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Preamble
-
This Roads and Bridgss Design Manual 'ik&
prepwed by the MhIstry of Public Works Roads Administration in coopmtictn with Kuwait
Municipality and Mini-
of In-.
This Manual shall be uwd as a n u b for the
design of Roads and &Jdgem in -ke St8te of
Kuuvslt. It will be the mpmslbility of the
deelgner to ensure that the guWhes cmblned
in this manual are applied properly and modiffed
where appropriate to meet the approved
standards of engineering and safety, subjecf to
the obtaining the newssary approvals.
Tbls Manual shall be read together with typiml
drawings of the MPW - Roads Admjnlstratlon
The Designer a l l obtah approval for the design
fm all rekwnt authortth, including Minlstry of
Public Works, Ministry of Interior and Kuwalt
Munldpality.
+
lh
The MinWy d Public Works intends to update
r$ Lip LUl W ~E JIj j 31
thts Manual on mular bas@and ~ e l ~ ~ m
anye g &i$y~ z+ -9 J u q* &
suggestions for mprowemsnf.. AH 8ugpesUons
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A
J.
and requests for darkations shall be forwarded
0 ~e hm "ndof be
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Admfnktrrrtiq.
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*&*I
Ministry of Public Works
Roads Administration
Design Manual for Roads and Bridges
Edition 1, March 2004
The Design Manual for Roads and Bridges is divided into four separate parts.
Please refer to the relevant part for a table of contents.
PART 2 - Kuwait Bridges and Highway Structures Design Manual
PART 3 - Kuwait Highway Drainage Design Manual
PART 4 - Miscellaneous (not currently used)
PART I Kuwait Highway Design Manual
Ministry of Public Works
Roads Administration
PART I
Kuwait Highway Design Manual
Edition 1
March 2004
K w i t Highway Design MantmI
fable ofContents
TABLE OF CONTENTS
1.1
Kuwait Road Hierarchy ...................................
.
.
.
.................................................................
A-I
1.2
Determining the Road Class .................................................................................................
1.3
Local Roads .............................................................................................................................
1-5
1.4
Secondary Roads ..................................................................................................................
1-6
1.5
Primary Roads .........................................................................................................................
"I4
14
1.6 Special Roads..........................................................................................................................
1-6
2.1
Introduction ..............................................................................................................................
2-1
2.2
2.5
............................................................................................................ 2-1
Level of Service (LoS).........................
... ...............................................................................
2-1
Design Vehicles .......................................................................................................................
2-7
Pedestrians ..............................................................................................................................
2-8
3.1
Generat.....................................................................................................................................
3-1
3.2
Selection of Design Speed.......................................................................................................
3-1
3.3
EffectofTerrain........................................................................................................................
3-2
3.4
Relationship with Posted S p e d .......................................W
3.5
Existing Roads .....................
.
.
............................................................................................
3-3
3.6
Locations where Design Speed Changes ................................................................................
3-3
3.7
Interchanges ............................................................................................................................
3-3
3.8
Reduction below Standards .....................................................................................................
34
4.1
General.....................................................................................................................................
4-t
4.2
Eye-height and Object Height ......................................
4.3
Stopping Sight Distance (SSD) ..........................
.
.
.................................................................
4-1
4.4
Safe Passing Sight Distance (SPSD) ......................................
4.5
Decision Sight Distance (DSD) ..............................................................................................
44
4.6
Maintaining Sight Distances................................................................................................ 4-5
4.7
Provision of Safe Passing Sight Distance...............................................................................
44
5.1
Generat...................................................................................................................................
5-1
5.2
........................................................................................
Maximum Superelevation..........
.
5-2
5.3
Minimum Curvature..............................................................................................................5-2
2.3
2.4
Definitions............
....
4
.
.
Kuwait Highway D e a n Manual
Table of Contents
5.4
Calculation of Superelevation...........................
.......................................................................5 4
5.5
5.6
Transition Curves ................................................................................................................
5.7
LateralClearances .................................................................................................................. 5-9
5.8
Visual Appearance of Horizontal Geometry .......................
54
Widening on Curves ............................................................................................................... 5-7
5.9
.
.
...........................................5-11
Horizontal Curves on Local Streets.....................................................................................
5-14
6.1
General .................................................................................................................................
6-2
6.2. Vertical Curves ...................................... ,................................................................................. 6-2
6.3 Maximum Gradient ............................................................................................................
6-5
6.4
Minimum Gradient ......................,............................................................................................
6-6
6.5
Visibd~ty....................................................................................................................................
6-7
6.6
Choice of Longitudinal Profile ..................................................................................................
6-7
6.7
Visual Appearance of Vertical Geometry ................................................................................ 6-7
6.8
Combining Horizontal and Vertical Alignment......................................................................
6.9
Vertical Clearances ...........................................................................................................
6-10
6.10
..
Local Roads ..............
..,..
6-8
..............................................................................................
6- 10
General....................
.
.
..........................................................................................................
7-1
Limits of Right of Way ............................................................................................................ 7-1
Side Slopes .........................
.........
.........................................................................................7-2
Verges ......................
.
.
.........................................................................................................
7-3
Service Reservations...............................................................................................................
7-3
Shoulders and Kerb Clearances ...................
.
.
...................................................................
7-4
Clearances to Structures .........................................................................................................7-5
Clearances to Safety Barriers...............................................................................................
7.9
8
7.6
Lane Widths ............................................................................................................................
7-7
...................................7-7
7.10
Median Widths ................................................................................
7.If
Cross Slopes......................
.
.
...........................................................................................
7-9
7.12
Gutters and Drainage Ditches .........................................................................................
7-10
7.13
Other Elements within the Cross-Section ..........................................................................
7-10
................................................................. ...................
HIGHWAY FACIUTIES
8-1
8.1
General..............
.
.................................................................................................................
8-1
8.2
Pedestrian Facilities ........................
.
.
................................................................................8-1
8.3
Public Transport Facilities .......................................................................................................
8-5
8.4
Parking Facilities ..........................
.
.......................................................................................
8-7
8.5
Kerbs .......................
.
.
........................................................................................................
8-9
Kuw% HigRwy Design lhQenuel
TMe of Contents
9
8.6
Fences ....................................................................................................................................
8-10
8.7
Safety Barriers......................................................................................................................
8-11
8.8
Energy Absorbing Barriers.....................................................................................................
8-17
8.9
TraPficCalming...................................
.
.
............................................................................8-18
8. t 0
Landscaping.......................................................................................................................
8-22
8 I
Ut~l~ties
....................... .
.
..................................................................................................
8-23
..
LOCAL ROADS
..........................................
9-1
introduction ..............................................................................................................................
9-7
Badc Design Parameters ......................................................................................................
9-2
Intersections.............................................................................................................................
943
..
...................................................................................
.
.
94
Pedestrian Fac~l~ties
......................
f rafic Calming .......................................................................................................................
94
Turning Areas...........................................................................................................................
94
Driveways..............................................................................................................................
..9-6
Summary of Design Parameters............................................................................................9-8
10
...................................................................................................
SECONDARY ROADS
10-1
10.1
introduction.........................................................................................................................
10-1
10.2
Basic Design Parametem..................................................................................................
10-1
10.3
10.4
Intersections.......................................................................................................................
104
..
Pedestrian Facrl~ties........................
.
.
.
...........................................................................
I04
10.5
Traffic Calming ...................................................................................................................
104
10.6
Summary of Design Parameters......................................................................................10-4
11.1
Introduction.....................................................................................................................
11-1
11.2
Basic Design Parameters ...................................................................................................
11-1
11.3
Intersections .......................................................................................................................
1 3
11.4
11.5
Service Reads..................................................................................................................
1-3
..
............................ .
....................................................................
Pedestrian Facil~ties
.
.
11-4
11.6
Summary of Design Parameters .......................................................................................
114
121
Introduction.......................................................................................................................
12-1
12.2
Basic Design Parameters...................................................................................................
12-1
12.3
Intersections.......................................................................................................................
12-3
12.4
Senrice Roads....................................................................................................................
123
12.5
..........................
...............................................
........................ 12-3
Pedestrian Fac~f~ties
.
.
12.6
Summary of Design Parameters........................................................................................
12-3
..
iii
K m i t Highway Design IWenual
Table of Contents
Introduction ........................................................................................................................
33-1
Intersection Spacing ..........................................................................................................
13-1
Selection of Intersection Type ...........................................................................................
13-2
Choosing between Roundabouts and Signalised Intersections ........................................
134
13-5
Design Vehicles ...............................................................................................................
Siting of Intersections ........................................................................................................
138
Intersection Types (1) - Major 1Minor Intersections ........................................................ 13-6
-
Intersection Types (2) Roundabouts.............................................................................
13-8
13-9
Intersection Types (3) - U-turns ......................................................................................
-
Intersection Types (4) Signalised Intersections.............................................................13-f 0
Intersection Types (5) - Interchanges..............................................................................13-10
Introduction ........................................................................................................................
14-1
Safety.................................................................................................................................
14-1
Types of Major l Minor Intersection ............................................................................ .... 14-1
Capacity ..............................................................
...........................................................14-7
....................................................................................
Pedestrian Considerations........
.
14-7
Alignment ...........................................................................................................................
14-7
..
Visiblllty...............................
.
.
........................................................................................
14-8
Corner Radii..................................
24-10
...................................................................................
Lane Widths ................................................................................................................... 14-12
Islands.....................................................................................................
.......................14-14
Tapers............................................................................................................................14-16
.
.................................................................
14-18
Right-turning Roadways ............................
Deceleration and Queuing........................................................................................... 14-18
Turning Length................................................................................................................
14-21
Staggered T-intersection Spacing ............................................................................
14-22
Drainage .....................................
.....................................................................................
14-22
Summary of Design Process ......................................................................................... 44-22
15.1
lntroducfion ......................................................................................................................
15-1
15.2
General Principles ....................................................................................................
15-1
15.3
General Features of a Roundabout...................................................................................
15-2
15.4
Capacity of Roundabout................................................................................................
15.5
Minimum Size of Island....................................................................................................
154
15.6
.................................................................
Inscribed Circle Diameter ....................
.
.
15-6
15-3
Kuwait Highway Design Manuel
Table of Contents
Circulating Pavement........................................................................................................
15-7
Entry Width .........................................................................................................................
15-8
Entry Path Deflection.....................................................................................................
5 - 9
Entry Angle ......................................................................................................................
5- 11
Entry Radius ..................................................................................................................... 15-12
Gradients ..........................................................................................................................
5-12
Exits ..................................................................................................................................
15-12
.
.
....................................................................................................75-12
Visibility..................
Crossfall and Drainage .....................................................................................................15-17
Right-turning Roadways .................................................................................................
15-18
Safety at Roundabouts....................................................................................................
15-20
16
......................................................................................................................
U-TURNS
16-2
General..............................................................................................................................16-1
Entry Taper.......................................................................................................................16-3
.
.
Deceleration Length ........................................................................................................ 16-3
Queue Length and Protected Length .................................................................................
164
Channelising Nose Width .......................................
Reduced Median Width ..................................................................................................6
4
U-turn Lane Width ..............................................................................................................
164
Median Width ...................................................................................................................
164
................................................................................
6-4
Summary ..........................................................................................................................16-5
U-turn Diameter..................................................................................................................
16-5
Median Widening...............................................................................................................
6-6
Local Bulbing......................................................................................................................
16-6
Mouth Treatment ....................
....
General.............................................................................................................................
17-1
Applicability of Major J Minor Intersection Principles ....................
....
..................... 7 - 1
Specific Requirements at Signalised Intersections............................................................7 - 1
Width of Medians..............................................................................................................
7-l
Sire of Islands ....................................................................................................................
17-3
Vehicular Swept Paths ......................................................................................................
17-3
Location of Pedestrian Crossing Facilities ......................................................................
.17-3
Width of Pedestrian Crossing Facilities ....................
,
.......................................................
174
Designing for Queue Lengths in 'left-turning Lanes .......................................................
174
Signalised Roundabouts .......................
.
.
.
......................................................................
174
U-turns at Signalised Intersections ..................................................................................17-5
Tabla of Contents
18
.................................................................
GRAPE SEPARATIONS AND INTERCHANGES
18-1
Introduction ........................................................................................................................
18-1
Types of Interchange ...................................................................................................
18-1
.
...........................................................
18-15
Selection of Interchange Type..........................
..................................................................
18-17
.
.
.
.
Lane Provision ....................................
18-19
. .. .............................................................................
Diverge Design ...............................................................................................................
18-19
Merge Design .............................................................................................................. 18-27
Connecting Roadways .....................................................................................................
18-35
.
........................................................
13-37
Spacing of Merges and Diverges.......................
Weaving...........................................................................................................................
18-38
........18-38
Link Roads .............................................................................................................
Other Design Considerations......................................................................................... 18-39
Design Speed ....................
. . ..
--
Chapter I
H$hwey Classific~tlon
?.I
Kuwait Road Hierarchy
Kuwait has a defined road hierarchy, which assists in standardising the approach to
highway design and maintenance, and benefits the end user through a logical and
systematic classification of roads.
The different categories of road within the hierarchy, together with their principal
distinguishing features, are shown in Table 1.1 ..
Table 1.1: Kuwait Road Hierarchy
Road Class
General Descriptfon
Local Roads
Intended for short journeys only
No access control
Access to adjacent land must be achieved
Secondary Roads
Intended to distribute traffic through a district or to sewe a
place d local importance
Minimal access control
Access to adjacent land is very important
Primary Roads
Intended for through traffic, but with lower design standards
than the Special Road Network
Access by means of at-grade intersections (signalised or
roundabout) or grade separated interchanges
Access to adjacent land becoming a relevant consideration
Special Roads
Intended for fast and free-flowing through traffic
Full access control using grade separated interchanges, or
Service roads that serve land adjacent to the highway and
connect to the main line by free-flow ramps
Speclal and Primary Roads are always divided roads (with a median), whereas Local
Roads are undivided. Secondary Roads may be either diwided (majorlurban) or
undivided (minorlrural).
Figure I .Iillustrates the principles of the road hierarchy by reference to a typical
neighbourhood.
The present road hierarchy has been determined and the future pattern established'.
Figure 1.2 shows the network of roads as defined for the year 2012.
The road hierarchy distinguishes between roads on the basis of differences in traffic
service and land service, making it a suitable tool for both planning and engineering
design purposes. It also separates diflerent classes of roads on the basis of required
highway design features.
Page 1-1
Kuweit Highwey Design Menuat
Figure 1.1: Illustration of the Road Hierarchy
Page 1-2
Figure I.2: Kuwait Road Hierarchy
Source: KuwaH Traffic S!gns ~ a n u a ?
Page 1-3
K m l t Highway Design Manual
Chapkr I
Highway Classification
-
If is necessary to distinguish between urban and rural areas. Note that this refers to
the predominant characteristics of the adjacent land use and does not necessarily
conform to any legal or administrative boundaries.
' 1
-
Table 1.2 summarises the principal features of each road class.
Table 1.2: Characteristics of Roads by Class
Land sewice
Trafflc
service
toca l
Roads
Secondary
Roads
Primary Roads
Special Roads
Land access
the primary
consideratron
Land access
and traffic
movement of
equal
impoflance
Land access a
secondary
consideration
No access or
restricted
access from
service roads
Traffic
movement the
secanday
consideration
Land access
and traffic
movement of
equal
Traffic
movement the
primary
Optimum
Urban: >200rn
Rural: ~ 1 . 5 k m
Urban: >l
km
Rural: >2km
Unintermpted
Free flow
mobility
consideration
importance
.
>loom
spacing
Urban: as
required
Rural: HOOm
Nature of
traffic flow
Interrupted
flow
Interrupted
flow
Passenger
All types
except semitrailers and
above*
All types
Primary
Roads
Secondary
Roads
Local Roads
Special Roads
Primary Roads
Secondary
Typical
intersection
Vehicle type
. and service
ve hicks**
flow except at
intersections
All types
Connect to
Secondary
Roads
Local Roads
Special Roads
Primary Roads
Roads
..
"In industrial areas, SecondafyRoads should ammrnodste all types of vehicle
* In industrial and in rural areas, t ~ & smay have to be catered for.
Speed limits on roads may differ, even within the same class of road. In selecting the
posted speed, that is, the speed limit displayed to drivers by means of road signs, it
is normal practice to undertake a vehicle speed sunrey, and to adopt a value close to
the observed 85th-percentile speed.
-
Determining the Road Class
-
In Kuwait, it is the planners' role to review and determine the road class and the
width of the right of way. Given this information, the highway designer should review
the traffic volumes and the functional requirements of the road, and then determine
the appropriate standards for all elements of highway provision in accordance with
the guidance contained in this manual.
In areas where new development is taking place, it may be beneficial for the works to
be phased, possibly providing a lower, interim, standard of provision while always
Page 1-4
I
Kuwait Highway Design Manuel
ensuring that the ultimate configuration can be achieved. Similarly, where
redevelopment of an existing area occurs, it is important that the class of the road be
reviewed to check whether its status has been affected by the redevelopment.
The design details and facilities to be provided on a road are not entirely dictated by
its class. The cross section for a secondary road for example, may vary from a oneway street to a four-jane divided road. The geometric design of the road is affected
by the following factors:
Design speed
Design vehicles
Composition of the traffic stream
Pedestrians
=
Safety
Traffic volume
Adjacent land use
Climatic conditions
---
Terrain
Economics of the area
Aesthetics
Sociological factors
Public preferences
In certain areas of Kuwait, it is particularly difficult to classify roads from their
adjacent land use, and therefore at some locations roads may not display the
characteristics typical of their class. For example, the number of accesses may be
higher than average, more parking may occur, or there may be a greater than normal
number of intersections. Should the designer consider that the road class is
inappropriate under the specific circumstances, he should review and agree the class
with both the Ministry of Public Works and Kuwait Municipality.
The following sections introduce each of the classes used in Kuwait.
1.3
Local Roads
A significant percentage of a city network comprises local roads, which are designed
to allow vehicles to reach the frontage of properties from a secondav or primary
road. The main function of local roads is to provide land access, and they generaliy
carry low volumes of traffic. They serve residential, commercial or industrial land
uses. Trips made on local roads wilt generally have an origin or destination actually
on the local road or in immediately adjoining areas. In planning the layout of a local
road network, care should be taken to avoid creating routes which could be attractive
to through traffic, or which encourage high speeds to the detriment of safety.
As this is the lowest class in the road hierarchy, direct access is permitted to all
abutting properties.
Local roads can be grouped into two categories, rural local roads and urban local
streets.
Page 1-5
Kuwait Highway Desbn Manual
1.4
Secondary Roads
The function of secondary roads is to collect traffic, from local roads to primary roads,
and to distribute trafific flow from primary roads back to the local roads. Access to
properties is normally allowed on secondary roads. In rural areas, the function of
secondary road is twofold, to provide access to adjacent land and to carry traffic into
areas with sparse development,
1.5
Primary Roads
Primary roads are of a lower design standard than special roads. Their intersections
with other primary roads and lower class roads can be either grade-separated or at
grade (roundabouts or signalised).
Primary roads 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 class roads to the lower class roads and vice versa.
f .6
Special Roads
Special Roads are designed to move heavy volumes of high-speed traffic (under free
flowing conditions). Special roads form only a small percentage of the roads in the
road network, but they pedorm a crucial role in segregating fast through traffic from
slower moving local traffic. High traffic volumes generate the need for a Special
Road, which in turn necessitates fully controlled access. This is achieved with either
grade-separated interchanges, or sewice roads that serve land adjacent to the
highway and connect to the main line by free-flow ramps.
In rural situations, the function of a special road is to connect major cities or industrial
areas, and to provide the major routes for international traffic movements.
In urban areas, the function is to provide high-standard routes connecting areas of
major traffic generation.
Third Kuwait Master Plan Review (draft, 1997).
* Kuwait Traffic Signs Manual, 1988.
Page 1-6
Kuweit HChwey Design Manuel
Chapter 2
Traffic
2.1
Introduction
The volume of traffic that will use a new road facility 1s the major determinant of the
scale of provision. It is important therefore that a robust estimate of future vehide
usage of the road is available to the designer at the outset. It is normal to select a
Design Year which typically may be fifteen to twenty years afler the opening of the
road.
For a given traffic Row and the purpose of the road, the designer can identify its
class, for example Special Road Network,Primary or Secondary. Factors such as the
number of lanes and the type and scale of the interchanges or intersections influence
the ease of use of the road, and its ability to perform Hs function satisfactorily.
This matter is dealt with by the concept of Level of Service, and it is normal practice
for a new facility to be designed to have a high Level of Service (that is to say, to
have very significant spare capacity) in its opening year, but to have much lower
Level of Serwice (nearing capacity) at the end of its design period.
In order to discuss this further, it is necessary ta introduce some definitions.
2.2
Definitions
Definitions of the terms used in this section of the manual can be found in the
Glossar)r. The reader's attention is particularly drawn to the definitions of the
following terms:
Prevailing Road Conditions
Prevailing Traffic Conditions
Capacity
Traffic Volume
Annual Average Daily Traffic (AAPT)
Design Hour Volume (DHV)
Design Speed
Operating Speed
Level of Service (LoS)
r
Service Flow Rate
Free Flow Speed (FFS)
2.3
Level of Sewice [LoS)
Level of Service is a quality measure describing operational conditions within a
stream.
LoS takes account of many factors, including:
Speed
Travel time
Traffic interruptions
Page 2-4
Mwei! Highway De&n Manusl
Chapter 2
Freedom to manoeuvre; that is, to change lane, accelerate or decelerate.
Driving comfort, which is subjective, and depends on the perception of each
individual driver.
Six levels of Service A, B,C , D,E and F are defined in Highway Capacity Manual for
Urban Streets, Signalised Intersections, Unsignalised Intersections, Pedestrians,
Bicycles, Two Lanes Highways, 'Multilane Highways, Freeways, Ramps, and Transit
facilities. Level A is the highest and level F is the lowest. The lower the level of
Service, the greater is the traftic density, and the higher is the likelihood of delays
occurring through the interaction of vehicles within the traffic stream. In this chapter
Level of Service concepts are presented for special road sections and pedestrian
facilities, for other facilities the reader is advised to refer to HCM 2000'.
'
The characteristics of each LoS band for a m o t o ~ r a ysection are shown in Table 2.4.
Table 2.1: Characteristics of Level of Sewice for Special Road Sections
Criteria
FFS
120 kmlh
Maximum density (pculkmlln)
Maximum vlc
Maximum Service Row rate
(pculhlln)
22
0.92
2200
28
1.00
2400
16
0.70
1740
22
28
0.91
2135
1.00
2350
11
0.48
16
0.70
28
1 .OO
700
1100
1600
22
0.90
2065
2300
7
0.28
tl
0.44
22
28
630
990
16
0.64
1440
0.87
1955
1-00
2250
7
11
16
0.35
840
0.55
1320
0.77
7
0.33
770
1t
0.51
1210
7
0.30
1840
+
FFS = 110 kmlh
Maximum density (pclkrnlin)
Maximum vlc
Maximum service flow ate
(pcu/hlln)
FFS 100 kmih
Maximum density (pclkmlin)
Maximum vlc
Maximum Service flow rate
(pculhlln)
FFS = 90 kmlh
Maximum density (pclrlkmlln)
Maximum vie
Maximum service Row rate
(pculhEln)
Source: Highway Capachy Manual"
Operating characteristics for the six LoS are shown in Plate 2.1 to Plate 2,6.The LoS
are defined to represent reasonable ranges in the three critical flow variables: speed,
density, and flow rate.
t o S A describes free-flow operations. Free-flow speeds prevail and vehicles are
almost cornplletely unimpeded in their ability to manoeuvre within the traffic stream.
The effects of incidents or point breakdowns are easily absorbed at this level.
Page 2-2
Chapter 2
Trame
toS B represents reasonably free flow, and free-flow speeds are maintained. The
ability to manoeuvre within the traffic stream is only slightly restricted, and the
general level of physical and psychological comfort provided to drivers is still high.
The effects of minor incidents and point breakdowns are still easily absorbed.
LoC C provides for flow with speeds at or near the FFS of the freeway. Freedom to
manoeuvre within the traffic stream is noticeably restricted, and lane changes require
more care and vigilance on the part of the driver. Minor incidents may be still
absorbed, but the local deterioration in service will be substantial. Queues may be
expected to form behind any significant blockage.
.
LoS D is the level at which speeds begin to decline slightly with increasing flows and
density begins to increase somewhat more quickly. Freedom to manoeuvre within the
traffic stream is more noticeably limited, and the driver experiences reduced physical
and psychological comfort levels. Every minor incident can be expected to create
queuing, because the traffic stream has little space to absorb disruptions.
At its highest density value, LaS E describes operation at capacity. Operations at this
level are volatile, because there are virtually no usable gaps in the traffic scene.
Vehicles are closely spaced, leaving little room to manoeuvre within the traffic stream
at speeds that still exceed 80 Krnlh. Any disruption of the traffic stream, such as
vehicles entering from a ramp or a vehicle changing lanes, can establish a disruption
wave that propagates throughout the upstream traffic flow. At capacity, the trafic
stream has no ability to dissipate even the most minor disruption, and any incident
can be expected to produce a serious breakdown with extensive queuing.
Manoeuvrability within the traffic stream is extremely limited, and the level of physical
and psychological comfort afforded to the driver is poor.
LoS F describes breakdowns in vehicular flow. Such conditions generally exist within
queues forming behind breakdown points.
A suitably high Level of Service appropriate to each situation should be selected and
used for design, and it should be appreciated that for many of the hours of the day
the road will in fact operate at a higher LoS. Table 2.2 gives guidance for selecting
appropriate Levels of Service in the design year for roads. It should be noted that at
intersections, the relevant LoS is normally one level lower than that shown.
Table 2.2: Guidelines for Selecting Level of Sewice In Kuwait
Page 2-3
Plate 2.1: Level of Service A
Plate 2.2: Level of Sewlce B
Kuwait Highway Design Manuef
Chapter2
Traflc
Plate 2.5: Level of Sewlce E
Plate 2.6: Level of Service F
Page 2-6
LoS is heavily dependent on the relationship between the demand (the predicted
future design Row) and the capacity of a road. These concepts properly lie outside
the scope of a geometric design manual, and have been introduced here to assist the
designer to understand the work of the traffic engineer. In all casesIis necessary for
the highway designer and the traffic engineer to work closely together. The traffic
engineer will have the major input into elements where purely geometric
~
in particular:
considerations do R O predominate,
The prediction of future flows
The assessment of capacities and Levels of.Service
The selection of appropriate service volumes
The design of weaving sections
The design of signalised and roundabout at-grade intersections (which depend
on the results of detailed traffic calculations)
The design of U-turn facilities
The primary measure of effectiveness for the Level of Service for differing types of
facility will be assessed in accordance with the criteria specified in the Highway
Capacity Manual', as given in Table 2.3.
Table 2.3: Primary Measures of Effectiveness lor LoS Dennition
'
Type of Facility
-
Measure of Effectiveness
Special Roads:
Basic read segments
Density
Weaving areas
Speed
Merges and diverges
Density
Primary Roads
Density
Secondary Roads
Speed
Local Roads
Speed
Signaiised intersections
Average total delay
Unsignalised intersections
Average total delay
Pedestrians
Space, Delay
Source: Highway Capacity ~anual"
2.4
Design Vehicles
The entire range of the fleet of vehicles using Kuwait's roads has to be
accommodated safely and comfortably, and the standards set out in this manual
respect this fact.
The opeiating characteristics of different vehicles influence the capacity of the road
network. This is reflected in the use of the Passenger Car Equivalent as a vehicle
unit; larger and slower vehicles (which physically cover more road space and take
more room due to their slower acceleration capabilities and greater braking needs)
are counted as being equivalent to a number of passenger cars. Table 2.4 gives
broad equivalents for trucks and buses; for a more detailed assessment, the designer
is referred to the Highway Capacity Manual1.
Page 2-7
K w i t Highway Design Manual
Table 2.4: Passenger Car Equivalents of f rucks and Buses
Level terrain
1.7
Recreational Vehicles
1.2
Source: Highway Capauty IWanual1
The physical dimensions (including operating characteristics such as turning circles)
are important in determining lane widths, headroom, sight distances and turning radii.
The design vehicles used in the United States are listed in AASHTO' and are
identified in Table 2.5. A check on typical vehicles in use on the roads in Kuwait
confirms that the adoption of these design vehicles is also appropriate to Kuwait.
,
Table 2.5: Design Vehicle Parameters
1
m
Width
m
Length
m
Min.
Design
Turning
Radius m
Min.
Inside
Radius
rn
1.3
2.1
5.8
7.3
4.4
3.4 -4.1
2.4
9.2
12.8
8.6
Height
Description
Code*
Passenger Car
P
Single Unit Truck
SU
Single Unit Bus
BUS
3.2
2.6
12.2
12.8
8.0
Articulated Bus
A-BUS
3.4
2.6
18.3
12.1
6.5
Intermediate Semi-trailer
WB-12
4.7
2.4
13.9
12.4
5.9
Intermediate Semi-trailer
WB-15
4.1
2.6
16.8
13.9
5.2
Inter-statate Semi-trailer
WB-19
4.1
2.6
20.9
14.1
2.4
I nter-state Semi-trailer
WB-20
4.1
2.6
22.4
14.2
1.3
Triple Semi-trailer1
Trailers
W8-30T
4.1
2.6
32.0
13.9
3.0
Turnpike Double Semitrailerflrailers
WB-33D
4.1
2.6
34.8
18.4
4.5
Motor Home
MH
3.7
2.4
9.2
12.7
7.9
Car & Camper Trailer
PTT
3-1
44.8
13.1
5.3
Car & Boat Trader
PI&
-
2.4
2.4
12.8
8.9
2.8
Motor Home and Boat
Trailer
MH,s
3.7
2.4
16.2
15.7
10.7
I
Note that the designation WB relates to approximate wheelbase; -12
denotes a trudr whose wheelbase is
' around IZm.
2.5
Pedestrians
Pedestrians need to be carefully considered when roads are being designed. They
are present in every road environment, unless specific measures are taken te provide
for them outside the road corridor, for example by means of fences and footbridges
on motorways. Adequate provision for pedestrians should therefore be made, using
Page 2-8
Kuwait Highway Design hi8n~8/
features such as sidewalks, pedestrian crossings, trafiic signal facilities and grade
separated crossings, with kerb details, ramps, bus stops etc being given special
attention.
It is important to consider the type of pedestrian using the area. If near a school, for
example, the designer should have the young clearly in his mind, and therefore
should provide more protection, better visibility between driver and pedestrian, and
enhanced signing, when compared to other areas.
Elderly people also require special consideration as they oflen move more slowly and
may suffer from poor sight and hearing deficiency. In locations where it is appropriate
to design specifically far the needs of elderly people, the following points should be
borne in mind:
Assume lower walking speeds for the elderly and infirm
Provide wider refuge islands
Consider different surface textures at crossing points
Minimise crossing distances
Provide wider footpaths and sidewalks
Design for wheel chairs, for example by providing kerb-cut ramps at crossing
points
Provide paved footpaths and sidewalks
The width of sidewalk should accommodate the predicted pedestrian volumes. Table
2.6 shows the LoS criteria to be adopted in the design of sidewalks. In the absence
of pedestrian traffic forecasts, it is desirable to provide a sidewalk of at least 3.0m
width. Greater widths are probably necessary near pedestrian generation sources
such as schools, mosques, commercial areas or recreational areas such as sports
venues or cinemas.
In designing pedestrian facilities, an aim should be to provide routes that follow as
closely as is practical, the geographical desire lines for movement on foot. Where
this would lead to haphazard, random or dangerous crossings of traffic streams, it is
appropriate to consider whether pedestrians can be channelled by guide fences or
other features to locations where purpose-designed safe crossings are to be
provided.
Table 2.6: Average Flow LoS Criteria for Footpaths and Sidewalks
LOS
Space (m2fp)
P
A
B
C
0
E
F
Fllow Rate
(plrninlrn)
Speed (mls)
1
>5.6
46
>3.7-5.6
>
6-23
I
~1.27-1.30
r2.2-3.7
> I .4-2.2
~23-33
>3349
>0.75-1. I 4
c0.75
>49-75
Variable
>1.22-1.27
>1.14-1.22
>0.75-1.14
~0.75
-
>1.30
-
vlc Ratlo
-
e0.21
>0.21-0.31
>0.31-0.44
>0.44-0.65
N.65-f .O
Variable
Highway Capacity Manual 2000, Transportation Research Board, National
Research Council, 2000.
A Policy en Geometric Design of Highways and Streets 2001, M S H f 0,
2001.
