.20 T. No method ensures that only a single
truck is on the bridge. Therefore, assume that two trucks of the same size could be passing on the
bridge simultaneously.
However, some bridges, particularly off-system, are load posted assuming only one rating truck even
though they may be wider than 5.50 M. This condition usually occurs due to the volume of truck
traffic, structure width or approach roadway width, striping, runners, etc. making them functionally
one-lane bridges for trucks.
It is important to recognize that even though a bridge may have been designed to an H-15 loading, it
may not need to be load posted due to considerations discussed previously, such as reinforcement or
member size in excess of the theoretical amount, more liberal load distribution now used in analysis,
and LF analysis methods which usually increase Inventory Ratings significantly more than the original
design loading.
The recommended load posting of all off-system bridges must be supplied to the affected localities.
HIB will provide the necessary posting signs and placement hardware.
Figure 13-3 On-System Load Posting Guidelines
Permit Loads will not be allowed on bridges that are load posted.
If the bridge has not been rehabilitated or replaced in 24 months then the structure shall be closed.
I.F. – Inspection Frequency.
OR – Operating Rating (Item 64)
IR – Inventory Rating (Item 66)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-26
Figure 13-4 Off-System Load Posting Guidelines
Permit Loads will not be allowed on bridges that are load posted
If the bridge has not been rehabilitated or replaced in 24 months then the structure shall be closed.
I.F. – Inspection Frequency
OR – Operating Rating (Item 64)
IR – Inventory Rating (Item 66)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-27
Figure 13-5 Typical Load Posting Signs
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-28
13.4.5.3 Procedures for Changing On-System Bridge Load Posting
The following table outlines the procedure for changing the load posting of an on-system bridge.
Table 13-1 Changing Load Posting of an On-System Bridge
Step
1
Responsible
Party
Inspection
Contractor
2
RBD
3
Inspection
Contractor
Traffic
Authorities
Inspection
Contractor
4
5
Changing Load Posting of an On- System Bridge
Action
Complete "Recommend change in Bridge Load Zoning" Form,Makes a request
that involves a new limit or a reduction of a current load limit, attach the most
recent inspection report, plans (lay-outs and structural details), and any load
ratings that support the recommended change
Review the request and supporting documents, and if review supports the
recommended change issues an instruction order.
Notify the the Traffic Authorities of any valid load restriction order
Will erect signs indicating proper load limit
Will verify if the proper load limit has been erected and record the date of
erection
Under the following conditions, Inspection Branch should submit a completed Form showing reasons
for restriction removal.
Repair or rehabilitation of a bridge that increases load capacity and eliminates a load
restriction.
Construction of a new bridge that replaces one with a load restriction.
13.4.5.4 Procedures for Emergency On-System Bridge Load Posting
The following table outlines the procedure for changing the load posting of an on-system bridge in an
emergency.
Table 13-2 Emergency Load Posting of an On-System Bridge
Step
1
2
3
4
5
Responsible
Party
Ins pe cti on
Contra ctor
Ins pe cti on
Contra ctor
RBD
Changing Load Posting of an On- System Bridge
Action
Noti fy the RBD tha t a n e mergency l oa d res tri cti on i s re qui red.
Identi fy defici encie s tha t jus ti fy the pla cement of a n e me rgency loa d l i mi t
De termine the loa d l i mi t, i f requi red a nd verba l l y a uthori ze a n emerge ncy loa d
res tri cti on for a peri od not to exce ed 60 da ys i f neces s a ry
Is s ues a n order a uthorizi ng tempora ry loa d l i mi ts a nd s peci fyi ng the dura tion
of the tempora ry l i mi t
Noti fy the the Tra ffi c Authoriti es of any bri dge loa d res tri cti on
Ins pe cti on
Contra ctor
Tra ffi c Authori ties Wi ll e rect s i gns immedi a tel y i ndi ca ti ng e mergency l oa d l imi t
If the emergency load limit is required for a period longer than 60 days, Inspection contractor should
submit a request to the RBD for the emergency load restriction to remain in place for another 60 days.
If the bridge is not replaced or repaired before the emergency load restriction extension expires, the
Inspection Contractor should submit a request to the RBD for a permanent load restriction following
the procedure for changing on-system bridge load postings.
13.4.5.5 Closure of Weak Bridges
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-29
Bridges with less than an HS-3 Operating Rating capacity must be closed. These policies must be
followed for on-system bridges and are strongly recommended for the municipalities with jurisdiction
over off-system bridges. Bridges with Inventory Ratings less than HS-3, but with Operating Ratings
greater than HS-3, may remain open for a limited amount of time. If it is desired to leave a bridge in
this category open, then the inspection frequency must not exceed six months and the bridge must be
categorized for Priority 1 rehabilitation or replacement. If after 24 months the bridge has not been
rehabilitated or replaced, then it should be closed.
13.4.5.6 Off-System Bridge Closure Procedures
If inspection reveals deterioration that affects an off-system bridge’s ability to safely carry vehicular
traffic, the department may use the following procedure to recommend that it be closed for safety
reasons:
Table 13-3(a) Off-System Closure Procedures
Step
2
Responsible
Party
I ns pecti on
Contra ctor
RBD
3
RBD
4
Tra ffic
Authorities
I ns pecti on
Contra ctor
1
5
6
I ns pecti on
Contra ctor
Recommending Off- System Bridge Closures
Action
Wi l l immedi a tel y notify the RBD if i t determi nes tha t a bri dge s hould be
clos ed ba s ed on the res ults of i ns pecti on they conducted.
They wi ll verify a s s oon a s pos s ibl e the condi ti on of a bri dge recommended
for cl os ure by Ins pection Contra ctor.
Wi l l immedi a tel y notify the the Tra ffic Authorities of a va li d cl os ure
recommenda tion.
Wi l l cl os e the bridge a nd notify the RBD when the bri dge i s clos ed to
tra ffi c.
Wi l l verify closure of the bri dge when it receives notifi ca ti on a nd wil l i ncl ude
a photo or certi fi ed documenta tion veri fyi ng clos ure i n the bridge ins pection
fi l e a nd wi ll prompt upda te the Bri dge I ns pection da ta ba se to refl ect the
cl osure s ta tus of the bri dge. (See Item 41 i n the coding _gui de)
If the bri dge wi ll rema n clos ed for a n extended peri od of time, they wil l veri fy
a nd document with a photo tha t the bri dge i s s ti l l cl os ed to tra ffic a s pa rt of
the regul a r inspection cycle .
13.5 Routing and Permits
13.5.1
Overview
This Chapter includes discussion of the following topics:
Role of the Bridge Inspection Engineers, and the Traffic Authorities
Permits
Example Comparison of Inventory, Operating, and Permit Loads
13.5.2
Role of Inspection Engineers and the Traffic Authorities
One of the responsibilities of the Bridge Inspection Engineer is to assist the Traffic Authorities in the
evaluation of over-height and over-width permit routes based on experience. The current electronic
Bridge Inventory Files are expected to be accurate; however, should the values for clearances in the
Bridge Inventory Files appear suspect, the actual plans should be reviewed and/or a field visit made
prior to issuing a permit. The Traffic Authorities issues the permit only after review by the RBD.
A supplementary role of the Bridge Inspection Engineer is to notify the Traffic Authorities of any
changes to bridge load postings, particularly for bridges which have never been previously posted.
The Traffic Authorities shall maintain a master set of maps showing the various width, height, and
load restrictions on all highways.
All permits are issued by the Traffic Authorities with the cooperation of the RBD. For overweight
permits, the Traffic Authorities also works closely with the RBD. Any super-heavy permits must also
be coordinated the RBD for structural evaluation of the bridges on a proposed route. This process is
fully explained below.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-30
The Traffic Authorities, in conjunction with the owner-mover, selects a preliminary route based on
known information in the Bridge Inventory Files, day-to-day construction status, road closures, and
other known route restrictions.
13.5.3
Permits
13.5.3.1 Over-height and Over-width Permits
Permits are required for over-height or over-width loads. The routing of these loads usually depends
on data contained in the electronic Bridge Inventory File. These types of loads do not normally
require a structural evaluation of the affected bridge unless the weight and axle load distribution is
such the overweight permit may also be required.
The electronic Bridge Inventory file gives the values fro available clearances as Items 51 (Roadway
Width), 52 (Deck Width), 53 (Vertical Clearance Over Roadway), 54.2 (Vertical Clearance Under
Bridge), 55 (Lateral Under-clearance on Right), and 56 (Lateral Under-clearance on Left). These
items taken together usually give sufficient information to define the limits for the passage of overheight and over-width vehicles.
The Bridge Inspector can quickly access the electronic Bridge Inventory file to determine if the
proposed route is capable of handling the proposed over-width or over-height load. Truss bridges are
particularly of concern for both these types of loads since many are in the 5.5 M – 6.5 M width range,
and vertical clearance to the portals is often less than normal current design clearances.
The electronic Bridge Inventory file gives vertical clearances to the least millimeters of clearance over
the roadway, including shoulders rounded down to the nearest millimeter. The posted clearance
signs are normally 76.3 mm less than this value. The clearance symbols maintained on the Traffic
Authorities permit maps are rounded down to the next 150 mm below the posted clearance. For
instance, if the actual recorded clearance is 4320 mm, the clearance sign is 4240 mm, and the permit
maps show the maximum available clearance as 4110 mm. Occasional over-height loads can
therefore be permitted for heights slightly over the limits given in the Traffic Authority permit maps
provided there is close coordination between the RBD and the owner-mover with pre-move specific
measurements taken.
Normally, over-width permits are granted simply on the basis of available Roadway Width (the clear
distance between curbs or railings). If the over-width load is configured such that the load will
adequately clear bridge railings, then moves may be granted for loads significantly wider than the
Deck Width with the careful cooperation of all concerned parties including escort vehicles and traffic
control. Damage and or removal of signs and delineators may occur for some over-width permits.
RBD personnel should ensure that all such temporary changes be corrected immediately after the
permit load has passed.
13.5.3.2 Overweight Permit Loads
Misconceptions often arise about the relationship between Operating Ratings and Overweight Permit
Loads. The primary difference is that Overweight Permit Load analysis usually assumes only one
load on the bridge, which therefore allows the use of single-lane load distribution. The Operating
Rating is based on the standard AASHTO load distribution given in the current Standard
Specifications for Highway Bridges for multi-lane distribution for bridges over 5.50 M in width. This
distribution implies two or more of the Operating Rating trucks being on the bridge side-by-side at the
same time.
The other major difference is that Operating Ratings and Overweight Permit Loads use different load
multipliers, resulting in permit load analysis being significantly more liberal than Operating Rating
analysis. The current Operating and Inventory Ratings, the age and type of structure, the span
lengths, and the Condition Ratings are reviewed for any structure proposed on a permit route. Any
Condition Rating of 4 or less acts as a flag to the permit route reviewer who will then request more
detailed information on the structure, including the written inspection comments. Reduced strength in
a portion of a bridge can often be avoided by controlling the load path of the Overweight Permit Load
across the bridge.
13.5.3.3 Super-heavy Loads
Overweight Permit Loads are classified as “routine” or “super-heavy.” Routine Overweight Permit
Loads may be allowed in the regular traffic stream, sometimes with escorts if the load is also overlength or over-width. Therefore, the standard AASHTO load distributions are appropriate since there
may be a legal truck alongside the routine permit truck crossing a bridge at the same time.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-31
The term Super-heavy Permit Load usually designates total loads over 115.6 T gross to represent the
lower range of a typical super-heavy load and consists of a 6.5 T steering axle followed by four
groups of three axles, each totaling 27.3 T. Any configuration with multiple axles with a gross load of
over 115.6 T is considered a super-heavy load and requires structural evaluation of individual bridges.
Loads with individual axles or axle group weights that exceed the maximum permit weights are also
considered to be super-heavy. Any load exceeding 91.0 T with a total overall length of less than 29.0
M is also considered super-heavy.
The Super-heavy Permit often requires that the load cross all bridges straddling a lane line in the case
of four or more lanes on a two-way bridge, or straddling the center line for a two-lane bridge. This
procedure ensures that other legal trucks will not be alongside the super-heavy load and also gives
better load distribution. The AASHTO load distributions used for super-heavy loads are therefore
usually single lane, thus allowing higher Super-heavy Permit gross loads to safely cross the bridge.
A printout of the proposed list of bridges to be crossed is reviewed by the Traffic Authorities and the
RBD. Often, based on experience of the evaluator and other guidelines, it is necessary to structurally
evaluate only a fraction of the bridges on an extensive proposed super-heavy route. Any bridges on
the route which have Deck Condition Rating or Superstructure or Substructure Component Ratings of
4 or less, trigger the need for review of the actual written Bridge Inspection Record. This bridge-bybridge evaluation is one of the primary reasons that the data in the electronic Bridge Inventory Files
must be accurate and up-to-date.
Super-heavy Permit Loads are usually speed-controlled on bridges, sometimes as slow as a walk
speed to minimize impact forces.
Many Super-heavy Permit Loads also have greater than the usual 1.83- M axle gage. The gages for
Super-heavy Permits can commonly be as much as 6.10 M with 16 tires on each axle line. Methods
of load distribution for these special carriers cannot directly use the customary AASHTO distributions,
which are based on 1.83- M axle gages with four tires on an axle line.
13.5.3.4 Other Differences between Overweight Permits and Operating Rating
There are other major difference between Operating Ratings and Overweight Permit Loads.
The Operating Rating is usually based on Load Factor (LF) criteria, which use multipliers of 1.3
applied to both the dead and live loads. The live load has an additional allowance of up to 30 percent
for impact. Note that Inventory Rating uses a significantly higher live load multiplier of 2.17. The
result for either Operating Rating or Inventory Rating is compared to the yield or ultimate strength
capacity of the members. A “phi” strength reduction factor (usually from 1.0 to 0.85) is also applied for
concrete members.
Overweight Permit Load analysis usually assumes a factor of 1.0 applied to both the dead and live
loads. Ten to 30 percent is added to the live load for impact, depending on the speed control and type
of load suspension system. Stresses are compared to an allowable maximum of 75 percent of the
yield capacity of steel members or 75 percent of the ultimate capacity for concrete members. The
reciprocal of 75 percent is 1.33; thus it can be seen that Overweight Permit Load analysis with AS
methods has essentially the same factor of safety as an analysis using LF criteria. This result will be
demonstrated below by a specific example comparison.
13.5.3.5 Overloads on Posted or Substandard Bridges
Occasionally a request is made for a Routine Overweight Permit or a Super-heavy Overweight Permit
to cross a load-posted bridge. Traffic Authorities does not allow overweight permits for posted
bridges. However RBD can allow overweight vehicles to cross load-posted bridges only when there is
no other route. For these cases, RBD qualified Contractors perform structural evaluation of the
bridge(s) in close coordination with the mover of the load. The evaluations may consider the use of
shimmed mats, temporary shoring, or specialized moving equipment that allows redistribution of the
load between axle groups as the load crosses.
Certain other bridges that are not load posted may not be capable of carrying Routine Overweight
Permit Loads or Super-heavy Permit Loads. Bridges that are in this category include, but are not
limited to, continuous flat slabs with original H-15 designs. These bridges have short spans and were
designed with the single H-load pattern truck placed along the span for maximum design conditions.
Many of these bridges when rated with the now required HS-load pattern, and even using LF analysis,
will rate at significantly less capacity than other types of bridges designed with H-load patterns.
These bridges, though not currently load posted, must be carefully evaluated when overload permits
are considered. This is the primary reason that the original design loads given in the electronic Bridge
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-32
Inventory Files should be entered correctly. Often these bridges have been widened, and the
widening design load has been incorrectly entered as the original design load.
13.5.3.6 Pre- and Post Move Inspection
Another occasional responsibility of the Bridge Inspection Supervisor/ Engineer is to inspect bridges
before and after the passage of a particular overweight permit load. A representative of the ownermover should be present at these types of inspections. Cast-in-place short span slab bridges,
particularly those which have been widened from an original H-10 design to an H-15 or H-20 design,
are susceptible to cracking by overloads.
Unusual bridges, such as arch spans, segmentally constructed post-tensioned spans, or long-span
plate girder bridges, may also need special attention before, during, and after the move of an
overweight permit load. It has been found that simple attention to the sounds made by a bridge when
the load passes will call attention to possible broken diaphragm connections or lateral wind bracing
connections that actually act as torsional bracing for curved and/or heavily skewed structures.
13.5.4
Example of Inventory, Operating, and Permit Loads
13.5.4.1 Typical Continuous I-Beam Bridge
To further demonstrate the differences between the various types of analyses, a typical standard
bridge is chosen for comparative analysis. This bridge is a three-span continuous I-Beam bridge
originally designed in the 1950s and 1960s. These Bridges were commonly designed to H-15 loads
(13.6 Tons).
This bridge has a 7.90 M. roadway between faces of railings and is composed of four 762 mm deep
wide-flange rolled beams with relatively short cover plates at the interior supports. The beams are
spaced at 2240 mm, and the slab is 1650 mm. An elevation and cross-section of the bridge are
shown in Figure 13-6. The design is non-composite, meaning that the slab is assumed to slip
longitudinally along the top flanges when loaded. The beams are 36W135 continuous with 254 mm.
x15.875 mm x 4268 mm cover plates top and bottom at supports.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-33
Figure 13-6 Typical I-Beam Bridge Elevation and Cross-Section
13.5.4.2 Rating Analysis Steps
The steps used in the typical rating analysis for the structure are describes below.
1.
Calculate Dead Load. Using the total steel weight given in the plans, subtract
calculated weight of beams including cover plates and check that remainder is about
5 percent of beam weight. This result represents the diaphragms, connections, and
other miscellaneous steel. If this number is not about 5 percent, determine the
discrepancy. Sometimes the total weight in the plans is in error, but this check usually
gives the rater verification for the estimated dead load. Use the total steel weight,
which includes the diaphragms, as a uniform load per LF, distributed equally to one of
the interior beams. Use the total slab quantity given in the plans calculated as a
uniform load per LF also distributed equally to an interior beam. Verify by comparison
to the dead load of slab for a typical interior beam using the slab thickness. Add in
dead load for any overlay and railings.
2.
Compute Dead Load Moments. Dead load moments need only be calculated at
critical locations such as the maximum positive moments for each span and the
negative moments at the interior supports. The analysis should use the actual span
lengths center-to-center of bearing, and not the nominal span lengths. It is preferable
to use a computer program, but hand analysis from continuous beam coefficients is
also acceptable. The normal sizes of cover plates over supports will “draw” up to
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-34
about 6 to 12 percent more negative moment, and will reduce positive moments when
compared to a constant cross section analysis, which is assumed when using
continuous beam coefficients or other similar tables or charts. Almost all continuous
beam designs used influence coefficients for a constant cross section.
3.
Determine Controlling Live Loading Conditions. Some computer programs do
this determination automatically, but there is risk in using these programs unless the
user is familiar with their limitations and assumptions. One popular program is
BMCOL51, which is a continuous beam analysis program. It allows any pattern of
live load to be moved in increments along the beam, which can have cover plates and
any areas of composite section if necessary. Thus it is particularly suited to the
analysis of super-heavy loads. It can also identify the locations where the
concentrated load(s) for lane loads must also be placed. Most continuous beams will
have the following live load maximum moments:
a. Max positive moment in end and center spans will usually be from an HS-20
live load with 4.20 M center-to-center of trailer axles. However, for very long
plate girders, the lane loading criteria may sometimes control positive moment.
b. Max negative moment will also usually be from the HS pattern, perhaps with
more than 4.20M between the trailer axles if total length of first plus second
spans is less than about 21.30 M. If the sum of the first two spans is more
than about 22.90 M or 24.40 M, then the negative moment will be from lane
loading of the two adjacent spans with the concentrated loads applied at the
critical positions in the two spans.
4.
Calculate the Moments and Load Ratings. Apply the appropriate load factors for
the various ratings to both the dead and live load moments at each member location
being investigated. Subtract the dead load effect from the member capacity at yield
(if load factor analysis) or from the member capacity at allowable stress (if allowable
stress analysis). The remainder is the live load capacity. Ratio the remainder to the
calculated live load value at the location and multiply by the live load ton designation.
The result is the member rating at that location. It is best to understand this basic
process rather than use a set formula for calculating the load rating.
5.
Tabulate the Maximums. Identify the locations for which stresses and ratings are to
be calculated. Often the maximum positive moment sum of dead plus live effects will
not be at the point of maximum dead load or live load moment. This condition is
another reason to use a computer analysis such as BMCOL51.
6.
This program allows the combination of dead and live loads to be investigated at all
points along the continuous member with proper consideration of the effects of cover
plates and composite regions, if any. The maximum moments in the end spans may
not be the same, even though they have the same span length, due to the
unsymmetrical live load pattern. For the results discussed in the remainder of this
section, Program BMCOL51 was used with 21.00– 25.14 – 21.00 M spans.
13.5.4.3 Results for I-Beam Bridge
An H-pattern was used for comparison (normally not necessary) with no railing and no overlay as an
additional check on the original design using allowable stresses. This design pre-dated the 1965
design shown on the standard plans and obviously was done using an allowable stress of 124 MPa.
In 1965 many standard details were changed to specify “H.Y.C.” structural steel which is equivalent to
ASTM A-36. However, the design load was kept the same, and no change was made in the size of
the cover plates. An HS loading, using the allowable stress or load factor methods, and Inventory
Rating or Operating Rating methods was also made for comparison. The various analyses are
summarized in the following table:
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-35
Table 13-3(b) Comparison of Analyses for Example Bridge
Loa ding
Ana l ysi s Method
H (1) N
AS -IR
1s t or 3rd Span
H 20.08
Support
H 14.24*
Middl e Span
H 18.94
H (2) N
AS -IR
H 23.46
H 17.59*
H 22.28
HS (3) N
AS -IR
HS 15.78
HS 17.60
HS 14.84*
HS (4) Y
AS -IR
HS 12.65
HS 10.40*
HS 11.48
HS (5) Y
LF - IR
HS 15.84
HS 17.80
HS 14.97*
HS (6) Y
LF -OR
HS 26.40
HS 29.67
HS 24.96
N = Li ght Ra il i ng a nd no overl a y
Y=T501R ra il ing a nd 2-in overl a y
AS=Al l owa bl e Stres s
LF= Loa d Fa ctor ,
OR=Opera ti ng Ra ting
I R = Inventory Ra ti ng
*= Controll i ng Ra ting
13.5.4.4 Discussion of the Analysis Comparisons
The various analyses summarized in Table 13-3(b) are discussed in the sequence of the loading
number. Current bridge rating analysis usually requires only loadings HS (5) and HS (6). However, if
the resulting rating is significantly different than the design load, then solutions similar to loadings H
(1) or H (2) may be necessary to determine the reasons for the difference.
1.
H (1) - Used to verify analysis with an assumed allowable stress of 124.02 MPa which
is appropriate for A7 steel. Also assumed to have no overlay and light railings. Note
that the controlling rating of H14.24 is close to H-15. There would be an overstress of
2.5 percent if exactly H-15 loading was used. Designing up to a 5-percent overstress
was very common for these structures.
2.
H (2) - This comparison analysis was made with an allowable stress of 137.80 MPa,
which is appropriate for A36 steel. The remainder of the following comparisons are
also with A36 steel.
3.
HS (3) - This comparison is with an HS truck. Note that the controlling HS14.84 rating
implies a total Individual rating truck load of 26.7 T, which compares with the H17.6
rating truck of 17.6 T.
4.
HS (4) - This analysis demonstrates the effect of using the actual current in-place
modern railing, a T501R retrofit railing in this case, and a 50 mm overlay. This
amount of overlay is very common for structures of this age. Note that the controlling
rating shifts from the end span to the support due to the added influence of the
greater uniform dead load. The reduction in the rating is 30 percent simply due to the
added dead load.
5.
HS (5) - This analysis demonstrates the current IR for the bridge using LF analysis
methods. The HS14.97 rating implies a single inventory rating truck load totaling 27 T
or two trucks side-by-side totaling 54 T.
6.
HS (6) - This analysis demonstrates the current OR for the bridge using LF analysis
methods. The HS24.96 rating implies a single operating rating truck load totaling 45 T
or two trucks side-by-side totaling 90 T.