KweH Highway Design Manual
I
Chapfer5
Design Speed
3.1
General
Drivers vary their speed of driving in accordance with the road layout and their
perception of the prevailing conditions, modified to a certain extent by the
performance of their vehicles. The main factors that influence speed are visibility,
curvature, road width, surface condition, potential conflict points (for example
intersections) and speed limits or other similar regulatory features. M i l e it would be
unrealistic to design the features on a road to cater for the very fastest of drivers, it is
nevertheless essential to ensure that the vast majority of road users can, in good
conditions and with light traffic, drive safely at a consistent speed appropriate for the
type of road.
The concept of a design speed, which ensures that all features on a road are capable
of being traversed safely at a given speed, is the factor that links the majority of the
geornetdc design parameters used by the highway engineer, particularly stopping
distances, horizontal and vertical alignments, and cross-sectional elements.
I
3.2
Selection of Design Speed
For the design of a new feature on an existing road, the existing speed of traffic on
the route can be measured. It is normal to set the design speed as the 85th
percentile speed. If the improvement is part of a strategy to upgrade the entire route,
it would be more appropriate to design the feature as if it were part of a new road.
When considering a new road, the selection of the design speed is based on the
designer's experience of other existing roads that perform a similar function, in the
context of the role of the road within the hierarchy.
Factors that influence this choice include road class, urban or rural location,
development density, economics and terrain. For local roads in particular, the
objectives of the planners should also be taken into acco~nt,~especiall~
if there is a
desire to keep traffic speeds low in a 'calmed' environment.
Table 3.1 shows the ranges of mainline design speeds that are to be adopted for the
Kuwait road hierarchy'.
nrarnrng sign provlslon.
conslaerarlon should be given to increasing the normal
KuwaH Highway Design Manual
Table 3.2: Recommended Posted Speed
3.5
Existing Roads
It is importand that Table 3.2 is not used in reverse. The design speed of an existing
road should not be determined from the posted speed, but from the 85th percentile
speed obtained from a survey of the actual speed distribution of vehicles using the
road. The selected design speed may in turn suggest that a different posted speed
may be appropriate after the improvement has been completed.
Where a new road leads directly into an existing road, care must be taken to avoid a
discontinuity in standards. If the existing road has a lower design speed than the
improvement, consideration should be given to design of the interface zone of the
new road to make the transition less abrupt.
In all cases, posted speeds should be properly indicated by traffic signing in
accordance with the Kuwait Traffic Signs ~ a n u a l ' .
3.6
Locations where Design Speed Changes
Similar considerations apply where the design speed changes along the length of a
new road, for example, at the interface between urban and rural conditions. The
driver should never be presented with an abrupt downward change in the standard of
provision.
Where there is a change to a lower design speed, it b desirable to provide values
above the minimum standards for sight distances and for horizontal and vertical
curvature over the initial length of the lower design speed section.
3.7
Interchanges
The ramps (or connecting roadways) within a grade-separated interchange should
normally have a lower design speed than the mainline.
Table 3.3 sets out the appropriate values.
Page 3-3
KuwsM Highway Design Manual
ch8pkr 3
Design Speed
fable 3.3: Minimum Design Speed for Connecting Roadways
3.8
Reduction below Standards
In certain circumstances it may be uneconomic to design an alignment to the
prescribed standards, and consequently it may be necessary to reduce the standard
of the road, perhaps only locally. As the consequences of such reductions could be
significant, the following guidance shall be taken as mandatory.
Having selected the relevant design speed for the length of route under
consideration, this design speed shall be maintained throughout, and not locally
reduced.
At a site of particular difficulty, if a reduction from the value(s) prescribed for that
design speed is proposed, this shall only be permitted after receiving specific
authorization from the Ministry of Public Works, Kuwait Municipality and the Ministry
of Interior.
.
Kuwait Traffic Signs Manual, State of Kuwait, 1988
A Policy on Geometric Design of Highways and Streets, AASHTO, 2001
Page 3 4
Kuwait Higltway Design Mnnuai
Chapter 4
Sight D i s t a m
4.1
General
In order to undertake a manoeuvre safely, a road user must have sufficient fomard
visibility. Three situations in which forward visibility is particularly important are:
Stopping prior to reaching a stationary oktructfon
Overtaking on an undivided road
Making a decision where a choice of actions presents itself
The corresponding distances for these three situations are:
Stopping Sight Distance(SSP)
Safe Passing Sight Distance (SPSD)
Decision Sight Distance (DSD)
The sight distance is always measured in a straight line between points on the
centreline of each traffic lane. On horizontal curves, the most critical lane is the
nearest to the centre of the curve.
In order to meet Eha required sight distance, roadside objects on the inside of a curve
may need to be set back fuFther from the edge of the travelled way than would be
normal on a straight section of road. Further details are given in Chapter 5.
4.2
Eye-height and Object Height
The visibility envelope for sight distance is the area between the driver's eye-height
and the object height.
The visibility envelope shall be checked in both the horizontal and vertical planes,
between hrva points in the centre of the lane nearest to the centre of the curve. On
divided roads, both carriageways should be checked.
For design purposes, the minimum eye-height is taken as 1.05m and the maximum is
2.4m.
The minimum height of the stationary object is 0.1 5m1and a maximum height of 2.0m
is used.
For passing purposes on undivided two-way roads, the object height is taken to be
the same as the driver eye-height, the range therefore being between 1.051~1
and
2.4m.
4.3
Stopping Sight Distance (SSD)
The visibiiity envelope for SSD is shown in Figure 4.1, namely:
Driver eye-height
1.05m to 2.40m
Object height
0.15m to 2.00m
SSD is made up of two elements, namely perception-reaction distance and braking
distance. Further information on the formulae for calculating these elemenls can be
found in AASTHO'.
Page 4 1
Iluweit Highwey QesignManuel
Chapter 4
Overhead
obstnrctian
Figure 4.1 r Vislbillty Envelopes for Stopping Sight Distance
The SSDs for design purposes are given in Table 4.1. Grade affects the breaking
distance, and therefore longer SSDs are required on downgrades. Upgrades shorten
the breaking distance, but no change is made to the SSD. The "level' values should
be used for all upgrades.
Table 4.1: Stopping Sight Distance for Design
4.4
Safe Passing Sight Distance (SPSP)
SPSD applies to undivided two-way, two lane roads, in which a vehicle undertaking a
passing manoeuvre moves into the lane used by vehicles travelling in the opposite
direction.
Kuwail Highway Deshn Manuaf
I
I-'
I
Chapter 4
Sight Distance
The visibility envelope for SPSD is shown en Figure 4.2, and is as follows:
Driver eye-height
Object height
/
1.0511-1
to 2.40m
1.05m to 2.40111
Object height
Driver
eye height
\
-
Overhead
obslruetion
<wM~&&/
1.05m
Driver
eye height
2.40m
1.05~1
Object height
Figure 4.2: Visibility Envelope for Safe Passing Design Distance
The SPSD is the summation of four phases undertaken during a passing manoeuvre:
The initial manoeuvre
The occupation of the left lane
The clearance length
The opposing vehicle distance
Further details of the calculation of these phases are included in AASHTO'.
Although grade does have an effect of SPSD, no specific adjustments are to be
made. However, designers should be aware of the desirability of increasing the
visibility beyond the minimum standard if passing is to be accommodated on a length
of road with significant grades.
The values of SPSD for use in Kuwait are shown in Table 4.2.
Page 4-3
Kuw~itHighmy Design Manuel
Chapter 4
Table 4.2: Safe Passing Sight Distance for Design
4.5
Decision Sight Distance(DSD)
At certain points on the road network, a driver must make a decision as to which
route to follow, or whether there is a need to stop, and it is essential that adequate
visibility is provided to allow the decision to be made in suitable time. DSD to be
provided at intersections is covered further in the relevant chapters later in this
manual.
The DSD is longer than the SSD as the correct course of action may be to stop and
also because vehicles cover significant distance when manoeuvring without a
reduction in speed.
The visibility envelope far DSP is the same as for SSD, shown
namely:
Driver eye-height
1.05m to 2.40m
Object height
0.15m to 2.00m
on Figure
4.1,
DSD consists of the following elements:
Detection and recognition phase
Decision and response phase
Manoeuvre
Further details of the calculation of these phases can be found in AASHTO'.
DSD is measured from the vehicle location to the hazard (for example the stop sign,
the start of the bend or the gore of the ramp terminal) and the values for varying
design speeds are given in Table 4.3. fhere are no adjustments required for grades.
DSD should be provided where any of the following circumstances apply:
Unusual or unexpected manoeuvres required at interchanges or intersections
Significant visual distractions, such as traffic control devices and illuminated
advertisements
Changes in the road cross-section, such as a lane drop
Typical examples of such situations are:
A rural road leading directly to a STOP control
Page 4 4
Kuweit Highway Deslgn Manual
Chapter 4
Siuht Dislance
An urban road leading directly to a STOP control (sign or signals)
An off-ramp leading to an abrupt change in direction
The approach to a lanedrop or major fork
A complex weaving section (with more than two entries and exits)
It may not always be possible to provide full DSD and in these situations
consideration should be given to increasing the normal warning sign provision.
Table 4-3: Decision Slght Distance for Design
4.6
Maintaining Sight Distances
Sight distances should be checked at the design stage by direct measurement from a
plan to 1 :f 250 scale or larger. Care should be taken to ensure that no substantial
objects obstruct the sightlines, including traffic signs, barriers and bridge parapets.
However, isolated slim objects such as lighting columns, sign supports and individual
tree trunks can be ignored.
On existing roads, sight distances are measured directly on the ground, by
observation from the relevant eye-height to a target at object height, along the
centreline of each lane.
SSD should be maintained throughout the length of the route under consideration,
and this may welt have a constraining influence on the design of other geometric
elements of the road. DSD should be provided under the circumstances described in
Section 4.5.
On horizontal curves,it is necessary for obstructions to vision that are located on the
inside of the curve ta be adequately set back from the edge of the travelled way. In
particular, appropriate setbacks should be provided to the face of barriers and bridge
parapets located on the inside of the curve, and verge or median widening may be
necessary to accomplish this.
In cuttings, the side-slopes may interfere with forward visibility, and sight distances
should be checked three-dimensionally.
Page 4-5
Kuwafi Hignway Design ~Wanuel
On vertical crest cunres, the minimum values of curvature set out in Chapter 6 of this
manual are adequate to cater for SSP,but it is always necessary to check to DSD,
where relevant.
On vertical sag curves, the upper bound of the sight distance envelope should be
checked where there is an overhead obstructiomn
to visibility such as an overbridge or
a sign gantry.
Provision of Safe Passing Sight Distance
It is not necessary for passing to be possible throughout the length of a two-way
undivided road, but frustration and dangerous manoeuvres can result if there are
insufficient opportunities provided to allow vehicles to pass each other safely. As a
minimum, half the route length should permit safe passing. Where this cannot be
achieved, consideration should be given to the provision of an auxiliary lane. Further
details can be found in AASHTO'.
' A Policy on Geometric Design of Highways and Streets 2001, AASHTO, 2007
.-
Page 4-6
Kuwafi Highway Design Menw1
Chapter 5
Horizonta! Alignment
General
Road users should be able to travel along a roadway safely at a continuous uniform
design speed, and the horizontal alignment must be designed to permit this.
Factors that influence the degree of horizontal curvature of a road include:
Safety
Design speed
Topography, adjacent land use and obstructions
Vertical alignment
Maximum allowable superelevation
Road classification
Cost
All of these factors must be balanced to produce a good alignment. Poor design will
lead to a reduction in the safety and capacity of the road.
In addition to the specific guidance given in this section, there are a number of
general considerations that are important in designing a safe and economic design.
They are particularly applicable to high speed situations and are listed below.
It is preferable to use a curve of greater radius than the minimum value quoted,
retaining the use of minima to more critical locations.
Compound circular curves, which consist of two or more arcs joined end-to-end in
one direction, should be used with caution and should be avoided where
conditions permit the use of a simple curve. Where compound curves are used,
the radius of the flatter cuwe should not be more than 50 percent greater than the
radius of the sharper curve. This consideration however does not necessarily
apply at intersections and roundabouts, where lower speeds pertain.
Reverse circular cunres, which consist of two arcs curving in opposite directions,
on high speed roads should include an intervening transition section of sufficient
length to accommodate the reversal of superelevation between the circular
curves. If there is a length of normal crown tangent between the curves, then the
distance between reverse curves should be sufficient to accommodate the
superelevation runoff and the tangent runout for both curves. Where the
superelevation is to be reversed without an intervening normal crown section, the
length between the reverse curves should be such that the superelevation runoff
lengths abut, thus providing only an instantaneous level section across the
pavement. Further details can be found in Section 5.5.4 of this manual.
8roken-back curves, which consist of two curves in the same direction connected
with a short tangent, should not be used. They are not expected by drivers and
are not pleasing in appearance.
=
Horizontal alignment should be consistent with other design features and
topography. In particular there is a need for ca-ordination with vertical alignment,
and this is discussed in Chapter 6 of this manual.
On divided roads, consideration may be given to providing independent
horizontal and vertical alignments for each carriageway.
Page 5-1
K m f t Highway Design Manual
Chapter 5
Hon'f~nt~f
Alignment
r
5.2
Maximum Superelevation
,
On a straight length of road, transverse drainage is accomplished by the use of
crossfall at a standard rate of 2%. On an undivided road, the surface normally falls
outwards from both sides of a central crown line (this arrangement being called
normal crown), while on a divided road the surface of each pavement normally falls
outwards from the median.
On horizontal cunres, this crossfall makes it more difficutt for drivers on the outside of
the curve to make the turning manoeuvre, and so at radii below a certain value, it is
necessary to eliminate this adverse crossfall by making the whole road fall towards
the inside edge of the curve. The resulting superelevation is 2%.
On tighter curves, a higher superelevation value can be adopted to assist drivers in
travelling around the corner.
The maximum superelevation is governed by the speed of the slower vehicles,
whose drivers find it both unexpected and diffrcutt to have to exert a steering force
against the direction of the curve. In Kuwait, rain following a long dr)r period can
result in low road surface friction factors, and therefore the use of relatively steep
cross falls is to be avoided.
The maximum superelevation to be used in Kuwan is shown in Table 5.1.
Table 5.7 E Maximum Superelevation
5.3
Minimum Curvature
There is a direct relationship between the speed of a vehicle, the radius of the curve,
the superelevation and the side friction between the tyre and the road surface.
where
R = radius of cunre (m)
V=
vehicle speed (kmh)
e =
superelevation (%) divided by 100
f,
=
side friction factor
The side friction factor has been found from observations to lie in the range 0.35 to
0.50 on dry roads, but on wet surfaces it may drop to around 0.20.On the grounds of
safety, it is normal to adopt even lower values for design purposes. Table 5.2 shows
Page 5 2
i.
Kuwait Highway Weslgn Mgnual
Chapter 5
Horizontal Alignment
the values to be adopted, which vary linearly from 0.170 at 30 kmlh to 0.113 at 120
kmlh.
Table 5.2: Side Friction Factors for Design
I
Design Speed
Side Friction Factor
30
0.170
40
0.164
50
0.157
60
0.151
70
0.145
80
0.138
90
0.132
100
0.325
110
0.179
120
0,173
-
Accordingly, for a given design speed, minimum radii can be determined for a range
of superelevation rates, and these are given in Table 5.3.
On local residential streets with design speeds of 50kmh and less, full
superelevation should not be provided, as this can give drivers the impression that
higher standards apply and accordingly, operational speeds are likely to be greater.
The radii shown in columns (3) to (5) of Table 5.3 can be used, but with
superelevation limited to 2%.
Table 5.3: Minimum Horizontal Curvature
Design
Speed
1
Mlnfrnum Radii {rn)
Superelevation
Superelevatian limited to 2% (refer to paragraph a b m )
Page 5 3
K m i f Highway Design Manuel
Chapter 5
Horirontal Alionment
At intersections other than roundabouts, the normal crown or superelevation of the
main road should be continued through the intersection, with the minor road
longitudinal profile tying in to the main road cross-sectional profile.
At roundabouts, different considerations apply, and these are dealt with in Chapter
15 of this manual.
5.4
Calculation of Superelevation
The superelevatian for a given design speed is calculated as follows;
'
'
For radii in column (1) of Table 5.3 and larger
superelevation.
- Normal crown of 2%, with no
-
For radii in the range lying between column (2) and column (1) Crossfall of 2%
towards the inside of the curve.
For radii in the range lying between column (5) and column (2)
calculated in accordance with the following formula:
5.5
Transition Curves
5.5.1
General
- Superelevation
Drivers naturally follow a transitional path as they change from a straight to a circular
curve and good highway design reflects this fact. The introduction of transition curves
- ,
also improves the appearance of the alignment and assists in the introduction of
superelevation prior to the circular curve.
There are a number of transition curve types available to the designer and the use of
the Euler spiral (or clothoid), rather than other types such as the cubic parabola, is
prescribed for Kuwait. In the spiral or dothoid, the degree of curvature varies directly
with the length along the curve.
Transitions are not required with circular curves whose radii are equal to or greater
than those given in Column (1) of Table 5.3. They are also not required on roads with
design speeds of 70kmlh or less.
Figure 5.1 shows the layout of a typical transition curve joining a straight (tangent)
alignment to a circular curve.
Page 5-4
K m h Hwwey Design Manuel
Chapter 5
Hmiantai Alignment
Tangent
--,
/
I
I
I
Transition curve
Straight
R
= Radius af circular curve
TS =
SC =
S
=
Tangent to spiral
Spiral to circular wrve
Shift (offset ofcircular curve)
Figure 5.1: Typical Arrangement of Transition Curve
5.5.2
Length of Transition Curve
The length of the transition curve (TS to SC on Figure 5.1) depends on the radius of
the circular curve into which it leads. It is defined by the following formula:
where
'L, = length of spiral (m)
V = design speed (kmlh)
q = rate of change of centripetal acceleration (mls3)
R = radius of circular curve (m)
The value of q is primarily dictated by comfort considerations, and a value of 0.3rn/s3
is desirable. However a figure of 0.6rn/s3 can be adopted where this assists the
design. By way of illustration, Table 5.4 gives rounded values of the computed spiral
lengths for the radii in Column (4) of Table 5.3.
The maximum transition length is limited to d ( 2 4 ~m,
) where R is the radius of the
circular curve. The designer should ensure that the transition length used is below
this value.
Page 5 5
K m i f Highwey Design Manual
Chapter 5
Hmf ontal ATqnmenf
Table 5.4: Basic Spiral Lengths for Minimum Radii at 6% Superelevation
6% superelevation (
5.5.3
Length of Superelevation Application
Superelevation shall not be introduced, or adverse camber removed, so gradually as
to create large almost flat area of carriageway, to cause driver discomfort or to kink
the edges of the carriageway. A satisfactory appearance can usually be achieved by
ensuring that the carriageway edge profije does not vary in grade by more than about
0.5% from the line about which the carriageway is pivoted, and by ample smoothing
of all changes in edge profile. As a minimum, superelevation should be applied over
the length derived from the following formula.
L=
where
1.5xWxA
L = length required to accommodate the change in superelevation (m)
W=
width of carriageway over which change in superelevation occurs (m)
Ae = change in gradient (%)
The minimum lengths required to accommodate the change in superelevation have
been calculated for a range of superelevation rates and carriageway widths, and are
given in Table 5.5. If longer lengths are used, then the change in gradient will be
less than 0.5% and the designer should check the alignment for flat spots that may
cause drainage problems.
Table 5.5: Minimum Length Required to Accommodate Change in Superelevation
Page 56
.,
Kuwait Highway Design M~nual
chapter 5
Horizonial Alignment
5.5.4
Application of Superelevation
Figure 5.2 shows typical methods of developing superelevation by rotating about the
edges and about the centre of the road. The designer should use the most
appropriate method to suit the situation. For divided roads, greater consideration of
topography, cut and fill, catchments and median drainage is required and the
designer should consider the possibility of adopting different vertical andlor horizontal
geometry for the two separate pavements.
The formula for the reverse curve over which the superelevation is to be applied is:
where
Y = offset of channel, relative to the line about which the carriageway is
pivoted, at distance x, m
x=
distance from start of application, rn
s = maximum offset of channel superelevation, relative to the line about
which the carriageway is pivoted, rn
L = length of application of superelevation, rn
If transitions are proposed, superelevation or elimination of adverse camber shall
generally be applied on or within the length of the transition curwe and from the arc
end. On roads without transitions, between % and X of the cant shall be introduced
on the approach straight and the remainder at the beginning of the curve,
5.6
Widening on Curves
The rear wheels of vehicles do not exactly follow the track of the front wheels, and
therefore.it is necessary to widen the pavement on low radius curves,
Wdening on curves of lesser radius than T25m is dealt with in Table 14.6 of this
manual, which covers right turning at intersections but is equally applicable to lowradius curves elsewhere.
It should be noted that widening is dependent on vehicle geometry (particularly on
wheelbase),lane width and curve radius.
Widening should be applied, in both directions d travel, to produce the lane width on
the circular curve as shown in Table 5.6. On divided roads it is only necessary to
widen the outer Fane of both pavements, all other lanes remaining at their normal
width.
Tabla 5.6: Minimum Lane Wldth on Cunres
Radius (m)
Lane Width (m)
>A25 to 300
>300to 400
More than 400
normal width
Nde: For ndil of 125m and below, referlo Table 14.6 for details of lane widths
Page 5-7
K m i l Highway Design Manuel
Chepbhr 5
Hotizonlel Alignment
Tangent
runout
SuperelwaBon runoff
1
Normal
crown-
SE:
Runoff slope
P
.--
----
Outside edge of pavement
-----
/
Grade
T-
=a
?T
-,.A-
A
-
----ZL-
-
control Inside
.. edge
- of-pavement
.
.-
'
Pavement rotated about centrellm
Tangent
runout
Swperelwation runqff
r
_
I
I
vr Runoff slope
/
I-
,'
--/
--------inside edge of pavement
=..
B
_.
.D Inskle edge-Profile
4-
A
,
-
% - -
control
Pavement mtated about insEde edge
Tangent
runout
Superelevation runoff
,
--7
I
5:
Nmal
--..
--$Grade
----.._
R U Mslope
---.
- -
Inside edge of pavement
A
B
I
,
r
C
--'
D Outside edge
-'
Profile control
Pavement rotated about outside edge
Notes :
A = Normal crown
0 = Adverse amber elimhated
C = Superelevation at normal crossfall rate
D = Full superelevation
Figure 5.2: Development of Superelevation
Page 5 8
KWH
HIphwey Design Manual
It is good practice to provide all the additional pavement width by widening on the
inside of the curve, as shown on Figure 5.3. Widening is developed over the length
of the transition, thus maintaining the full widening around the circular portion of the
curve.
Figure 5.3: Application of Pavement Widening on Curves
Lateral Clearances
Generally, no structures aparl from slim roadside furniture such as sign posts and
lighting columns are allowed to fall within the roadside service resewations, and this
normally provides a verge area over which sight lines can be maintained. However in
some locations, there may be a significant obstruction to sight lines within the right of
way, or the radius of the curve may be sufficiently tight that the sight distance
envelope extends outside the right of way. It is important to check that the setback to
obstructions is such that proper sight distances are maintained.
Sight distances are measured between points on the centreline of the traffic lane and
the setback (measured from that line), within which visibility must be maintained, is
given in Table 5.7 to Table 5.9.
When designing two-way, undivided roads, the Safe Passing Sight Distance (SPSD)
should be considered, and this is detailed in Chapter 4.
If SPSD is to be maintained around a curve, a large lateral clearance may be
required, as indicated in Table 5.8, and this is likely to be ~neconomical. Radii
should generally only be used on two-way undivided roads where full SPSD can be
provided within the allocated Right of Way.
The minimum setback to maintain Decision Sight Distance (DSD), given in Table 5.9,
has been calculated using the worst case DSDs from Section 4.5 in this manual. IF
the setback values are required for one of the other scenarios, then the designer
should use the formula given below.
The simplified formula an which these tables are based is:
where
x = offset (m)
R = radius of curve (m)
D = sight distance (m)
Page 5 9
Tabk 57: Minimum Setback to Maintain Stopping Slght Distance (Level Road)
;et (m) from Centreline of Nearest Lane, for Design Speed of
. Radius
(m)
80kmlh
60kmlh
7Oknrlh
200
4.8
7.0
300
3.0
4.6
7.1
400
2.3
3.5
2.8
90kh
IOOkmlh
5.3
8.1
10.8
4.2
6.4
8.6
IlOkmlh
100
500
Table 5.8: Minimum Setback to Maintain Safe Passing Sight Dishnce
12.3
12Okmlh
K m i i HEghwey Design Manual
Chapter 5
Horizontal Aligtpent
table 5.9: Minimum Setback to Maintain Decision Slght Distance (Urban, No Stop
Situation)
5.8
Visual Appearance of Horizontal Geometry
The aim of good alignment Is to combine the various components in a manner that
results in the road being perceived by the road user as a free-flowing, harmonious
form without visual discontinuities, while also providing a safe route with adequate
sight distances.
The principles of flowing alignment are closely linked with the way in which the driver
sees the read line and in particular the shape of the road edges.
Small changes in direction should be avoided, as these are likely to appear
unsatisfactory from the vehicle.
When two straights are connected, the use of a short horizontal curve is likely to
cause the impression of a kink, as illustrated in Figure 5.4.
Page 5-1 1
Kweil Highwey Design Manual
Figure 5.4: The Effect of a Short Cuwe Between Two Straights
The use of a larger radius can improve the appearance, but it Is not possible to avoid
the illusion of a sharp change in direction. The best results are likely to be achieved
with a flowing series of curves and transitions, and no straights.
However, on undivided two-way roads, straight lengths may be desirable in order to
achieve the required Safe Passing Sight Distance.
Abrupt changes in direction can be unsatisfactory on local roads as well as major
routes. In Figure 5.5 the straights have been joined without the use of a horizontal
curve. The appearance is improved when a horizontal curve is added, as shown in
Figure 5.6.
Page 5-1 2
K w i f H&hway Design Manual
Chapter 5
HdritontalAlignr#nt
Flgure 5.5: Angular Geometry on a Local Road
Flgure 5.6: Curred Geometry on a Local Road
Page 5-13
Kuwafl Highway Design PAenuel
Short straight sections of road should not be interposed between horizontal curves in
opposite direction because this will give the appearance of a kink. Similarly straight
section with curves in the same direction produce a 'broken-back' curve, which is
both visually unattractive and difficult for drivers to negotiate. The use of longer
transition curves or larger radii may remove this difficulty.
Figure 5.7 summarises alignments to be avoided and alignments to be sought where
possible.
Poor features
I
7 . Small change of direction
2. Short horizontal curve between two straights
3. Reverse curue with short tangent
4. Broken-back cuwe with short tangent
5. Out of balance alignment
Good features
i.Well-balanced alignment
2. Use of cunres rather than straights where feasible
Figure 5.7: Summary of Alignment Features on Divided Roads
5.9
Horizontal Curves on Local Streets
Vehicle speeds on urban local streets are considerably lower than on major roads.
Transition curves can be omitted, and a normal camber or 2Oh soperelevalion should
be provided, rather than the maximum permissible superelevation of 4. See Chapter
9 of this manual for further information.
The introduction of curves to residential roads is an effective form of speed control,
but small-radius bends Iinked by long straights can induce sharp brakinglacceleration
behaviour.
. If used as part of an overall traffic calming scheme, they can be beneficial. Curves of
a tight radius are permissible and are known as speed limiting bends.
information on f raffic Calming is given in Chapters 1 and 9 of this manual.
Further
The minimum radii to be provided at intersections are dealt with in the relevant
chapters later in this Manual.
Page 5 1 4
Kuwait Highway Design Menrrel
6.1
General
The vertical alignment consists of longitudinal gradients connected by vertical curves
and must be carefully designed in order that road users can travel safely at a
continuous uniform speed.
Factors that influence the design of the vertical alignment or longitudinal profile of a
road include:
Safety
Design speed
Topography and adjacent land use
Horizontal alignment
Earthworks balance
Road class
Drainage
Levels of access to adjacent properties
Vehicle operating characteristics
As with horizontal geometry, all of these factors must be balanced to produce a good
alignrnent. A poor vertical alignment will result in lower speeds and a reduction in the
safety and capacity of the road.
In addition to the specific guidance given in this chapter, there are a number of
general considerations, which are important in designing a safe and economic
vertical alignment. These are outlined below and are particularly applicable to highspeed situations.
A smooth profile with gradual changes, consistent with the class of road and the
character of the terrain, is preferable to a vertical alignment with numerous sharp
breaks and short lengths of uniform gradient.
A roRer coaster or hidden dip type of profile should be avoided.
A smoothly rolling profile, rather than a straight profile, can often result in
economy of construction, without sacrificing operating characteristics and
aesthetics.
A broken-back profile (two vertical curves in the same direction separated by a
short section of uniform grade) is not desirable, particularly in sags, where a full
view of the profile is possible.
In flat terrain the profile is oflen controlled by drainage considerations. It is
important that adequate falls (both longitudinal and transverse) are provided so
that water drains freely from the road surface. The height of the profile above the
surrounding ground may be governed by the need to provide drainage structures
under the road. In areas where, after rain, surface water is known to stand above
ground level, or where the groundwater table is immediately below the surface,
the profile should be designed so that the lowest part of the road surface is at
least 0.5m above that water level. If the water table is a permanent one, then this
figure should be increased to 1.Om, due to the possibility of capillary action.
Page &1
KWB& Highway Design Manuel
Chapter6
VerficalAlignment
=
In areas of rock, it Is desirable that the profile of the lowest part of the road
surface should be at least 0.3m above the rock level, in order to avoid
unnecessary rock excavation.
Vertical curves that are substantially longer than the length required for stopping
sight distance are generally mere aesthetically pleasing.
Superelevation runoff occurring on a vertical cunse designed to near-minimum
standards requires special attention to ensure that minimum vertical curvature is
maintained in all lanes. Both edge profiles should be checked and adjusted
.
where necessary, in order to maintain the desired minimum vertical curvature.
It is not desirable for intersections to occur on sections of road that have steep
gradients, and the design should seek to avoid this situation.
The primary determinant of the vertical alignment is the topography, including the
levels at tie-ins of intersecting roads, utilities 20 be crossed and thresholds of
adjacent properties. Good design should seek to minimize the extent of earthworks
required.
It is conventional to denote an uphill .gradient (in which levels increase as the driver
advances along a profile) as positive (*ye), and a downhill gradient as negative (-ye).
6.2
Vertical Curves
A vertical curve is a curve on the longitudinal profile of a road, which allows for a
change of gradient. Vertical curves should be provided at all changes in gradient
except at intersections and on local roads and streets where the change in grade is
less than 1.Ox.
Vertical curvature is designed to provide for comfort, for SSD at the design speed,
and where appropriate, for DSD and for SPSO on undivided roads.
A crest curve is a vertical curve that is convex in shape, and which reduces upgrade
andlor increases downgrade. Conversely, a sag curve is a vertical curve that is
concave in shape, and which increases upgrade and/or decreases downgrade, Crest
and sag curves are illustrated in Figure 6.1.
Page 8-2
Kuwait Highway Desbn Menual
chapter 6
VerticalAlignment
Crest Vertical Curves
'
Sag Vertical Curves
G,and G2= Tangent gradients (%)
-
A = G1 G2= Algebraic difference in gradients
VIP = Vertleal interseclionpoint
VC F Length of vertical curve (rn)
X = Distance at any point on the curve measured from point PC (m)
e
= Height frpm curve lo VIP a4 VCn (m)
Figure 6.1: Types of Vertical Cuwe
Source: Adwled ham MsMo'
A parabolic curve with an equivalent axis centred on the VIP is normally used in
highway design. The rate of change of gradient at svccessive points on the curve is
a constant amount for equal increments of horizontal distance along the curve. Thus
the rate of change of gradient is equal to the difference between the start and end
gradients of the curve divided by the horizontal distance between them, or ANC.
The reciprocal of this value, VCIA, is the horizontal length in metres required to effect
a 0.01 change in gradient and is a measure of curvature, the K value. In other
words, the length of the vertical curve is calculated from the following formula:
VC= K x A
Elevations along the curve for any distance 'X' can be calculated using the following
formula:
where
X, = Elevation at distance X along the curve
PC,
= Elevation at point PC
Page 63
Kuwait Highway Design Manuel
Chapter6
Vertical Alignment
Height 'e'may be calculated from:
The position of high or low points can be calculated from the following formula:
,
If X is negative or if X 3 VC, then the cunre does not have a high or low point.
Far crest curves visibility requirements determine the minimum K values that can be
used. For sag curves, the need to achieve SSD within the length illuminated by
headlights Is generally the determining factor. Adoption of the K values given in
Table 6.1 will normally meet the requirements of visibility, but SSD should always be
specifically checked because the horizontal alignment of the road and the presence
of crossfall, superelevation and features such as signs and structures adjacent to or
above the pavement all interact with the curvature to determine the visibility.
Table 6.1: Minimum Vertical Curvature for Dlvided Roads
Where DSD is to be maintained over a crest curve, significantly flatter curves are
required, with K values as shown in Table 6.2.
Page 6-4
Chapter 6
Veftical Alignment
mn
Table 6.2: Minimum Crest K Values for Decision Sight Distance (Worst Case)
Ij
I
For undivided roads, where the horizontal alignment has been designed to allow
passing, the crest curvature should also provide far Safe Passing Sight Distance.
Conversely, there is no merit in providing a passing crest if the horizontal SPSD does
not permit passing. K values to permit passing on vertical curves on two-lane
undivided roads are given in Table 6.3. M e r e passing is not permitted, the
minimum values for divided roads given in Table 6.1 may be used for undivided
roads.
Table 6.3: Minimum Crest K values to Permit Passing an Two-way, Undivided Roads
I
I
6.3
Maximum Gradient
The selection of suitable maximum gradients is heavily dependent on vehicle
characteristics, particularly those of trucks. There are two considerations, namely the
maximum gradient and the length over which it is appropriate for it to occur.
The maximum gradients far use in Kuwait are given in Table 6.4.
Page 6-5
Kuwait Highway Design Menwrl
Chapier 6
Vedical Alignment
Table 6.4: Maximum Gradient
Road Class
Maximum Gradient (%)
Special Roads
4
Primary Roads
6'
Secondary Roads
6
Local Roads
8
In industrial areas, gradients should preferably be limited to 6%. In residential areas
where properties lie adjacent to the road, the desirable maximum gradient is 3%.
At grade-separated interchanges, the maximum grade for on and off ramps may be
up to 2% greater than the corresponding maximum gradient permitted on the main
line.
Gradients approaching at-grade intersections, signalised intersections, or
roundabouts should not exceed 2% (up or down) for a minimum of 15m before the
Stop or Give W a y line.
Even relatively gentle upgrades, if continued for a sufficiently long distance, will slow
trucks considerably. The guidelines given in Table 6.5 for the maximum length of
sustained gradient are based on a speed reduction for trucks of 15kmlh.
Table 6.5: Critical Grade Lengths
If gradients are sustained for greater distances, then truck speeds fall accordingly.
Consideration might also be given to the provision of a climbing lane. Should a
scheme including a climbing lane be considered in Kuwait, the designer is referred to
Part 1 of Section 1 in Chapter 6 of the DMRB', or to Chapter 3 of AASHTO'.
Minimum Gradient
Although from a vehicle operating point of view there is no reason why a road cannot
be level, drainage considerations generally make this inappropriate.
A level road with a normal crown sheds water from the crown to the edge of the
pavement, but longitudinal drainage is not possible and large areas of ponding occur
at the kerb. While it is possible to tackle this by channel grading (the use of varying
KuwaH H&hwey Design Manual
Chapter 8
Vertical Alignment
falls outwards from the crown to create rise and fall along the kerb line) or by over the
edge drainage, neither of these arrangements is completely satisfactory, and it is far
better to arrange for the main line profile to have a longitudinal gradient. The
minimum desirable longitudinal gradient for satisfactory drainage is 0.5%. An
absolute minimum of 0.3% may be used bn Local Roads only.
6.5
Visibility
It is particularly important to check that there are no restrictions to visibility caused by
safety barriers, median kerbs, bridge piers, etc, especially at locations with both
horizontal and vertical curvature.
Visibility at sag curves is usually not obstructed unless overbridges, signs or other
features are present. This should be checked using the upper bound of the visibility
envelope for the relevant Sight Distance.
If, at crests, the sight line is across a landscaped verge, consideration should be
given to adopting a lower verge profile so that the maximum overall height of the
landscaping, when mature, is kept below 0.5rn.
6.6
C haice of Longitudinal Profile
The vertical alignment is controlled mainly by geometric standards but should also be
influenced by the nature of material in the cuttings and by earthworks considerations.
Ideally, a balance should be achieved between cut and fill, with the calculations
making due allowance for shrink and swell, and for suitable and unsuitable material.
6.7
Visual Appearance of Vertical Geometry
This section should be read in conjunction with Chapter 5, Horizontal Alignment. As
with horizontal alignment, the ideal solution for vertical alignment (when topography
and other controlling factors permit) is a series of well modulated vertical curves,
proportioned so that they avoid the problems discussed below.
The sag curve plays an important part in achieving internal harmony in the alignment
since, unlike the crest curve, its whole length is often visible at the one time. As is
the case with horizontal curves and straights, when a sag curve is used to join two
tangent grades, the curvature must be sufficiently large to avoid the appearance of a
kink.
Tangents, especially short ones, between two sag cutves can result in an awkwardlooking profile.
Figure 6.2 summarizes types of vertical alignment to be avoided and those to be
aimed for in the design process.
Page 6-7
KWH
H&bwey Design Manuel
Figure 6.2: Summary of Vertical Alignment Features
6.8
Combining Horizontal and Vertical Alignment
To obtain a satisfactory alignment it is important to integrate the vertical and
horizontal geometry, and to consider the road as a three-dimensional unit. Where
possible, the horizontal and vertical alignment should be in phase, with
corresponding elements in the horizontal and vertical planes beginning and ending
-approximatelytogether.
It is not always possible to keep vertical and horizontal elements entirely in phase
with each other, but provided that the amount by which they are out-of-phase is
small, this is not likely to worsen the visual appearance significantly. A modest
degree of overlap (in comparison with the length of the element) may even make a
positive contribution to the integration of the geometry.
Page 6 4
Kuwait Highway Design Manual
Chapter 6
Vertkel Alignment
In general longer, coincident curves are preferred but if prevalent conditions prevent
their use, it is nevertheless possible to achieve significant improvement by the use of
longer overlapping curves. A summary of desirablelundesirable combinations of
alignment is provided in Figure 6.3.
HorizmH a m
curve rcithin its lw.
W i n i n g a lrxlv aest
cllrve vrithin its lengtk
S M vertical uxw
betwaenQladesina
M z m l mve
Hwiwntal mfdlm+y
a straight and starting
masagamewhich
fdlm a arxk
\
rzxcn
Hwizmtal and vertid
J
a r m in phase (the v
m
i 1
continmtymoffenbe
j W b y M % M e
horizontal elements slrghtly
leadlrg the verttd ones)
-
-
w
I
J
possible US8 three
dimenriaableomsad
avwd the use of straights
Usead1b a l a m d m
dmensimdigmmt
!3q am?joined ky a
level length orgrade
and w r r f r q alwg a
straigM f d l d b$a
horizontal m a
Crest cllrve fdtby
a sag cxlrve oaxlning
dong a straigM f d l m
by a hwizmal a m
A t a m length k w m
averti~al~urveanda
mmpud-
Reversehwitantalarrve
with the change in
arrvature situated at the
top ofa sharp crest arrve
-
Oul d phase H i m
W l y balanced
Figure 6.3: Summary of Desirable I Undesirable Alignment Combinations
I
Page 6-9
K w i t Highway Design Manual
cnapler s
Vertical Alignmnt
6.9
Vertical Clearances
Minimum vertical clearance (or headroom) is specified to prevent vehicles, or their
loads, from coming into contact with any overhead structure.
The preferred clearance for new construction Is 6.0m. The minimum clearance for
new construction is 5,5117.This is to be provided across all trafficked lanes, including
any shoulders or edge strips. The maintenance headroom of 5.3m must be available
at all times. This makes an allowance of up 200mm for pavement overlay, which
may be applied during the maintenance of the road.
Minimum clearance shall be provided to all structures and roadside furniture
overhanging the pavement, including all bridges and building structures, sign
gantries, overhead cables and suspended lighting.
Where a road passing underneath a bridge is on a sag curve, the headroom needs to
be increased to allow for the limiting effect of the sag. Table 6.6 provides the details.
Table 6.6: Additional Clearance to be Provided on Sag Curves
Where a public utility specifies a minimum vertical clearance to its plant, then the
greater of the clearances must be provided for. Protective measures such as guard
wires may be required at ovehead cable crossings. Advice should be sought from
the Ministry of Electricity and Water when planning works in the vicinity of their
installations.
Where a road passes beneath overhead cables, the designer can maximize the
vertical clearance by positioning the road as close as possibte to an electricity pylon,
where the cable will be considerably higher than at the centre point between two
pylons. For minimum horizontal clearances to electrical apparatus, advice should be
sought from the Ministry of Electricity and Water.
6 10
Local Roads
There are a number of considerations particularly relevant to local roads and streets
(including access roads and cul-de-sacs) that should be borne in mind.
Residential and Commercial Areas:
Match threshold levels in areas of existing development
Preferred maximum slope across housing plots is 3%
Ktnvaf! Highway Design Manuef
Chapter 6
Vertical Alignment
Valley points, where water may collect, should be kept away from residential
accesses
Road levels should preferably be below, rather than above, the level of adjoining
properties
Vertical curves should generally be at least 30m in length
-
On local roads and streets, a change in vertical alignment is offen best made
where there is a sharp horizontal bend
Levels of existing utilities may dictate the vertical alignment of new roads
The preferred maximum longitudinal gradient for a footpath is 5%. The absolute
maximum longitudinal gradient, for use over short lengths of footpath, is lo%,
and although steps may be used to achieve a steeper grade, these are not
preferred because they limit access by wheelchairs
The maximum change in gradient between a driveway and a road or property
should be7% and the profile rounded to eliminate vehicle grounding.
Low retaining walls or planters may be used ta assist in matching road levels to
existing plot boundaries, but must not be allowed to present a hazard to vehicle
or pedestrian traffic
Industrial Areas (or where industrial traffic is present):
Maximiurn gradients should be 6% to accommodate heavy vehicles comfortably
After long er steep downgrades, heavy vehicles may require additional level
areas for braking purposes
Sudden changes in transverse or longitudinal gradient should not occur, so that
vehicle loads remain stable
" A Policy on Geometric Design of Highways and Streets 2001, AASHTO, 2001
DMRB, The Highways Agency, UIK Department of Environment, Transport, Local
Government and the Regions, UK Government, various dates
Page 6-1 2
7
CROSS-SECTIONAL ELEMENTS
7.1
General
This Chapter considers the geometric elements of a typical road cross section. The
limits of the road cross section are governed by the width of the available right of
way. This is normally determined at the planning stage.
Chapters 9 to 12 contain drawings showing examples of typical road cross sections
adopted in Kuwait and the purpose of this chapter is to discuss the geometric
characteristics of the various components that together make up the cross section.
The basic elements of a road cross section are as follows:
limits of Right of Way (7.2)
Side Slopes (7.3)
Verges (7.4)
.
Service Reservations (7.5)
Shoulders and Kerb Clearances (7.6)
Clearances to Structures (7.7)
Clearances to Safety Barriers (7.8)
Lane Widths (7.9)
Median Widths (7.10)
Cross Slopes (7.11) .
Gutters and Drainage Ditches (7.12)
i d-J
- -
1.6
1.
,:,:*.a
;;
, -
Other Elements within the Cross-Section (7.1 3)
Typical urban and rural cross sections are shown in Figure 7.1.
ROW
Flgure 7.1 : Cross-sedlonalElements
7.2
Limits of Right of Way
The limits of the right of way form the outer boundary of the cross section. In Kuwait
the width of the right of way is proposed at the planning stage. The chosen width of
the right of way should permit the design of a well balanced cross section, taking into
account the road class, the projected traftic flows, the topography, the surrounding
land uses and any other relevant parameters (such as grade separation provision).
Table 7.9 summarizes the typical Kuwait provision of overall right of way width for
various road classes. More details can be found in Chapters 9 to 12. The values are
Page 7-1
K m i t Highway Desbn Manual
Chapter 7
Cmss-SectionalElements
for guidance only and may be increased to allow for the space taken up by
earthworks, utilities or structures such as bridges or tunnels.
Table 7.1: Preferred Width (and Range) of the Right of Way In K w a %.(m)
All road furniture such as signing, lighting, barriers and structures, should be
.
positioned within the right of way.
Side SIopes
Side slopes fall into two categories, embankment slopes and cuffing slopes. Cuttings
have a back slope leading from the surrounding terrain to a drainage ditch and a fore
slope leading up from the ditch to the verge and the pavement. The design
considerations for a fore slope are the same as for an embankment, whereas a back
slope is designed as a cutting.
Side slopes serve two primary functions, enabling the vertical alignment of the road
to be achieved and providing structural stability to the road itself. Where side slopes
exist, they also serve a secondary function. They provide a surface over which outof-control vehicles may travel and recover. Their design, therefore, also seeks to
minimise the overturning of such vehicles.
The angle of the side dopes depends on the slope material. Rock cuttings in hilly
areas can be stable at relatively steep angles. Embankments of granular material
require shallow angles. In areas prone to wind-blown sand, slope angles should be
avoided as they create eddies that lead to the deposition of sand drifts an the
pavement.
An adequate Geotechnical Investigation should be carried out. The investigation will
provide scientific guidance regarding the maximum slope for cut and fill, and the
criteria for benching or erosion protection, if required.
In general, embankment side slopes should fall away from the verge at a slope of 1
in 6 (16%) or flatter. It is usual to provide a safety barrier where embankment slopes
are steeper than *f in 3 (33%) or where the overall height of the slope is greater than
6m. Flatter slopes are preferable, provided that there is adequate fall for drainage.
Slopes in cutting are determined by the nature of the material in which they are
excavated. Other than in rock, slopes should preferably not exceed 1 in 3 (33%).
If there is insufficient width to provide side slopes in accordance with these
guidelines, the use of retaining waHs or some method of slope stabilisation should be
considered.
The edges of cutting and embankment slopes should be rounded and smoothed to
meet the existing topography.
Page 7-2
-
1
Kuwait Highway Design Manual
Chapter T
Cross-Sectional Ekrnents
The intersection of slope planes in the cross section should be rounded to simulate
natural earth forms. The rounding and smoothing of slopes helps to rninimise sand
drifting and the wash out of sand or other loose material from embankment edges.
In rock cuttings, ditches and a debris verge should be provided. These will facilitate
surface water run off, and create a safe landing and catchment area for any possible
rock fall. The additional width also serves as a useful area for rock face maintenance.
Side slopes under the back spans of open-span, overbridges should be paved, and
the aesthetics and economics of the w e r bridge rather than other considerations will
normally dictate the slope. 1 in 7% (67%) is generally regarded as a maximum.
7.4
Verges
The verge acts as a buffer zone between the edge of the pavement (kerb or back-ofshoulder) and either the side slope or the surrounding physical features. The verge is
normally unpaved in rural areas. In urban areas, the verge may include landscaping
and a paved footway.
The verge provides stability to the edge of the pavement construction, reducing the
chances of damage due to erosion. It also accommodates road furniture, such as
signs, signals, lighting and structures.
Utilities, such as electricity and water, are laid underground alongside roads and
should be allowed for within the highway right of way. Such services are usually laid
in the verge, which may need to be significantly wider than would normally be
required for traffic safety reasons.
Verge widths vary from a desirable minimum of 2.25m (for traffic safety reasons) up
to the limits of the right of way.
Generally, a paved verge is designed with a 2.5% crossfall towards the road
pavement for drainage purposes. However, with wider paved verges, crossfall should
be designed towards specific drainage collection points located within the verges
themselves.
It is important to ensure that road furniture or landscaping within the verge does not
impinge on the sight distances required for the design speed of the road. Isolated,
slender obstructions can be ignored, but massive or continuous obstructions need to
be identified and appropriate measures taken to achieve the sight distance
standards. One typical method is by means of verge widening, and this is dealt with
in Chapter 5. Particular care should be taken at intersections, where the number of
signs and other items of street furniture is greater than on the open road.
If soakaways are to be installed within the verge, this may also have an influence on
its width, particularly if sewices are present.
7.5
Service Resewations
Due investigation of utilities should be made at the outset of the design process by
direct liaison with the relevant Authorities. The necessary width of the service
reservation should then be agreed with the Ministry of Public Works, Ministry of
Communications, Ministry of Electricity and Water, and Kuwait Municipality prior to
the commencement of design.
Although the recommended cross sections in Chapters 9 to 72 have been designed
to allow for the inclusion of services, it may be that the width required by the Utility
Authorities is greater than the width that the designer can provide within the right of
Page 7-3
-
Kuwefi Highway Design Manual
Chepftrr7
Cross-SecfionalElements
way. Under such circumstances, it is important to reach a proper agreement with all
the relevant parties before the design is finalised.
7.6
-
1
-
Shoulders and Kerb Clearances
The addition of a paved outer shoulder to the outer edge of a road has many
advantages and is usually warranted on the basis of the following factors:
Provides a place for safe stopping in the event of mechanical difficulty, flat tyre or
other emergency,with minimal disruption to traffic flow.
a
-
Offers a clear route for emergency vehicles to reach the scene of an accident.
Provides space that may enable avoiding action to be taken in order te escape a
podential accident situation.
Improves storm water drainage by allowing water to be discharged further From
the running lanes, thereby preventing ponding on the travelled way during heavy
rain,
-
(
J-
Increases sight distance on horizontal curves and lateral clearance to signs and
other obstructions.
Creates a feeling of openness that helps to reduce driver stress.
Provides structural suppoFt to the pavement edges.
-
Provides additional running lanes for diversions and space for road maintenance
operations.
Outer shoulders are not usuatly required on urban local or secondary roads, because
the kerbs provide structural support and disabled vehicles can generally find safe
places to stop in driveways and side streets. Nevertheless, the adoption of outer
shoulders on secondary roads in industrial areas can be beneficial.
-
On special and primary roads, inner shoulders are commonly provided on the median
side of the pavement, but these are normally narrower than the outer shoulders.
Shoulders should generally be constructed to Ehe same design as the travelled way,
so that the shoulders can carry traffic during maintenance operations.
Outer shoulders should normally be designed to the same crossfatl as the adjacent
running lane.
When providing shoulders, consideration should be given to means of discouraging
vehicles from casually using them as an extra lane during times of high traffic flows.
This practice compromises the safety of the road and fuels driver frustration.
'Rumble Strips' (a series of raised or lowered strips) perpendicular to the flow of
traffic can be provided.
The requirements for shoulders are summarized in Table 7.2.
7.6.2
Kerb Clearances
Where a kerb is provided, there is a tendency for drivers to steer a distance away
from it. This phenomenon is termed 'shying', The greater the speed, the greater the
distance drivers will shy away from the kerb. Shying is accommodated by the
provision of a suitable kerb clearance additional to the width of the adjacent lane.
Where there is a shoulder, there is no need to provide kerb clearance.
Page 7-4
--
1
-
-
-
ChapIsr 7
Crvss-Secthel Elements
A kerb clearance of 0.6m should be generally be added to the width of the lane
adjacent to kerbed edges on roads with a design speed exceeding 80kmlh.
In some instances it may be beneficial to delineate the clearance to the kerb by
means of a painted edge line. Under such circumstances, the kerb should be set
0.6m back from the painted line, which is coincident with the edge of the adjacent
lane. Table 7.2 provides a summary of the normal requirements for kerb clearances.
Table 7.2: Shoulders and Kerb Clearances
Rural Undivided
Urban
none or 0.6 none
.-
none
none or 0.6
Primary Roads
Rural
Urban
Special Roads
7.7
I
1.2
none
nla
3.0
1.2
none
- 3.0
none
Clearances to Structures
It is important that structures and other obstructions are set back adequately from the
edge of the travelled way. The width of the necessary 'clear zone' is dependent
principally on the design speed of the road, but also varies according to the side
slope of the earthworks, if any.
Table 7.3 sets out the relevant values for clearance to structures.
Page 7-5
Kuwa# Hbhwey Design h48nuef
Chepter 7
Cmss-SecfmnelElements
Table 7.3: Clear Zone Wldth (m)
Design
Speed
{kmlh)
Emban krnents
Side Slope
Side
f :6 or
Slope 1 :S
Flatter
At
Grade
Cuttings
-
Side Slope Side Slops Side Slope
I :6 or
Steeper
t:5and
Flatter
than 1:4
1:4
60
5.5
5
5
5
5
5
70
8.5
6.5
6.5
6.5
6
5
6.5
80
8.5
6.5
6.5
6
7.5
10
7.5
10
13.5
10
14
10.5
10.5
14.5
11
11
_
'
5
.
9.5
10
8.5
"Safety barrier is provlded where side sbpe exceeds 7:5
Sourn: AdapW from Table 3.1 of Roadsick Design ~uide'
These distances are measured from the nearest edge of the travelled way and
therefore include the width occupied by shoulders, service reservations and verges.
Where the 'clear zone' cannot be kept completely free from obstructions, safety
barriers should be provided to protect the driver of an errant vehicle from colliding
with the structure or other obstruction.
Additionally, adequate sight disbances should be maintained throughout the length of
a route. This may necessitate further setting back of structural walls, piers,
abutments etc, and may require safety barriers to be set back further than normal.
Refer to Chapters 1, 5 and 6.
Clearances to Safety Barriers
As a general rule, safety barriers should be placed as far from the travelled way as
possible, however, it is also desirable to maintain a uniform clearance in order to
provide the driver with a certain level of expectation. Table 7.4 sets out the relevant
minimum clearances.
Table 7.4: Desirable Minimum Lateral Clearance to Safety Barriers
Page 7-6
-.
KmtY Highway Design Manual
Chepter 7
Crass-Sectionel Elements
Ends of barriers should be flared away from the road, as described in Section 8.7.4
of this manual.
7.9
Lane Widths
Lane widths have a great influence on the safety and comfort of driving. In particular,
the lane width on an undivided road must be sufficient to provide adequate clearance
between passing vehicles.
The standard lane width for roads in Kuwait is 3.7m. Wowever, this may be reduced
to an absolute minimum of 3.0m where standard lane widths cannot be provided and
with the approval of the MPW. In industrial areas, a lane width of 3.75m is more
appropriate, as set out in Table 7.5. In some instances the lane width may be
widened to accommodate the manoeuvring requirements for parking in an adjacent
parking lane.
At signalised intersections lane widths may be reduced, the absolute minimum being
3.0rn.
For lane widening on curves see Section 5.6 of this Manual.
Edge lines are provided within the kerb clearance or shoulder width, and lane lines
are included within the lane width.
Table 7.5: Normal Lane Wdths [m)
7.10
Median Widths
7.10.1
General
Medians are used ta separate opposing traffic lanes on multi-lane roads. (Separate
advice regarding the outer separation between a service road and the main line is
given in Section 7.13.2).
Medians provide protection from interference by opposing traffic, rninimise headlight
glare, provide additional space for crossing and turning vehicles within at-grade
intersections, allow pedestrian refuge in urban areas, and may provide space for
utilities and for the creation of future additional lanes.
Medians may range in width from as little as t.2m in an urban area to 20m or more in
a rural area with street lighting, drainage and landscaping. Median width depends on
the extent of the right of way available and the functional requirements of the median.
Page 7-7
K m i t Highway Design Menual
Chephr 7
Cross-SectFonel Elements
On Special Roads, medians are normally provided with safety barriers, to eliminate
head-on collisions. Rural divided roads may be similarly treated.
It is recommended that urban medians should be kerbed. Rural medians should
generally be provided with a 0.6m or 1.2m shoulder and not kerbed; a depressed
median is preferred as this improves drainage of the road. A kerbed median is
desirable where there is a need to control left turn movements and is also used
where the median is l o be landscaped.
Special attention should be given to drainage of medians. If the median is kerbed and
paved, the median surface should be designed to have slopes of 2% and should fall
away from the centre of the median. Non-paved medians should fall towards the
centre at a rate of 1 in 6 (17%) when self-draining, but consideration should be given
to the provision of additional storage capacity or outlets to allow for storm conditions.
Paved medians may require positive drainage systems incorporating manholes or
culverts. All drainage inlets in the median should be designed with the top flush with
the ground and the culvert ends provided with safety gratings, so that they will not be
hazardaus to out of contro! vehicles that stray into the median.
It is common practice to landscape medians. This is seen to provide a better
environment and reduce driver stress. Careful consideration should be given to the
choice of planting to ensure that SSD is not impaired. Furthermore, the upkeep of the
landscape and growlh of the plants should be designed for minimal maintenance.
Where two abutting sections of road have different median widths, a smooth
transition should accommodate this difference. The transition should be as long as
possible for aesthetic reasons and should preferably occur within a horizontal curve.
Table 7.6 sets out the minimum widths for certain functional requirements of
medians.
Table 7.6: Minimum Median Widths for CerZaln Functions (m)
-
nla not applicable other considerationsgovern
7.10.2
Narrow Medians
. Narrow medians are those less than 4.0m wide and are used where there is a need
to provide a divided road, but where the available right of way does not permit
greater median width. They are net wide enough to accommodate effective left turn
lanes.
The minimum median width to provide a safe pedestrian refuge (away from
signalised intersections) is 3.5m.Pedestrians' freedom to cross at locations with a
mmwer m@ian should be actively discouraged by the provision of physical
chtacles sw31as guardrails.
Itis mrnrmgtdedthat narrow medians not be used on rural roads. In urban areas, a
arrow mewn should not be considered.if it Es possible to provide an intermediate or
W e medlm.al,that parlicular location, while maintaining acceptable standards for
ihe ramairfmg cwss section.elemerrts.
7.10.3
lnterrnedikbMedians
~ntermsdi&lvviidth.medians an those in the range 4.0m to 8.Orn. ~ h &
an gankally
wIBs enough b provide for a leff turn lane: A 6.0m wide median permits the
Idrduetiafi of some landscaping.
M W & ~ ,wide
~ :M
~ more
~ provide space for effective landscapkg and may be
@r., , - , sewiees and drainage. Wide medians may also be used to absorb
-I
dikimtm across the road reserve.
Wide medians s h o d not be implemented at the expense of reduced verge widths.
7.10.5
Norma1 Widths for Medians
The normal median provision is shown on Table 7.7, together with the minimum
,..-
requirements.
4
+.
Table 7.7: Medlan Wldtha (m)
Secondary Roads
Primary Roads
I
Special Roads
."
;
i r I.
5.1
I I - l r
.C--',IT-
I
.
.
I
,
,/-*
,
1. = a d , ' ' ? ;
blt
I&
Urban
Rural
Minimum 2.0
Normal provision 6.0
Mhirnurn 4.0
Normal provision 6.0
Minimum 2.0
Minimum 6.0
Minimum 2.0
Normal provision 8.0 to 10.0
Minimum 6.0
Normal provision 8.0 to 10.0
INormal provision 8.0 to 10.0 I Nomal provision 8.0 to 10.0 1
Hots: Marrower widths may te appropriate at signalbed intemdons.
Mdien w k h my inamam to wit vkibilky raquftemenl
:
I
-
1
I
.
,
i
Every effort should be made to provide the normal provision,.values In
. Table
,
7.7.
%
;.I
7.1I
1
Cross Slopes
Embankments aligned at right angles to the road can create significant safety
hazards for out-of-control vehicles that have strayed off the pavement. The
recommendedmaximum slopes are set out in Table 7.8 below.
Kwail Highwey Design Manual
Chepter 7
Cross-Sectional Ekrnents
Table 7.8: Maximum Cross Slopes
Condition
Absolute maximum - Special Roads
Absolute maximum - Rural Primary Roads
Absolute maximum - Urban Primary and Secondary Roads
Desirable maximum all locations
Absolute maximum - all other locations
Maximum slope
1 in 10 (10%)
1 in 6 (17%)
I
1 in 6 (17%)
1 in 5(20%)
1 in 4 (25%)
Where available land is at a premium, side slopes rnay need to be steepened beyond
the values given in Table 7.8. At these locations safety barriers parallel to the main
line can be provided to contain errant vehicles. For further details refer to the
Roadside Design ~ u i d a ' .
7.12
Gutters and Drainage Ditches
Where roads are kerbed, the part of the pavement adjacent to the kerb acts as a
gutter, collecting rainwater and conveying it to gullies spaced at appropriate intervals.
Where a kerb clearance is provided, the gullies can be located within that zone but
where the kerb abuts the edge of the travelled way, consideration should be given to
the use of side-entry gullies or the adoption of combined kerbIdrainage units.
Drainage ditches are generally provided between the back slope and fore slope of a
cutting, and often at the toe of an embankment. The design of surface water
drainage systems is not within the scope of this manual and advice should be sought
from the Ministry of Public Works.
7.13
Other Elements within the Cross-Section
7.13.1
Auxiliary Lanes
Auxiliary lanes are additional to the normal through lanes and are introduced in
specific locations to serve a particular purpose. This purpose may be one or more of
the following:
as a speed change lane
as a climbing lane
as a turning lane
as additional storage space
as a method of rnaintsining lane 'balance
Speed change lanes are used either for acceleration or deceleration, and their design
is dealt with in Chapter 18 (Grade Separations and Interchanges) or in Chapter 14
(At Grade Intersections).
'Climbing lanes may be introduced on steep up-gradients, or on sustained up-gradient
of lesser severity. Critical gradient lengths, above which provision should be
considered, are given in Chapter 6 (Vertical Alignment),
Turning lanes permit turning vehicles to undertake the necessary manoeuvre clear of
the through traffic. Details are given in Chapter 14 (At Grade Intersections), Chapter
15 (Roundabouts), Chapter 16 (U-Turns) and Chapter 17 (Signalised Intersections).
Page 7-10
.
Kuwait Highway Design Menual
Additional storage space is required at some at-grade intersections, and design
issues associated with widening for this purpose are dealt with in Chapter 15
(Roundabouts) and Chapter 17 (Signalised Intersections).
Lane balance issues are dealt with in Chapter 18 (Grade Separations and
Interchanges).
7.13.2
Service Roads
Senrice roads are roads that run roughly parallel with, and are connected to, the main
through route of Primary Roads and Special Roads. They are generally of lower
design speed and preferably restricted to one-way traffic flow.
Service roads segregate the higher speed through traffic from the lower speed local
traffic and reduce the number of access points onto the main line. The provision of
service roads reduces the interference to traffic flow on the main line, makes the best
use of road capacity and results in a safer road.
Service roads may also provide an alternative route if maintenance is required of the
main line, or in case of an emergency.
The width of the service road should be at least 5.0m and is dependent on the type
and turning requirement of the traffic i.a. whether light vehicles, buses, delivery
lorries or heavy goods vehicles are expected to use it. Further considerations include
the type and number of access points and the type and nature of street parking, if
required,
Service road connections to Primary Roads should be designed as atgrade
intersections (in accordance with the guidelines given in Chapter 14) while those for
Special Roads should be designed as off-ramps and on-ramps {as specified in
Chapter 18).
Where service roads are provided, there is a need for a separation between them
and the main line. This is known as the outer separation, and its absolute minimum
width is 1.2m. This distance aHaws for the provision of a central pedestrian guardrail
only and is not sufficient to accommodate any traffic signs. If traffic signs or other
street furniture are to be placed in the outer separation, the desirable minimum width
is 2.0m. A wider outer separation, giving greater scope for landscaping, thus
enhancing the appearance d the road and its adjacent development, is preferred.
The designer is referred to AASHTU~for further detailed explanation and guidelines
for the layout of service roads and areas.
7.13.3
Bridges
Bridges within grade-separated intersections should be designed using the normal
parameters contained within this manual, unless it is uneconomic to do so, in which
case each situation should be considered on its own merits.
The designer should establish the clearance requirements and the applicable
design speeds, controlling gradients and vertical curvature limits before beginning
preliminary design.
Bridges with long spans, large angles of skew, tapers or splays, small radius
curvature, or large superelevation should be avoided, as they are likely to be
costly and difficult to construct.
It should be possible to continue the full standards of the adjacent sections of the
route across the bridge.
KWH Highway Design Menuel
Chaphr 7
Ctvss-Seclional Elements
Aim to provide a straight structure. If horizontal curvature is unavoidable, then the
bridge should be on a circular curve rather than a transition, and the radius
should be as large as possible.
Avoid tapers and flared ends. If this is not possible, aim to start such changes in
cross section at a pier position.
Aim to provide bridges on straight grades (maximurn 6%, minimum 0.5% to
permit longitudinal drainage) rather than on vertical curves, If this is not possible,
do not adopt a crest curve of less than K=30.
=
Avoid sag curves on bridges. They are unattractive visually and cause difficulties
with drainage.
Aim for bridges to have symmetrical spans. This is often achieved by ensuring
that both abutments are at the same elevation.
Variation in the profile of one kerb line relative to the other is to be avoided. It
leads to a deck that appears warped, and is more difficult to construct. If it must
occur, the variation should be applied uniformly over the length of the deck.
The combination of horizontal and vertical geometry must be carefully considered
in order to visualize the aesthetics of the final design.