Note that the OR of solution HS (6) is equal to 5/3 x the IR of solution HS (5) which directly reflects
the difference in the live load rating factors.
13.6
13.6.1
Bridge Programming
Basis for Bridge Rehabilitation or Replacement
A bridge is considered to be Structurally Deficient if it is not able to carry the truck loads expected of
the bridge. The highway or road system on which the bridge is located affects the expected truck
loading. For instance, a bridge on the Interstate highway system must be considered able to have an
Inventory Rating of at least HS-20, while a bridge on an off-system county road would be considered
adequate to carry its necessary truck loads if the Inventory Rating was HS-15.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-36
A bridge is considered to be Functionally Obsolete if the deck width, vertical clearance, waterway
adequacy, or approach roadway alignment is not adequate for the traffic type, traffic volume, or
expected flood waters.
13.6.2
Bridge Program
13.6.2.1 Qualification for Rehabilitation or Replacement
HIB projects are selected using a prioritization process that calculates a score for each candidate
bridge project. The score considers Average Daily Traffic (ADT), cost per vehicle, bridge condition,
roadway width, and the bridge Sufficiency Rating. The scoring process is referred to as the Eligible
Bridge Selection System (EBSS). The selection of bridges is made yearly in the order of descending
TEBSS scores for the on- and off-system eligible bridges. However, bridges with one or more critical
deficiencies may also be selected, regardless of EBSS score. Such critical deficiencies are defined
as extremely low Condition Ratings, Sufficiency Ratings, or load capacities. For instance, bridges
which are closed, or that have a Deck Condition plus Superstructure Condition Rating of 10 or less,
automatically qualify. Bridges that have Sufficiency Ratings less than 30 also automatically qualify.
13.6.2.2 Eligible Bridge Selection System (EBSS)
The Sufficiency Rating, established during the biennial bridge inspections, plays an important role in
selecting which of the bridges are eligible for rehabilitation or replacement. In order for a bridge to be
considered eligible, it must have a Sufficiency Rating of 80 or less and be either Structurally Deficient
or Functionally Obsolete. These three terms are defined in following subsections with the same titles.
If the Sufficiency Rating is below 50, the bridge is eligible for replacement or rehabilitation if the
anticipated replacement costs are greater than 120 percent of the rehabilitation costs. Rehabilitation
may be considered if the Sufficiency Rating is between 50 and 80. Bridges cannot be considered
eligible if their Sufficiency Rating is greater than 80.
13.6.2.3 Structural Deficiency
A bridge is considered Structurally Deficient if there is a Condition Rating of 4 or less for:
Item 58 (Roadway) or
Item 59 (Superstructure) or
Item 60 (Substructure)
or if there is an Appraisal Rating of 2 or less for:
Item 67 (Structural Condition) or
Item 71 (Waterway Adequacy)
Item 71 is considered only if the last digit of Item 42 (Type of Service Under the
Bridge) is 0, 5, 6, 7, 8, or 9
13.6.2.4 Functional Obsolescence
Three methods establish if a bridge is Functionally Obsolete:
1.
An Appraisal Rating of 3 or less for Item 68 (Roadway Geometry), and Item 51
(Bridge Roadway Width) is less than the following:
Table 13-4 Functionally Obsolete
I tem 29 (ADT)
Item 51 (Roa dwa y Wi dth)
equa l to l es s tha n
Curb to Curb (feet)
250
20
750
22
2700
24
5000
30
ADT greater than 35,000 requires review by HIB Bridge Division
2.
An Appraisal Rating of 3 or less for either of:
Item 69 (under-clearances) or
Item 72 (Approach Roadway Alignment)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-37
Item 69 is considered only if the last digit of Item 42 (Type of Service Under the
Bridge) is 0, 1, 2, 4, 6, 7, & 8
3.
An Appraisal Rating of 3 or less for either of:
Item 67 ( Structural Condition) or
Item 71 ( Waterway Adequacy)
13.6.3
Sufficiency Ratings
13.6.3.1 Calculation of Sufficiency Ratings
The Sufficiency Rating of a bridge is determined during the biennial bridge inspection and is intended
to indicate a measure of the ability of a bridge to remain in service. Calculations for Sufficiency
Ratings utilize a formula that includes various factors determined during the bridge field inspection
and evaluation. The items considered below are those described in the instructions for coding guide.
Ratings are on a scale of 1 to 100, with 100 considered as an entirely sufficient bridge, usually new;
an entirely deficient bridge would receive a rating of 0. Only bridges that carry vehicular traffic receive
a Sufficiency Rating.
An interactive program can be used to calculate Sufficiency Ratings and determine Structural
Deficiency and Functional Obsolescence. One of those programs is called BRISUF and it calculates
the Sufficiency Rating based on data entered through an interactive prompt process
Whether using the prompted program BRISUF or hand calculations, the Sufficiency Rating (SR) is
calculated by the equation:
SR = S1 + S2 + S3 - S4
A discussion of how to arrive at each variable immediately follows.
S1 is the Structural Adequacy and Safety (55 maximum, 0 minimum) calculated by the equation:
S1 = 55 - ( A + I )
A is the Reduction for Deterioration (not to exceed 55 or be less than 0) based on the lowest value of
Item 59 (Superstructure Rating) or lowest value of Item 60 (Substructure Rating):
if
2 then A = 55
if = 3 then A = 40
if = 4 then A = 25
if = 5 then A = 10
if
6 then A = 0
if = N then A = 0
I is the Reduction for Load Capacity (not to exceed 55 or be less than 0) calculated by the following
equation and table: I= 0.2778 ( 36 - AIT )
AIT is the Adjusted Inventory Tonnage, calculated by the following table of multipliers based on Item
66 (Inventory Rating):
Table 13-5 Adjusted Inventory Tonnage
1s t di git of
I tem 66 i s …
AI T=2nd & 3rd di gi ts
of Item 66
mul tipl ied by …..
AUGUST 2010
1
1.56
2
1.00
3
1.56
4
1.00
5
1.21
6
1.21
9
1.00
REVISION NO. 03
BRIDGE INSPECTION 13-38
S2 is the Serviceability and Functional Obsolescence (30 maximum, 0 minimum) calculated by the
equation:
S2 = 30 -[J + ( G + H ) + I ]
J is a Rating Reduction (not to exceed 15) calculated by the following equation and tables:
J=A+B+C+D+E+F
If Item 58
(Deck Condition)
3 A=5
=4 A=3
=5 A=1
6 A=0
=N A=0
If Item 67
(Structural Evaluation)
3 B=4
=4 B=2
=5 B=1
6 B=0
=N B=0
If Item 68
(Deck Geometry)
3 C=4
=4 C=2
=5 C=1
6 C=0
=N C=0
If Item 69
(Under-clearances)
3 D=4
=4 D=2
=5 D=1
6 D=0
=N D=0
If Item 71
(Waterway Adequacy)
3 E=4
=4 E=2
=5 E=1
6 E=0
=N E=0
If Item 72
(Approach Roadway Alignment)
3 F=4
=4 F=2
=5 F=1
6 F=0
=N F=0
(G + H ) is a Width of Roadway Insufficiency (not to exceed 15) calculated by the following
relationships. The values for X and Y are first found by the following two equations: X (ADT/Lane) =
Item 29 (ADT) ÷ First two digits of Item 28 (Lanes) Y (Width/Lane) = Item 51 (Roadway Width) ÷ First
two digits of Item 28 (Lanes)
Use following three conditions of (1), (2), or (3) to then obtain the values for G and H :
1.
For all bridges except culverts : (Item 43.4, Culvert Type, must be blank or 0)
a. If Item 51 (Roadway Width) + 2 feet is less than Item 32 (Approach Roadway
Width), set G = 5
b. If Item 51 (Roadway Width) + 2 feet is greater than or equal to Item 32
(Approach Roadway Width), set G = 0
2.
For one-lane bridges (including one-lane culverts):
a.
If the first two digits of Item 28 (Lanes) = 01, and Y < 14 set H = 15
b. 14
c.
3.
AUGUST 2010
Y
Y < 18 set H = 3.75 ( 18 - Y )
18 set H = 0
For bridges with two or more lanes (including culverts):
a. If 1st two digits of Item 28 = 02 and Y
16, set H = 0
b. If 1st two digits of Item 28 = 03 and Y
15, set H = 0
REVISION NO. 03
BRIDGE INSPECTION 13-39
c.
If 1st two digits of Item 28 = 04 and Y
14, set H = 0
d. If 1st two digits of Item 28 = 05 and Y
12, set H = 0
If any one of the above four conditions is met, do not continue with further determination of H since no
lane width reductions are necessary.
Otherwise, determine H based on the following values for X (ADT/Lane) and Y (Width/Lane):
If
X
50
50 < X
125
125 < X
375
375 < X
1350
X > 1350
and
Y<9
Y 9
set
H = 7.5
H=0
Y < 10
10 Y < 13
Y 13
H = 15
H = 5.0 (13
H=0
Y)
Y < 11
11 Y < 14
Y 14
H = 15
H = 5.0 (14
H=0
Y)
Y < 12
12 Y < 16
Y 16
H = 15
H = 3.75 (16 Y)
H=0
Y < 15
15 Y < 16
Y 16
H = 15
H = 15.0 (16
H=0
Y)
Note that in any case, the value of (G + H ) cannot exceed 15.
I is a Vertical Clearance Insufficiency (not to exceed 2) set by the following:
1.
If Item 100 (Strategic Highway Corridor Network, also called STRAHNET) is greater
than 0 and Item 53 (Min Vert Clearance over deck) 1600 set I = 0 Item 53 (Min Vert
Clearance over deck) < 1600 set I = 2
2.
If Item 100 (STRAHNET) is equal to 0 and Item 53 (Min Vert Clearance over deck)
1400 set I = 0 Item 53 (Min Vert Clearance over deck) < 1400 set I = 2
S3 is the Essentiality for Public Use (not to exceed 15) calculated by the equation:
S3 = 15 - ( P + M )
P is the portion for Public Use (not to exceed 15) First calculate K which is a value based on
the previously calculated S1 and S2 : K = ( S1 + S2 ) ÷ 85 P = (Item 29 (ADT) × Item 19
(Detour Length) × 15) ÷ (200,000 × K)
M is the portion for Military Use (not to exceed 2) If Item 100 (Strategic Highway Corridor
Network, also called STRAHNET) is greater than 0, set M = 2 If Item 100 (STRAHNET) is
equal to 0, set M = 0
Note that in any case, the value of ( P + M ) cannot exceed 15.
S4 is a Special Reduction which is used only when S1 + S2 + S3 is greater than or equal to 50.
S4 is calculated by the following equation: S4 = R + S + T
R is a Detour Length Reduction (5 maximum, 0 minimum) R = [ Item 19 (Detour Length) ]4 x [
5.205 X 10-8 ]
S is a Structure Type Reduction set by the following: If the 1st digit of Item 43.1 (Main Span
Type) is 7 or 8 (Movable, Suspension, or Stayed), or if the 2nd digit of Item 43.1 is 2, 3, 4, 5,
6, or 7 (portion of structure is beside or above roadway), set S = 5 Otherwise, set S = 0
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-40
T is a Traffic Safety Feature Reduction set by Item 36 (Traffic Safety Features) which rates
the adequacy of the bridge railings, transitions, and approach guard fences:
If 1 or none of the 4 digits of Item 36 are 0, set T = 0
If 2 of the 4 digits of Item 36 are 0, set T = 1
If 3 or the 4 digits of Item 36 are 0, set T = 2
If all 4 of the digits of Item 36 are 0, set T = 3
13.7
13.7.1
Bridge Records
Overview
13.7.1.1 Summary
This presents the specific requirements for inspection records for Libyan bridges. Records must be
prepared and kept in a consistent manner, whether done by RBD personnel or by Contractors.
This chapter includes discussion of the following major topics:
Definition of Terms
Contractors Requirements
Coding Guidelines
Forms
Calculations
Data Submittal
Bridge Folder
13.7.2
Definition of Terms
13.7.2.1 Bridge Record Terms
A partial list of definitions related to bridge inspection is provided in various chapters of this Manual.
The following discussion of Bridge Records includes some specific terms:
Bridge
A structure, including supports, erected over a depression or an obstruction, such as water, a
highway, or a railway; having a roadway or track for carrying traffic or other moving loads; and having
an opening measured along the center of the roadway of more than 6M between faces of abutments,
spring lines of arches, or extreme ends of the openings for multiple box culverts or multiple pipes that
are 1.50M or more in diameter and that have a clear distance between openings of less than half of
the smallest pipe diameter.
Bridge Folder
The file for each bridge maintained by the District Bridge Inspection Coordinator. The Bridge Folder
has dividers on which the various bridge record documents can be fastened in a specific order.
Bridge Identification
The unique 12-digit number assigned to any structure meeting the definition of a bridge. The number
includes the 3-digit Shabiya Number, the 4-digit Control Number, the 2-digit Section Number, and the
3-digit Permanent Structure Number. The Planning Department assigns the road and city street index
numbers, which begin with a letter instead of number. This off-system index number uses the same 6
digits assigned to Control and Section for on-system highways. The Permanent Structure Number for
off-system bridges is assigned by the district.
Bridge Inventory File
This consists of electronic data of RBD’s bridge inventory, inspection, and appraisal files for each
bridge on a public roadway in Libya. The data can be entered from a completed coding form or can be
are entered directly from an input screen of any appropriate data entry device. The instructions for
coding guide describe the step-by-step data entry requirements.
Bridge Record
The over-all collection of data including the Bridge Folder with completed forms, printout of coded
electronic data, sketches, cross sections, photos, etc. It also includes the Bridge Inventory File stored
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-41
on electronic media. The Bridge Record also includes the bridge plans, if available, copies of which
should be in the Bridge Folder. Some of the bridge plans may also be available on electronic media
in the form of computer-aided drafting (CAD) drawings.
Culverts
Multiple-barrel box culverts or multiple-pipe culverts are sometimes classed as bridges and a
complete Bridge Record is made. The 1994 AASHTO Manual defines a bridge as any structure
carrying traffic (highway or railroad) having an opening measured along the centerline of the roadway
of more than 6.0 M between the limits of the extreme openings of abutments, arches, or multiple
boxes. This definition has created the anomaly in some cases where, for instance, three 1.80 M
multiple box culverts installed at more than about a 15-degree skew to the roadway must have a
Bridge Record. If the same three box culverts are installed perpendicular to the roadway, they have
no Bridge Record. The AASHTO definition continues for multiple-pipe culverts by stating that they
may be classed as bridges provided the distance between individual pipes (the fill) is less than half
the adjacent pipe diameter. To facilitate consistency in future recording of culvert installations, a
separate subsection titled Multiple-Pipe Culverts is contained in this chapter.
Elements Data
The supplemental electronic bridge inventory, inspection, and appraisal data taken for RBD, the data
are entered on forms, but entry from a prompt screen of an appropriate data entry device can also be
used. The Elements: Field Inspection and Coding Manual describes the step-by-step data entry
requirements.
Engineer
The Professional Engineer having responsibility for ensuring the accuracy of the information
contained in the Bridge Record. A pre-qualified Contractor that has a Consulting Engineer on board
engaged by HIB to perform routine bridge inspections is also considered in the following discussions
to be covered by the term Engineer. The same basic procedures are used by RBD personnel as are
required for Contractors.
Forms
Specific forms such as Bridge Inspection Record Form, Bridge Appraisal Worksheet Form, Bridge
Inventory Record Form. Some forms may be developed as needed for specific types of data or
classes of structure.
NBI Sheet
A printed copy with abbreviated names of the numerical data in the electronic Bridge Inspection File.
NBI stands for National Bridge Inventory, which must include all the information required by HIB.
Permanent Structure Number (PSN)
A unique three-digit number assigned to any structure meeting the definition of a bridge. It is part of
the 12-digit Bridge Identification. PSNs are assigned by Control in ascending order as the bridges are
built and are not necessarily in sequence along the Control or Section. An on-system bridge replaced
by a new bridge at the same location will have a new number assigned. A widened or reconstructed
bridge will retain the same number. Shabias assign similar unique numbers to off-system bridges. An
off-system bridge replaced by a new bridge will retain the same PSN. A bridge with a longitudinal
open joint in the middle will have two PSNs, even if the substructure is common.
Route Over or Under
A bridge at intersecting highways is defined as an underpass or overpass based on the inventory
hierarchy of the two routes. This description is used where required on all forms, plans, etc. The
lower route takes precedence if the highways are of equal hierarchy.
Signing and Sealing.
The Engineer must sign and date many of the documents prepared for a bridge inspection.
Work Authorization.
Authorization issued by HIB to a Contractor (Engineer) to perform inspections of bridge structures.
The Work Authorization is normally issued for a specific period of time with a commencement and
ending date specified. To receive Work Authorizations, Contractors must pre-qualify by
demonstrating that they and their staffs are competent to inspect bridges.
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-42
13.7.3
Contractor Requirements
13.7.3.1 General Requirements
Contractor (Engineers) engaged by RBD to perform routine bridge inspections must adhere to the
following general requirements in addition to those normally expected for Contractors.
The Contractor (Engineer) must inspect each bridge in accordance with the information given in this
Manual and must record the findings electronically and on the appropriate standard forms. The
Engineer must uphold a reasonable standard of care for routine inspections, which is understood to
imply an attentive visual and auditory inspection aided by routine inspection tools as afforded by
customary means of access.
The Engineer must inspect the bridges within the assigned inspection areas only and must verify the
bridge locations. A qualified Inspection Team Leader must be present at each bridge site during the
bridge inspection. When the inspections are completed, reports are to be returned to RBD within 30
days from the date of inspection. However, bridges needing special consideration (which includes all
bridges that have any Condition Rating of 4 or lower) must be brought to the immediate attention of
the RBD, both verbally and in writing. If the inspection indicates significant deterioration of any
structural element, documentation such as notes, measurements, sketches, and photos must be
included.
13.7.3.2 Tools and Safety Equipment
Routine inspection tools are listed in this Manual. The Engineer is required to use hard hats, safety
vests, traffic cones, vehicle safety lights, and “Bridge Inspection Ahead” or “Survey Crew Ahead”
signs for all bridges being inspected. The inspections must be conducted with minimal disruption to
traffic.
Coordination with Housing and Infrastructure Board- Roads and Bridge Department (HIB-RBD)
A 216 x 279 mm copy of the bridge location map, with the bridge location highlighted, must be
included as part of each Bridge Record.
New bridges located by the Engineer require approval from RBD before an identification number
(Permanent Structure Number) is assigned and before authorization can be given for the Engineer to
inspect the bridge and add the data to the Bridge Record. Bridge locations must be indicated on the
map(s). The Engineer must create a new Bridge Folder, complete all forms, and input all data
required for the electronic Bridge Inventory File to ensure a complete and accurate record. The
Engineer must not inventory or inspect a bridge that is under construction. If the bridge opens to
public traffic at a reasonable time within the work authorization period, RBD may direct the Engineer
to inventory and inspect the bridge.
13.7.4
Coding Guidelines
13.7.4.1 Summary of Instructions (for on-and off-system bridges)
The Engineer must adhere to the step-by-step instructions for entering the data in the electronic
Bridge Inventory File as presented in the detailed instructions for coding guide. The Coding Guide
also includes interpretations, examples, and other data input guidance. The Coding Guide follows a
“card” data input sequence summarized on a five-page form not actually used for written entries but
used as an input reference guide. A form could still be used, but data are usually directly input
electronically using prompt screens on a computer, or screen images of the “card” data sequences. In
any case, the resulting electronic Bridge Inventory File for each bridge is in a consistent format. The
data entry procedures apply to both on- and off-system bridges. The electronic Bridge Inventory Files
contain a record for each Bridge Class Structure. The definition of a Bridge Class Structure is
described in Item 112 in the “Instructions for Coding Guide.”
13.7.4.2 Multiple-Pipe Culverts (for on- and off-system bridges)
To achieve future consistency in recording information, the following clarifications are to be used for
creating or maintaining Bridge Records for multiple-pipe culverts:
Do not remove any existing multiple-pipe culverts from the Bridge Inventory File. The
installation may already be in the prioritization process for repair or replacement, and the
process should not be disrupted.
Do not create Bridge Records for any new multiple-pipe culverts that are individually less
than 1500 mm in diameter even if the total installation, including fill between pipes, is
more than 6.0 M along the roadway. Inspections of smaller diameters would be difficult to
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-43
make and the results would probably be of dubious quality. It is also very inconsistent
engineering logic to require inspection of, for instance, an installation of five 1200 mm
pipe culverts and no inspection of an installation of four or fewer pipes of the same
diameter.
Bridge Records must be made and maintained for multiple-pipe culverts that are
individually 1500 mm or greater in diameter, providing the total installation meets the 6.0
M length criterion.
13.7.4.3 Data Quality (for on-and-off system bridges)
Data quality for all information kept for each bridge, and in particular the electronic Bridge Inventory
Files, cannot be overemphasized. The data in the files must be kept in as up-to-date condition as
possible. Data updates reflecting changes to an existing on-system structure must be made within 90
days of the evaluation or inspection that denotes the change in status. New, rebuilt, or rehabilitated
structures also must be reported within 90 days of job completion. The data update time limit is 180
days for off-system structures.
13.7.4.4 Elements Data (only for on-system bridges)
Element-specific data are to be recorded for each bridge.
The step-by-step instructions for entering the electronic Elements Data are presented in the Elements:
Field Inspection and Coding Manual. The instructions in the “Elements: Field Inspection and Coding
Manual” also include interpretations, examples, and other data input guidance. The Engineer must
determine the element-specific data, quantities, and condition states for each on-system bridge. HIB
requires the Engineer to complete or demonstrate completion of special training for recording
Elements Data. There are currently 6 “Element Matrix” forms presented in the “Elements: Field
Inspection and Coding Manual.” These data supplement but do not replace those data normally
recorded for the electronic Bridge Inventory File. The Elements Data are also recorded electronically.
A copy on computer diskette in the required format is submitted to the RBD.
13.7.5
Forms
13.7.5.1 General Forms Information
Specific forms and other information used to record the necessary bridge data are briefly described
below for both on- and off-system bridges. The same data are kept for both on-and off-system
bridges except as noted. The forms and necessary information are to be completed for each bridge
and placed in each file of the Bridge Folder in the proper order. Subsection 13.55, Ratings and Load
Posting, discusses Bridge Inspection Record Form and Bridge Appraisal Worksheet From and relates
them directly to the Condition Ratings and Appraisal Ratings.
13.7.5.2 Bridge Inspection Record, (for on- and off-system bridges)
This three-page form presents the inspection information for the basic components of the bridge. The
Engineer enters a rating for each element of each component. For any element rating of 7 or below,
written comments explaining the rating must be included on the form. The signature of the Inspection
Team Leader must be on the form and it must be signed and dated by the Engineer.
13.7.5.3 Bridge Appraisal Worksheet, (for on- and off-system bridges)
This two-page form presents a one-digit rating for each of the traffic safety features, the structural
evaluation, the deck geometry, the under-clearances, the load posting, the waterway adequacy, and
the approach roadway alignment. It is also to be completed in accordance with the “Instructions for
Coding Guide.” Unlike BIR Form, BAW Form requires written comments supporting all the appraisal
ratings. These ratings and associated written comments must be verified by the Inspection Team
Leader and reviewed by the responsible Engineer. A date and signature are required for this form.
13.7.5.4 Bridge Structural Condition History (for on- and off-system bridges)
This form summarizes the current and previous inspection records. If the form exists in the current
Bridge Folder, it should be updated. If no Structural Condition History form is in the Bridge Folder,
create one based on all the previous and current inspections in the folder. The Engineer must enter
the date(s) of inspection, the Engineer’s name, and the various component ratings in the proper
columns of the form. This form does not require signing. However, the last entry date must reflect the
latest inspection.
13.7.5.5 Bridge Inspection Follow-Up Action Worksheet (only for on-system bridges)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-44
This form summarizes the areas of deterioration and makes recommendations for bridge repair. The
number for the HIB R&B Department should be clearly shown on the form.