The presence of bridge parapets may obstruct visibility splays. If this is the case,
the road or bridge geometry should be altered accordingly.
The foward visibility requirements on a sag c u m underneath a bridge should
always be checked.
For furfher details on bridges, refer to the Kuwait Bridge Design Manual.
7.3 3.4
Tunnels
The design of major tunnels is a specialist subject and lies outside the scope of this
manual.
Elsewhere on the road network, shorter lengths of tunnel or underpass may be
required and these should be designed using the normal parameters contained within
this Manual. ff it proves uneconomic to do so, each situation shoutd be considered on
its own merits.
The following general guidance is given:
the funnel sho J d be as short as practicable.
The tunnel should be straight, if possible.
For maximum driver comfort, the aim should be for the tunnel layout to be to the
same design speed as the remainder of the route.
The mainline cross section (lane, shoulder, edge strip and median widths) should
desirably be continued through the tunnel.
Horizontat curvature in tunnels restricts forward visibility and widening on the
inside of the curve is generally required if proper SSD is to be maintained.
Full verticd clearance should be maintained.
Vertical curvature can also restrict visibility and the relevant sight envelopes given
in Chapter 4 should be provided.
When selecting grades for tunnels, consideration shoutd be given to driver
comfort and also to ventilation requirements.
Page 7-12
The design should avoid the need for traffic signs to be provided within the
tunnel.
Merging, weaving or diverging movements within a tunnel are highly undesirable.
On-s1Sps and off-slips should not be provided within funnels, nor for 300m beyond
the ends of the tunnel.
Closed Circuit Television coverage connected to a constantly manned control
room should be provided.
Emergency telephones and fire fighting points should be provided.
A raised emergency pavement or similar 'kerbed area (minimum width 0.8m)
needs to be provided for drivers of stalled vehides and for maintenance
operatives.
Roadside Design Guide, AASHTO, 1989
A Policy on Geometric Design .of Highways and Streets 2001, A4SHT0,ZOOl
Kuweil Highwey DeMn Manuel
Chepier8
Highway Facilltks
8.1
General
This Chapter draws together a variety of facilities associated with the road and its
corridor that are not addressed elsewhere in the manual. these are:
Pedestrian facilities
Public transport facilities
Parking facilities
It then deals with the following specific items of road furniture and provides guidance
on their design and provision:
Kerbs
Fences
Safety barriers
Energy absorbing barriers
Finally, it gives advice on:
Traffic calming
Landscaping
Utilities
8.2
Pedestrian Facilities
Pedestrian facilities fall into three categories, whose generic names are as follows
Crossings - those which cross a road
Footpaths - those which are independent of the road system
Sidewalks those which run generally parallel to a road
8.2.1
Sidewalks
All urban roads should allow space for sidewalks, unless they are being specifically
designed to prohibit walking. The decision on whether or not to provide a paved
sidewalk depends on a number of factors.
Firstly, planning policy for the area may well dictate that paved sidewalks should be
provided. Secondly, it is recommended that one be provided if the maximum hourly
pedestrian demand exceeds 20 persons per hour in a residential area, and 100
persons per hour in a commercial or industrial area. Thirdly, adjoining land use has
an influence on provision. An office building, for example, may generate low
pedestrian traffic levels, but it would be appropriate to have a paved sidewalk.
In general, in an urban area, a paved sidewalk is provided unless conditions dictate
otherwise.
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.
In rural areas, each case should be examined on its own merits, Generally, sidewalks
are rarely required, except along sections of road where there is substantial
residential or commercial development. In such situations, footpaths may be located
Page 8-1
K w a i t HQhwey Design Manual
Chapter i9
Hiahwev Facilities
remote from the road, often along the outer edge of the right of way, adjacent to the
property line.
Preferred widths for sidewalks are given in Table 8. I .
Table 8.1: Preferred Minimum Width of Sidewalk (m)
Urban
Road Class
Minimum
Desirable
Secondary Road
I
3.5 or more
1.8*
. Where provided within
verge width, sidewalk
should be 1.8m to
1.8*
-Special Road
Rural
None
3.5m
None
*Minimum dimensions may be used subject to agreement fmm the MinMries of Publk Works. Cornrnunlcatlonsand
Ekdrichy and Water regarding access to their underground apparatus
The minimum width of a sidewalk is '1.8rn, but generally, the desirable value should
be provided. This should be increased near schools, sports venues, mosques,
commercial areas or other areas with high pedestrian volumes.
The width of sidewalks should accommodate the predicted pedestrian volumes.
Table 8.2 shows the standards for sidewalks in Kuwait. The design pedestrian flow
is the number of pedestrians per minute averaged over the busiest 15-minute period.
The sidewalk width relates to the clear and available width, and should not include
areas occupied by trees,planters or street furniture such as lighting columns or road
signs. Where the back of the sidewalk is walled, the available width should be
reduced by 0.5m. Where shop windows form the back boundary of the sidewalk, a
reduction of l .Om should be made
Table 8.2: Sidewalk Widths to Accommodate Pedestrian Flows
The service flows in the Table correspond to AASHTO' Level of Service N B (6rn
width and below) or BIC (above 6m width).
Sidewalks mag be constructed of interlocking paving blocks, asphalt or concrete, and
should generally be laid at a crossfaflof 2.5% towards the road, so as to facilitate
drainage. Smooth surfaces, such as marble, should be avoided.
Other than in commercial areas with on-street parking, and where wider footpaths
are generally provided, it is desirable to provide a separation strip of 1.2m or more
between the kerb and the sidewalk. This strip acts as a buffer between vehicular and
Page 8 2
I:
,fa
'- ijW@bian traffic. Pedestrians should be discouraged from using the strip by the use
- 1 .
,
-;bw@
4~#1phnling,
raised blocks or pedestrian fences.
movement is relatively compatible with traffic movement on local streets,
es less compatible on roads of higher category in the hierarchy. The at& s i n g of Special Roads by pedestrians is extremely hazardous and should
- ' w e r r t e d . Fences should be introduced to prevent unauthorised crossing, and
~
~ should be~ channelledn to convenient
s bridges or subways located at a
. ~ ~ hspacing.
t e It is unreasonable to expect pedestrians in an urban area to
&YJW
by more than 400m from the centreline of their desire line for movement.
C w - i n g s are often provided on sidewalks at road overbridges or underpasses, but
specif5c'pedestrian structures may also be needed between these points.
The 'choiceof dedicated crossing facilities is as follows:
= Unwnfrolled marked crossing ('Zebra'). This crossing is marked with stripes on
the pavement in accordance with the Kuwait Traffic Signs Manual (KTSM)*. It
should generally be provided on roads with a posted speed of 6OkmA-i or less,or
on unsignalised right-turning roadways within a signalised intersection, where
adequate Safe Crossing Sight Distance is available (see Chapter 4).
Controlled marked crossing ('Pelican'). Signals are used to bring traffic to a haR
and to indicate to pedestrians that they may cross with care. Stripes on the
pavement are provided in accordance with the KTSM. This type of crossing
exists most frequently within a signalised intersection, but can be provided on a
free-standing basis on roads with a posted speed of 80krnlh or less.
Grade-separated crossing. This form of crossing is invariably required on Special
Roads, and may also be justified on Primary Roads, depending on traffic volume,
trafic speed and the number of pededrians crossing the road. It is provided by
means of a footbridge or pedestrian subway, or by a sidewalk on a grsdeseparated road crossing.
The need for a pedestrian grade separated structure should be investigated for each
parlicular location, based on consideration of the pedestrian generation sources, the
travel patterns of pedeslrian movements, the pedestrian volumes, the classification of
road to be crossed and its traffic levels, the adjacent land use, the location of any
adjacent crossing facilities, the pedestrian accident record, and any other relevant
social and cultural factors.
Where a structure is to be provided, it must accommodate handicapped pedestrians
and those with wheelchairs. Ramps should be to a preferred maximum grade of 8%,
with an absolute maximum grade of 10% for use in difficult locations. Level landing
areas of at least 1.5m length should be incorporated so that no individual ramp
section is longer than 9.0m. Handrails should be provided on ramps and on steps
that are provided as an alternative shorter route.
The width of the facility should be a minimum of 2.5m between walls or railings.
M e r e large volumes of pedestrians are anticipated, structure widths should be
assessed on the basis of Level of Senrice C D ,with a maximum pedestrian flow of 80
persons per minute per metre of effective width, which is the actuat width minus
O.5m.
Lengths of pedestrian fence in the vicinity of the stnrcture will deter pedestrians from
crossing the road at grade. Lengths in excess of 50m may be required dependerlt on
site conditions.
K m i t Highway Desbn Menuid
Chapler 8
Highwey Feeilittes
Where the road is at the level of the surrounding ground, footbridges are generally
preferred to subways, and should be designed to be in keeping with the surrounding
area in terms of geometry and architecture. The required vertical clearance for
pedestrian bridges over roads is 6.0m,as set out in Chapter 6.
Pedestrian subways should be well lit with dear, unobstructed visibility. Pedestrians
approaching the subway should have a clear view through to the exit. The desirable
clear headroom for pedestrian movement is 3.0m1 but under no circumstances
should it be less than 2.5~1.
Specific consideration needs to be given to the drainage
of underpasses, for the removal of both surface water and high groundwater.
On divided roads, where at-grade crossing is permissible, random crossing should be
discouraged. Crossing movements should be collected together in locations where
proper facilities can be provided. Where grade-separation 1s not warranted,
dedicated crossing points with pedestrian refuges should be provided. The majority
of crossing demand is likely to occur at intersection locations, but mid-block
pedestrian demand needs to be recognised, quantified, and if appropriate, provided
for.
As indicated in Chapter 7, the refuge areas in the median should be a minimum of
3.5m wide if pedestrians are to be accommodated, but this may be reduced to a
minimum of 2.0m at signalised intersections (see Chapter 17).
Where a width of 3.5m or more is available, the crossings of the two carriageways
should be staggered using a 'sheep-pen' arrangement in the median, so that
pedestrians cannot approach and cross both carriageways in a straight line. Figure
17.1 shows a 'sheep-pen' with a 'refbright' stagger, which is generally appropriate at
a signalised intersection. On an open road, the ideal arrangement is reversed and a
'right-left' stagger is used because it enables pedestrians in the median to walk
facing oncoming traffic, thus obtaining the best view.
The width of the pedestrian crossing should generally be 3.0mt but at demand levels
above 10 pedestrians per minute, this should be increased as set out in Table 8.3.
Crossings wider than 5.0m should not normally be provided.
Table 8.3: Width of At-Grade Pedestrian Crossings
Design Flow
(pedestriansEmin)
Recommended Pedestrian
Crossing Width (m)
Up to 10
3.0 (minimum)
12
3.6
15
4.5
20 and above
6.0 {maximum)
More than 30
Consider grade separation
In order to provide for the safe and convenient movement of able-bodied pedestrians,
as well as disabled persons, dropped kerbs should be included at all at-grade,
pedestrian crossing points.
Dropped kerbs, as shown in Figure 8.1, are located within the sidewalk. They should
be at least 0.9m wide and sloped downwards towards the road surface at a gradient
of 8% or less. The edge of the ramp adjacent to the road should be flat and set
25mm above the level of the road pavement. Drainage should be carefully
Page 8 4
K w a I Highway Design Man&
Chapter 8
Highway Facililies
considered so that there is no ponding at the crossing point, but gully gratings should
not be placed in ramp areas as they may cause a hindrance to wheelchairs.
t l I '
Road Pavement
Normal kerb profile
Sldewalk
I
9
Dropper kerb
Dropped kerb
Io be 25mm above
road channel level
-
4
I
I
I
I
1
I
I
I
I
I
---+--------------------J
A Max. fall B Z
Dropper kerb
__
/,#----
i ----&-
-+-
_*--*
A**/--
Normal kerb profile
-I
I I
Figure 8.1: Dropped Kerb
8.2.3
Footpaths
Footpaths remote from the road should be provided where justified. The minimum
width is 2.0rn, but where large volumes of pedestrians are anticipated, widths should
be assessed on the basis of a maximum pedestrian flow of 60 persons per minute
per metre of effective width. In this context, effective width is the actual width of the
path, less 0.5m if it is bounded by a fence or wall. The maximum longitudinal grade
should not exceed lo%, Chapter 6 refers.
8.3
Public Transport Facilities
The location of bus stops is primarily the concern of the transport operator, who will
seek to provide stops within reasonable walking distance of trip generators 'and
attractors. The resultant bus stop spacing is normally three to four stops per
kilometre in urban areas. The designer should consult with the transport operator to
Page 8-5
Kuwait Highway Design Manual
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. It is therefore
preferable to provide bus bays, as shown on Figure 8.2.
Upstand kerb
Block paved
pedesttianarea
Shelter for
waiting passengers
Block paved
colour differentiated,
waiting area for buses
May be reduced to 4.25m
absolute min., if no shelter
is provided
For single bus only, may be
reduced to f 2m
In different circumstances may
reduced to an absolute
min. of 12m
Figure 8.2: Bus Bay
On Prirnav and Secondary Roads (and on Local Roads and Streets, if they are used
by buses), it may be acceptable to permit buses to stop by the kerb, provided that:
The bus stop area is kept free from parked vehicles, and
The bus stop is not located close to a majorlminor 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 SPSD.
Parking should be prohibited beyond the bus stop area over a distance of 12m before
and 8m beyond the bus stop area.
It may also prove beneficial to provide a signalised crossing before a busy bus stop
so as to serve bus passengers.
Kuwait Highway Desbn Manusf
Chaptar8
Highway FaciIitms
Bus stops on undivided roads should be staggered beyond each other, so that the
rim of crossing pedestrians from one bus is not obstructed by the presence of
another bus travelling in the opposite direction. This arrangement also ensures that
where two buses are dropping off passengers simultaneously, the buses do not pull
out into the crossing pedestrians dropped off by the other bus.
When providing bus stops in the vicinity of intersections, the following points should
be borne in mind:
It is preferable to locate bus stops on the exit side of the intersection. A distance
of at least 1Om 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 lay-by to the start of any right-turning manoeuvre or
auxiliary lane should generally be adequate, but the lay-by 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
bus stop on the approach side of the intersection, with the bus lay-by located at
the start of an extended right-turning auxiliary lane.
If a bus stop is located on the approach to a roundabout or signalised
intersection, it should normally be located clear of any queuing vehicles, so that
there is no loss of capacity at the intersection.
8.4
Parking Facilities
8.4.1
General
The need for parking is determined by the existing and future development of the
immediate surrounding area. Consultation is required with the Ministry of Public
Works and Kuwait Municipality to determine the future development plans and the
amount of an-street and off-street parking required.
Where possible, parking should be provided away from the road, in conveniently
located parking lots designed for the purpose. However, it is beneficial to provide
kerbside parking on local and secondary roads where the adjacent land-use
warrants.
Kerbside parking should not be provided:
Within sight triangles at intersections, in order that visibility can be maintained
and pedestrians can cross safely
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 the inside of bends, in order that adequate forward visibility can be
maintained and that any encroachment into the path of oncoming vehicles is
eliminated. However, parking on the outside of bends on local streets may be
acceptable
At pedestrian crossing paints, to minimise the width to be crossed by pedestrians;
In advance of pedestrian crossing points, so that pedestrians can clearly see and
be seen. An absolute minimum of 5m free of parking should be provided, and
ideally Safe Crossing Sight Distance, as set out in Table 17.3, should be provided
at non-signalised crossings
Page 8-7
Kuwsll Highway Design Manuel
At hydrants
On local roads, within 5m of the tangent point of any intersection
At any other location where it would create unsafe conditions
Chapters 9 to 12 provide details of standard cross sections for the various categories
of road, with recommended parking arrangements clearly shown. These should
normally be adopted, unless local circumstances dictate otherwise.
8.4.2
Parallel Parking
Parallel parking may be provided adjacent to the outer lane of the road. On a oneway road it is recommended that parallel parking should not be provided on the left
side of the traffic flow. Any parking located on the lefl side should be angled.
Parallel parking should only be provided on secondary or local roads, or on service
roads fronting primary or special roads.
The standard width required for a parallel parking lane is 2.8rn, each bay being
nominally 7.0m in length, but this may be reduced to an absolute minimum of 6.0m.
Where residential development is dense and the requirement for additional on-street
parking is great, it is possible in exceptional circumstances to use an absolute
minimum bay width of 2.2m. At such width, the opening of a driver's door
encroaches significantly into the adjacent running lane.
As vehicles entering and leaving the parking lane interfere with the passage of
through traffic, it is important to check that there is adequate capacity available. The
capacity of a through lane adjacent to a parallel parking lane depends on the amount
of parking activity and the availability of spaces, but as a guideline, a .figure of 1200
pculh should be adopted.
Angled Parking
8.4.3
If the width of' available right of way allows, consideration should be given to the
provision of angled parking bays. These may be perpendicular to the road, or at
some intermediate angle, in order to ensure that vehicles drive forwards into the bay
and reverse out.
The preferred parking bay size for angled parking is 2.8m wide by 5.6m in length.
This provides a generous layout that is easy to use. If required, the size may be
decreased to an absolute minimum of 2.5m by 5.0rn. Intermediate values of width
andlor length may also be used.
The amount of space that the bays occupy within the cross section of the road
depends on their angle relative to the road, as shown in Table 8.4 below,
Table 8.4: Angled Parking -Width occupied within Cross Section of the Road (for a
2.8m x 5.6m Bay)
Parking Angle
Width Occupied
(mE
I
Page 8 8
45*
6.00
60"
6.25
75"
6.00
90"
5.60
K m i t Highway Design Manuel
Cheptsr 8
H&hway Facilities
Adequate space to manoeuvre into an angled bay should be provided, and this may
require the adjacent through fane to be wider than normal. If space permits, it is also
good practice to provide a buffer lane between the edge of the travelled way and the
nearest end of the parking bay. This is particularly beneficial on service roads and
secondary roads. The minimum widths for adjacent through lanes and buffer lanes
are given in Table 8.5.
-
Table 8.5: Angled Parking Minimum Width for Adjacent Through Lane
1.Om minimum
For two-way operation, the minimum through lane width is 8.0m,but because twoway operation is seldom adopted unless bays are at 9Q0,
this criterion rarely governs.
In order for vehicles to manoeuvre into the bays, it is important that the speed of
through traffic is kept low. Advice on Traffic Calming is given later in this chapter.
The flow on the through lane passing the angled bays should not be greater than
1000 pculhour. If this figure is likely to be exceeded, then the elimination of the
parking bays and the creation of a separate parking lot should be considered.
8.5
Kerbs
Kerbs are to be used on all urban roads. Kerbs are to be used on rural roads at
locations where there is a need to give a clear delineation of the road edge, for
example, at intersections.
There are a number of types and combinations of kerbs available, each with
particular applications. Some, which are in regular use, are discussed below.
Normal Kerbs are upstand kerbs or raised kerbs. These are used to define the
boundary between the pavement and the sidewalk. Upstand kerbs may also be
supplied with an integral channel block, to permit drainage from the road channel.
Upstand kerbs are available in a range of sizes and shapes, allowing installation on
curves of various radii. The designer is advised to check the availability and
dimensions of kerbs with the suppliers, as the full international range may not be
available in Kuwait.
Edge Kerbs are used where a paved area joins an unpaved area, and are laid level
with the surface of the paved area.
Channel Blocks are laid within a paved area, level with the paved surface, and
permit surface water to drop into a pipe to be collected and taken away.
Flush Kerbs are laid to the same (or nearly the same) level as the adjacent surfaces
on both sides. Uses include driveways and pedestrian crossings, where the kerbs
are laid level with the adjacent sidewalk and 25mm above the pavement. Sometimes
it is effective to use an upstand kerb laid on its back to provide a flush kerb
arrangement.
Page 8-9
Kuwait Highw~yDesign Manuel
Chapter 8
Highway Facilities
Special kerb elements available from manufacturers include dropper kerbs and
quadrants. Additionally, the higher profile New Jersey Barrier or British Concrete
Barrier may be appropriate for use as bridge parapets, safety fencing or for security
reasons.
Figure 8.3 shows a typical kerb section.
Figure 8.3: Typical Kerb Sectlon (Type B l )
Where there is a need to install a safety barrier alongside a kerbed section of road,
the barrier design, kerb design and drainage design should be carried out together.
The kerb may affect the choice of safety barrier type and it is important to ensure that
the combined drainagelkerb arrangement does not impair the safe operation of the
safety barrier.
8.6
Fences
There are many different types of fence used within the road right of way, each
having its own particular application. The main types and their uses are listed below.
Boundary Fences delineate and separate private property from the road [right of
way. There is no standard design for a boundary fence, but it should be appropriate
for the adjacent land use.
Animal fences are provided to prevent animals from entering the right of way. The
height and nature of the chosen fence depends on the type of animal to be
contained, for example camels or goats.
Acoustic: Fences may be required to tower the traffic noise level in sensitive
situations, such as where a matoway passes close to properties in a residential
area. The fence forms a barrier, which both shields and reflects the sound, thus
making acoustic conditions more acceptable in the protected area. Many designs of .
proprietary fence are available, most being solid and close-boarded.
Page &I0
Headlight'Femm may be irrtrodud, generally in a median, at locations where it is
desirable to m h i s e the glare of the headlights of oncoming vehicles. This is likely
b occur an W d s on rural, un-lit, divided roads* or where two-way senrice roads run
adjacent to special Mprimary roads.
Pedestrian kn'css m y be required where thew are signiffcant numbers of
pedestrians w sidewalk or at other venues where crowds may gather. The fence
is designed ta h m e t the movement of pedestrian traffic and to reduce lhe risk of
pedestrians sa5derttsllly stepping from the sidewalk into a tram lane. It is
particularly umfd m diwumghg pedestrians from crossing at hazardous IocEitions
and channeltirig pedestrians to dbsignated crossing points.
Pedestrian k h a s ean a h be used away from the road edge, for example to direct
pedestrians a l e q footpath to a dedicated, grade-separated crossing. In this
eircumstanaes,the: Wee needs tci be high (around Zrn), long (typically up to 500m on
either side E$ W e d
n fadlity)
~ and strong enough to withstand wSfhrl damage.
Alternatively, a fence m the median may serve the same purpose. It should be high
mmugh, ad^ be M i n d in a manner, to deter pedestrians from climblng over R. If it
$ s elmpi@B m i b q a;
~ heZgM of I.5m,with the diagonal rather than horizontal
w
n
&
m
y h-M*.
~ a r r ' ~proprietary
&
designs of pedestrian fence am available, but it should be noted
that they are designed to constrain pedestrians, and are not capable of withstanding
any sign5qcanf vehicle- impact. Where the main risk is from errant vehicles rather
than straying pedestriatls, safety barriers (not pedestrian fences) should be used.
8.7
Safety Barrhm
8.7.1
General
-1
A safety barrier is a longitudinal barrier used to protect errant vehicles from impact
with objects located along a road corridor. f is normally warranted if the
eonsequences of the vehicle striking the barrier are considered to be less serious
than those that wauM result if the vehicle were to continue unchecked. It functions
by containing and rediM*ng the errant vehicle.
A saf;ety barrier, may also be used to protect pedestrians and cyclists from out of
.confro1vehicles.
Safety barriers may be located In either the verge or median, depending on their
particular function.
I
~ ~ 7 . 2Pmvisicrnof Safety Barriers
The deckion on whether w not to provide a safety barrier can own be simplified
using the following analysis, with costs being considered where the decision is
I
marginal.
Option 1: Remove or reduce the hazard so that it no longer requires to be
protected
8
I
83.2.1
Opfiqn 2: Install an appropriate safety barrier
Option 3: Leave the hazard unprotected
Medians
Head-on impact wHh an opposing vehide could lead to fatalities and so a continyous
safety barrier is often provided in the median of a dMdeel road to separate opposing
traffic. Such a barrier should always be provided on special roads and should be
Kuwait Hbhway Design Manual
considered on other roads caving large traffic volumes at high speeds, or where
there is a fall across the median.
8.7.2.2
Embankments
The provision of safety barriers should be considered when slopes are steeper than 1
in 5 (20%) or the height of the slope is greater than 6m. The barrier should always
be located on the verge, fomard of the top of the slope, and not on the slope kself.
Where barriers are not to be provided, rounding of the top of the slope reduces the
chances of an errant vehicle becoming airborne.
8.7.2.3
Cuttings
Safety barriers are seldom required in cuttings. Exceptions include where there is
steep rock face or where large boulders of other obstacles are located in the cutting
slope.
8.7.2.4
Roadside ObsEacies
A safety barrier should only be installed if it is clear that the result of a vehicle striking
the barrier would be less severe than the accident resulting from hitting the
unprotected object. Generally, if the clearance from the object to the edge of the
travelled way is greater than 10m, protection is not required.
8.7.2.5
Protection of Bystanders
This is normally only justified where sensitive land use adjoins an unusual feature on
a road. An example might be if a school playground is located on the outside of a
sharp bend at the foot of a downgrade.
Page 8-12
KMR
Highway Design Manuel
Table 8.6: Guidance on the Provision of Safety Barriers
8.7.3
Types of Safety Barrier
There are three generic types of safety barrier, namely flexible, semi-rigid and rigid
and these are briefly described in the following sections.
For further information on the different types of safety barriers, the designer should
refer to the British Design Manual for Roads and Bridgess and the AASHTO
publication Roadside Design ~ u i d e ~For
. details of specific safety barriers, the
manufacturers' technical literature should be referred to.
8.7.3.1
.
Flexible Barriers
Flexible systems are generally more forgiving than other systems, because much of
the impact energy is dissipated by the deflection of the barrier and lower impact
forces are imposed on the vehicle. There are two basic types of flexible system:
Cable fence, normally comprising 4 strands of tensioned cable. Cable fences
redirect impacting vehicles afler sufficient tension is developed in the cable, with
the posts in the impact area providing only slight resistance. However, the closer
the post spacing, the less the barrier can deflect. An irnporfant feature d the
cable fence is that, ater most impacts, lt returns to its original position, .and
damaged posts are easily replaced.
Page 8-1 3
K m i f Highwey Design Manuel
chapter 8
Highway Facilities
Standard steel beam section mounted on relatively weak posts. This system acts
in a similar manner to the cable fence. It retains some degree of effectiveness
affer 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 with a relatively narrow restraining width, is
vulnerable to vaulting or vehicle under-rfde caused by incorrect mounting height
or irregularities in the approach terrain.
8.7.3.2 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 I.5m.
Semi-rigid barriers usually remain functional after moderate collisions, thereby
eliminating the need for immediate repair. There are a number of different types on
the market, each system having its own performance requirements and capabilities.
A few examples are listed below.
*
BOX Beam
Open Box Beam
W-Beam (corrugated beam)
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 SQkmlh, the semi-rigid system
should be tensioned. Tensioned systems usually require a minimum length to be
effective and are unable to be installed on sharp radii (typically 50m minimum length
and t50m minimum radius). Individual barrier manufacturers' specifications should
be adhered to.
8.7.3.3 Rigid Barriers
Rigid systems offer no deflection when hit by a vehicle. The impact energy is entirely
absorbed by the vehicle. For high angle and high-speed impacts, vehicles may
become partially airborne and in some cases may reach the top of the barrier. For
shallow angle impacts, the roll angle toward the barrier imparted by high centre of
gravity vehicles may be enough to permit contact of the top of the vehicle with
objects on top of or immediately behind the barrier, for example bridge piers.
For these reasons, rigid barrier systems are not generally recommended for use on
roads with design speeds over IOOkmlh, and the designer should carefully evaluate
on higher speed roads.
their prop~sed~adoption
Commonly used rigid systems are the New Jersey Barrier in the USA, and the British
Concrete Barrier in the UK.
Typically, the system is relatively low cost, has generally effective performance for.
passenger-sized vehicles and has maintenance-free characteristics.
Page 8-74
-T!w&w*=
hlt end-on by an emrit vehicle.
1
I:,
I
I
B
I
I
I*
I
m
h 'ersr~ttrrlto W@ ihs most appmpriate system fa s o h
Transition ssdions of safety barrier act as a link between lengths of different strength
or rigidity, and are necessary:
To prdvide continuity of protection when lwo ,differentbarriers join; or
Where a barrier joins another barrier system such as a bridge parapet 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 a s the stronger of the two sections
that 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 15m to f 8m.
Drainage features such as dilches 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.
8.7.3.8
Selection of Barrier Type
The selection process is not easily defined, but the most desirable system is one that
offers the required degree of proteetionat the lowest total cost.
Table 8.7 summerisas the factors to be considered.
I
Page 8 15
Kuwait Highway Desigr Mmd
Tabfa 8.f: Citeria for Choice of Barrier Type
Criteria
Comments
General
'
Performance
Capability
The barrier must be structurally able to contain and redirect the
design vehicle.
Deflection
The expected deflection of the barrier should not exceed space
available for deflection.
Site Conditions
The slope approaching the barrier and the distance from travelled
way may preclude use of some barrier types.
Compatibility
The barrier must be compatible with its planned end treatment and
capable of transition to any other adjacent barrier type.
Cost
Standard barrier systems are relatively consistent in cost, but high
performance barriers can cost significantly more.
Aesthetics
Occasionally, aesthetics is an important consideration in safety
barrier selection.
-
Maintenanm
8.7.4
Routine
Few systems require a significant amount of routine maintenance.
Cotlision
Generally, flexible or semi-rigid systems require more maintenance
after a collision than rigid or high performance barriers.
Materials
Storage
The fewer the different systems used, the fewer stock items needed
and the smaller the storage space required.
Simplicity
Simpler designs tend to cost less and are more likely to be
reconstructed properly on site.
Field
Experience
The performance and maintenance requirements of existing
systems should be monitored to identify problems that could be
lessened or eliminated by using a different barrier type.
Placement
if a roadside barrier is warranted at a certain location and the type of barrier to be
used has been selected, the designer must then specify the layout required.
Elements of the design that must be considered are:
The set-back between the travelled way and the face of the barrier, referred to as
the shy-line offset
The clearance between the barrier and the object being protected
The flare rate
The run-out length
The length of need
. Details on these elements can be found in AASHTO1sRoadside Design Guide4.
8.73
Underground Obstructions
Where there is a risk of driven posts or standard concrete footings interfering with
cables, ducts or pipes, and the alignment of the safety barrier cannot be adjusted to
avoid the obstruction, or where the depth of pavement construction is such that the
standard driven post or concrete footing would not penetrate into the subgrade,
Page 8-16
special posts or footings should be provided subject to the approval of the Ministry for
Public Works.
8.7.6
Existing Systems
Wdh the development of technology and undersfanding of this subject, it is usual to
find that older installations are sub-standard and do not meet current recommended
performance levels, Such installations will require upgrading to current standards at
some point, and the replacement of each installation should be considered on a siteby-site basis.
8.8
Energy Absorbing Barriers
Energy absorbing barriers, also known as crash cushions or impact attenuators, are
protective devices that prevent errant vehicles from impacting fixed objed hazards.
This is achieved by rapidly slowing a vehicle down, and if possible, bringing it to a
safe stop before the point of impact with the hazard. Some designs of energy
absorbing barriers also have the capability to deflect and redirect a shallow-angle
impact.
Energy absorbing barriers 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 senre ta
lessen the severity of an impact with a fixed object, unlike safety barriers, which
attempt to redirect the vehicle away from the object.
Energy absorbing barriers work on one of two principles:
absorption of kinetic energy
transfer of momentum
In the first case, hydraulic energy absorbers or crushable materials absorb the kinetic
energy of a moving vehicle. This can be achieved by the use of water filled
containers from which the water will be expelled in a collisicn, or by a progressively
crushable, mechanical array of elements. Crash cushions of this type require a rigid
backstop 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
freestanding sand filled containers. Devices of this type require no rigid backstop.
Energy absorbing barriers are generally appropriate for cars travelling at speeds of
up to 100 kmlh, but not for trucks and buses, although clearly they would have some
effect in reducing the severity of a head-on impact.
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.
For optimum performance, the barrier should ideally be on a relatively level surface.
Kerbs should not be provided as they may cause the vehicle to become airborne,
There are many different designs of energy absorbing barrier systems, each having
its own particular merits and applications. In the selection process, the road designer
must consider the site characteristics, cost, maintenance requirements, and
structu~aland safety characteristics of the different systems.
Further general reference on this subject is given in AASHJO's Roadside Design
Guide4. For details of any specific energy-absorbing barrier, the manufacturer's
technical literature should be referred to.
Page 8-17
Kuwait Highway Design Man&
Cfiepfer 8
Highway Facililbs
8.9
Traffic Calming
8.9.1
General
Excessive vehicle speed is a significant factor in the majority of accidents in urban
areas. The vehicles concerned may not have 'exceeded the posted speed, but may
have been travelling faster than the prevailing conditions required.