An extra copy of this form is required for each on-system bridge. These extra copies are grouped with
copies for other bridges with the RBD. These extra copies must be submitted to the RBD at the end
of each series of inspections or at the end of the inspection Work Authorization if done by a
Contractor.
13.7.5.6 Bridge Inventory Record, (for on- and off-system bridges)
This two-page form presents a detailed description of the structure along with a detailed elevation
sketch on the reverse side.
Sketches are not required for off-system bridges if copies of the plans are in the Bridge Folder.
Sketches are not required for on-system bridges if plans are maintained in general files by HIB R&B
Department. However, a notation to this effect should be shown on the reverse side of the form along
with the Plan File reference number.
If no changes have been made to the structure and the existing description and sketch properly
represents the field conditions, a new form is not necessary. The existing form must remain in the
Bridge Folder with no modification by the Engineer.
If no Bridge Inventory Record is in the Bridge Folder, the responsible Engineer must complete a new
form. The number for the Bridge Maintenance Section should be clearly shown on the form. The form
must be signed and dated by the Engineer.
If significant structural modifications have been made to the bridge, a new Bridge Inventory Record,
including a detailed sketch showing the changes from the plans on file, must be completed. The new
form must be signed, sealed, and dated by the Engineer.
The Bridge Inventory Record with sketch serves as the best available “as-built plans” if copies of the
original plans are not available. When plans are available and copies are included or the HIB file
location referenced, a detailed sketch on the reverse side of the form is not required.
13.7.5.7 Bridge Inventory Record Revision (for on- and off-system bridges)
This form is to be used only for minor, non-structural changes to the Bridge Inventory Record. This
form does not require signing. However, a date is required.
13.7.5.8 Channel Cross-Section Measurements Record (for on- and off-system bridges)
This two-page form is completed or updated for each bridge over a waterway (wet or dry). There is
space on the form for four chronological cross-sections (covering approximately eight years). The fifth
and following channel cross sections should be recorded on a new form and the original form retained
in the Bridge Folder. This form is not required for bridge-length culverts. The cross-section
measurements are recorded for the upstream side of the bridge starting at the first abutment. They
must be from the top of the bridge railing or parapet down to the channel bed. These measurements
are made at each bent, each significant change in the channel bed, and at the mid-point of the
channel. The horizontal distance is recorded between each vertical measurement as well as the
cumulative horizontal distance from the beginning of the first abutment. Several additional reference
dimensions are recorded, including top of water level as shown on the form. The responsible
Engineer must add comments on the back of the form. This form require a date and signature.
A sketch on this form is required only for span-type bridges. Bridge-length culverts do not require an
upstream channel sketch or an update to any such sketch that may already be in the Bridge Folder.
Calculations of sediment material quantities will not be required. If there is an existing channel crosssection, plotted to scale, it should be brought forward into the current sketch and the new data plotted
on it in different color ink and referenced with the Engineer’s initials and date. For all bridges that
have plans available, the current channel section must be plotted on a copy of the bridge layout
sheet(s) made from the plans. Two copies of the layout must be inserted in the Bridge Folder. One
copy must be plotted with the current channel cross section and marked as a “work copy” and one
copy must be identified as a “master copy” with no plot of the current channel cross section. If plans
are not available, a sketch is to be drawn to scale. However, the horizontal and vertical scales may
differ if convenient. This sketch does not require signing or sealing. However, a date is required for
each plot or verification of the current channel cross section.
13.7.5.9 Under-clearance Sketch (for on- and off-system bridges)
A sketch on this form is required for all grade separations, including pedestrian, utility, and railroad
underpasses. All necessary dimensions and reference points must be shown. Item 54.2, described in
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-45
the instructions for coding guide, must reference the minimum vertical clearance (to the nearest
millimeters) under the structure. The vertical clearance sign must read 75 mm lower than the actual
measured vertical clearance. Ultrasonic measurements cannot be used. This sketch does not
require signing. However, a date is required.
13.7.5.10 Bridge Summary Sheet (only for off-system bridges)
This one-page form summarizes each component rating, provides recommendations for structure
upgrades, indicates previous and observed and recommended load postings, records current status
of all signs, and denotes materials needed to properly load post the bridge if necessary. The
Engineer must, where appropriate, provide a recommendation for minimum or moderate upgrading for
each bridge with an Inventory Rating of HS-13 or less. The recommendation should consider the
capabilities of the local jurisdiction. The Engineer must document the condition, location, and number
of all signs in place on the date of inspection at all load-posted bridges. The load limit shown on
existing signs must also be recorded. These signs must appear and be legible in the bridge
photographs. The form must be signed and dated by the Engineer.
13.7.5.11 Recommended Change in Bridge Load Zoning, (only for on-system bridges)
This form presents a request for changed load restrictions for an on-system bridge. It must be signed
and dated by an Engineer. If it involves a new limit or a reduction of a current load limit, it must be
accompanied by the most recent inspection report, plans (layouts and structural details), and any load
ratings that support the recommended change.
13.7.6
Calculations
13.7.6.1 General Calculation Requirements
Bridge load rating calculations must be provided in accordance with currently accepted HIB bridge
inspection procedures as described in this Manual and in the HIB Bridge Manual. Note that the
methods of calculation are different for on- and off-system bridges.
The dating and signing of documents must be in accordance with the requirements given in this
chapter.
13.7.6.2 On-System Bridge Calculations
Typically, on-system bridge plans are on file at the RBD office and the plans contain documentation of
the original design load capacity. Load rating analyses (calculations) are usually not required for onsystem bridges. However, the Engineer is required to provide load rating analysis for all on-system
bridges that have any Condition Rating of 4 or less. All on-system bridge files for all bridge types
must contain documentation to support any recommended changes in load ratings. If the Engineer
agrees with the previous calculations, a concurring signed and dated statement must be provided.
All load rating calculations for on-system bridges must be performed using the Load Factor (LF)
method as presented in the AASHTO Manual for Condition Evaluation of Bridges with no exceptions.
Ratings must be calculated and presented to RBD with only an HS-loading for all on-system bridges
for which calculations are required. Some additional analyses may involve bridges that have section
loss or damage to structural members. In these cases, the responsible Engineer is required to verify
and document the conditions of the deficient members and incorporate those findings in the analyses.
All calculations and documentation referring to load-rating capacity are required to be signed and
dated by a qualified, Professional Engineer.
13.7.6.3 Off-System Bridge Calculations
The calculations for off-system bridges may be performed using a Bridge Load Rating (BLR)
computer program, which calculates load ratings using a working stress (WS) analysis method.
However, either WS or LF analysis is acceptable. All steel and truss bridges must have calculations
for the load ratings of all applicable structural elements including the deck, stringer or beams, truss
members, bent caps, and piling or columns. The BLR program will give Inventory and Operating
Ratings for both H- and HS-loadings. However, the recommended load-posting sign must continue to
be based upon Figure 8-1, Simplified Load Posting Procedure, which relates calculated H-load rating
to an equivalent load posting, sign type, and weight limit.
Load rating documentation, including assumptions, is required in the bridge files for all bridges,
including bridge-class culverts. Any assumed load ratings for concrete structures and recommended
load postings must be in conformance with current HIB policies. These policies are described in
Subsection 13.4 Customary Rating Procedures, Rating Concrete Bridges with no Plans, Recording
Appraisal Ratings, Bridge Posting. All off-system bridge files, for all bridge types, must contain
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-46
documentation to support any recommended changes in load ratings. If the Engineer agrees with the
previous calculations, a concurring signed and dated statement must be provided.
All calculations and documentation referring to load-rating capacity are required to be signed and
dated by a qualified Professional Engineer. However, it is acceptable to only initial and date the
calculations, and sign, and date the Bridge Summary Sheet for off-system bridges rather than each
page of the calculations.
Special attention is called to the coding of Items 41, 41.1, and 41.2 of the electronic Bridge Inventory
Files (see coding guide) relating to operational status and load-posting limits. These items must be
verified and revised, if needed, for all bridges and bridge-class culverts. The Engineer must
immediately notify the RBD of any bridges recommended for closure and must include details and
calculations. RBD will set a time to discuss the concerns with the Engineer to review the findings if
bridge closure is necessary.
13.7.6.4 Simplified Load Posting Procedure
This procedure is appropriate for computing posting loads equivalent to the inventory rating.
Approximations are involved which make this procedure unacceptable at load levels higher than the
Inventory Ratings.
The posting load in pounds is the product of the RATING MULTIPKIER and the INVENTORY
RATING in Tons for the standard “H” truck. In selecting the RATING MULTIPLIER from the table use
the longest simple span length or 80% of the longest continuous span length, whichever gives the
longest span length for the bridge. If the resulting span length is 48.0 M or greater, then the bridge
should receive an analysis more exact than this procedure.
The recommended posting increments are listed below. Round off to the nearest increment listed.
Post axle and gross load for span lengths 12.0 M and greater. Post axle load only for span lengths
12.0 M and less. Weight limit signs should conform to the Traffic Management Section of HIB Design
Criteria. The recommended signs are R12-2Tb or R12-4Tb, except if the axle load is noted use signs
R12-2Tc or R12 -4Tc.
EXAMPLE 1:
10.0M Simple Span Slab & Girder Bridge, H14 Rating
Axle = 14 x 660 Kgs = 9240 Kgs
Post 21,000 tandem axle (Signs R12-2Tc)
EXAMPLE 2:
36.0M Pony Truss. H7 Rating
Axle =7 x 660 = 4,620 Kgs
Gross = 7 x 1045 Kgs = 7315 Kgs
Post 4545 Kgs axle or tandem and 7273 Kgs Gross (sign R 12 -4Tb)
EXAMPLE 3:
9.0 M – 12.0 M – 9.0 M Continuous Slab Bridge with 7.6 M slab approach spans, H10
Rating
0.8 x 12.0 M = 9.0 M > 7.6 M = Use 7.6 M span
Axle = 10 x 673 Kgs = 6730 Kgs
Post 673 Kgs Axle or tandem (Sign R 12 -2Tb)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-47
Table 13-6 Load Posting Tables
SPAN
RATING
MULTI PLI ER
AXLE
OR
GROSS
TANDEM
METER
Kgs ./H-TON
‹6
727
7.6
704
9.1
682
10.7
659
Kgs /H-TON
12.2
659
1410
13.7
659
1340
15.2
659
1270
18.3
659
1180
21.3
659
1140
24.4
659
1110
27.4
659
1090
30.5
659
1070
36.6
659
1040
42.7
659
1020
48.8
659
1000
LOAD INCREMENTS
LOAD I NCEMENTS
FOR AXLE OR
FOR GROSS LBS
TANDEM Kgs
2270
3640
3410
4540
4540
5450
5680
6360
6820
7270
7940
9090
9540
10910
10910*
12730
12730*
14540
14540*
16360
18180
20000
21820
23640
27270
30910
34540
* Axl e l oa d e xce e ds 9090 Kgs . Si ngl e a xl e
l i mi t, the re fore pos t for ta nde m a xl e
(Si gns R 12 -2Tc or R 12- 4Tc)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-48
Table 13-7 Load Posting Signage
R12 – 2Tb
R12 – 2Tc
R12 – 4Tb
60mm x 90 mm
13.7.7
R12 – 4Tc
60 mm x 105 mm
Data Submittal
13.7.7.1 General Data Submittal Requirements (for on- and off-system bridges)
When HIB contracts for bridge inspections by Contractors, the Contractors must provide monthly
submissions of prepared Bridge Folders unless otherwise directed by the RBD. Folders can be
submitted to the RBD by mail or in person.
Bridge Folders prepared by RBD personnel must be documented, signed and dated in the same
format as herein described.
All data included in the Bridge Folder are prepared to meet the requirements given in this Manual.
Updates to the electronic Bridge Inventory File must be made within 90 days for on-system bridges
and 180 days for off-system bridges.
13.7.7.2 Photographs (for on- and off-system bridges)
The Engineer must provide 100 mm x 150 mm color photographs of each bridge for the bridge
inspection files. The photos must be suitably mounted, two on a page, with compatible adhesive on
216 mm x 280 mm paper. Spray-on adhesive is not acceptable. Each photo must have a descriptive
caption and must note the approximate compass direction the photographer was facing. Each photo
will have a date taken as part of the caption unless the date is automatically printed on the photo.