Traffic calming is a generic name for speed reduction techniques through road
design. The objective is to alter the driver's perception of the road so that he drives
at a speed that is appropriate.
Traffic calming should never be implemented on special or primary roads. Some
elements of traffic calming may be appropriate on urban secondary roads. Calming
techniques are particularly relevant in the design of local streets.
The designer st-~ouldensure compliance with Kuwait Traffic Law and the General
Traffic Department (GTD), MPW and Municipality regulations when designing traffic
calming measures.
8.9.2
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
r
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 trafic
To limit vehicular atmospheric pollution
To reduce traffic noise levels
The introduction of an area speed limit can assist in achieving these objectives, but
unless the road is designed appropriately by incorporating relevant traffic calming
measures, the posted speeds are likely to be disregarded by many drivers.
8.9.3
Factors for Consideration
The following questions should be considered before the introduction of a trafficcalmed zone in an existing neighbourhood:
What is the posted speed? What are the prevailing traffic speeds? Are these
appropriate for the area, given its architectural, ecological and social framework?
Is there any unnecessary traffic passing through the area? Can it be
accommodated on the surrounding roads?
Is there a History of accidents in the area? Is speed a contributory factor?
What traffic regulations exist in the area at present?
What are the physical features of the area; curves, gradients, intersection
spacing?
Page 8-18
Muwaft Highway Design Manuel
chapter a
Highway Fecilitbs
-
What are the access requirements of the activities that are undertaken in the
area?
The following factors are important in the design of a traffic calmed environment,
whether on existing roads or in a new area:
Selection of the desired target speed and hence design speed of the read
elements.
Identification of those places where specific calming measures need to be
introduced, for example, if there are long straight sections of road.
Consideration of bus movement.
Assessment of the level of on-street parking required. Parked vehicles or suitably
designed parking bays can sometimes act as trafficcalming features in their own
right.
8.9.4
Types of Traffic Calming Measure
There are a number of techniques available to the designer. Any proposal for traffic
calming measures should be developed in close liaison Mth the Ministry of Public
Works, the Ministry of Interior and Kuwait Municipality, and must be formally
approved before impternentation.
There are four generic types of calming technique, namely traffic engineering
measures, visual or aural features, horizontal alignment features and verlicaf
alignment features.
8.9.5
Traffic Engineering Measures
8.9.5.1
Intersection Priority Change
This can be introduced to break up a length of road that has priority through a series
of intersections. Care needs to be taken in the signing of such a measure.
8.9.5.2
One-way Streets
y
The introdudion of short lengths of one-way operation can create a 'mare -like road
system that discourages 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 carriageway to sidewalk or landscape use.
8.9.6
Visual or Aural Features
8.9.6.1
Bar Markings
These are coloured road markings that can be laid across the road to draw attention
to a change in speed limit. They are also perceived by a change in tyre noise.
8.9.6.2
Entry Treatment
When drivers enter a calmed road or area, they can be alerted by the use of different
visual signals, such as paving colour, texture or material. Alignment features are
often provided in association with entry treatments.
8.9.6.3
Gateways
Gateways are a form of entry treatment, Added vertical features, such as walls or
fences that are positioned at right angles to the road and close to the travelled way,
give a visual effect of narrowness.
Page 8-19
Kuwait Highway Design Manual
8.9.6.4
Over-run Areas
An area of the road pavement is surfaced, textured or coloured differently so that it
appears to narrow the travelled way, but can still be over-run by larger vehicles that
are unable to manoeuvre within the delineated path.
The presence of long sight lines can be a contributory factor to high speeds. Planting
serves two purposes, firstly, to provide an enhanced environmental appearance, and
secondly, ta assist in keeping sight lines as short as possible, compatible with the ,
very low design speeds that traffic calming adepts.
8.9.6.6
Rumble Devices
Textured areas of pavement, which cause tyre noise to be perceptibly different, raise
driver awareness.
8.9.7
Horizontal Alignment Features
8.9.7.1
Speed Limiting Bends
These are tight cunres, with inner kerb radii ranging from lorn to 1%. Speed limiting
bends should only be used in combination with other elements that make it evident to
drivers that traffic calmed behaviour is expected. Drivers should be able to see the
bend clearly on the approach, but sight distances around the bend should be
deliberately reduced by the provision of planting or hard landscaping. A stopping
sight distance of 35m should be provided.
8.9.7.2
Build-outs
These are local protrusions of the sidewalk into the pavement area, effectively
narrowing the vehicular travelled way. They are often provided in combination with
vertical features.
8.9.7.3
Chicanes
These consist of a pair af build-outs on alternate sides of the toad;but not opposite
each other, thus creating horizontal defle~tionsthat can only be negotiated by
vehicles travelling at low speeds.
8.9.7,4
False Roundabouts
These consist of small roundabouts where there are no intersecting roads.
8.9.7.5
Medians
On an undivided road, the introduction of a median, which may be raised or flush with
the travelled way, reduces lane widths and achieves visual narrowing. If space
permits, the median can be planted, which improves the amenity of the road and
prevents excessive forward visibility.
8.9.7.6
Pinch Points
The road is deliberately narrowed to prevent two-way operation. 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.
Chapter8
I
H i p m y Facilities
Vertical Alignment Features
Sidewalk Crossovers
These allow pedestrians to continue at sidewalk level across the mouth of an
intersecting minor road, 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 700 to 200mm high and 4m
long (parallel to t r a f k direction), which can only be crossed comfortably by vehicles
travelling at very low speeds.
Speed Cushions
These are a form of flat-topped road hump, which only extends across part of the
travelled 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.
Thermoplastic Mumps
These are small road humps constructed of thermoplastic material and typically
40mm high and up to 0.9m long (parallel to traffic direction).
Speed Bumps
These are small road humps, typically up to 75mm high. They are normally 0.3m
long (parallel to traffic direction) and laid in threes, at 1.3m centres.
Designing fhe Traffic-calmed Payout
This is best achieved in a design team that incorporates mest or all of the following
people:
i
A road design engineer
A town planner
*
A road maintenance engineer
A road safety practitioner
A landscape architect
A representative of the residents
Best results are normally obtained by the balanced use of a number of the
techniques identified above. The finished scheme should convey the message that
drivers need to travel slowly, take care, and make aHowances for children and other
pedestrians. Limiting forward visibility is one of the principal ways of achieving an
irnpressibn of 'intimacy' rather than the usual spadcusness.
Features used out of context can increase the risk of accidents. Encountering a
maximum height speed hump when travelling at 50kmlh on a straight alignment, for
example, can cause loss of control and damage to the vehicle.
Refer also to Chapter 9, Local Roads
I
Page 8-21
KuweH Highway Dasign Manual
Chapter 8
Highway FmiIb;es
8.10
Landscaping
Apart from amenity benelits, the landscape treatment of medians and verges can
have practical advantages. By ground sculpting, perhaps in conjunction with
planting, the alignment of the road can be made more obvious to drivers. Hard
landscaping can have a practical value, for example, in protecting an embankment
from erosion.
Landscaping provides reference points that enable drivers waiting to exit from a
minor road to judge the speed of oncoming vehicles. This is particularly useful where
a majorlminor intersection is located in open land, with a lack of natural reference
points. Planting can also provide a positive background to the road signs and can
visually unite the intersections component parts. Limiting the view to that necessary
for the driving task helps avoid driver distraction.
Specialised planting, which is generally more appropriate in urban than rural areas,
requires significant maintenance if it is to be successful. The preferred watering
method is an automatic irrigation system supplied from a brackish water main.
Approval for any such scheme must be sought from the MPW, Kuwait Municipality,
PAFFR and MEW. If a brackish water main is unavailable, care should be taken to
ensure that watering can take place without tankers having to obstruct the travetled
way at any time.
A well-defined maintenance programme should be developed if extensive planting is
used, to ensure that the planting does not obscure other traffic movements or traffic
signs at any time.
Grade-separated intersections offer great scope for sympathetic landscaping; to
improve their appearance, to reduce visual impact, and to take advantage of the
earthmoving that takes place to achieve the vertical alignment of the various roads.
In rural areas, planting should be restricted to indigenous species and be related to
the surrounding landscape. In the desert, for example, planting of non-local species
would appear incongruous and landscape treatment is therefore oflen restricted to
ground sculpting.
Wlthin at-grade intersections, the areas required for visibility envelopes should only
be planted with species that have a low mature height, so that when they are fully
grown they do not impinge on the visibility envelope. Higher and denser species of
bushes and trees can be planted outside visible envelopes. N t h roundabouts, it is
usual to adopt such planting towards the centre of the island. In all cases, due
allowance must be made for mature growth.
Apart from the amenity benefits, the landscape treatment of roundabouts can have
practical advantages. By earth sculpting, in conjunction with planting, the presence
of the roundabout can be made more obvious to approaching traffic. The screening
of traffic on the opposite side of the roundabout can reduce driver distraction and
confusion. Planting can provide a positive background to chevron signs and direction
signs on the central island, whilst visually uniting the various vertical features and
reducing the appearance of clutter.
'The planting of roundabout central islands of less than lorn in diameter is
inappropriate as the need to provide adequate forward visibility leaves only a small
central area available for planting. Such a restricted area for planting will be out of
scale with the roundabout as a whole.
A ring of black and white paving, laid in a gently sloping chevron pattern inside the
central island perimeter, can improve the prominence of central islands.
Kuw8ir Highway Design Men&
Chapter8
Highway Facilities
Sculptures or other works of public art in the central islands of roundabouts can
provide a focus for the traveller, and if designed and positioned correctly, can prove
an asset to the surroundings.
Lighting of landscape features can enhance their appearance at night, but care
should be taken to avoid distraction or dazzle to drivers.
8.1 1
Utilities
Rights of way provide adequate space for the road and allow the public utilities
sufficient space for existing and proposed plant. M e r e space for utilities is limited,
'wayleaves' outside the right of way may sometimes be obtained by contacting the
planning authority.
The utilities to be accommodated include the following:
Telephone
Electricity
Sanitary Sewerage
Surface Water and Land Drainage
Brackish Water
Freshwater
Oil and Gas
Each Utility Authority has its own working procedures and works specifications.
These should be referred to when designing the road construction and drainage
facilities.
Particular consideration may be required to the position of soakaways, if right of way
width is restricted. Where space is limited, soakaways may be lowered, by the
addition of ring sections, to allow shallow utilities, such as telephone, to pass above
the soakaway chamber. However, in new roads, priority should be given to road
related utilities such as drainage and lighting.
' A Policy on Geometric Design of Highways and Streets 1994, AASHTO, 1995
Kuwait Tramc Signs Manual, 1988
Design Manual for Roads and Bridges, Department of Transport, UK (Document TD
79/85, Safety Fences and Barriers)
Roadside Design Guide, AASHTO, 1989
Page 8-23
This C&
deals only with those roads that are defined within the hierarchy as
1-1
&, and gathers together the &vice contained in various locadbns within this
rnanud lF9p secondary, primary and special roads, see Chapters 10, 11 and 12
'~,qw-
Los;;rl,,;f@ad~.
h a w the function of providing access to land-use activities that generate
ad
the demand for travel.
m,
s8gerirepally link to secondary roads. which in turn give aceess to the
hiihet=swtusroads within the network. They are almost without exce~tionundivided
r&s of two-way, hnro-law or one-way, siniletane width, carrying typically less than
100vehlhin the design year.
9-1.l Rural Local Raads
4'-
-
9.1.2
Rural local roads should be .related to topography from the standpoint of drainage,
economics, amenities and access to adjacent properties. Predicted traffic volumes
have an influence on the design of the road and its intersections.
Urban Local Streets
Urban lo&l streets also include short ackesses, small loops, culde-sacs, servicing
areas and parking lots.
Local streets should be designed to minimise through traffic movements, with street
patterns selected to reduce vehicle travel distances and speeds, Traffic circulation
should nat have to rely on extensive regulations or signs In order to function properly.
Application of basic cross-sections with few simple at-grade intersections will
produce a layout capable of catering for the relatively tow trafiic levels that
characterise the urban local street. Traffic volumes on local roads are not a major
design consideration.
It is accepted that local streefs may not ahays be free from obstruction. Cars
stopping to set down passengers and vehicles undertaking maintenance operations
are just two examples where focal streets may be temporarily or partially obstnrcted.
In residential areas, because of their function, local streets have a high level of nonrnotorised activity, caused primarily by fhe movement of pedestrians and children at
play. The roads therefore need to be designed in a way that reflects this, and leaves
the motorised driver in no doubt that his needs are not the overriding ones in the
local environment. Traffic generators such as schools, mosques and shopping
facilities should be carefully considered in the overall design. Pedestrian activity
levels may be high, and conflict with moving traffic should be minimised. Adequate
levels of kerbside parking should be provided, without obstructing visibility or
jeopardising the safe operation of the road.
In commercial and industrial areas, the prime function of the tocal street is to provide
access to premises. The type of vehicle necessary to service the adjacent land-use
activity generally determines the scale and layout of the street and its intersections.
K m i t Highway Design Manual
9.2
Basic Design Parameters
9.2.1
Design Vehicle
Local roads are generally designed to accommodate P, BUS and SU vehicles only.
In rural areas, however, consideration should be given to the likely usage by vehicles
larger than these, and due allowance made. In industrial areas, the design should
generally be designed to accommodate vehicles up to W8-15, with a degree of
encroachment into other traffic lanes being acceptable, but a more generous
provision may be warranted by the nature of the industrial activity.
Roads leading to parking lots are normally designed to carry only P vehicles, but a
check should Be made that SU vehicles can gain access, with encroachment, as
necessary, for maintenance purposes.
9.2.2
Design Speed
The design speed of a rural local road should respect the nature of the area in which
it is located. In the absence of other determining factors, the recommended design
speed is 60kmh. tn areas where the terrain is more difficult, lower speeds down to
30krnIh are appropriate.
The design speed of a local street should be such as to allow rnotorised travel at a
reasonable pace relative to the other activities of the area, and the permitted values
lie between 3Okrnlh and 50kmh. In the absence of any other determining factors, the
recommended value is 5Okmlh.
Traffic calming is a suitable technique for use on aH local roads and streets, and the
recommended design speed with traffic calming is 30kmlh.
Where a design speed of less than 50kmh is selected, it is important that the design
parameters, particularly in respect of visibility and horizontal curvature, are kept close
to their minimum permitted values. If greater levels are provided, higher traffic
speeds are encouraged.
Most local roads and streets should have a posted speed of 45kmh or lower, as local
conditions dictate. Consideration should be given to the nature of the non-motorised
movements when selecting posted speeds. For example, a tower posted speed may
be appropriate near a school, and will be necessary in an area that has been traffic
calmed.
9.2.3
Level of Service
Level of senrice is not a relevant consideration for local roads, due to the relatively
small amount of vehicular traffic that they carry.
9.2.4
Sight Distances
The stopping sight distance (SSD] relevant to the design speed should always be
provided on a local road. The SSD requirements and associated vertical curvature K
values are shown in Table 9.1. For increased SSD on roads that are on a
downgrade, refer to Table 4.1.
Page 9-2
Kuwert Highway D
e
w Manual
Chspter Q
Lacat Roads
Tabk 9.1: Stopping Sight Distance and Associated Vertical Cuwature for Local Roads
Passing considerations may apply, exceptionaly, on some local roads. Safe Passing
Sight Distance (SPSD) should only be catered for on long rural local roads and the
requirements are detailed in Table 9,2.
Table 9.2: Safe Passing Sight Distance and Assoclated Vertical Curvature for Locall
Roads
Decision Sight Distance (DSD) is not a relevant consideration on urban local roads,
but should be considered for rural local roads. The requirements for DSD
approaching a rural stop are detailed in Table 9.3.
Table 9.3: Decision Sight Distance and Associated Vertical Curvature fur Rural Local
-Roads
Design Speed
(kmlh)
Decision Sight
Distance (rn)
Minimum K value for
Vertical Crest Curves
50
70
8
60
95
14
70
115
20
80
140
30
-
K M S Highway Design Manual
9-2.5
Gradients
Local roads are the most flexible of all roads in respect of gradients. The upper h i t
for gradients an local roads is 8%.
There are some constraints on the maximum gradient that may be provided:
In industrial areas, the presence of trucks makes an upper limit of 6% desirable.
Where a local road abuts the frontage of a residential plot, it is desirable to limit
the gradient to 3%.
Where a local road approaches a 'Give Way' or 'Stop' intersection, the last 15m
should be at a gradient not exceeding 2%.
.
The preferred minimum gradient to be adopted on a local road is [1.5%, with an
absolute minimum of 0.3%, and drainage should be checked carefully to ensure that
ponding does not occur.
Critical gradient length criteria are not relevant to local roads.
9.2.6
Superelevation and Grossfall
The maximum superelevation for horizontal curves on a rural local road is 4%.
Crossfalls of 2% outwards from the crown line should normally be provided on
straights.
In order to discourage excessive speed on urban local streets, it is often prudent to
limit the superelevation to 2%.
Where longitudinal gradients are very low, consideration may be given to increasing
crossfalls on straights to a maximum value of 3%, if this helps to eliminate flat areas
and consequent ponding hazards.
9.2.7
Horizontal Cuwature
The minimum radii for horizontal curves on rural local roads and urban local streets
are set out in fable 9.4 and Table 9.5.
Table 9.4: Minimum Radii for Rural Local Roads
Page 9 4
K u w ~ i Highwey
t
Design Manuel
Ch8pWf g
Locel Roads
Tabla 9.5: Minimum Radii for Urban Local Streets
OR traffic calmed urban local streets, even tighter curves may be introduced as
speed-limiting bends, where the designer considers that vehicles will travel extremely
slowly. These bends should have an inner curb radius of 15m,but this may be
reduced to lorn, typically on cul-de-sacs. On such speed-limiting bends, the
maximum available foward visibility should be restricted to the Stopping Sight
Distance appropriate for a design speed of 30krnk, namely 35m.
9.2.8
Widths
Lane widths on local roads should be as shown in Table 9.6.
Table 9.6: Lane Widths on Local Roads
Lane Width (m)
Single Lane Roads
2 Lane Roads
5.00
Rural
3.70
Urban
4.00
-
Urban Industrial
4.00
Lane widening may be required on curves on local roads and'streets, For curves of
over 325m radii, the recommended lane widths are as set out in Table 5.6. On
curves with radii of 1Om to 1 00m, Table 14.6 (Case 1) gives the width requirements,
but it is anticipated that there may be some encroachment by larger vehicles into the
opposing lane. The designer should consider carefully both the design vehicle that he
wishes to accommodate and the degree of encroachment that he considers to be
acceptable from a safety viewpoint.
The use of vehicle swept path templates or suitable computer software greatly
simplifies the task of designing curves on local roads. This process should always be
used when designing traffic-calmed layouts with speed limiting bends.
Consideration should be given to providing the widened area on the inside of the
bend in a distinctive paving material, for example, deeply textured paving blocks to
encourage drivers of cars and other smaller vehicles to drive an the unwidened
section of the road.
Urban local streets are kerbed, but no kerb clearance is required. Parking lanes may
abut the running lanes.
Rural local roads are generally unkerbed, but are provided with 0.3m wide shoulders.
Page 9-5
Kuwait Highwey Design Menu81
Chapler9
Locel Roads
9.3
Intersections
Local roads generally have majorlminor intersections, the spacing for which is
dependent on the layout of the development.
9.4
Pedestrian Facilities
Sidewalks should normally be provided on both sides of a local road in urban areas,
but in rural areas sidewalks are rarely necessary, given the significant shoulder and
verge widths that normally exist.
Sidewalk widths greater than 3.5m are desirable. However, minimum sidewalk widths
be used. Widths should be checked for adequacy to handle the
anticipated flows in the vicinity of major pedestrian generators (see Table 8.2).
. of 1.8m may
Pedestrian crossings are not normally required on local roads.
9.5
Tramc Calming
Local Roads are generally well suited to the application of traffic calming techniques,
and the designer is referred to Section 8.9 for details.
The complete range of traffic calming measures may be considered for adoption on
local roads, Best results are obtained when an entire area is considered from the
outset, with traffic calming and speed reduction features designed into the geometric
layout. However, the application of traffic calming techniques to established areas
could still yield safely benefits and improve the environment for pedestrians and
children.
9.6
Turning Areas
Cul-de-sacs should be provided with a turning area at the enclosed end to allow
vehicles to turn around and return along the road (where vehicles larger than SU and
WB-'I5 are expected, a loop or through road should be used instead of a cul-desac).Figure 9.1 shows a range of fypical turning areas, with their dimensions.
In a circular turning area, an outside kerb diameter of 20m is ample for private cars,
26m for a WB-I2 vehicle, and 30rn for SU and WB-I 5. A 20m diameter also permits
an SU truck to turn by backing once. These circular turning areas can be
accommodated within a square courtyard with 20m (or 26m or 30m) sides.
9.7
Driveways
Care should be taken in the siting of driveways that give access to properties
adjacent to the road. Driveways should be sited so as to cause as little disturbance
as possible to the main through traffic. Driveway widths of 3m or 4m are normally
adequate for residential properties. However, driveways leading to schools,
mosques or apartment blocks, where traffic volumes are expected to be higher,
should be at least 6m wide to allow for two-way traffic. The appropriate sight
' triangles for majorfminor intersections should be applied to driveway access points.
Page 9-6
KuwaH Highway Design Manuel
CWhrO
Lmal Roads
20m
min.
Square End
(with angle parking)
Square End
(minimum)
Circular a
t
Hammerhead
(Dimensions in brackets relate ta SU Design Vehicle)
Figure 9.1: Turning Areas
Page 9-7
K m i l Highway Oeshn Manual
Chapter S
Local Roads
9.8
Summary of Design Parameters
Table 9.7summarizes the key geometric parameters relating to the preferred design
speeds for local roads and streets.
Table 9.7: Summary of Geometric Panmeters for Local Roads and Streets
l o w e r radii are permissiblefor speed-limitingbends.
Typical cross-sectional elements relating to focal roads are shown on the Figures that
follow.
Page 9-8
F.W. & B.W. PIPES
S.W. SEWER
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F.W. & B.W. PIPES
I
Kuwait Highmy DesMn Manuel
Cheater9
Page 4 1 0
Kuwait Highway Design rWanual
Chapter T O
Secmdary Reeds
10.1
Introduction
This Chapter deals only with those roads that are defined within the hierarchy as
secondary roads, It gathers together the advice contained in various locations within
this manual. The function of secondary roads is to cater for short-distance trips at
relatively low speeds and to provide a means of access to and from the primary road
network (for local roads, see Chapter 9, and for primary and special roads, refer to
Chapters I 1 and 12).
Rural secondaw roads can be either divided or undivided roads and should be
designed to accommodate the highest possible standards compatible with traffic and
topography.
Urban secondary streets, which are normally divided roads, cater equally for mobility
and access. Access control should be used primarily to ensure that access points
conform to desired standards for location, design and safety. Minimisation of conflict
points, adequate handjing of turning traffic and minimisation of conflict with
pedestrians are desirable design goals. Traffic volumes in the design year will
determine the scale of facility to be provided.
En residential areas, secondary roads provide the link between local streets and
primary roads, and also serve the frontage development along their length, with
kerbside parking being provided as necessary.
In commercial areas, secondary roads link primary roads to local roads that lead to
parking areas. Secondary roads may also have kerbside parking. Access points to
adjacent properties are relatively infrequent.
In industrial areas, secondary roads are designed to handle the movements of larger
vehicles in accordance with the nature of the industry that they serwe, and are often
provided with shoulders that can act as kerbside parking lanes. Access points to
adjacent properties are relatively infrequent.
10.2
Basic Design Parameters
10.2.1
Design Vehicle
In general, the geometry of secondary roads should be adequate to handle vehides
up to SU and BUS, but not semi-trailers In industrial areas, however, all sizes and
types of design vehicle should be catered for.
10.2.2
Design Speed
The design speed of a secondary road should lie in the range 6Okmlh to 100kmlh. A
lower value of 50kmh may be adopted, if necessary.,in fully developed urban areas
or in hilly rural areas where topography is a major constraining factor.
In the absence of other relevant considerations, the recommended design speed for
a rural secondary road is 80kmlh and for an urban secondary road is 60kmk.
10.2.3
Levels of Service
Level of Service C is normally adopted for design purposes on secondary roads, but
traffic volumes will rarely be high enough for this to result in practice, even in urban
areas.
Page 10-1
Kuwait Highwey Design Manuel
Ch8phW 10
Secondary Roads
10.2.4
Sight Distances
The stopping sight distance (SSD) relevant to the design speed should always be
provided on a secondary road. SSD requirements and associated vertical curvature
K values are as shown in Table 10.1 (for increased SSD on roads which are on a
downgrade, refer to Table 4.1).
l a bte 10.1: Stopping Sight Distance and Associated VertFcal Curvature for Secondary
Roads
On undivided secondary roads, adequate opportunities for passing should be
provided. If passing is ta be permitted, the relevant Safe Passing Sight Distance
(SPSD) should be provided and the requirements are given in Table 10.2. On urban
secondary roads, which are either divided or normally connect to a divided primary
road (where passing can safely take place), passing considerations are rarely
relevant.
Table 10.2: Safe Passing Sight Distance and Associated Vertical Curvature for
Secondary Roads
.Decision Sight Distance (DSD) is not a relevant consideration on urban secondary
roads, but should be considered for rural secondary roads. The requirements for
DSD approaching a rural stop are detailed in Table 10.3.
Page 10-2
Kuwair Highway Design Menual
Table 10.3: Decision Sight Distance and Associated Vertical Curvature for Rural
Secondary Roads
10.2.5
Gradients
The maximum longitudinal gradient for a secondary road is 6%, although flatter
gradients should be achieved where possible. Where residential properties abut the
road, a maximum gradient of 3%should be sought.
The critical gtadient length set out in Table 6.5 should not be exceeded.
The minimum gradient to be adopted on a secondaty road is 0.5%.
10.2.6
Superelevation and Crossfall
The maximum superelevation for a secondary road is 4% in urban areas and 6% in
rural areas. Normal crossfall of 2% outwards from the median (on a divided road) or
from the road centreline (undivided road) should be provided on straights.
10.2.7
Horizontal Curvature
The minimum radii for horizontal curves are set out in Table 70.4 below,
Table 10.4: Minimum Radii for Secondary Roads
10.2.8
Widths
Urban secondary roads are kerbed and should be provided with lanes that are 3.70rn
wide, except in industrial areas, where 3.75m should be provided. A Kerb clearance
of 0.6m is required on roads with design speeds exceeding 80kmlh. Parking lanes
may abut the running lanes, and in an industrial area, it is good practice to provide a
continuous 2.8mwide outer shoulder, which can also be used far parking.
Page 10-3
Kuweft Highway Desan Manuel
Rural secondary reads (both divided and undivided) are generally unkerbed, and
have 3.70m wide Fanes and 0.3m outer shoulders.
Median widths depend on circumstances, but the preferred width is &Om.
10.3
Intersections
Secondary roads are generally characterised by at-grade intersections, and all types
(including signalised and roundabouts) are suitable for use on secondary roads.
10.4
Pedestrian Facilities
10.4.1
Sidewalks
Sidewalks should normally be provided on both sides of an urban secondary read
and should be provided, where justified, on rural secondary roads.
In locations with high pedestrian flows, the width of the sidewalk depends on the level
of pedestrian activity, as given in fable 8.2. In other locations, a minimum width of
1.8m applies, but widths of 3.5m or more are desirable. In rural areas, footways are
not normally required, but where provided, should be 1.8m to 3.5m in width and
located within the verge.
"f4.2
Pedestrian Crossings
Generally, it should be possible for pedestrians to cross a secondary road without the
assistance of any special facility.
Grade-separated crossings (bridges and subways) are only likely to be justified in
exceptional circumstances.
Crossings incorporated within signalised intersections can be provided on
secondary roads, normally where they intersect with primary roads.
=
Signal controlled, marked, at-grade crossings {of the "pelican' type) are unlikely to
be necessary.
Uncontrolled, marked, at-grade crossings (of the 'zebra' type) are only
apprapriaje on urban secondary roads with a posted speed of 60kmlh or less.
10.5
Traffic Calming
Although secondary roads are designed to handle short-distance trafic movements,
traffic calming may be provided where considered appropriate. Measures that may
be adopted, where clear benefit can be shown, include bar markings, entry
treatment, gateways, rumble devices, false roundabouts and medians. Section 8.9
gives full details.
10.6
Summary of Design Parameters
Table 10.5 summarises the key geometric parameters relating to the preferred
design speeds, for secondary roads.
Page 1W
Kuwait Highway Design Manual
Table 10.5: Summary of Geometric Parameters for Secondary Roads
Minimum Vertical Clearance (m)
I
5.5
I
I
5.5
T h i s Qure relates to the approach to a STOP (sign or signals). In other cases Zhe figure is 230m. It is not normalb
necessav to provide Declsion SigM Distance on an urban secondary road.
Typical cross-sectional elements relating to secondary roads are shown on Figures
that follow.
pageIa5
Kuweif Highmy Design Manuel
Page 10-6
K w i t HIghwey Design Manual
Chapter 10
Semndarv Roads
Kuwait Highway Design Menual
Chepfar 11
Primary Roads
7 1.I
Introduction
This Chapter deals only with those roads that are defined within the hierarchy as
primary roads and gathers together the advice contained in various locations within
this manual. It should be noted that special roads, whose design characteristics
enable them to cany greater volumes of traffic with fewer access points, are dealt
with in Chapter 12. Previous Chapters deaf with local roads (Chapter 9) and
secondary roads (Chapter 10).
The function of primary roads is to provide high-speed, high-volume links between
major points in both the rural and urban road networks. Primary roads are divided
roads, normally of four or six lanes.
Rural primary roads are designed on the basis of traffic volume needs, and should be
constructed to the highest standards possible, The geometric design is determined
from the selected design speed and design traffic volumes, taking into account the
type of terrain and the general characteristics of the alignment. Direct access to
adjoining development should rarely be permitted.
Urban primary roads have mobility as their main determinant, with limited service to
adjacent development. Where greater development access is required, service roads
are often provided. In major centres of activity, the arterial street system must cater
far vehicular mobility while recognizing and providing for a significant level of
pedestrian activity.
1.2
Basic Design Parameters
The geometry of primary roads should be adequate for all sizes of design vehicle.
11.2.2 Design Speed
The permitted range of design speed for a rural primary road is from 120kmlh down
to 80 kmlh. For urban primary roads, the range is 700kmlh down to 60kmh. It may
be necessary in hilly terrain to adopt lower design speeds.
In the absence of other relevant considerations, the recommended design speed for
a primary road is 120kmh (rural) and 80kmh (urban).
11 2 . 3
Levels of Service
Level of service €3 is normally adopted for design purposes on all primary roads, but
in urban areas, heavily developed parts of the network may necessitate the use of
Level of Service C.
11 -2.4
Sight Distances
The stopping sight distances (SSD) and associated vertical curvature K values are
set out in Table 11 .I(For
. increased SSD on roads that are on a downgrade, refer to
Table 4.1).
Kuwall HighwayDesign Wnml
Cheprw i f
Primer),Roads
Tabla 11.l
: Stopping Sight Distance and Associated Vertical Curvature far Primary
Roads
As all primary roads in Kuwait are divided roads, passing is not a relevant
consideration. Decision Sight Distance (DSD) shou'ld be provided at relevant
locations in accordance with the guidance set out in Section 4.5 and in Table 11-2.
Table 11.2: Decision Sight Distances and Associated Vertical Curvature for Prlmary
Roads (Worst Case)
11-2.5
Grades
The longitudinal profile of a Primary Road should be designed to suit the topography.
The maximum grade permitted is 6%, but flatter grades should be achieved where
possible.
The critical grade length set out in Table 6.5 should not be exceeded.
The minimum grade to be adopted on a Primary Road is 0.5%.
1I.2.6
Superelevation and Crossfall
The maximum superelevation for all urban Primary Roads is 6%. In rural areas, the
maximum is 8%. Normal crossfall of 2% outwards from the median should be
provided on straights.
Page 11-2
Kuwait Highmy Deslgn Manuel
11 -2.7
Horizontal Curvature
The minimum radii for horizontal cunres are set out in Table f 1.3 below.
Table 11.3: Minimum Radii for Primary Roads
The maximum superelwation in urban areas is 6%.
.11.2.8
Widths
Urban Primary Raads are kerbed and should be provided with lanes that are 3.7m in
width. At lower design speeds, no kerb clearance is required. At design speeds in
excess of 80krnJh, an outer shoulder of 1.2m and a median shoulder of 0.6m are
provided.
Rural Primary Roads are not kerbed, and have 3.7m lane widths with a 3.0m outer
shoulder and a 1.2m median shoulder.