Digital photographs will be accepted at a minimum resolution of 1024 x 768. They are to be
presented in the same format and dimension as described above.
The following photos must be present in each Bridge Folder as a minimum:
1.
AUGUST 2010
Roadway View. Photos must be taken along the centerline of the roadway looking
“down the bridge” showing views of the bridge as seen from the roadway. The
direction should normally be in the increasing station direction, if known, or in the
increasing direction of the field reference markers. Long or curved bridges may
require multiple photos at different bridge locations.
REVISION NO. 03
BRIDGE INSPECTION 13-49
2.
Elevation View. Photos must be taken of the bridge showing the complete length.
For some bridges it may be impossible to show the entire structure due to length,
curvature, or vegetation. In these cases, oblique angles at greater distances are
acceptable. However, multiple photos attempting to show every part of the bridge
should not be submitted.
3.
Underside View. Photos must be taken of the underside of the bridge showing the
typical type of superstructure. Bridges with several types of superstructure will require
additional photos.
4.
Stream or Roadway below Bridge. Photos should be taken from below the bridge
showing the stream or roadway as it passes under the bridge. Any scour or
significant erosion that is present should be photographed.
5.
Weight Limit Signs. Photos must be taken on both approaches to document the
actual signs in place, missing, or damaged. The photos must show the position of the
signs with respect to the bridge. The weight limit on the signs should be legible in the
photos.
6.
Upstream and Downstream Channel Views. Photos must be taken to document
the condition of the channel upstream and downstream of the bridge. These photos
should be taken from the bridge.
7.
Photos of Components with Poor Condition. Photos must be taken of all elements
that result in Component Ratings of 4 or less on the Bridge Inspection Record. Details
of the Condition Rating for the deficient elements must be noted in the photo
captions. However, multiple photos are not needed within a deficient element. For
instance, a poor superstructure component rating due to a deficient floor beam does
not mean that detailed photos must also be taken of all the elements making up the
superstructure component.
8.
Photos of Unusual Features. Photos should be taken of features which, in the
opinion of the inspector, are unusual, non-standard, or poorly repaired. For instance,
a bridge railing field fabricated from non-standard parts which may not be equivalent
to an acceptable bridge railing should be documented by close-up photos. The
Engineer must determine if it is appropriate to submit these photos as part of the
Bridge Record. Photos of utility attachments should also be made with enough detail
to show the type, condition, and attachment hardware used.
13.7.7.3 Electronic Media (for on- and off- system bridges)
The Engineer must provide all applicable electronic data for the Bridge Records on a CD/DVD or
Flash Memory stick. Multiple bridges may be submitted on the same diskette; however, they should
be grouped by local jurisdiction, maintenance section, etc.
13.7.7.4 Presentation of Documents (for on- and off-system bridges)
The Engineer must ensure that all inspection results submitted to the Bridge Inspection Division are
typed, using the current versions of the electronic forms where applicable, and are of such quality that
legible reproductions can be made on a typical office copy machine. All copies and records submitted
to be placed in the Bridge Folder should be 216 mm x 280 mm unless another size is allowed by HIB
for the specific application. However, copies of bridge plans may be A3 size paper.
The Contractor Engineer must provide the RBD with the following information in list format at the end
of the Work Authorization. These lists are not placed in the individual Bridge Folders. The lists should
be grouped by jurisdiction such as shabiya,, municipality, city, maintenance section, etc.
1.
List of bridges recommended for special inspections. This list must include only
bridges to be added to the current list of bridges with fracture-critical details or
bridges with the need for underwater (scuba diver) inspection. Bridges currently on
the fracture-critical and underwater lists need not be placed on this new
recommended list.
2.
List of bridges with poor condition rating. This list must include all bridges that
have an individual element or component with a Condition Rating of 4 or less.
3.
List of bridges with over-height load damage. This list must include all bridges
which have damage from over height loads or which have had repairs made after
such damage. The extent of the damage must be documented on the Bridge
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-50
Inspection Record, and Item 128 of the electronic Bridge Inventory File must be
coded.
4.
List of bridges with cracked pre-stressed beam ends. This list must include all
bridges that have pre-stressed box beams or pre-stressed concrete beams with
cracks at or near the beam ends. Photos of these cracks must be taken. If common
to several beams in the bridge, only representative photos are needed. The severity,
number of cracks, and specific location of each cracked beam must be indicated.
5.
List of bridges requiring changes in Operational Status. This list must include all
bridges that do not meet current HIB load posting policy requirements for posting load
restrictions. This policy is described in Chapter 5 in the subsection titled Load
Posting. The bridges on this list should be grouped by local jurisdiction. Bridges are
not to be placed on this list which currently have a load posting and for which no
change is required.
6.
List of bridges requiring vertical clearance changes. This list must include all
bridges requiring changes in the vertical clearance data as indicated by Item 54.2 of
the electronic Bridge Inventory File (see the coding guide). Even though only minor
changes in the actual vertical clearance may have occurred due to a pavement
overlay, the updated data are necessary so RBD can maintain the information
needed for over-height load permits.
7.
List of bridges with suggested changes to “blocked” data fields. This list must
be submitted for changes to the blocked data recommended by the Engineer. These
data will be reviewed and updated only by the HIB R&B Department.
13.7.7.5 Original and Duplicate Files (for on-system bridges)
For each on-system bridge, the Engineer is required to submit to the RBD one original and one
duplicate Bridge Record. One additional copy of the Bridge Inspection Follow-Up Action Worksheet
(only used for on-system bridges) will also be required. This worksheet is described in the Forms
section of this chapter.
1.
Original Bridge Record. The original bridge record must be submitted clipped into
the six-sided Bridge Folder discussed in the following Bridge Folder section of this
chapter. The order of the various forms, sketches, photos, etc in the Bridge Folder
must be made uniform with no exceptions. This original Bridge Record will contain
the originals of all documents created or updated by the Engineer, including photos.
2.
Duplicate Bridge Record. A duplicate file must be submitted and clipped into a
manila folder that must contain copies of all the documents prepared by the Engineer,
including color copies of all the mounted photograph sheets with captions.
13.7.7.6 Additional Files (for off-system bridges)
For each off-system bridge, the Engineer must submit one Original Bridge Record as described
above, and one set of Summary Reports which are described below. A Duplicate Bridge Record is
not required for off-system bridges.
13.7.7.7 Summary Reports (for off-system bridges)
The items to be included in the Summary Reports must be grouped for all the bridges within each
local jurisdiction. The bridges included in each local jurisdiction (regions, municipalities, cities etc.)
must be as agreed upon with the RBD. The arrangement and content of the Summary Reports will
be maintained. The Summary Reports are intended to summarize the bridge inspection findings,
maintenance or repairs needed, and load-posting requirements. The Summary Reports, whether
prepared by the Contractor or by RBD personnel, must be assembled as shown in a typical example
which can be obtained from the RBD. The Summary Report must be delivered to the RBD. The RBD
will forward the Summary Report to the local jurisdiction. Each Summary Report must include the
following information for each bridge:
Color copies of the mounted photograph sheets including captions
A copy of the Bridge Inspection Record
A copy of the Bridge Summary Sheet
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-51
13.7.7.8 Summary of New Load-Posting Materials (for off-system bridges)
This form is used to order the signs and hardware needed for each off-system bridge which requires a
change in the load posting. The Engineer must complete this form for each group of bridges within
each local jurisdiction. The bridges included in each local jurisdiction (shabiyas, municipalities,cities)
must be as agreed upon with the RBD. This completed form will be used to ensure that the
necessary materials are available to load post the bridges in each local jurisdiction. The Engineer will
submit this form to the RBD. It must never be submitted in any form to any local jurisdiction. This
form does not require signing. However, a date is required.
13.7.7.9 Scour Records and Reports (for on- and off-system bridges)
Many bridges are susceptible to scour of the foundations and abutments from flowing water. These
bridges are screened and classified for their potential for scour. Various scour reports, calculations,
and photos are necessary to document the scour potential. The scour information for most bridges
can usually be directly included in the Bridge Folder. However, some bridges have extensive scour
data, and the location of external scour files must be cross-referenced in the Bridge Folder. The RBD
must determine the amount of scour documents to be included with each Bridge Folder.
13.7.8
The Bridge Folder
13.7.8.1 Folder Information (for on- and off-system bridges)
The original records, sketches, plans if available, and latest information on each bridge on Libya
highway system are kept in a consistent and regular manner by RBD.
13.7.8.2 Folder Assembly (for on- and off-system bridges)
Each Bridge Folder must have an encompassing folder containing two dividers to which documents
can be fastened. Beginning with the inside surface of the front cover (hereafter called Side 1) and
ending with the inside surface of the back cover (Side 6), the information consists of and is assembled
in the following order in the Bridge Folder.
For the Duplicate File required for on-system bridges, which is placed in a manila folder without
dividers, the information should be assembled in the same order from top to bottom, ignoring the
“Side” number.
Side 1
1.
Location Map with bridge highlighted
2.
All current inspection photos (including those with low condition ratings)
3.
All other photos from previous inspections in chronological order (negatives may be
removed at the discretion of the HIB R&B Department.
Side 2
1.
Bridge Summary Sheet (off-system)
2.
Bridge Inspection Follow-Up Action Worksheet (on-system)
3.
Bridge Inspection Record
4.
Bridge Appraisal Worksheet
5.
Current Load Rating Calculations or copies of bridge plans; a reference to the HIB
R&B Department Plan File Designator or “Tab Number” for the plans is also
acceptable
6.
Bridge Inventory Record (must include proper sketch(s) if bridge plans are not on file)
7.
Bridge Inventory Record Revisions (if applicable)
Side 3
1.
Under-clearance Sketch (if applicable)
2.
Upstream Channel Cross-Section Measurements (if applicable)
3.
Upstream Channel Cross-Section Sketch (if applicable)
Side 4
1.
AUGUST 2010
NBI Sheet (printout of the electronic Bridge Inventory File)
REVISION NO. 03
BRIDGE INSPECTION 13-52
2.
Secondary Scour Screening Form (if applicable)
3.
The list of scour susceptible bridges with their scour classification
4.
Any scour-related reports or documents (if applicable); reference to the HIB file
location is also acceptable
5.
All scour photos
Side 5
1.
Elemental Data Inspection Records
2.
Special Inspection Records and Reports (Underwater Inspection, Fracture Critical
Inspection, etc)
Side 6
1.
Bridge Structural Condition History
2.
Previous inspections and all attachments in reverse chronological order (the most
recent information is attached on top)
3.
Bridge plans if available
13.8 Attachments
1.
Bridge Inspection Record
2.
Bridge Appraisal Worksheet
3.
Bridge Structural Condition History
4.
Bridge Inspection Follow-up Action Worksheet
5.
Bridge Inventory Record
6.
Bridge Inventory Record Sketch
7.
Revision to Bridge Inventory Record
8.
Channel Cross-Section Measurements Record
9.
Under-clearance Record
10.
Bridge Summary Sheet
11.
Recommended Change in Bridge Load Posting
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-53
ATTACHMENT 13-1 Bridge Inspection Report
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-54
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-55
BRIDGE INSPECTION REPORT
Page 3 of 3
Comment Sheets: (Per Item, if any)
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-56
ATTACHMENT 13-2 Bridge Appraisal Worksheet
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-57
ATTACHMENT 13-3 Bridge Structural Condition History
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-58
ATTACHMENT 13-4 Bridge Inspection Follow-up Action Worksheet
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-59
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-60
ATTACHMENT 13-5 Bridge Inventory Record
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-61
ATTACHMENT 13-6 Bridge Inventory Record Sketch
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-62
ATTACHMENT 13-7 Revision to Bridge Inventory Record
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-63
ATTACHMENT 13-8 Channel Cross-Section Measurements Record
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-64
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-65
ATTACHMENT 13-9 Underclearance Record
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-66
ATTACHMENT 13-10 Bridge Summary Sheet
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-67
ATTACHMENT 13-11 Recommended Change in Bridge Load Posting
AUGUST 2010
REVISION NO. 03
BRIDGE INSPECTION 13-68
14 Electrical, Instrumentation, Control and Automation (EICA)
14.1
Applicability
This section defines the design requirements for Electrical, Instrumentation, Control and Automation
systems and equipment for use in infrastructure projects. This includes, but is not limited to, the
following:
Water reclamation plants
Wastewater plants
Potable water plants
Water and wastewater pump stations
For power supply and distribution the specifications provided by the General Electric Company of
Libya (GECOL) shall be applied.
Responsibility for the supply and installation of electrical distribution equipment and facilities is also
governed by an agreement report dated Aug 20, 2008 between “EGW”, Electrical, Gas and Water
Department and “HIB”.
14.2
General Requirements
All electrical components and equipment shall be suitable for their intended duty with respect to the
following:
Electrical supply and load requirements
Environmental conditions (particularly corrosion resistance)
Mechanical properties
Ingress Protection (IP rating)
Area classification (Hazardous Areas)
All relevant specifications
The minimum operating life of all equipment and components shall be 20 years based on continuous
energized operation.
Energy efficient systems and designs shall be utilized throughout to minimize energy usage.
The location of all electrical equipment and instrumentation shall account for access and maintenance
requirements.
Where multiple process units are provided, the ability to take one unit out of service for maintenance
and cleaning shall be provided.
Where SCADA systems are provided, the control and monitoring of each process shall be fully
integrated with the SCADA system whether or not the control is provided by a proprietary control
panel or centralized PLC.
Labels and safety signs shall be written in Arabic with English and be unambiguous, durable and
legible.
14.3
Environmental Protection
All materials, equipment, finishes, brackets etc. shall be durable and corrosion resistant and shall be
suitable for installation in a corrosive atmosphere.
All components and complete assemblies shall be rated to withstand ambient conditions of up to 50°C
and 100% relative humidity.
Termination of cabling and raceways to equipment shall maintain the IP rating of that equipment.
Where there is no mention of ingress protection ratings of equipment in the specifications, the
equipment supplied shall be protected in accordance with BS EN 60529 and the following minimum
ratings:
IP42 Indoors, clean locations
IP54 Indoors, dirty locations
IP55 Indoor, damp locations
AUGUST 2010
REVISION NO. 03
EICA 14-1
IP65 Outdoors
IP68 to depth 5 metres where flooding may occur.
Equipment housings and enclosures shall be constructed from materials that are resistant to the
effects of weather (outdoor applications) and from exposure to process or sample media in solid, fluid
or gaseous form.
14.4
Equipment Standards and Certification
The control and electrical equipment and conductor installation shall be designed, installed, and
tested in accordance with applicable laws and regulations of Libya and the relevant international
standards.
A copy of the EU Declaration of Conformity certificate shall be available on request and shall confirm
compliance with the following directives as applicable:
2006/95/EC Low Voltage Directive
2004/108/EC Electromagnetic Compatibility Directive
98/37/EC Machinery Directive
Alternatively, electrical equipment may be certified by a third party or tested to a foreign standard by a
recognized body (e.g. UL, CSA) with demonstrable equivalence to a relevant EN/IEC standard;
supplied with supporting reports or certificates (including conditions of use/acceptability, where
appropriate) and CE marked with declaration of conformity to the relevant EN standard.
Other standards and regulations might apply depending on environmental conditions, access
arrangements, risks to health & safety, or the intended use of the equipment being provided. It is the
Designer’s responsibility to assess the suitability of the equipment being offered, usually with
reference to the declaration of conformity.
For example, the declaration of conformity might indicate that the panel is BS EN 60439 compliant,
but this would be unsafe for use in a hazardous area, unless the declaration also indicates that it is
suitably zone rated in accordance with BS EN 60079 and suitably certified by the relevant authority.
14.5
System Voltages
The electrical system shall utilize the following voltages where applicable:
11 kV, 3 phase, 50 Hz – GECOL supply
3.3 kV, 3 phase, 50 Hz – As required for large motors
400 V, 3 phase & neutral, 50Hz – LV supply and site distribution
110 V, 50 Hz – Control circuits and instrumentation
24 Vdc – Instrumentation.
14.6
Supply Design Considerations
The design shall consider the following supply characteristics:
Maximum prospective short circuit current (PSCC)
Type of system, e.g. TN-S, TN-C-S, IT, or TT (as defined in BS 7671)
Maximum earth loop impedance of the earth fault path external to the installation
Type of circuit breaker or isolating device
Voltage, current and short circuit data and ratings of the circuit breaker or isolating device
Coordination of protection devices; and
Load capability of the supply source, particularly the effects on the supply voltage of the
starting of new equipment and any fault contributions from new equipment.
14.7
Harmonics
14.7.1
Harmonics - General
The design of the electrical system shall be such that any harmonics generated by the plant do not:
Exceed the limits as defined in the IEC 61000 series of specifications at the ‘Point of
Common Connection’ (PCC)
Cause incorrect operation of plant or equipment
AUGUST 2010
REVISION NO. 03
EICA 14-2
Cause overheating of any electrical equipment or conductors
Adversely affect any electrical system or equipment that is connected to the network
within the plant
14.7.2
Earthing and Bonding
All earthing and equipotential bonding shall be in accordance with BS EN 7671 and BS EN 7430.
Any new earthing system shall be integrated with the existing earthing system.
Prior to designing the earthing system, the type of supply system earthing e.g. TN-C-S, IT or TT (as
defined in BS 7671) and the external earth fault loop impedance shall be obtained from GECOL.
All exposed conductive parts shall be connected to a protective conductor in accordance with specific
conditions for each type of system earthing.
Simultaneously accessible exposed conductive parts shall be connected to the same earthing system.
Equipotential bonding shall be installed to reduce the touch voltage between the conductive parts of
the systems and accessible exposed conductive parts of the installation.
Supplementary bonding shall be installed to bridge non-conducting sections and connections (other
than welds) between metallic fixtures, e.g. raceways, pipe joints, cable tray and handrails.
14.7.3
Exposed Conductive Parts
All exposed conductive parts, including but not limited to the following shall be connected to the main
equipotential bonding either directly or via supplementary connection:
Main protective conductor
Main earthing conductor
Earthing conductor(s) in all equipment including socket outlets, light switches fittings and
raceways.
Metallic water and gas pipes
Exposed metal structures
Central heating and air-conditioning systems and equipment
Metallic fences and gates
Lightning conductor systems
Earth mats
Metallic steel reinforcement used in concrete construction.
14.7.4
Functional Earths (Instrument earths)
Where a functional earth is required, it shall comprise a dedicated earth network connected to a
dedicated functional earth bar with a single connection to the Main Earth Terminal (MET) at source.
There shall be no other interconnection between the MET and functional earthing systems.
14.8
Lightning Protection
Lightning protection systems shall be designed in accordance with BS EN 62305: 2006 Protection
Against Lightning with particular reference to:
BS EN 62305-1 General Principles
BS EN 62305-2 Risk Management
BS EN 62305-3 Physical Damage to Structures and Life Hazard
BS EN 62305-4 Electrical and Electronic Systems within Structures
14.9
Low Voltage Switchgear and Control Gear
Type tested and partially type tested low voltage (LV) switchgear and control gear assemblies shall be
designed in accordance with BS EN 60439.
BS EN 60439 shall not be applicable to self contained: ICA and Instrumentation assemblies,
enclosures, push button stations, local Emergency Stop enclosures etc.
Forms of separation for LV switchgear and control gear shall be selected in accordance with BS EN
60439-1 and the following criteria:
AUGUST 2010
REVISION NO. 03
EICA 14-3
14.9.1
Form 1 or Form 2 Panels
Form 1 or Form 2 panels shall be allowed under the following circumstances:
The panel incomer fuse does not exceed 100A TPN and
The panel is for building services only or
The panel is a distribution board only or
The panel is for a single package plant process unit with drives not exceeding 7.5kW.
14.9.2
Form 3b Type 2 Panels
Form 3b type 2 panels (loose switchgear assemblies) shall be allowed under the following
circumstances:
The panel incomer fuse does not exceed 400A and
The panel is for building services only or
The panel is for power distribution only or
The panel is for a single package plant process unit, with drives not exceeding 22 kW.
14.9.3
Form 4a Type 2 Panels
Form 4a type 2 Panels shall be provided where:
Standby plant or other plant is required to continue operation during maintenance, to
ensure continuous drinking water quality, or wastewater discharge consent.
Standby plant or other plant is required to continue operation during maintenance to
ensure process performance.
14.10
Rotating Electrical Machinery
Rotating electrical machinery shall be designed in accordance with BS EN 60034. Equipment
covered by this specification may also be subject to superseding, modifying or additional
requirements in other publications, for example, BS EN 60079 for electrical installations in hazardous
areas.
Rotating machinery shall be provided with Class H or F insulation systems based on a maximum
ambient temperature of 40ºC unless otherwise specified.
Motors rated at 75 kW and above shall be protected by a Motor Protection Relay that provides the
following functions:
Thermal overload
Earth fault
Phase unbalance
Under current
Self supervision
Failsafe operation
Bearing grease shall be of the 120ºC thermal capability type.
14.11
Factory Assembled Distribution Boards
Factory assembled distribution boards shall comply with BS EN 60439-3.
The distribution boards shall be single phase and neutral or three phase and neutral as required for
each application.
The minimum degree of ingress protection shall be IP42.
Electrical loads shall be connected to distribution boards so that phases are balanced within 5% of
each other.
14.12
Miniature Circuit Breakers (MCBs)
Miniature circuit breakers shall comply with BS EN 60898.
AUGUST 2010
REVISION NO. 03
EICA 14-4
Miniature circuit breakers shall be current limiting type. In all cases the minimum breaking capacity
shall be greater than the prospective short-circuit current (PSCC) at the point where the MCB is
installed.
MCB’s shall be DIN rail mounting type.
Miniature circuit breakers must have fixed ratings that shall be clearly indicated. The fixed rating is
available between the range of 5 amps to 100 amps.
All MCB’s shall provide overload protection using thermal overload trip and short circuit protection by
instantaneous magnetic overload trips. MCB’s must be selected for each application in relation to
their type.
Type B - General purpose use (close protection)
Type C - Commercial and industrial applications with fluorescent fittings
Type D - Applications where high in-rush currents are likely (transformers, welding
machines)
14.13
Low Voltage Industrial Circuit Breakers
Industrial circuit breakers shall comply with BS EN 60947 and shall be either moulded case type
circuit breakers (MCCBs) or air type circuit breakers (ACBs).
Industrial circuit breakers shall be selected for each application in relation to their categories as
follows:
Category A – designates circuit breakers that are not specifically intended for selectivity
with devices on the load side, e.g. discrimination is provided up to certain fault levels,
above which discrimination with devices on the load side is not guaranteed.
Category B – designates circuit breakers that are specifically intended for selectivity with
devices on the load side. This category of circuit breaker will incorporate some type of
time delay.
14.14
Electrical Isolation
The design shall include a means of providing total circuit isolation that is lockable in the ‘OFF’
position for all electrical supplies to equipment.
Equipment isolators shall be clearly marked with the relevant equipment and circuit source reference.
Local control panels provided by equipment vendors shall be fitted with a door interlocked rotary fuse
switch that is lockable.
Local electrical isolators shall not be required, provided that:The point of isolation, e.g. MCC or Distribution Board and the circuit reference number, is
identified on (or adjacent to) the item of plant and equipment and
The means of isolation provided elsewhere is lockable.
14.15
Standby Generator
14.15.1 Standby Generators – Design Standards
Standby generators shall be designed in accordance with GECOL Design Specifications GDA 4000
and GES 60731.
Standby generators for back-up power supplies shall be either:
One or more permanent standby diesel generators complete with facilities to
automatically start when the main power supply fails.
A mobile diesel generator to be used when necessary.
In both the above cases, the electrical system may be arranged so that the generator can supply the
whole site or just ‘essential’ loads.
Generator earths shall be provided for all installations.
14.15.2 Standby Generator Ratings
Standby generator ratings shall be based on the following internationally agreed definitions:
AUGUST 2010
REVISION NO. 03
EICA 14-5
Standby Rating – Applicable for supplying emergency power for the duration of normal
power interruption.
Prime Rating - Applicable for supplying power in lieu of mains power supply for an
unlimited number of hours.