Median i i d t h s on Primary Roads depend on circumstances, but are normally 8.0m to
10.0m.
Section 11.6 contains further details and typical cross sections:
11.3
Intersections
Primary Roads are generally characterised by at-grade intersections, although gradeseparation is permissible and may be more appropriate in certain instances.
Not all at-grade intersections are suitable for use on Primary Roads.
On Primary Roads in urban areas, four-leg, majorlminor intersections should not be
used and three leg, rnajorlminor intersections and U-turns should be avoided
wherever possible. Signalised intersections and roundabouts are appropriate types of
intersection to use.
On rural Primary Roads, signalised intersections should not be used, as experience
elsewhere has shown that the risk of high-speed accidents can be unacceptably
high. Roundabouts may be preferable, but often grade separation will be considered
appropriate.
1 1.4
Senrice Roads
Parking is generally discouraged on or abutting the through running lanes of a
Primary Road, as this could lead to excessive speed differentials and unexpekted
manoeuvres.
Page f 1-3
Kuwek Hbhw~yDeign Manuel
M e r e parking is required in order to serve the fronting land uses, service roads are
the preferred facility. These are roads provided parallel to, and physically separated
from, the mainline (see Section 7.1 3.2). It is normal for service roads to have a single
one-way running lane of at least 5.0m width, and adjacent parallel or angled parking
bays on the side adjacent to the development, with an appropriate buffer lane being
provided where possible (see Section 8.4.3).
11.5
Pedestrian Facilities
11.5.1
Sidewalks
Sidewalks should normally be provided on both sides of an urban Primary Road, and
should be provided, where justified, on rural Primary Roads.
In locations with high pedestrian flow, the width of the sidewalk depends on the level
of pedestrian activity, as given in Table 8.2.
In other locations, the widths set out in Table 1I.4 should be provided.
Table q4.4: Preferred Sidewalk Width for Primary Roads
Desirable Width (m)
Urban
Rural
3.5 or more
1.8m to 3.5m
-
-
Minimum Wdth (m)
1.8
7-8
11-5.2 Pedestrian Crossings
It can 'be hazardous for pedestrians to cross primary roads, and adequate thought
should be given at the design stage to the requirements for pedestrian crossings.
Grade-separated crossings (bridges and subways) are always acceptable
Primary Roads, but may not always be cost-justified.
on
Crossings incorporated within intersections are normally provided on Primary
Roads.
Signal controlled, marked, at-grade crossings (of the 'pelican' type) are generally
the norm for mid-block crossings on urban Primary Roads.
Uncontrolled, marked, at-grade crossings (of the 'rebra9ype) are only acceptable
on urban Primary Roads with a posted speed of 60kmlh.
11.6
Summary of Design Parameters
Table 11.5 summarises the key geometric parameters relating to preferred design
speeds for Primary Roads.
Page 1 1-4
Kuwea Highwey Design Manual
Table 11.5: Summary of Geometric Parameters for Primary Roads
Typical cross-sectional elements relating to Primary Roads are shown on the Figures
that follow.
Page 11-5
Kuwait Highway Design Menu81
Chapter f f
Primary Roads
Page 11-7
Kuwait Highway Design Menuat
Chepkt 12
SpeciaE Roads
Introduction
This Chapter deals only with those roads that are defined within the hierarchy as
Special Roads and gathers together the advice contained in various locations within
this manual. Local Roads, Secondary Roads and Primary Roads are dealt with in
Chapters 9, 10 and 1 1 respectively.
Special Roads represent the highest standard of road provision in KuwaR. h e y
provide high-speed, high-volume links between the main population centres and
sene long-distance traffic moving to or from Kuwait. The prime determinants are
mobility and safety, and access is strictly controlled.
A Special Road may senre adjoining land uses between grade-separated
interchanges by means of direct free-flow ramps connecting to service roads.
Special Roads are divided multi-lane roads. Their geometric design is determined
from the selected design speed and design traffic volumes, taking into account the
type of terrain and the general characteristics of the alignment.
Basic Design Parameters
Design Vehicle
The geometry of Special Roads should cater for all sizes of design vehicle.
Design Speed
The permitted design speed for Special Roads is 120kmlh to 80krnh in a rural area,
and 100krnlh to 80krnn-Ein an urban area.
In hilly terrain, it may be necessary to adopt lower design speeds for special roads.
In the absence of other relevant considera2ions, the recommended design speed for
a Special Road is 120kmJh (rural) and 100kmIh (urban).
Levels of Service
Level of service B is adopted for design purposes on Special Roads generally, but in
hilly terrain or in heavily developed parts of the urban network, level of service C may
be applied.
Sight Distances
The stopping sight distance (SSD) and associated veFtical curvature K values are set
out in Table 12.1 (for increased SSDs on roads that are on a downgrade, refer to
Table 4.1).
Page 12-1
K m i t Highway Design Manual
Chepler 12
Specie! Roads
Table 12.1: Stopping Sight Distance and Associated Vertical Curvature for Special
Roads
As all Special Roads are divided roads, passing is not a relevant consideration.
Decision Sight Distance (DSD) should be provided at relevant locations in
accordance with the guidance set out in Section 4.5 and in Table 11 -2.
Table 12.2: Decision Sight Distances and Associated Vertlcal Curvature for Special
Roads (Worst Case)
12.2.5
Gradients
the longitudinal profile of a Special Road should be designed to suit the topography.
The maximum gradient permitted is 4% and flatter gradients should be achieved
where possible.
The critical gradient length set out in Table 6.5 should not be exceeded. The
minimum gradient to be adopted on Special Roads is 0.5%.
12.2.6
Superelevation and Crossfall
The maximum superelevation for special roads is 8%. Normal crassfall of 2%
outwards from the median should be provided an straights.
12.2.7
Horizontal Curvature
.The minimum radii for horizontal curves are set out in Table 12.3 below.
Page 12-2
I
Kuwait Highway Design Manuel
Chapter 72
Specie! Roads
Table 12.3: Minimum Radii for Special Roads
Minimum Radii (m)
Design Speed
(kmlh)
.
-
-
-
4% Superelevalion
6% Superelevation
8% Superelevation
80
285
255
230
90
375
335
305
p
p
p
p
I00
480
430
395
110
600
535
500
120
740
655
590
Special Roads should be provided with lanes that are 3.7m in width. The number of
lanes is based on capacity considerations.
Outer shoulders should always be provided, with a minimum width 3.0m, Median
shoulders of 1.2m should also be provided.
Median widths depend on circumstances, but are normally 8,Om to 10.0m. In urban
areas, this may be reduced to an absolute minimum of 2.0m, where land-use
constraints exist.
12.3
Intersections
All intersections on Special Roads are grade-separated interchanges.
12.4
Service Roads
m e r e access from a Special Road is required in order to serve the fronting land
uses, service roads are provided. These are roads provided parallel to, and
physically separated from, the mainline (see Section 7.13.2). They are connected to
the main line by means of ramps designed to the same standards as apply at gradeseparated interchanges (see Chapter 18).
12.5
Pedestrian Facilities
Because Special Roads are pedestrian-free zones, pedestrian crossings are always
grade-separated and sidewalks are not provided.
12.6
Summary of Design Parameters
Table 12.4 summarises the key geometric parameters relating to preferred design
speeds for Special Roads.
Page 12-3
KurmR Highway Design Manual
Chapter 52
specie! ~ o a d s
Table 12.4: Summary of Geometric Parameters for Special Roads
-
Page 1 2 4
Typical cross sectional elements relating to Special Roads are shown on the Figures
that follow.
.b -
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KuwaH~yhaQnMenwd
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Kuwait Highway Design Menuel
Chapter 13
-
-
InterseEthns Genemi
13.1
C
Introduction
This Chapter provides advice on the main factors that affect the choice between
different types of major 1 minor intersections, on the positioning of such intersections
and on suitable types of layouts.
An intersection is a point in the road network where two or more roads join or cross.
This may be achieved at-grade. There are three basic types of at-grade intersection,
namely major I minor intersection, roundabout and U-turn. These are dealt with in
Chapters 14 to 16 of this Manual respectively. Each of these types may be
signalised, and additional material relating to signalised intersections is given in
Chapter 17.
Bridges or underpasses can provide 'inter-district' access by taking Secondary
Roads either over or under Primary or Special Roads, thereby eliminating the need
for local traffic to negotiate a major intersection.
Where one or more bridges or underpasses are provided and the roads are
interconnected, the resulting intersection is an interchange. Some interchanges
incorporate at-grade intersections within their layout, while others permit only
merging and diverging movements and are known as free-flow interchanges. The
design of interchanges is dealt with in Chapter 18 of this Manual.
Intersections are widely recognised as the primary locations of accidents on all
roads. Significant importance is therefore attached to safety in the development of
intersection design. A number of safety issues must be addressed during the design
development process. These include visibility, driver perception, signing and road
marking, trafk control and pedestrian access.
Intersections may be upgraded in capacity terms as an area is developed. For
example, an existing major 1 minor intersection may have its capacity increased in
the future by the provision of 'free right turns1 or the addition of signals, and a
signalised intersection may be designed to allow for conversion to an interchange in
the future. This manual generally presents intersections in order of increasing
complexity and capacity.
!
f 3.2
Intersection Spacing
The geographical position of the roads within the network will dictate the location of
main intersections. Intermediate intersections are usually a function of the
surrounding area and its current or future development.
In urban areas, residential properties, together with commercial and industrial sites,
generate significant demand for both short and long-distance travel. Consequently,
there is a need for frequent access points so that traffic from the local road network
may cross, join and leave the main roads.
In contrast, rural environments have fewer developed areas, and access needs are
intermittent. The over-riding demand on the main road is for through traffic movement
and intersections occur much less frequently.
The spacing of intermediate intersections is therefore a balance between the needs
of through traffic on the road and the requirement to access adjacent development. It
is important to note that the needs of through traffic take priority, and in particular., no
access should be permitted between interchanges on a Special Roads.
Page 13-1
KuweR Highwey Design Manuel
Factors that should be taken into account when determining the need for an
intersection (and hence the spacing of intersections along a route) include:
the class of road within the hierarchy
the general intersection spacing that applies to the road class
* the potential traffic demand for access to and from the main road
the length of the alternative route if no intersection is provided
the design speed and posted speed of the road
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:
the provision of service roads to collect local traffic movements together
the closure of minor roads at the main road (with the provision of appropriate
turning facilities) provided alternative access is readily available.
Because of all the factors described above, it is not possible to apply strict and
rigorous standards for the spacing of intersections. The minimum distance required
between intersections is normally controlled by the length required for slip roads and
the length of the intervening weaving sections, as determined from the projected
traffic flows.
The information set out in fable 73.1 should therefore only be used as broad
guidance when considering the minimum spacing of intersections.
Table 13.1: Minimum Intersectton Spacing (measured centre-todentre)
Intersection Spacing (m)
Road Class
Urban Areas
Rural Areas
Special Road
1000
2000
Primary Road
400
1500
Secondary Road
700
100
no minimum specified
100
Local Road
13.3
I
Selection of Intersection Type
.The choice of intersection type is heavily influenced by the volumes of traffic
predicted to use it. A robust estimate of future traffic flows should be available to the
designer at the outset, either from surveys of current traffic and estimates of future
growth, or from traffic prediction models. It is good practice fo consider the heaviest
movements first when choosing an intersection type and planning its layout.
Particularly high Rows may require their own dedicated turning lane or exclusive
connecting link roads.
Page 73-2
Although it is not possible to be precise when defining traffic levels for different types
of intersection, it is clear that certain layouts are most suitable for traffic flows that lie
within particular ranges. Figure 13.1 gives broad guidance to assist the designer in
making an initial assessment of the most suitable intersection type, but this' choice
must be reviewed as the design progresses.
'
I
;
*
-
.
.*
,
,
'.
.
.
.I.?,AS
.
m ,
,,.
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.
>!"
a
;., -. *- .
1
-
20'
90
40
50
MAlOR ROAD FLOW x IPMDT
10
70
g0
Flgure 13.1: Guidance on lnitlal Selection of tntersectlon Type
Source: msedon materklin the UK DMRB'
r,
'
,:.
.
In the interests of safety, the intersections dong a length of a road should not involve
different layout types, even though all may be permitted. A primary arterial, which
generally has interchanges along its route, for example, should not have an isolated
roundabout or signalised intersection. The safest schemes are generally the ones
that present the driver with no surprises.
Table 13.2: PermHted IntersectJon Types in Urban Areas
Atgrade Intersecttow
Road Class
-,J?
TJ
4.1
-
,
C>.rP I m111-d=,
l,,>*.a:i--
-
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+
, &&
,i.>
7 s
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-
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z
Special Road
4e
I
I
3
v
Secondary Road
+
+
11
z i!
9s
a=
- .. -
xr- I.
*srr!F..
Primary Road
Local Road
I
0
v
Q
J
J
J
+
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-e
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4
Kuwait K i k y Design MenueE
Table 13.3: Permitted Intersection Types In Rural Areas
Secondary Road
Local Road
e
e
e
+
J
c,
In all cases, it is necessary to check that the chosen intersection type has adequate
capacity to handle the projected traffic levels, and close liaison with the traffic
engineer is essential in developing the layout and lane provision.
13.4
Choosing between Roundabouts and Signalised Intersections
A number of safety, operational, economic and environmental factors should be
taken into consideration when choosing between a roundabout and a signalised
intersection.
13.4.1
Safety
Roundabouts have been demonstrated to be generafly safer than other forms of atgrade intersections, both in terms of crash frequency and severity. The frequency of
crashes is related to the number of conflict points and the magnitude of conflicting
flows. A conflict point is the location where the paths of two vehicles diverge, merge
or cross each other. For typical intersections with four, single-lane approaches, a
signalised intersection has 32 conflict points, whereas a roundabout has only 8.
The severity of a collision is determined by speed at impad and the angle of impact.
For roundabouts, speed control is provided by the physical, geometric features. For
signalised intersections, restraint relies on the driver obeying traffic control devices.
A series of roundabouts can have a secondary traffic calming effect on streets by
reducing vehicle speeds. As speed control is provided by the roundabout geometry,
speed reduction can be realised at all times of the day and on streets of any traffic
volume.
Roundabouts are only recommended for single carriageway or dual, 2-lane
carriageway junctions. For dual 3-lane carriageways or greater, it is difficult to
provide sufficient entry deflection and the resulting speed control.
1 3.4.2
Operation
When operating within their capacity, roundabouts function with fewer delays than
other intersection types, as it is often unnecessary for traffic to come to a complete
stop at the Give Way line. When there are queues on the approach arms, traffic
within the queues usually continues to move, and this is more tolerable Ze drivers
than stopping completely.
-
Kuwait Highwey Design ManuaE
mapier f3
Inienectmns - Germ&
&
At roundabouts, a13 movements are given equal priority, regardless of whether the
approach is a local street or a major arterial. This may result in more delay to the
major movements than might otherwise be desired. Therefore, the overall street
classification system and hierarchy should be considered before the junction type is
- *
-
selected.
It is common practice to coordinate traffic signals on arterial roads to rninimise stops
and delays. Traffic control systems move vehicles through their controtled areas in
platoons by adjusting traffic signal times to suit the required progress. The
introduction of a roundabout into a coordinated signal system may interfere' with
these platoons, thereby reducing the progressive movement of traffic, and is
therefore not recommended.
13.4.3
Economics
Roundabouts usually require more space for the circular roadway and the central
island than the rectangular space inside signalised intersections. Roundabouts can
often have significant right-of-way impacts on the corner properties at intersections.
Conversely, if a signalised intersection requires long or multiple turn lanes to provide
sufficient capacity or storage, a roundabout with similar capacity may require less
space on the approaches.
Signalised intersections have equipment that requires constant power, periodic light
bulb and detection system maintenance and regular signal timing updates. However,
roundabouts can have higher landscaping costs. Power failure at signalised
intersections is disruptive and potentially dangerous. Power failure has minimal
effect on roundabouts.
The service life of a roundabout is significantly longer than for a signalised
intersection, typically 25 years as opposed to 10 years.
13.4.4
Environment
Roundabouts may reduce noise and air quality impacts if they lessen vehicle delay
and the number and duration of stops, as compared with fixed-time signalised
intersections. Vehicle-actuated signals, in certain instances, may cause less delay,
less fuel consumption and less emissions than roundabouts, as long as traffic
volumes are low.
Roundabouts
communities.
requirements
central island
provided.
13.5
offer the opportunity to provide attractive entries or centrepieces to
The parts of the central idand that are not subject to sight distance
offer opportunities for aesthetic landscaping. Hard objects in the
that directly face the entries are a safety hazard and should not be
Design Vehicles
The range of design vehicles for use in Kuwait is given in Chapter 2 of the Manual,
and it is anticipated that designers will have access to computer software that
enables these different vehicles to be 'driven" around an intersection layout in order
to check that adequate space has been provided and that the kerb radii are
appropriate. In the absence of such software, reference should be made to
AASHTQ~,which provides relevant swept path templates.
Intersections should be designed with due regard to the types of vehicles likely to use
them. In residential areas, for example, a Single Unit Truck or Bus (SU or BUS) could
be appropriate, whereas for an industrial area, a semi-trailer (perhaps WB-15) might
be relevant.
Page 13-5
Kinwit Highway Design Manual
Chapter ff3
-
fntersections Genemf
Occasional use by a particular type of heavy vehicle, for example once per day or
less frequently, would generally not be sufficient to govern the geometric design.
More regular use would suggest that the dimensions of that vehicle should determine
the layout to be provided.
13.6
Siting of Intersections
In selecting locations for intersections on new-build or major improvement schemes,
the designer should seek to ensure that the siting:
is appropriate with respect to adjoining intersections
*
avoids places where the main alignment is on a sharp curve
avoids the need for intersecting roads to meet at small angles
enables the grades of the minor legs to be reasonably flat
avoids the tops of crest cunres in rolling terrain.
f 3.7
-
Intersection Types (1) Major I Minor Intersections
Figure 13.2 shows the most common form of intersection on minor roads. This
comprises an at-grade intersection between two roads, one of which (the major
alignment) passes through the intersection while the other (the minor alignment
terminates there, usually at right-angles to the major road. Traffic control normally
consists of Give Way or Stop signs and markings, displayed to drivers on the minor
road.
Where the minor alignment is skewed to the main line, there is an increase in the
potential for accidents, due primarily to the limited visibility available to the driver on
the minor road. This can be a particular difficulty on acute angles, where emerging
lefl-turning truck drivers may not be able to look to the right along the main road.
Equally, a small angle can make it difficult for the emerging driver to know whether to
look over his left shoulder or to try to use his rear-view mirror (with its inherent blind
spot).
Figure 13.2: Simple T Intersection
1 3.7.2
Four-leg Intersection [Crossroads)
As shown in Figure 13.3, this comprises the at-grade intersection of two roads, both
of which continue through the intersection, usually intersecting at or near right
Page 13-6
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Kuwelt Highway Design Manuel
angles. One is designated the major alignment, while the other, the minor alignment,
is usually governed by Give W a y or Stop signing.
Crossroads, by their nature, have a high number of potentially conflicting vehicle
paths, and so their provision is generally not recommended.
Figure 13.3: Simple Four-leg Intersection
13.7.3
Staggered Four-leg lntersection
As an alternative to the Crossroads Intersection, consideration could be given to
providing a Staggered Intersection. This comprises two T-intersections on opposite
sides of the main alignment, so that crossing vehicles join the main road and then
leave it, rather than crossing it directly. Although this arrangement, which is shown in
Figure 13.4, is preferable to a crossroads, special care should be taken in design to
ensure that there is adequate storage for leR-turning vehicles, and that there is
adequate stagger length between the two Intersections. A left-right stagger is
preferred.
Page 13-7
K m d H i g h m Design Menual
Chapter 13
Intersections Genenl
-
a) Leit I Right stagger
b) Right / Left stagger
Figure 13.4: Staggered Intersection
13:7.4
Free Right Turns
Free Right Turns may be provided at major I minor intersections if provision can
improve the operation and capacity of the intersection. Right-turning roadways
should be considered where land-take considerations permit, and are generally
warranted when the right-turning flow exceeds 25% of the approach volume.
Signalisation
Major I minor intersections work on the principle that each vehicle in the minor
stream has to select a safe gap in the major stream in order that conflict does not
occur. Signal ~ontrolis also an appropriate and frequently-used method of
eliminating conflicts at an at-grade intersection,through time-separation of Rows, and
is dealt with in Section 73.10.
The provision of 'Free Right Turns' roadways, which are not signalised, can provide
significant additional capacity at a signalised intersection. They will generally be
warranted on capacity grounds, but may also be provided, where land-take permits,
in order to reduce delays to right-turning traffic. Pedestrian crossing movements
should be carefully considered, and 'Zebra' or 'Pelican' crossings provided where
appropriate.
13.8
-
Intersection Types (2) Roundabouts
Roundabouts are a special form of at-grade intersection, characterised by a one-way
circulatory road around a central island. Approaching traffic gives way to circulating
.traffic, and then, when a suitable gap appears, joins the flow running counterclockwise around the island until it reaches the required exit. This type of layout can
accommodate three to six legs. Figure 13.5 shows a typical four-leg roundabout.
Page 1 9 8
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KuweiI Highway Design Msnual
Chapfer13
Intersections Generel
-
T r a f i deflection
island
/>
Figure 13.5: Typical Four-Leg Roundabout
13.9
-
Intersection Types (3) U-turns
On divided roads, side roads are often connected to the main alignment by three-leg
T-intersections that permit only right turning movements. These *right-in, right-out"
intersections can only be accessed from the main road by vehicles travelling in one
direction and so opportunities need to be provided for vehicles moving the opposite
direction to turn around. This can sometimes be achieved at a roundabout or a
signalised intersection, but often, a dedicated U-turning facility must be provided.
Figure 13.6 shows a typical layout.
figure 13.6: Typical U-turn
Page 13-9
Kuwait HgRway Design Manual
Chapter 13
-
Intersections General
13.10
-
Intersection Types (4) Signalised Intersections
While not, strictly speaking, an intersection type in its own right, signalisation may be
provided on a number of at-grade layouts to control the movement of traffic and
thereby improve safety and increase capacity. .
Signalised intersections may be designed as such frorn the outset, or signals may be
added to a major 1 minor, roundabout or U-turn layout at a later stage. Figure 13.7 is
an illustration of a four-leg signalised intersection.
Figure 13.7: TypicaE Four-leg SlgnaHsed Intersection
3.1 I
-
Intersection Types (5) Interchanges
This type of intersection removes all major vehicle conflict frorn the main line by
means of grade separation, although certain elements within the interchange may be
designed as at-grade intersections. Where no at-grade elements exist, an
intersection is generally referred to as a free-flew interchange.
A typical Diamond Interchange (which includes two signallised intersections) is shown
in Figure 13.8, while Figure 13.9 shows a typical Free-flow Interchange.
interchange types are wide ranging, and this subject is dealt with more fully in
Chapter j 8 of this Manual.
Page 13-10
Kuwnfl Highmy Design Manual
Chepfer13
Intersections General
-
Figure 13.8: Diamond Interchange
Figure $3.9: Free-flow Interchange
t
Design Manual for Roads and Bridges, The Highways Agency, Department of
Transport, Local Government and the Regions, UK Government, various dates
A Policy on Geometric Design of Highways and Streets, 2001, AASHTO, 2001
Kuwatt Hlghwey Design Manuel
14.4
Introduction
This section provides advice and standards for the geometric design of major 1 minor
intersections with regard to traffic operation and safety. Major 1 minor intersections
provide the simplest arrangement where two roads join. Their operation relies on one
of the roads (the major road) being given priority, by means of signs and road
markings, over those on the other (the minor road). Accordingly, they are appropriate
where roads of generally low status within the hierarchy intersect.
14.2
Safety
The rate of accidents is usually higher on urban roads than on rural roads. Most
vehicular and pedestrian accidents occur at major I minor junctions. Poorly judged
left turn movements onto and from the major road and dangerous overtaking
manoeuvres usually accompany these accidents. Consequently, the designer should
review each intersection on an individual basis.
Major / minor intersections are safest when the angle of intersection of the road
centrelines lies in the range 60° to 120°, and the designer should seek to achieve this
within the centrefine alignment.
14.3
Types of Major I Minor Intersection
There are two suitable types of major E minor intersections for use in Kuwait. These
are three-leg intersections (T-intersections) and four-leg intetsections (Crossroads
and Staggered Intersections), f-intersections are further subdivided into simple,
flared and free right turn arrangements.
These are dealt with in general terms in this section, and subsequent sections of this
chapter give guidance on the various geometric elements required for the proper
design of all major 1 minor intersections.
fable 14.1 gives guidance on the selection of suitable types of intersections, given
the different classes of the major and minor roads.
Page 14-1
Kuwait Highway Design Manuaf
Chepter 14
At Grade InlerseEtions
Table 14.t: Suitable Major I Minor Intersection Types
Major leg
Minor leg
Type
Suitable layouts
Local Road
Local Road
3-leg
Simple T
Flared T with minor leg splitter island
#-leg
Simple crossroads
Staggered intersection
34%
Simple T
Flared T with minor leg splitter island
T with kerbed median (rural roads)
T on divided road with median opening
Signalised or mundabout (rural roads)
4-leg
Simple crossroads
Staggered intersection
Signalised or roundabout (rural roads)
Secondary
Road
Local Road
Secondary
Road
3-leg
'
Flared T with minor Reg splitter island
T with kerbed median (rural roads)
T on divided road with median opening
Signalised or roundabout
Primary Road
Secondary
Road
4-leg
Signalised or roundabout
3-leg
Ton divided road with median opening
Ton divided road without median opening
Signalised or roundabout
Interchange
4-leg
Primary Road
34%
4-'eg
Special Road
Primary Road
Special Road
14.3.1
Signalised or roundabout
Interchange
f on divided road without median opening
Signalised or roundabout preferred
interchange
Signafised or roundabout
Inferchange
Interchange
3-leg Intersections
14.3.1.I Simple T Intersection
Figure 14.1 shows the simplest form of major I miner intersection. Where the kerb
lines on both roads intersect, a radius is provided to assist turning manoeuvres, but
no other geometric changes are made to the cross section of either road. This form
of intersection is most suited to residential areas.
Page f 4-2
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KuwH Highway Design Manual
Ch~pterf 4
A l Grade Fntersections
i
Figure 14.1 F Simple T-intersection
In industrial areas where kerb radii are designed to accommodate heavy vehicles,
the mouth of the intersection can become very wide, and it is good practice to
provide a splitter island on the minor leg,
Where the minor road intersects the main tine at an angle outside the range 70 to
110 degrees, the provision of a splitter island enhances safety and reduces the width
of the paved area.
14.3.1.2 Flared T with Minor Leg Splitter Island
A splitter island can be provided to separate left turns on undivided roads, to control
problems arising when drivers "cut the cornef. In this layout, as shown in Figure
14.2, the right of way on the minor mad is widened in order to provide the additional
space to accommodate a splitter island.
This layout is particularly suitable for use (in both urban and rural areas) where any
of the following conditions apply:
There are significant levels of pedestrian movement across the minor leg.
More than one-third af the traffic approaching on the minor leg turns left.
The intersection is used regularly by turning trucks or buses.
A prominent island location for a 'stop" sign is desired, paflicularly in rural areas.
Figure f4.2: Flared T with Minor Leg Splitter Island
Where the minor road makes a skew approach to the main line, the introduction of a
circular curve on the minor approach alignment may bring the minor leg nearer to the
perpendicular, if the Right of Way width permits. The objective is to seek an angle in
Page 14-3
KuwaH Highwiy Design Manual
CAapfer f 4
Al Grade Intemectims
the range 70 to 110 degrees, Where the intersection angle lies outside the range 60
to 120 degrees, consideration should be given to the provision of a right-turning
roadway in order to reduce the width of the bell mouth.
Flaring may also be applied to the main line, in special situations, to provide space
for through vehicles to pass those waiting to turn left. In this case it is preferable ta
maintain the alignment of the centreline and provide the necessary widening
asymmetrically on the opposite side to the minor leg.
14.3.1.3
Intersection with Main Line (Kerbed Median)
In this arrangement, as shown in Figure 14.3, a kerbed median is provided along the
major road. A single through lane is provided in each direction, and the layout is
designed to discourage potentially hazardous passing manoeuvres in the vicinity of
the intersection. This type of layout should only be used in rural areas, and is
normally warranted where more than one left-turning vehicle is expected to be
waiting on the major leg at any one time.
Figure 14.3: T-intersection with Main Line Channelisation
The provision of the auxiliary left-turning lane requires additional .cross-sectional
width. Wldening can be achieved either symmetrically about the major road
centreline (as shown in Figure f4.3), or asymmetrically (with the through lane on the
minor road side being maintained on a straight alignment).
14.3.1.4
Page 1 4 4
T-intersection on a Divided Road, with Median Opening
This type of intersection is sometimes used on a collector or secondary arterial to
provide access at a mid-block location. Figure 14.4 represents a typical example.
The layout is such that it can be readily converted to a signalised intersection if the
demand warrants it.
-
Kuwait Highway Design Manual
Chapter 14
At Grade Intersections
Figure 14.4: T-intersectionon a Divided Road, with Median Opening
In Kuwait, a layout on a divided read that permits left turns both into and out of the
minor road it is not considered suitable. The left turning movement from the minor
road is normally omitted and may be catered for at a U-turn an appropriate distance
further downstream. Weaving considerations then become a significant factor in the
design process. Alternatively, if all movements are to be provided at the intersection
then a roundabout or signalised solution is generally required.
14.3.1.5 T-intersection on a Divided Road, without Median Opening
This arrangement, as shown in Figure 74.5, is the most frequent type of mid-block
connection onto a Primary Road. If it is provided in conjunction with a pair of U-turns,
adequate weaving capacity on the Primary Road both before and after the
intersection should be ensured.
At a future date, this layout can easily be converted to operate with a median
opening, and signalisation may be added.
Figure 14.5: T-intersection on a Dlvided Road, without Median Opening
Page 14-5
Kuweii Highway Design Manual
Chap&t 14
At Grade Inierseetions
14.3.2
4-leg Intersections
14.3.2.1 Simple Crossroads
The layout shown In Figure 14.6 is only suitable for use where Local Roads meet
other Local Roads or Secondary Roads and where low traffic volumes are expected.
This is because of the number of conflicting vehicle paths through a crossroads.
Minor leg splitter islands should always be used, in order to improve driver
comprehension of the layout and to provide a suitable and prominent location for
Stop signs to be sited.
Figure 14.6: Simple Crossroads
14.3.2.2 Staggered T-intersection
At some locations, a Staggered T-intersection is preferable to a simple crossroads
layout, since it reduces the number of potentially conflicting vehicle paths. On the
other hand, it provides hrvo intersection locations in close proximity rather than one
intersection. As with the crossroads layout, this type of intersection is only
considered appropriate when connecting Local Roads either to each other or to a
Secondary Road.
Figure 14.7 shows two alternatives, the lewright stagger and the rightrleft stagger.
The IeWright stagger is generally preferred, because the queuing of left-turning
vehicles on the major road occurs on the approaches to, rather than within, the
intersection.
Page 1 4 4
Kuwaft Highwey Design Manuel
Chapter 14
At Grade Intersections
VARIES
Mln 30m
a) Left t Right stagger
. .
b) Right l Left stagger
Figure 14.7: Staggered T Intersection
q4.4
Capacity
The road hierarchy (Table 14.1) limits the selection of intersection type, however, it is
necessary to check that the selected intersection type has adequate capacity to
handle the predicted traffic demand. Close liaison with the traffic engineer is required
at an early stage.
If there is a lack of capacity, consideration should be given, firstly to the adoption of a
major J minor layout of a higher standard, and secondly to the provision of a
signalised intersection. In the tatter case, it is always preferable to begin the design
process afresh rather than simply to impose signals on a layout designed for majorI
minor operation.
Where there are high volumes of left-turning vehicles on most approaches, a
roundabout may be a suitable solution.
14.5
Pedestrian Considerations
Major 1 minor intersections can pose problems for pedestrians, especially in areas
with dominant pedestrian Rows, or where the entry to the minor road is wide and
lacks a splitter island. The needs of pedestrians should be borne in mind. If there is
a need Yo provide a signalised pedestrian crossing on one leg, then the intersection
should be signalised as a whole.
14.6
Alignment
The alignment of the main line through an intersection is determined in the normal
manner by the application of the standards relevant to the 'Design Speed, as set out
in Chapters 5 and 6 of this Manual.