Generator sizing shall take into account the plant control philosophy and peak loads caused, in
particular, by motor starting.
14.16
Uninterruptible Power Supplies (UPS)
Uninterruptable power supplies (UPS) shall be provided for equipment which does not have intrinsic
back-up when loss of power supply would cause an unacceptable level of corruption of important
electronically stored data, disruption of process control programmes or damage to electronic
components.
14.17
Equipment for Use in Hazardous Areas
All mechanical and electrical equipment selected for use in a hazardous area shall have undergone
an appropriate conformity assessment procedure to demonstrate compliance with the essential health
and safety requirements of European Directive 94/9/EC (ATEX 95).
Where dangerous concentrations and quantities of flammable gases, vapours, mists or dusts may be
present in the atmosphere, protective measures must be applied to reduce the likelihood of explosion
due to ignition by arcs, sparks or hot surfaces, produced either in normal operation or under specified
fault conditions. The protective measures used shall be in accordance with BS EN 60079 for
electrical equipment and BS EN 13463 for non-electrical equipment.
All electrical equipment including fixed, portable, transportable and personal, and installations,
permanent or temporary systems for use in hazardous areas shall comply with BS EN 6007914:2008.
Where the equipment is required to meet other environmental conditions, for example, protection
against ingress of water and resistance to corrosion, additional methods of protection may be
necessary. The method used should not adversely affect the integrity of the enclosure.
14.18
Switchgear Rooms and LV Substations
Switchgear rooms shall be fully equipped with lighting, small power and ventilation as required to be
fully operational.
Unless specified otherwise, low voltage (LV) substations shall be 11/0.4kV types and shall be in
accordance with GECOL specifications.
14.19
Cabling and Containment Systems
Cable selection, sizing and installation shall be in accordance with the current edition of the IEE
Wiring Regulations BS 7671.
All cables shall be run continuously from terminal to terminal without intervening joints.
Cable containment systems may be a combination of cable ladder, cable tray, conduits, and duct
systems as required. Containment systems shall be sized in compliance with the requirements of BS
7671.
Power, control and instrumentation cables shall be segregated to prevent interference.
Intrinsically safe circuits shall be segregated from other circuits in accordance with the relevant parts
of BS EN 60079-14.
Junction boxes shall be segregated so that control signals are separate from power cables.
Instrument and DC signal cables are to be physically separated from AV power circuits. Shrouds or
barriers shall be provided and as a minimum, terminals shall have a degree of protection rating IP2X.
All junction boxes shall be suitably sized for the particular applications and shall contain sufficient DIN
rail mounted terminals to terminate all incoming/outgoing cable cores, including spares and twisted
pair screens.
Junction Boxes shall be constructed of a suitable material and with an appropriate finish to withstand
the effects of a potentially corrosive atmosphere.
AUGUST 2010
REVISION NO. 03
EICA 14-6
14.20
Lighting
14.20.1 Street Lighting
For street lighting, the specifications provided by the General Electric Company of Libya (GECOL)
shall be applied.
All other interior and exterior lighting systems shall meet the requirements of the Chartered Institution
of Building Services Engineers (CIBSE) Lighting Guides.
14.20.2 Lamp Types
Lamp types shall be selected from the following:
Metal Halide (HID)
High Pressure Sodium Vapour (HPS/SON)
Low Pressure Sodium Vapour (LPS/SOX)
Mercury Vapour (MV)
Fluorescent
Compact fluorescent
LED
Metal halide shall be the preferred option where suitable.
Sodium vapor shall be considered for large internal floodlit areas such as warehouses, pump rooms,
etc.
Mercury vapor shall only be selected in situations where other more efficient types are not suitable.
Fluorescent and compact fluorescent types shall be used for interior and exterior task lighting and
room lighting.
External luminaries shall have a minimum IP rating of IP65.
14.20.3 Considerations
All external area lighting shall be controlled using a combined timer/photocell contactor assembly with
manual over-ride facility, except roof lighting which shall be controlled manually.
14.20.4 Emergency Lighting
Emergency lighting shall provide 3 hours minimum maintained emergency lighting and shall be
designed in accordance with BS 5266 and BS EN 50172.
All emergency luminaire circuits shall incorporate a test switch facility. This may be facilitated via the
following types of installation:
Individual circuit key switches
Self test luminaires
Centralized test systems.
Self-test luminaires shall comply with BS EN 62034 and meet the requirements of BS 5266 and BS
EN 50172.
For larger installations, the use of centralized test systems that comply with the above legislation
should be considered.
14.21
Electrical Rooms and Kiosks
Electrical rooms shall be provided for control panels, Motor Control Centres and communication
systems.
Electrical rooms shall be clean dry environments provided with the following building services:
Heating and ventilation as required for the equipment to be installed
Indoor lighting
Outdoor lighting
Emergency lighting
Small power distribution (3P&N 400Vac & SP&N 230Vac)
AUGUST 2010
REVISION NO. 03
EICA 14-7
Plant telephone
Fire alarm system
Cable duct and containment systems
Safety signs and notices
14.22
Instrumentation
All installations shall comply with BS 6739: 2009 - Instrumentation In Process Control Systems
Installation Design and Practice.
Instrumentation shall be installed and tested in accordance with the manufacturer’s instructions.
Instrumentation shall operate at 24 volts DC wherever practicable.
Analogue instruments shall operate under all process conditions and provide 4-20 mA outputs.
Relay outputs shall be configured ‘failsafe’.
All instruments shall be mounted at a height and in a location which is readily accessible for
maintenance and calibration.
Instrumentation to be used shall generally comprise, but not be limited to, the following types:
Flow
Level
Temperature
Pressure
pH
Dissolved Oxygen (DO)
Sludge Blanket
Mixed Liquor Suspended Solids (MLSS)
Turbidity
Colour
14.23
Flow Measurement
14.23.1 Electromagnetic Flowmeter
Where a magnetic flow meter is provided, it shall comply with the requirements of BS EN ISO 6817
and be appropriately sized and positioned in accordance with the manufacturer’s recommendations to
achieve the specified accuracy. The flow meter shall operate under all flow conditions.
14.23.2 Open Channel Measurement (OCM)
Measurement of liquid flow in open channels shall be designed and constructed in accordance with
the requirements of BS 3680-3B:1997, ISO 1100-1:1996. Flumes and associated channels shall be
designed to operate over the full range of flows without being drowned.
14.23.3 Variable Area Flowmeter (VA)
VA meters shall be used to monitor continuous sample flows to process analysers and continuous
sampling systems.
14.24
Level Measurement
Ultrasonic instruments shall be the preferred method of level measurement for control functions.
The use of multiple ultrasonic sensors in close proximity shall be avoided due to the risk of beam
interaction between adjacent devices.
For point level switching and applications not suitable for ultrasonic instruments, the following device
types may be used where appropriate for the conditions of use:
Conductivity probes
Capacitance probes
Encapsulated float switches
AUGUST 2010
REVISION NO. 03
EICA 14-8
14.25
Temperature Measurement
Temperature transmitters shall be either RTD (Pt100) or Thermocouple types.
Temperature switches used to provide alarm and control switch points shall have an adjustable range.
14.26
Pressure Measurement
Pressure transmitters shall be gauge pressure direct mounting diaphragm seal type.
Pressure switches used to provide alarm and control switch points shall have an adjustable range.
14.27
pH Measurement
Instruments shall be positioned to analyze a sample which is representative of the process water.
When pH is being used to control the dosing of chemicals, the pH instrument shall be installed
immediately after mixing. Measuring downstream of a chemical dosing point may introduce an
unacceptable time lag for the control of chemical dosing. If a bypass sampling loop is used in a
control application the pipe work shall be as short as possible.
Sufficient spare cable and space shall be provided for electrode removal to allow calibration when the
instrument is installed.
14.28
Dissolved Oxygen (DO) Measurement
Continuous DO monitoring shall be provided for the aeration zone and used to control the aeration
system.
Duplex systems shall be provided. Two separate instruments shall be installed at separate positions
for each monitoring station.
The transmitter shall be mounted adjacent to the sensor in order that local display readings can be
taken for calibration and maintenance.
14.29
Process Analyzers and Continuous Sampling Systems
Process analyzers are generally complicated systems and shall be properly applied and installed in
order to ensure a high degree of accuracy with trouble free operation. The exact requirements for
installation, services and sample conditioning, applicable to each type of process analyser, shall
require individual consideration and shall be carried out in accordance with the manufacturer’s
instructions.
In continuous sampling systems, the existing hydraulic pressure at the process shall be used to
provide the process fluid sample to the analyzer where this can meet the full requirements. The use
of pumps installed specifically for the purpose shall be avoided wherever possible.
Where the use of pumps to provide the process fluid sample is unavoidable, a duty/standby pump
arrangement shall be provided.
14.30
Control Valve Actuators
Actuators shall be designed to suit the valve or penstock being actuated and its performance
conditions. It shall be equipped for the type of operation, e.g., direct or modulating action. Actuators
shall be adequately sized to allow opening or closing against the maximum hydraulic loading
anticipated, allowing for the added torque at the extremes of travel.
Padlocking shall be possible in the selected mode.
The actuator design shall incorporate a motor integral reversing starter, local control facilities and
terminals for remote control and indication connections. The actuator shall include a device to ensure
that the motor runs with the correct rotation for the required direction of valve/penstock travel with
either phase sequence of the 3-phase power supply connected to the actuator.
14.31
Plant Control and Automation
14.31.1 Functional Design Specification
The plant control and automation system shall be designed in accordance with a Functional Design
Specification (FDS).
AUGUST 2010
REVISION NO. 03
EICA 14-9
14.31.2 SCADA System Architecture
The SCADA system shall comprise of a Master Station connected via Local Area Network (LAN) to a
network of Remote Transmitter Units (RTU’s) and/or PLC’s.
Field bus data communication networks shall be designed in accordance with BS EN 61158.
The Master Station shall be located in a central control room and shall include adequate Human
Machine Interface (HMI) screens to allow complete monitoring, trending and control functions as
defined in the FDS.
All SCADA/HMI shall run on Microsoft Windows operating systems.
System configuration and programmability shall be in accordance with IEC 61131-3.
14.31.3 Telemetry Outstation
A telemetry outstation shall be provided to transmit selected alarms and trend data to a remote base
station and/or mobile phones via GSM/GPRS.
Telemetry systems shall be compatible with the Libyan network. This currently operates on GSM900.
In remote areas that are not covered by GSM and that have no available power source, an alternative
to GSM is a battery powered UHF Radio RTU bridge system that can also use solar power to
recharge the system batteries.
For small sites with limited I/O requirements, and where no PLC exists, plant signals shall be
hardwired to a single telemetry outstation with I/O expansion if required.
On large sites, where one or more networked PLCs exist, a single telemetry outstation shall be
directly connected to one of the PLCs.
Transmitted signals shall be limited to alarms only. Control functions shall not be permitted from
remote base stations via telemetry.
AUGUST 2010
REVISION NO. 03
EICA 14-10
15 Telecommunication
All telecommunication work shall be coordinated with Libyan Post, Telecommunication and IT
Company (LPTIC) other utility service providers. The design shall be in compliance with LPTIC
Documents and HIB Master Specifications and Standard Details. The LPTIC Specifications and
design criteria should be issued to the contractors by HIB.
JULY 2010
REVISION NO. 03
TELECOMMUNICATION 15-1
16 Gas Distribution
All gas distribution work shall be coordinated with General Gas Company (GGC) of Libya and other
utility service providers. The design shall be in compliance with GGC Documents and HIB Master
Specifications and Standard Details. The GGC Specifications and design criteria should be issued to
the contractors by HIB.
JULY 2010
REVISION NO. 03
GAS DISTRIBUTION 16-1
17 Great Manmade River Requirements
All work conducted in the vicinity of the Great Manmade River shall be coordinated with Board of
Implementing and Management of the Great Manmade River Project (GMRP). The design shall be in
compliance with GMRP documents and HIB Master Specifications and Standard Details. The GMRP
specifications and design criteria should be issued to the contractors by HIB.
JULY 2010
REVISION NO. 03
GREAT MANMADE RIVER REQUIREMENTS 17-1
Download