Page 14-7
K m r Y Highway Design Manual
Chepler 14
At Grade Intersections
For the minor road(s), vehicle-operating speeds tend to be lower, as drivers either
accelerate away from the intersection, or anticipate on their approach that they may
have to bring their vehicles to a halt. Accordingly, the designer may use his judgment
in selecting the alignment elements, but should always ensure that vehicle speed can
be safely maintained, meets the anticipated, operating speed for the movements
concerned, and bears an appropriate relationship to the operating speeds on
adjacent sections of road. In all cases, the designer should check that the guidance
given in the following sections of this Chapter is adhered to.
Steep gradients should be avoided on minor leg approaches. The vertical alignment
should be flattened to a maximum gradient of 2% (up or down)far a minimum of 15m
before the Give Way or Stop line.
14.7
Visibility
14.7.1
Visibility on the Main Alignment
Drivers on the main line should be able to see the minor road entry from a distance of
1.5 times the Stopping Sight Distance (SSD) appropriate for the Design Speed. This
is to ensure that they can perceive the intersection and react to its presence. SSD
should also be provided to the back of any anticipated queues, for example of
vehicles waiting to turn left.
d4.f.2
Visibility on the Minor Road Approach
Drivers should 'be able to see the point at which they are expected to stop or give
way from an adequate distance. This means that at least full SSD appropriate to the
design speed of the minor road should be provided.
In the following instances, Decision Sight Distance (DSD), which is greater than SSD,
should be provided:
On a rural ioad leading to a stop sign
On an urban road leading to a stop sign or traffic signals
Where unusual manoeuvres are required at the intersection
Where there is a significant amount of visual distraction
See Section 4.5 of this Manual for further details.
At a f-intersection, consideration should be given to the use of planting (or to the
provision of other barriers to forward view) beyond the intersection. This provides an
approaching driver with a visual signal that the alignment is coming to an end.
At crossroads, other means of increasing the awareness of the driver of the
intersection layout should be considered. Splitter islands are always provided, and
they may provide a suitable location for a maximum size stop sign.
14.7.3
Visibility for Emerging Vehicles
Drivers of emerging vehicles need an adequate view of other vehicles whose paths
they intersect. This view should be perceived in good time, rather than when the
vehicle arrives at the give way or stop line. This leads to a requirement for sight
triangles, as shown in Figure 14.8.
Page 1 4 4
KuwaW W~hwayDesign Manual
,
.
Y
r
Fullwidth of intersection
5 -
.
Y
. :
-
----.------------ ---
-- - ---T.P.
T.P
Appmach triangle
# Cmssing triangle
For defination of distance X and Y
seu paragraph 14.8
There are two sight triangles, both of which have a visibifi envelope in the vertical
plane- that is the same as for Safe Passing Sight Distance(see Section 4.4 of this
.manual). The lower boundary for clear vision is therefore from a driver eye height of
1.05m to an object height also of 1-05rn.
Firatly, the approaching driver neds to see and comprehend the layout of the
intersection, and this is achieved through the provision of clear visibility, with no
obstructions, on the approach triangle. The reference line for this is the nearer edge
of the travelled way of the main alignment, and the full width of the intersection at the
reference line should be clearty visible from a point 15m before that line.
Secondly, the driver needs to be able to identify when it is safe' for him to proceed
into or across the traffic R o w on the main line, and this is achieved through the
provision of clear visibility at all points within the crossing triangk. The reference line
is again the nearer edge of the travelled way of the main alignment, but the distance
(Y) along this line, and the distance (X) back into the minor road, are both variable,
depending upon #e circum&ances. Table 14.2 and Table 14.3 k t out the relevant
information. Wdhin the crossing triangle, isolated obstructions to the sigM line (single
sign posts, lighting columns etc) are permissible, but c a n should be taken to ensure
that a combination of slim obstructions together do not block the vision of a driver.
table 14.2: 'X' Dlshncm for Crossing Sight Triangle
Chcumstances
-
.
. .
'X' Dlstiance(m)
(see Figure 145)
Normal
provision
In rural areas
15
In urban areas
I0
Minimum
provision
Generally
In densely developed urban locations
5
b2.5
K m i ! Highway Des&n Manual
Chapler 74
At Grade Inkcsections
-
Table 14.3: 'YWistances for Crossing Sight Triangle
Design Speed of
Major Road (kph)
'XI Distance (m)
(see Figure 14.8)
30
70
40
90
50
135
60
I35
70
760
80
180
90
205
100
225
130
245
120
270
If the major road is one way (or one half of a divided roadway, with only right turning
from the minor road being allowed), a single crossing sight triangle in the direction of
approaching traffic is necessary. If the minor road serves as a one-way exit from the
major road, no sight triangle is required, but adequate forward visibility for turning
vehicles should be provided.
14.7.4
-
-
Visibility on Rig ht-turning Roadways
-
Corner Radii
Corners may be of constant radius (simple) or may use s compound curve, ofwhich
the three-centred compound curve, shown in Figure 14.9, is in most general use.
This is described by its three radii, in the order in which a driver would encounter
them, together with the offset of the middle radius. Thus a 30m-l0m-60m, 1.5m
offset, describes a curve with an initial circular radius (Rl) of 30m, followed by a
section of cuwe with a radius (R2) of 1 Om whose centre is 11.5m{R2+offset) from the
extended channel line, followed by a curve with a radius (R3) of 60m.
Page 14-10
-
Vehicles parked within sight triangles obstruct visibility. Parking bays and access
driveways should therefore be located outside the triangles. Care should also be
taken in the placing of any signs, landscaping or items of street furniture within the
sight triangles, so that the obstructive effect is minimised.
The Stopping Sight Distance, which accords with the relevant speed, should be
provided, as described in Section 14.7.
14.8
I
Kuwait H i g b w y Design Manual
Chapter 14
At Grade Interseclions
Figure 14.9: Three-Centred Compound Cuwe
Table 14.4: Corner Radii at Major I Minor Intersections
Rural Roads
These arrangements are generally appropriate for vehicles up to the size of a bus
(BUS) or a single-unit truck (SU).Mere larger vehicles are anticipated on more than
an occasional basis, adequate radii should be provided, normally using a compound
curve.
Table 14.5 gives general guidance on curves, which should avoid encroachment on
to adjacent lanes, but the designer is referred to the extensive advice in AASHTO'
(Exhibit 9-79 and 9-20,and the accompanying Exhibits 9-21 to 9-28). Checking with
templates or by use of computer software is recommended where larger semi-trailers
are expected to operate regularly.
Table 14.5: Three-Centred Corner Radii for Semi-trailers
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Kuweit HIghw~yDesign Manual
Cheptar I 4
At Grade Inlerseclions
14.10.3 Corner Radii where Right Turning Does Not Occur
In circumstances where right turning does not occur, for example because it is
prohibited by traffic regulation or if it 3s catered for by means of a separate rightturning roadway, a kerb radius of around l m should be provided.
94.11
Cane Widths
14.11.1 Cane WidthsonThrough Lanes
The lanes on the major road, which continue through the intersection, should be the
same width as the lanes before and after the intersection.
14.11.2 Lane Widths on Left-turning Lanes on the Major Road
An auxiliary left-turning lane should be at least as wide as the adjacent through lane.
Where the left turn lane is protected, as shown in Figure 14.4, a width, which
provides 4m between the kerbs on the protected length, would be chosen. DoubleFane, len-turning lanes, if required, should always be signalised, and should comply
with the standards set out in Chapter 17 of the manual.
14.11.3 Lane Wjdths on Auxiliary Righi-turning Lanes
Depending on the volume and speed of turning traffic relative to through traffic, it is
sometimes appropriate to develop an auxiliary right-turning lane on the main
alignment in advance of the intersection. This allows turning vehicles to decelerate
clear of the through traffic.
The auxiliary right-turning lane, as shown in Figure 14.10, should normally be the
same width as the adjacent through lane.
Figure 14.10: Auxiliary Right-turning Lane
14.11.4 Lane Ndths on Right-turning Roadways
On right-turning roadways, added width is requited in order to cater for the swept
path of larger design vehicles. If large vehicles (typically WB-15 or larger) are to be
catered for, then the width should be checked using the swept path template for that
vehicle.
For radii above 12511,see Table 5.6 for details of lane widening requirements.
Page 14-12
Kuwait Highway Design Manual
Chapter 14
At Grede lnterseciions
On turning roadways longer than 30m, it is recommended that allowance should
normally be made for broken down vehicles. On shorter roadways, the designer
should consider whether or not to provide for this eventuality, bearing in mind the
presence of any alternative route for right turning vehicles that may exist within the
intersection.
Turning roadway widths are set out in Table 14.6.
Table 14.6: Width of Right-Turning Roadways
14.11.5 Lane Widths on the Minor Road Approach
For intersections without a minor leg splitter island, it is normal practice to maintain
the width of the minor road lanes up to the intersection.
For intersections with a minor leg splitter island, it is good practice to widen the
travelled way at the approach to the intersection. The minimum approach lane width
at the start of the splitter island should be 4.0m, or, if two separate approach lanes
are being provided, 2 x 3.5rn. The width of the lane entering the minor road at this
point should also be a minimum of 4.Qrn. This is illustrated in Figure 14.1f .
If the minor lag is a divided road, then no change in cross-section is required.
Consideration should, however, be given to signalising the intersection or to the
adoption of a roundabout,
Kuwait Highway Design Menuel
Chapter 14
At Gmde IntemeFlions
a) Single lane approach
b) Two lane approach
Figure 14.11: Minor Road Approach with Splitter Island
74.12
Islands
14.12.1 General
Physical or painted guide islands can usefully separate trafic movements. Minimising
conflicts by separation means that drivers are faced with simple decisions on their
choices of movement at any one time, thus enhancing safety.
74.32.2 Dimensions of Physical (kerbed) Islands
Splitter islands on the minor road shall be at least q.2m wide and 5.0m long, and
shall be set back by at least 0.5m from the nearest edge of the main line travelled
way. Where significant numbers of pedestrians are expected to use an island as a
means of crossing the minor road, its width should be 3.5m or more.
The median island at a T-intersection with a kerbed mainline (as shown in Figure
14.3) should be 12m wide (including median shoulders, ili any) immediately
downstream of the crossing point. This width can shelter buses and most single unit
trucks turning left from the minor road. Were use by longer vehicles is expected and
a roundabout is not feasible, the width needed for shelter is at feast the length of the
design vehicle.
The physical characteristics of the site and the swept paths of the design vehicles
usually determine the dimensions of other kerbed islands, but the area of islands
should generally be not less than 6m2 if kerbed or 3m2 if painted. For triangular
islands, this is approximately equivalent to a length of side of 3.5m (kerbed) or 2.5m
(painted).
14.12.3 Painted Islands
Painted islands should be delineated in accordance with the Kuwait Traffic Signs
~anual*.
Page 14-14
-
K u w d Highwey Design Mmuaf
Chepfer 14
A1 Grede lntemctiwrs
- -1
14.10.4 Physical (kerbed) Islands
fhe approach end of a physical island should be obvious to the approaching driver
and clear of vehicle paths. Guidance on the appropriate form of signage is contained
in the Kuwait Traffic Signs bIanual2.
For median islands in the major road (that is, for a kerbed single-lane), it is generally
appropriate to provide a nose down unit at the start of the island, as shown in Figure
14-12.
For splitter islands in the minor road, a nose down unit a2 the furthest end from the
intersection may be appropriate in a rural area, but in urban areas the island is
usually entirely delineated by upstand kerbs.
Other islands should be treated on their merits, but are generally unlikely to require
special nose treatment.
Nwma! upstand wrb
11
Nose dcnnrn unit
% W e M surfx&
Figure 14.12: Nose Down at the End of a Median Island
14.10.5 Offsets ta Physical Islands
It is normal to offset the nose of an island in order ta lead a driver more safely into
the kerbed path that he must follow. typical offsets are shewn on Figure 14.13 for
median islands and Figure 14.14 for triangular islands.
Splitter islands in the mouth of the minor road approach should be set back at least
0.6m from the through travelled way, and greater setback (or increased kerb radii)
may be warranted by the swept path of the chosen design vehicle, if BUS or larger.
Figure 14.1 3: Offsets to Kerbed Median Islands
Page 14-15
K w i f Highw8y Design M~nual
Chapksr 14
At Grade Intersections
SMALL
a""""
a) Mo Shoulder
b) Wflh Shoulder
Figure 14.14: Offsea to Kerbed Triangular Islands
14.13
Tapers
Median islands are used on a kerbed mainline (Figure 14.3) with staggered Tintersections (Figure 14.7). The rate at which the road width can safely be increased
on the approach to the median depends on the Design Speed of the main alignment,
and is set out in Table 14.7, W~deningat this rate can be applied on both sides of the
centreline.
For splitter islands in the minor road, the taper, if required, is applied at a maximum
rate of 1 :lo.
Page 14-16
-
-
Kuwait Highwey Design !d8rtua/
Chapter f4
At Grade Inlersections
7
1
Table 14.7: Taper Rates to Median Islands
14.13.2 Tapers to Auxiliary Lea-turning Lanes
Auxiliary left-turning lanes are found in kerbed main line layouts (Figure 14-31, at
staggered T-intersections (Figure 14.7) and on divided roads with a left turn from the
main alignment (Figure 14.4). Table 14.8 gives the taper rate to develop the auxiliary
lane.
'
Table 14.8: Left-Turning Auxiliary Lane Taper
Design Speed
(kmlh)
---.
1
Auxiliary Lane
Taper Rate
50
1 :5
60
1:5
7Q
1:5
80
f :8
90
1:8
100
7:10
f 10
1:lO
i20
1:lS
On divided roads, with design speeds of 80kmlh to120krnJh, the change in alignment
at both ends of the taper should be smoothed using large radius curves, the typical
radii being in of the order of 200m to 600m.
14.13.3 Tapers to Rig ht-turning Auxiliary Lanes
Where a right-turning auxiliaty lane is provided on the main alignment, it has a leadin taper of 1 :-I5(if it is an auxiliary lane prior to the intersection exit) or a run-out taper
of 1:15 (if it is an auxiliary lane beyond the intersection entry).
Page 14-17
K w i t Highway Design Manrref
C h w r 14
At Grade htemectians
14.12
Right-turning Roadways
Every right-turning roadway, whether it be major-to-minor or minor-to-major, has an
exit terminal, where it leaves one alignment, and an entry terminal, where it joins the
next alignment.
Exit terminals may be either direct or tapered. Entry terminals may be either 'Give
Way" or tapered. The choice of which terminal to adopt depends on a number of
factors, including the relative traffic volumes, speeds and the space available. The
choice should be made by the designer, in consultation with the traffic engineer.
Figure 14.1 5 is a composite layout showing the use of all four terminal types,
GIVE WAY ENTRY
Inner kerb tangential
to main alignment kerb
TAPERED
I
I
)\ I
4
-ED
ENTRY
1
I
Llnner kerb tangential
to minor read kerb
DIRECT
EXIT
1
I
Figure 14.q5: Rlght-turning Roadway Termlnalls
In the DIRECT EXIT terminal, the inner edge of the travelled way of the turning
roadway is directly tangential to the edge of the travelled way of the main alignment.
In the TAPERED EXIT terminal, the running width is increased over the tapered
section until it reaches the width of the turning roadway, then curves away
tangentially from that point. The taper rate should be as for a lead-in taper of 1:15.
In the GIVE WAY ENTRY terminal, the inner edge is directly tangential to the edge of
the alignment being joined. Traffic from the turning roadway therefore has no
merging area, but is directed by road signs to Give Way.
In the TAPERED ENTRY terminal, the turning roadway becomes parallel with the
edge of the travelled way of the main alignment, and then the width is reduced over
the tapered section, allowing a gradual merging of the two traffic streams. f he length
of the tapered section should be the same as that of a run-out taper of 3 :15.
14.1 3
Deceleration and Queuing
There are two situations to be considered, namely left-turning auxiliary lanes and
right-turning auxiliary lanes. In the former, queues can normally be anticipated, as
vehicles have to wait for gaps in the opposing stream of traffic. The length of the
auxiliary lane is therefore the sum of the deceleration length and the queue length. In
the latter case, however, queuing rarely occurs, and the length of the auxiliary lane is
the same as the deceleration length.
Page t4-1 B
Kuwait Highway Design Manuel
Chapter 14
At Grade Interseclmns
14.15.1 Deceleration in Left-turning Auxiliary Lanes
The provision of the braking distance element of Stopping Sight Distance to the back
of any stationary queue within a left-turning lane provides a safe situation under
heavy traffic flow conditions. It allows a more leisurely deceleration during periods of
lighter traffic flow when the queue is shorter. This is the basis for the absolute
minimum values set out in Table 14.9.
Table 14.9: Minimum Deceleration Length in Left-Turning Auxiliary Lanes
* On urban toads with interredion spacing less than 400m, see Section 14.15.2 for reduced standards
14.15.2 Queuing in Leflturning Auxiliary Lanes
The queue length is entirely dependent on the volume of traffic wishing to make the
lefl turn manoeuvre and the opposing Row on the main line. Advice should be sought
from the trafic engineer.
On urban roads with a design speed of 7Okrnlh or less and average intersection
spacing of 400m or less, it is often impractical to provide the full deceleration and
queuing length. It is normal to assume under heavy flow conditions that much of the
deceleration occurs in the through lanes, and so the overall length of the left-turning
lane should be taken as the longer of (a) the queue length, to cater for conditions
when the queue is at a maximum and speeds are low, or (b) the deceleration length,
to reflect the situation under light traffic flow when there is no queue present.
Protection of lefl turn lanes (as shown in Figure 14.4) may be beneficial, and, if
provided, the geometry should be the same as for U-turns (see Chapter 16).
14.15.3 Deceleration in Rig ht-turning Auxiliary Lanes
Deceleration in right-turning auxiliary lanes enables vehicle speed to be reduced
clear of the through running lanes to that commensurate with the radius of the right
turn.
For this. purpose, the speed commensurate with the right turn radius can be
assessed from the data in Table 14.1 0. The deceleration length can then be obtained
from the chart presented in Figure 14.16, using the appropriate speed curve.
Page 14-19
Kuwail H@way Deslgn Manual
Chapter 14
At Grade Intersections
Table 14.30: Speed Assessments forRight Turns at Intersections
The values obtained from Figure 14.16 represent the length of the auxiliary lane
(measured from the end of the lead-in taper to the start of the exit curve), as shown
on Figure 14.10. They should be increased by 20% for down gradients of 3% and
4%, or by 35% for down gradients of 5% or more. Up gradients theoretically reduce
the length required, but this should generally be ignored. Where spatial constraints
dictate, however, allowance for this shortening may be made, reducing the values
obtained from Figure 14.16 by 10% for up gradients of 3% and 4% up, and 20% for
up gradients 5% or more.
Page 14-20
K w i t Highway Design Manual
Chapter14
At Grade Intemecths
100
Deceleration length (m)
Figure 14.46: Deceleration Length In Right-Turn Auxiliary Lane
Turning Length
14.q6
Where the median gap caters only for left-turning vehicles into a minor road, the
layout should be similar to that for a U-turn, and Chapter 16 of this manual gives the
'
relevant advice.
Where (exceptionally) the median gap caters for left-turning vehicles into and out of
the minor road, the turning length (the median gap) should always be 12m or more. If
vehicles larger than single-unit trucks (SU) or buses (BUS) are anticipated, the swept
Page 14-21
K m i t Highway h s 5 n Menunl
Chapter 14
At Grade Intersections
path of the left turn should be checked and the median nose designed to suit the
relevant design vehicle. Further guidance is given in AASHTQ'.
q4.17
Staggered T-intersection Spacing
The separation between opposing legs of a staggered T-intersection (shown on
Figure 14.7) is offen dictated by physical considerations, but the following criteria
should be adopted:
For a leftlriqht stasqer
Absolute minimum separation
(where vehicles larger than SU are not anticipated}
Desirable minimum separation
50m
(to cater for largest size trucks)
For a riqhtlleft staqaer
Deceleration and queuing lengths in accordance with Section 4. T 5
Auxiliary lane tapers in accordance with Table 14.9
Minimum width of median island on the mainline*
m e auxiliary lane taper lengths may averlap
t 4.18
Drainage
The crossfall or normal crown of the main alignment should be continued through the
intersection, and the minor leg adjusted to tie in. Superelevation of turning roadways
is desirable, but should not exceed 4% in urban areas.
Consideration should be given to surface water drainage and care should be taken to
ensure that there are no relatively flat areas where ponding might occur.
34.13
Summary of Design Process
As the design of majorlminor intersections is a complex process, the flow chart in
Figure 14.17 is provided to guide the designer.
Page 1422
KuwaH Highway Design Manual
Chapter14
At Grade Intersections
'
lnitia! Sketch
Layout
Select Major I Minor
Configuration Layout
4
n
7
Trafk Engineering
Capacity Assessment
Standard Cross
Sections & Lane Widths
Consider Local
~onditiohs& Planning
Considerations
Select Leg Type
L
Select Suitable
I
,
4
Layout
I
Not OK I1
I
Preliminary Design
1 I
I
Check Process
Pedestrian Movements
Design Speeds
Turning Radii
Visibility
Lane Widths
Island Locations & Sizes
Turning Roadway Geometry
Deceleration & Queuing
Safety
Refined Preliminaw
Design Layout
u
Traffic Engineering
Capacity Analyses
t
J
,,,-
Not OK
I
Final Design
Figure 14.17: Summary of Design Process for Major I Minor Intersections
A Policy on Geometric Design of Highways and Streets 2001, AASHTO, 2001
Kuwait Traffic Signs Manual, 1988
-
Kuwait Highway Qeesign Manuel
Ch8phf $5
Roundabouts
+
15.1
Introduction
This section deals with the main geometric design features of roundabouts.
A roundabout can be provided on any class of road where at-grade intersections are
permissible. It is therefore an appropriate form of intersection on all roads except
Special Roads, where at-grade intersections are not to be used.
The designer's main concern must be to produce a layout that is inherently safe, and
to check that it has adequate capacity, rather than to allow capacity considerations to
override good layout practice. If capacity and safety cannot both be achieved, then
an alternative form of intersection should be sought.
Because of the interaction between traffic streams that occurs at a roundabout, the
calculation of capacity is complex and requires the use of relevant computer
software. The designer is therefore reliant on the input of the traffic engineer to
advise on whether a roundabout is likely to operate within capacity. The designer
may welt need to design and redesign the layout on an iterative basis to achieve a
layout that meets the traffic demand.
It is reasonable to assume that roundabouts on Local Roads will operate within
capacity, and it is likely that roundabouts on Secondary Roads can be designed to do
so too. On Primary Roads, adequate capacity may oflen be difficult to achieve whilst
maintaining a safe layout.
The roundabout elements of grade-separated interchanges (as described in Chapter
18 of this manual) should be designed as if they were at-grade roundabouts.
15.2
General Principles
The principal objective of roundabout design is to secure the safe interaction of tramc
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 locational constraints that
apply.
There is a balance to be struck in the design of a roundabout. In capacity terms, the
provision of wide approaches and circulating pavement is beneficial, but can lead to
high speeds through the roundabout under conditions of light traffkc flow.
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.
The guidance given in this Chapter sets out desirable geometric standards for the
various elements within a roundabout, but it is recognized that it may no2 always be
possible to achieve all the standards. The designer must then consider which of
them, if any, may be exceeded without a significant adverse effect on the accident
risk, and should consider whether an alternative form of intersection would be
preferable.
Kuwait H @ h y D e a n Manual
15.3
General Features of a Roundabout
15.3.1 Layout
A roundabout has a one-way circulating pavement around a central island that is
15m or more in diameter. The entries are
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.
Figure 15.1 depicts a typical arrangement. Entries from undivided roads should be
provided with kerbed median islands of roughly triangular shape where they meet the
roundabout. The medians of divided roads should be'widened in a similar manner.
Figure f 5.1: Typical Roundabout
15.3.2
Number of Entries
The number of entries recommended is either three or four. Roundabouts perfom
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 larger, and it is likely that higher circulating
speeds will occur. Six legs should be considered as the absolute maximum.
t 5.3.3 Signalised Roundabouts
Signals may be introduced on existing roundabouts, but a signalised roundabout
should not be serected for a new design layout.
15.3.4
Mini Roundabouts
Mini roundabouts with either kerbed or painted central islands o f
diameters are considered unsuitable for adoption in Kuwait.
Page 1 5 2
less than 15m
-
Rdundabouts
-7
15.3.5
The Design Process
As the procedure for the design of a roundabout is a complex one, Figure 15.2 sets it
out in the form of a flow chart.
Firstly, it is necessary to sketch an initial layout in sufficient detail for the traffic
engineer to advise on capacity issues. His response will give a first indication of the
entry widths that might be required in order that the layout can accommodate the
design year flows.
The designer then takes these widths, and refines the layout, checking the following
factors (referencesin brackets being to the sections of this chapter):
Is the central island an appropriate size? (15.5)
Is the Inscribed Circle Diameter adequate for the design vehicle? (1 5.6)
Does the circulating roadway accommodate vehicles entering side-by-side?
(15.7)
Have the required entry widths been achieved? (15.8)
Is the flare design adequate on each entry? (15.9)
* Is there adequate entry path deflection on each entry? (15.9)
Are all entry angles within the acceptable range? (15.10)
Is the radius on each entry above the acceptable minimum? (15.1 1)
Are desirable gradients able to be achieved? (15.12)
Does the geometry of the exits meet the guidelines? (15.13)
The result of this process is a preliminaq design, which again is assessed for
capacity. Any improvements that are suggested by the traffic engineer should be
considered and adopted where appropriate.
The designer then repeats the check process above, and makes further checks:
Is the visibility adequate? (5.14)
I
o
on the approach (15.14.3)
o
to the lefl(15.14.4)
o forward at entry (15.14.5)
o when circulating (15.74.6)
o
of any pedestrian crossing (15.14.7)
Can adequate crossfall be provided? (f 5.15)
Is drainage properly catered for? (15.15)
Are the safety criteria respected? (15.1 7)
This set of checks will then yield a final design, and it is prudent to refer this final to
the traffic engineer for his confirmation that it is operationally satisfactory.
45.4
Capacity of Roundabout
The capacity at a roundabout can be estimated using a gap acceptance technique
with basic parameters of critical gap and follow-up time. It has generally been
assumed that the performance of each leg of a roundabout can be analysed
independently of other legs. The approach capacity Qe is a function of circulating
Page 15-3
KuweH Highwey Design Manuel
Chapler V5
Roundabouh
flow Qc. The approach capacity is given by the following equations developed by
TRRL' and given in DMRB'.
Q, = k (F - FcQJ
where
k = 1 - 0.00347(0- 30)- 0.978 [(Tlr) - 0.051
F = 303 X2
F,=
0.210to(l+0.2X2)
tD = 1
* 0.5/(1+M)
M = exp [(D-60)110]
X S = v + ( e - v ) / ( I +2S)
S = 1.6(e-v)II
e = entry width
v = approachhalfwidth
.
I = effective flare length
S = sharpness of flare
D = inscribed circular diameter
0 = entry angle
a = entr)r radius
The equation of Qe is applicable to all roundabout types, except those that are
incorporated into grade-separated interchanges.
Table 15.1: Values of Geometric Parameters
The following steps should be used to calculate the capacity of a roundabout.
1. Define geometry and traffic conditions for the roundabout.
2. Determine the circulating flow, Q,, at each leg of the roundabout.
3. Callcutate the capacity, Qa, for each approach using the above equation.
4. Determine the valumelcapacity (VIC)ratio using approach volumes and Q,.
5. Assess the general performance of the roundabout on the basis of the VIC ratio.
The VIC ratio for each approach should be below 0.85.
Page 15-4
Kuwed Highway Design Manuel
Chapter f5
Reundebouts
Initial Sketch
Layout
Initial Sketch
Layout
Traffic Engineering
Capacity Analysis
4
Entry Widths
(Preliminary)
---
-I
I
I
I
i
I
I
I
I
I
1
1
Pavement Width
I
I
I
I
1
I Not OK
I
Entry Path Deflection
I
I
I
1
I
* Exit Geometry
I
I
I
I
I
Final Checks
Visibility
a
Crossfall
Drainage
Safety
Final Design
Layout
Engineering
* Traffic
Capacity Check
1
-----I
Final Design
Layout
Figure 15.2 : Design Procedure
Page 1 5-5
Kw8It Higbwy Design Menual
Chapter 15
Roundabavts
75.5
Minimum Sire of Island
The minimum diameter for a central idand is 15rn.
15.6
Inscribed Circle Diameter
The Inscribed Circle Diameter (ICD) is the diameter of the largest circle, which can be
inserted within the outline of the intersection, medians and median islands being
ignored for this purpose. Figure 15.3 shows how the ICD is measured.
Figure d 5.3: Inscribed Circle Diameter
The selected design vehicle determines the size of the smallest acceptable 1CD. It is
good practice to allow a tolerance of l m from both inner and outer kerbs, and typical
minimum lCDs are set out in Table 15.2. An ICD of 33m caters for all design vehicles
with the exception of W B - T O and WB-35.
It should be noted, however, that for roundabouts of below 40m ICD, it is 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 pad of the island by the rear wheels of
,articulated vehicles and trailers. These 'collars' should have the same profile as the
circulating pavement, but be paved in a distinctly coloured andlor textured material
and be edged with dropped kerbs with an upstand of 50rnrn.
There is no maximum prescribed ICD, as capacity, physical constraints and safety
requirements normally determine the roundabout dimensions at large or heavily
trafficked intersections.
Kuwait Highway DesfgnM~nual
Chapter i 5
Roundabouts
Table 15.2: Minimum Inscribed Circle Diameters by Design Vehicle
Reefer to Table 2.4 for detaits on design vehid-
3 5.7
Circulating Pavement
The circulating pavement should, if possible, be circular in plan, and its width should
generaliy net 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 lead to 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 linking these curves or joining them with straights between the
entry radius and the exit radius. 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 ta allow those vehicles that have
entered the roundabout side-by-side to continue side-by-side. Due allowance should
be made for increased width because of the curve, as set out in Table 15.3. For
island diameters of less than 30m, the width requirements should always be checked
using a relevant software package or wept path templates.
Paga 1 5 7
Kuweit Highwey Design Msnual
Table 15.3: Minimum Width of Glrculatlng Pavement
15.8
Entry Width
The relationship between entry width and capacity is highly significant. The most
effective way of increasing the capacity of an approach is by providing greater entry
width.
The Entry Width (e) is shown in Figure 15.4 and is measured from point A, where the
median side of the entry pavement meets the outer side of the circulating pavement,
to point B, perpendicular to the outer kerb.
Figure 75.4 also shows the Approach Half Width (v) which is measured between
points G and M, and which is used in capacity calculations, It is the width of the
pavement available to approaching vehicles prior to any widening.
$
WE-
Fi
: :'+
A Point of maximum entry deflection
at left hand and of Give Way line
e Entry width
v Approach half width
1!1
I
Effective flare length
Flgure q5.4: Average Effective Flare Length
It is good practice to add at least one extra lane to the number of lanes on the
approaching road, but as a general rule, not more than hrvo lanes should be added
and no entry should be more than four lanes wide. Each enZv lane should lead into a
corresponding allocation of road space on the circulating pavement. The practical
range for entry width is 6m to 15m, but for undivided roads, the upper limit should be
10.5m.
Page 1 5 4
Chepter 15
Roundabouts
-
The Average Effective Flare Length (I), as shown on Figure 15.4 is measured
between points C and F. The line DG is a parallel offset from the centreline (or edge
of median) AH at a distance of v. The line CF is a parallel offset from the kerbline t3G
at a distance of (e-v)12. Flare length I should not exceed loom, however, it should be
noted that beyond 40m,any expected extra capacity would be negligible.
There may be some cases, usually associated with low predicted flows, where
increased entry width is not operationally necessary. It is recommended nevertheless
that a minimum of two entry lanes be provided, as this gives greater flexibility in
dealing with abnormal flows, provides a passing facility in the event of vehicle
breakdown, and assist the manoeuvring of long*vehicles.
15.9
Entry Path Deflection
One of the most important safety checks is for vehicle path deflection on entry to a
roundabout. It is necessary to ensure that excessive speeds through the roundabout
cannot occur. For design purposes, the vehicle entry path should be such that the
radius of the tightest curve on the entry path does not exceed 100m (see Figure
15.5).
Figure 15.5: Entry Path Cuwature
15.9.f
Constructing the Entry Path
To define the entry path, the following assumptions are made:
The entering vehicle is 2m wide and takes the 'straight aheadmovement at a
four-leg roundabout and across the head of the T at a three-leg roundabout.
a
There is no other traffic on the approach and on the circulating pavement.
The driver negotiates the site constraints with minimum deflections,ignoring all
lane markings.
Page 1 5 9
Kuweif Highway Design MenW
Chapter 15
Roundabouts
The initial approach position for centreline of the entry path curvature (which must
be at least 50m before the Give Way line) is no closer than Im to the outer kerb
and no nearer than I m to the centreline of an undivided road or the inner kerb of
a divided road. (This ensures that all approach alignments are examined and that
no vehicle path can exceed the recommended maximum radius of curvature.)
The vehicle proceeds towards the Give Way line, and continues towards the
central island of the roundabout, with the centreline of its path never coming
closer than im to any kerb.
,
.
15.9.2
The centre line of the most realistic path that a vehicle would take in its complete
passage through the intersection, on a srnooth alignment, without sharp transitions
and meeting these assumptions, is then drawn to a scale not less than 1500 using a
flexible curve (or equivalent computer drafting techniques). Any reverse of curvature
in the vehicle path around the central island must be drawn so that there is no sharp
deviation between that curve and the entry curve. The exact path d r a m will be a
matter of personal judgment and the results should be examined for compliance and
consistency with the appropriate clauses in this Sedfon. Where path radii are close
to the permitted maximum of loom, more than one independent assessment of the
vehicle paths should be carried out.
Measuring the Entry Path Curvature
The entry path curvature is measured over the length of 20m in which the tightest
radius occurs, on the portion of the path in the vicinity of the 'Give Way' line (but not
more than 50m in advance of it). This is between points X and Y on Figure 15.5.
The tightest radius is measured by means of suitable curve Zempjates or an
appropriate computer technique.
1 5.9.3
Achieving Entry Deflection
One method for creating entry deflection on new schemes where there are no other
constraints is to offset the approach roads, as shown in Figure 15.6. This helps with
the overall design, reduces the size of roundabouts, minimizes land acquisition and
assists with the construction of 'easy exits'.
Figure 15.6: Staggered Approach Roads
Page 15-40
However, if is not good practice to generate entry deflection by sharply deviating the
approach roads to the left close to the roundabout and then to the right at entry.
w,,r
In urban areas, the restrictions on space available coupled with the turning width
requirements of large goods vehicles may necessitate small roundabouts which
s cannot provide sufficient entry deflection to the right by means of the central island
alone. In these cases deflection can be generated by means of enlargq trafiic
.islands or by means of mountable 'collars' as described in Section 15.6.
I l i
.
.
15.10.
Entry Angle
-ITI
.db
-, a+...:
,I# T,I
1
-
)I+;~J
-
be::
( ~ ~ l > ! ~ j 2 ~ f i t l
&
The entry angle (a) serves as a geometric proxy for the conflict angle between
entering and circulating streams. The method of measuring the entry angle is set out
-\, -,
[
in Figure 15.7.
rn
....
91') )U 1IU
p-rn-ril
.*a
-dP-,,
8 8
.
*
-5-,r
.
m ,r
@ = Entry angre
r = Entry radius
d
Figure 1S.7: Entry Angle
$, : it.
1 %
i-rQt:
f4 t l T t #
!x!
t, ;&' m':J
The line EF is midway between the outer kerb and the median line or the edge of
any median island. Where this curved line intersects the 'Give Way' line, the tangent
B'C is drawn. A'D' is the centreline of the circulating pavement. The entry angle (0)
is measured as the acute angle between the line B'C' and the tangent to A'D' at the
point of intersection between B'C' and A'D'.
The relationship btween entry angle and entry capacity is a weak inverse one; as
the angle increases, so capacity decreases slightly. However, care should be faken
in the choice of entry angle, because angles that are too high and angles that are too
low may both result in increased accident potential. The entry angle should if
possibleiie between 2 4 and 40°, with a figure of around 30° being the optimum.
Small entry angles force drivers into positions where they must either look over their
left shoulders or attempt a true merge using their mirrors (with the attendant
problems of disregarding the Give Way line and the encouragement of high entry
speeds).
Large enlry angles produce excessive entry deflection and can lead to sharp braking
at entries accompanied by 'nose to tail' accidents, especially in rural areas.
Kuwait Highway Design Menual
15.1 1
Entry Radius
The entry radius (r) is measured as the minimum radius of curvature of the outer kerb
line at entry, as shown on Figure 15.3. For some designs, the an: of minimum radius
may extend into the following exit, but this is not important provided that a half or
more of the arc length is within the entry region.
The optimum entry radius is 20m.
The minimum entry radius should be 6m (1Om if significant numbers of trucks are
anticipated).
Radii above 20m producing very little consequential increase in capacity.
Very large entry radii almost certainly result in inadequate entry deflection.
15.12
Gradients
It is good practice to keep longitudinal gradients within the range -2% to *2% at the
roundabout entries, around the circulating pavement and at the exits.
15.13
Exits
The principle of 'easy exits' should always be applied. A kerb radius of about 40m at
the mouth of the exit is desirable, but for larger, rural roundabouts, this may be
increased to suit the overall intersection geometry. In any case, the exit radius should
not be less than 20m or greater than 200rn.
At the beginning of an exit, its width, measured at right angles to the exit radius,
should allow far one traffic lane more than the number on the link downstream. For
example, if the downstream Fink is an undivided road with one lane in each direction,
the exit width should be the width of two lanes, and if the link is a four lane, divided
road, three lanes width should be provided on the exit. On an undivided road, this
extra width should be reduced on the outer edge in such a way that exiting vehicles
are not encouraged to encroach into the path of oncoming vehicles at the end of the
traffic deflection island. Narrowing should be achieved using a taper of between 1:$5
and 1:20, but if the exit road is on a right hand curve, it may be necessary to extend
the taper length and the length of the traffic defection island.
In exits leading to undivided roads, a minimum width of 6m should be maintained
adjacent to traffic deflection islands, to allow Zraffic to pass a disabled vehicle.
15.14
Visibility
The provision of good vision at roundabouts is an important factor, and adequate
visibility should be provided:
on the approach
totheleft
forward at the entry
on the circulating pavement
to any pedestrian crossing
15.14.1 Eye and Object Heights
Visibility to the left and across the central island of a roundabout should be
obtainable from a driver3 eye height of 4.05rn to an object height of 1.05n-1,and the
KuwH Hignway Design hdanuaE
envelope of visibility should extend to 2.4m above the road surface. All other
visibilities should be assessed in accordance with the envelope for Stopping Sight
Distance set out in Figure 4.1.
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 . l m above the pavement surface, and the envelope needs to be carefully checked
on sites where there are significant changes in gradient.
5.14.2 Obstructions within Visibility Envelopes
Signs, street furniture and planting should not be placed within the visibility
envelopes in such a manner that they obstruct visibility.
Isolated slim projections such as lamp columns, sign supports or bridge columns can
be ignored provided they are less than Q.5mwide.
The presence of pedestrians on sidewalks can impede visibility, and this should be
borne in mind when locating sidewalks in areas with high pedestrian activity.
15.14.3 Visibility on the Approach
On the approach to a roundabout, normal Stopping Sight Distance (SSD) applies, in
accordance with the appropriate design speed, as described in Chapter 4. The SSD
is measured to the Give Way line, as shown in Figure 15.8.
_
SSO
-- - - - ---,- +e-.
- -______-----+----
_ + + + _ _ _ _ _ _ _ _ - - - - - - - - - - - - -
- _ _ _ _ _ + _ _ _ _ - - - - - - - - - -
Divided Road
SSD
- --- -
A
-
--+-
_ _ +_ _ + _ _
-
---- m
---__I_
Undivided Road
Vehicle position centre d outer lane
Figure 15.8: Visibility on the Approach
Page 15-13
Kuwait H&hway Design Manual
Chapter $5
Roundabouls
3 5.14.4 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 centreline of the circulating pavement as indicated in Table
15.4 and shown in Figure 15.9.
Table 3 5.4: Visibility at Roundabouts
Inscribed Circle Diameter (m)
Visibility Distance (m)
--
140
Whole Intersection
>40-160
40
>60-S100
50
3 100
70
b. Half lane widlh.
carriageway over
which visibility shall be
obtained fram viewpoint d
Figure 15.4: Visibility to the Left from the Give Way Lfne
The area which should be able to be seen from the centreline of the inner approach
lane for a distance of 15m back from the 'Give Way' line, is as shown in Figure 15.10.
Page 1514
Chapter 15
Roundabouts
a. Visibility distance for
circulating tramc.
camiageway over
which visibility shall be
obtained from viewpoint 4
b. Half lane width.
I
Figure 95.10: Visibility to the Left from 15m behind the Give Way Une
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-falls and longitudinal grades does not restrict visibility.
Excessive visibility at entry, or intervjsibility between adjacent entries, can result in
approach and entry speeds greater than those, which are desirable for the
intersection geometry. The selective use of landscaping may be helpful E
n preventing
drivers approaching a roundabout from seeing the previous entry mouth until they are
15m from the Give Way line. Restricting the forward visibility along the approach
alignment so that it equals the SSD appropriate for the design speed of the approach
(which can be achieved using combination of alignment and landscaping techniques)
can bring safety benefits.
15.14.5 Foward Visibility at Entry
Drivers of all vehicles approaching the Give Way line should be able to see the full
width of the circulating pavement ahead of them for a distance 'a' (measured along
the centreline of the circulating pavement appropriate to the size of the roundabout,
as indicated in Table 15.3. The visibility should be checked from the centre of the
outer lane at a distance of 15m back from the Give Way line as shown in Figure
15.11.
Page 15-15
Kuwaft Highway Resign ManuaE
a. Visibitii distance for
circulating traffic.
b. Half lane width.
Area of circulatory carriageway
over which visibility shall be
obtained from viewpoint a
Figure 15.$1: Forward Visibility at Entry
15.14.6 Circulatory Visibility
Drivers of all vehicles circulating on a roundabout should be able to see the full width
of the circulating pavement ahead of them for a distance 'a' appropriate to the site of
roundabout, as given in Table 15.3. This visibility should be checked from a line 2m
outside the central island, as shown in Figure 15.12.
obtained from viewpoint 4
a. Visibiliy distance.
Figure 15.12: Circulatory Visibility
Page 1516
Cheplrtr 15
Roundabouts
It is oflen useful te improve the visibility of central islands by the use of landscaping,
but unless this is done with care the planting may obstruct circulating visibility.
15.14.7 Pedestrian Crossing Visibility
Roundabouts sometimes have pedestrian crossings across one or more legs.
Drivers of all vehicles approaching such a pedestrian crossing across an entry should
be able to see it from at least a distance equal to the SSD (as set out in Table 4.1 of
this Manual) appropriate for the design speed of the approach link.
Where a crossing is located on an exit (and is within 50m af the point at which
vehicles leave the circulating pavement), drivers of all vehicles at the Give Way line
of the previous entry should be able to see the full width of the crossing, as shown in
Figure 15.73. It is recognized, however, that in some urban areas, adjacent
development may prevent such a visibility splay being achieved.
b. Half lane width.
minimum area over which
unobstructed visibility is
required from view point 6
when crossing is within
50m of exit.
Figure 15.13: Visibility to Pedestrian Crossings at Next Exit
15.15
Crossfall and Drainage
Steep grades should be avoided on roundabout approaches, Where this cannot be
accomplished, they should be flattened to a maximum of 2% before entry.
Crossfall and longiludinal gradient combine to provide the slope necessary to drain
surface water from the pavement. Thus, the value and direction of the greatest slope
(resulting from the combination of crossfall and gradient) should always be taken into
account when considering drainage.
Generally speaking, superelevation is provided in order to assist vehicles when
travelling round a curve. Its values, when used, are equal to or greater than those
necessary for surface water drainage. Superelevation is not required on the
circulating pavement of roundabouts irrespective of their size, whereas crossfall is
required so that surface wafer can drain effectively. On the approaches and exits of
roundabouts, however, superelevation can be introduced to assist drivers in
negotiating the associated curves.
Page 15-17
Kuwait Highwoy Design Manual
Chapmr f5
Roundabouts
Crossfall on the circulating pavement can be inwards (towards the central island), a
normal crown profile, or outwards, Inward crossfall may be appropriate on very large
roundabouts, where circulating speeds are high, but elsewhere the fail should
normally be normal crown or oufwards.
To provide comfort and to enable drivers to remain in control, the maximum algebraic
sum of opposing crossfall grades at a crown line should not be greater than 5%.
Normal crossfall for drainage on roundabouts should not exceed 2%. To avoid
ponding, longitudinal edge profiles should be graded at not less than 0.5%.
The application of proper grades and crossfalls may not necessarily ensure
satisfactory drainage, and therefore, the correct siting and spacing of gullies is critical
for emcient drainage.
15.1 5.1 Entries
Curves may be tightened and the degree of superelevation should be appropriate to
the speed of vehicles as they approach the roundabout. It should not, however,
exceed 5%. In cases where superelevation is used, it should be reduced in the
vicinity of the Give Way line to the crossfall required merely for drainage, since with
adequate advance signing and entry deflection, speeds on approaches should be
reducing.
15. 5.2 Circulating Pavement
Values of crossfall should be no greater than those required for drainage. On larger
roundabouts, it may be beneficial for the crossfall to be inwards to assist vehicles.
A normal crown profile can be achieved in the following way. A crown line is formed
where the enty and exit pavements meet a conflicting inward crossfall on the
circulating pavement. This crown line can either join the end of the traffic deflector
islands from entry to exit (as shown in Figure 15.1 31, or can be arranged to divide the
circulating pavement in the proportion 2:1, internal to external.
The conflicting crossfall at the crown lines have a direct effect on driver comforf and,
if excessive, can be a significant contributory factor in load shedding and truck
rollover accidents. The maximum permitted algebraic difference in crossfall is 5%,
and lesser values are desirable, particularly for roundabouts with smaller ICDs. Care
needs to be taken during detailed design and at the construction stage to ensure that
a satisfactory pavement profile without sharp changes in crossfall is achieved. A
rounded crown is essential. With smaller lCDs it may be more appropriate to apply
outward crossfall across the full width of the circulating pavement.
15.15.3 Exits
Superelevation appropriate for the horizontal alignment should be provided where
necessary to assist vehicles to accelerate safely away from the roundabout.
However, as with entries, cross falls adjacent to the roundabout should be those
required for sutface water drainage. If the exit leads into a left hand curve,
superelevation should not be introduced too quickly and to such an extent that
vehicles tend to encroach into an adjacent lane.
15.16
~i~ht-turning Roadways
Segregated right turn lanes can provide an improved service to vehicles intending to
leave a roundabout at the first exit. Figure 15,14 shows a roundabout that
incorporates right-turning roadways.
Page 15-18
Figure 15.14: Segregated Right Turn Lane
The operation of the right-turning roadway can be impaired by traffic queuing to use
the roundabout itself, and the designer should ensure that entry to the roadway is
clear of likely queuing traffic.
The use of right-turning roadways in areas where pedestrians are expected to cross
should be considered very carefully. Crossing should only be permitted if adequate
sight lines are available and if the island is sufficiently wide to accommodate the
anticipated peak number of pedestrians. If these criteria cannot be met, pedestrian
fences should be introduced to prevent crossing, or the right turning roadway should
be omitted altogether.
Right turning roadways should be designed so as not to induce high speeds. The
design speed should not exceed that of either of the roads, and any desired speed
reduction should be achieved at the entry to the roadway rather than within it.
Forward visibility should be the appropriate SSD for the selected design speed.
Kuwait Highmy Design Manual
Cheplar15
Roundabouts
The width of the right turning roadway should be in accordance with Lane Wdths on
Right-turning Roadways in Chapter 14. Because tight turns can still be made by way
of the roundabout proper, the presence of a disabled vehicle on the right turning
roadway should not cause significant problems, and the designer should choose
whether or not to cafer for this occurrence.
,
The merging between the vehicles from a right turning roadway and the other
vehicles exiting the roundabout should take place within §Om of the roundabout,
while speeds are still comparatively Sow. Ideally there should not be a forced merge,
and Give Way operation may be necessary. Tapers should be designed in the same ,
manner as at major 1 minor intersections (see Right Turning Roadway terminals in
Chapter 14).
5.17
Safety at Roundabouts
Roundabouts generally have lower accident rates than signalised intersections of
similar capacity. The severity of accidents at roundabouts is also considerably lower
than at other types of intersectian.
The factor that has the greatest influence on safety at roundabouts is vehicle speed,
at either the entry or within the roundabout. Geometric features that can have a major
contributory effect in causing excessive entry and circulating speeds are:
Inadequateentry deflection
A very small entry angle that encourages fast merging manoeuvres with
circulating traffic
Poor visibility to the "ive 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
fatward 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 contribute significantly to
safety, allowing the intersection to be lei7 clear for following road users. This can
be achieved by adopting smaljer kerb radii on entry and larger kerb radii en exit.
Care should be taken with the choice of kerb type for the central island of a
roundabout. A safety problem can arise where profile barriers are used. They can be
a danger to vehicles over-running the entry. Profile barriers are designed for impact
at a glancing angle and more direct impacts can result in loss of control or
overturning of vehicles, unless the approach speed is low. Where profile barriers are
used on approaches, pedestrians should be prevented from crossing the road.
The Traffic Capacity of Roundabouts, RM Kimer, Transport and Raad Research
Laboratory report hR 942, Crowthorne, 1980
Design Manual for Roads and Bridges, The Highways Agency, Department of
Transport, Local Government and the Regions, UK Government, various dates
Page 15-20
Kuwaif Highway Design Manual
16.1
General
On a divided primary road, it is often possible to provide access to secondary roads
by adopting a "right-in, right-out" intersection arrangement. However, access is
denied to traffic travelling on the opposite carriageway. In most cases, this difficulty
is resolved by allowing U-turns to take place at the intersections tying before and
after the secondary road. In other cases, the solution is to provide for left turns
through the median, directly into the secondary road.
Serious consideration should be given to providing movements at conventional
junctions before opting for a U-turn facility.
The provision of U-turn facilities is therefore only appropriate in a limited number of
situations. U-turns should only be provided for one of the following reasons:
To accommodate a minor traftic movement beyond an intersection that is not
othewise catered for at that intersection, and where the next available
intersection is some way downstream.
To remove U-turning vehicles in advance of an intersection, if their presence
would hinder the safe and effective operation of that intersection.
Safety is a major concern at all intersections and U-turns can be particularly
hazardous, especially on high volume, high speed roads, The provision of a U-turn
facility must be carefully considered against the potential for accidents before
deciding whether to incorporate a U-turn into the design.
U-turn facilities should not be provided on Special Roads, as this movement should
be catered for within grade-separated interchanges.
'U-turns are not suitable For roads with more than three lanes in each direction.
U-turns should only be provided on Primaty Roads with the approval of the MPW and
Kuwait Municipality.
The following safety issues are of particular importance.
1. Entry to the U-turn: Vehicles enter the U-turn facility from the lane nearest to the
median, which normally carries the fastest moving vehicles. Deceleration should
take place clear of this traffic in a dedicated lane within the median. Adequate
median width and deceleration length must therefore be provided.
2. Stacking within the U-turn lane: Vehicles queuing to make U-turn manoeuvres
should be clear of the through traffic lanes. There should be sufficient length
within the U-turn lane for vehicles to decelerate and to stop at the back of any
queuing vehicles, even at peak times. If the volume of traffic making the U-turn
requires traffic to queue in the fast lane of the mainline, then a conventional
junction should be provided.
3. Lane discipline within the U-turn lane: At peak times, there is a tendency for
drive,rs to decelerate in the inner lane alongside the queue and to then force their
way in at the front of the queue. This practice is both anti-social and dangerous,
and closes down one through lane (thereby reducing capacity on the mainline).
The layout of the U-turn facility should discourage this practice.
4. Crossing of the opposing traffic: Drivers in the U-turn facility need an
unobstructed view of the approaching traffic, so that they can judge gap
acceptance or rejection. The vehicle should be at right angles to the approaching
traffic when waiting to cross the opposing flow. Lighting columns or trees in the
Page 1 6 1
Kuwait Highwey Dasign Manual
median of a curved alignment may obstruct sight lines. The U-turning driver must
be able to see and be seen.
5. Joining the main traffic stream: When the speed of approaching vehicles is high,
there is little latitude for error. The driver making the U-turn can choose to turn
very tightly into the inner lane or to swing more widely into the outer lane. The
approaching driver on the main line must anticipate that action and make any
lane-changing manoeuvre necessary, should the U-turning vehicle have chosen
too short a gap.
The width of the road should be sufficient that relevant design vehicle can make the
turn without encroaching beyond the outer edges of the pavement.
,
,
In some
instances, this leads to widening of the median, or, where this cannot be achieved,
the adoption of 'local bulbing' on the far side of the U-turn.
The median should be wide enough to provide a protected lane for U-turning vehicles
and an adequate inner radius for the manoeuvre.
U-turns are frequently associated with weaving movements, particularly where a pair
of U-turns is provided in conjunction with a right-in, right-out intersection. Weaving
capacity should always be checked to determine the weaving length required.
Wherever a U-turn facility is to be provided, the reciprocal U-turn should also be
provided. If a minor road has only right turns in and out, a pair of U-turns should be
provided in order to cater for the left turns, both in and out. This helps to present a
consistent layout to drivers.
U-turningvehicles follow paths that are close to the physical limits for the operation of
the vehicle. The layout should be checked, using a vehicle template for the design
vehicle, to ensure that swept paths remain within the travelled way.
Figure 16.1 shows the elements that make up the standard U-turn facility.
Channefisingnose width
7
1
Median width
figure 16.1: Elements 05 U-turn
Page 16-2
Kuweil Highway Design Manuel
Chepler f 6
U-Turns
16.2
Entry Taper
The entry taper is the length over which the U-turn lane develops from zero to its full
width. Table 1 8.1 gives the taper length, which depends upon design speed.
Table 16.1: U-turn Entry Tapers
At design speeds of 80kmlh and above, the change in alignment at both ends of the
entry taper should be smoothed using large radius curves, typical radii being in the
range 200m to 600m.
16.3
Deceleration Length
Minimum values for deceleration lengths are set out in Table 16.2.
Table 76.2: U-turn Deceleration Length (m)
Up-gradient
Design
Speed
(krnlh)
Greater Ihan %
'
(m)
60
75*
85*
95'
70
90"
105*
120*
80
115
130
145
90
135
155
165
100
160
185
210
110
185
21 5
245
120
215
250
285
Gradient
Level to ~ 4 % (m)
Downgradient
Greater than 4%
Iml
* On urban roads with intersection spacing less than 400m, see Section 18.4 for reduced standards.
Page 16-3
Kuwffit Hahway Design Manual
Chapter 16
U-Turns
36.4
Queue Length and Protected Length
The queue length is dependent on the volume of traffic wishing to make the U-turn
manoeuvre and the opposing flow on the main line. If the U-turn is signalised, the
timing of green light will dictate the queue length. In both cases, advice should be
sought from a traffic engineer.
Part of the queue length should be protected by a channelising nose, This should
extend over one third of the maximum queue length, subject to a minimum protected
length of 15m and a maximum of 30m.
On urban secondary roads, it may be impractical to provide full standard U-turn
facilities. Under heavy flow conditions, much of the deceleration will occur in the
through lanes. The length of the U-turn lane should be taken as the longer of either
the queue length, to cater for conditions when the queue is at a maximum and
speeds are low, or the deceleration length, to reflect the situation under light traffic
conditions when there is no queue present. The protected length should be the
minimum value of 4 5m.
16.5
Channelising Nose Width
The channelising nose, which is delineated by painted kerbs and preceded by retroreflective road studs, should normally be 2.0m wide. This may be reduced in urban
areas. The minimum width of around 0.3m is achieved by laying kerbs back-to-back.
16.6
Reduced Median Width
This width allows vehicles at the head of the U-turn to begin to turn while protected
by the median and should normally be 5m or more. In difficult locations this may be
reduced to a minimum of 2.0m (in rural areas) or 1 .Om (in urban areas).
"t.7
U-turn Lane Width
The standard width for a U-turn lane (between kerbs) is 3.7rn. The resultant width of
the unprotected part of the U-turn lane therefore lies within the range of 4.0m to
5.7rn.
16.8
Median Width
Combining these elements indicates that the desirable median width required is
10.7m or more, and the minimum is 5.0m. This is reflected in the standard crosssections, which provide a median width of at least 6m, except in restricted situations,
where U-turns should not be provided.
16.9
Mouth Treatment
The mouth of the U-turn lane should accommodate the swept paths of the design
vehicles used. Where a U-turn is designed to handle vehicles larger than cars,
greater width, by means of an over-run area of a different colour and texture from the
general travelled way, should be provided. An over-run area should be block paved
and edged with a kerb laid flat, with an upstand of 50mm above the adjacent
travelled way.
The minimum inner kerb radius at the U-turn mouth is 4.0m. The minimum outer
kerb radius is 14.0m for all vehicles, or 11.Om for cars only.
Page 16-4
KUWBI?HDhway Design Manual
Chapter I 6
U-rums
16.1 0
Summary
The values quoted in Sections 16.4 to 16.9 are summarized in Table 16.3 below.
Table 16.3: Summary of Various Geometric Factors
On some urban roads(see 16.4)
16.1
U-turn Diameter
The types of vehicles using the facility determine the U-turn diameter, and the
recommended minima are given in Table 16.4.
fable 16.4: Minimum U-turn Diameter
Situation
Minimum
Diameter (m)
Cars only
15
All vehicles
28
-
It can be seen that the space required for a general U-turn (28m) is greater than the
desirable minimum U-turn lane width (3.7m) plus the desirable minimum reduced
median width (5m) plus the typical width of a three-lane road ( 7 1.71~11,
which together
amount to only 20.4m. Similarly it is not possible to provide a car-only U-turn to
absolute minimum standards (3.7117+ 1m + 7.4m = 12.1 rn) on a two-lane road.
To prevent vehicles over-running the edge of the pavement or colliding with the kerb
under such circumstances, a wider median should be provided. Where this cannot
be achieved, local bulbing should be considered.
Page 16-5
Kuw& HQhway Design Manual
16.1 2
Median Widening
Where medians are widened in order to accommodate U-turns, the two pavements
should be designed independently, in accordance with the horizontal alignment
The widening can be applied
standards appropriate to the design speed.
symmetrically. Alternatively, one of the pavements can be maintained on its original
alignment.
16.13
Local Bulbing
Local bulbing allows vehicles making U-turn manoeuvres to pull over beyond the
edge of the travelled way.
Two local bulbing arrangements are shown in Figure 16.2. Layout A is intended for
Secondary Roads and is designed to provide additional road space to accommodate
the swept path of the U-turning vehicle. Layout B is intended for Primary Roads and
allows the U-turning vehicle to move completely into an auxiliary outer lane, and then
to accelerate and merge with the outer through lane.
A: Secondary Roads
€3: Primary Roads
Figure 16.2: Local 8ulbing Payouts
The bulb area in Layout A should be paved in a visibly different material (for
example, red brick pavers) so that drivers on the main line do not perceive the area
as either part of the through pavement or as a lay-by. The bulb area should be
separated from the rest of the travelled way by a kerb laid flat, with an upstand of
50mm.
In Layout 5, the bulb area may be denoted by colovred surfacing or painted
markings, but shouId be a contiguous part of the adjacent pavement or shoulder.
Dimensions are given in Table 16.5.
Page 1 6 4
Kuwait Highway Design Manual
Chapter 16
U-Turns
-
Table 16.5: Local Bulblng Recommended Dimensions
Radius (m)
Road Class
Layout A
Secondary Roads
Layout B
Primary Roads
Special Roads
I
Auxiliary Length (m)
Merge Taper
(11
(2)
(3)
(41
4
nfa
nla
1:s
nfa
8
50
1 :20
Grade separation should be provided
The Median Gap should be determined by the swept paths of the design vehicles to
be accommodated.
The Bulb Offset should be determined as follows.
For Layout A, the necessary U-turn diameter, up to a maximum offset of 4m. If
this is insufficient, then the median should be widened.
For Layout B, 4m (absolute minimum) to 8m (maximum). The auxiliary lane may
be reduced to 4m downstream of the manoeuvring area, and should continue at a
constant 4m width until the merge taper. Swept paths should be checked, and if
the arrangement described is insufficient, the median should be widened.
Page 16-7
Kuwea Highway Design M e n d
7.1
General
Signalisation uses the principle of time segregation to eliminate conflicting
movements and increase capacity at an at-grade intersection. Although it can be
applied to existing unsignalised intersections, the best results are obtained when an
intersection is designed from the outset to operate under signal control.
The details of the design depend heavily on the forecast traffic movements and
volumes, and the phasing of the signal operation will be similarly influenced. The
designer should therefore ensure that liaison with the traffic engineer takes place at a
very early stage in the design process, so that the operational needs can be properly
taken into account.
The purpose of this Chapter of the manual is not to set out the principles of signal
control and operation, for which the reader is referred to publications such as the US
Highway Capacity Manual', the US Manual of Uniform Traffic Control ~ e v i c e sand
~
the UK Design Manual for Roads and !3ridges3, but to provide guidance on the
geometric considerations which should apply to intersections operating under signal
control.
q7.2
Applicability of Major I Minor Intersection Principles
In general, the guidance given for major J minor intersection layout applies equally to
signalised intersections, with the following qualifications:
Sight triangles need to be provided so that the intersection operates safely even if
the signals fail. Where one route is clearly the mare important, then majorIminor
sight triangles are applied to vehicles on the minor approaches in the normal
manner. If all the intersecting legs are apparently of equal priority, then the sight
triangle should be checked at all approaches.
Lane widths are sometimes reduced at signals, but the minimum width should be
3.0m.
17.3
Specific Requirements at Signalised Intersections
Signal indications show the driver whether or not he should proceed, and it is
important that the signal heads should be clearly visible to the approaching driver
and ta the driver who has stopped as instructed. The designer is referred to the
Kuwait Traffic Signs Manuala.
Signals are usually located forward of the stop line. Double-headed signals may be
required where traffic lanes are being separately signalised. Overhead signals,
mounted on cantilevers or gantries, may be provided.
17.4
Width of Medians
Care should be taken to ensure that medians are wide enough to accommodate any
necessary signals and to provide a minimum clearance of 0.3m between the edge of
the signals and the edge of the travelled way. Table 17.1 gives details.
Page 17-1
Kmv8II Highway Design Manuel
Chapter 17
Signelised Intersections
Table 17.2: Minimum Median Width at SIgnalised lntersectiona
(to accommodate signal heads)
Situation
Minimum Median Width (m)
Single-headed signal
1.5 .
Double-headed signal
2.0
These minima are adequate to accommodate the occasional pedestrian who has
been unable te cross both halves of the road in the time available and so needs to
wait in the median.
However, if the signal phasing requires pedestrians to cross in two stages, or if no
specific pedestrian phase is provided, a wider median should be provided.
Consideration should also be given to the provision of a "sheep pen" arrangement,
such as shown in Figuse 17.1 below. This layout minirnises the risk of pedestrians
continuing beyond the median on the erroneous assumption that they have right-ofway over traffic on both halves of the road. The layout also provides a safer waiting
area in the median.
Pedestrian Fence
0.5m (Min)
1
t
0.5m (Mln)
Figure 17.1: "Sheep Pen" Arrangement for Pedestrians at Signals
(where crossing occurs in two separate stages)
Table 17.2 gives the minimum median width required to accommodate pedestrians in
straight across (i.e. conventional) and "sheep penn layouts.
Table 17.2: Minimum Width of MedFan at Signalised Intersections
(to accommodate waiting pedestrians)
Layout
Straight across
' "Sheep Pen"
Page 17-2
Mlnlmurn Median Wtdth (m)
2
3.5
'
Kuwail H b h w ~ yDesign Manual
Chapter I?
SignaIised Intersections
In areas where there is vety high pedestrian activity, the total area available to
pedestrians should be capable of accommodating the highest number predicted to
occur during a signal cycle. As a design guide, use 0.6m2of clear space per person.
17.5
Size of Islands
Similar considerations apply to the size of channelising islands within an intersection,
so that signal equipment (and signs) can be properly located and pedestrians can be
safely accommodated. The minimum size for a triangular island, regardless of these
factors, should be 6m2.
17.6
Vehicular Swept Paths
There should be adequate provision of road space to accommodate the selected
design vehicle(s), and this should be checked using computer software or the
relevant templates. Particular care should be taken where two or three lanes of traftic
turn together. In such situations, more than the minimum road space should be
provided.
The layout and space requirements for multiple-lane turning movements are a direct
consequence of the physical dimensions of the intersection and the radii of the turns.
Accordingly, no standard layouts and dimensions can be given, and the importance
of undertaking a proper analysis of swept paths using templates or software is again
ernphasised.
On right-turning roadways, the information in Table 14.6 should be adopted.
17.7
Location of Pedestrian Crossing Facilities
There are two main criteria for the location of a pedestrian crossing within an
intersection.
Firstly, the crossing should be sufficiently far foward of the stop line that crossing
pedestrians do not feel intimidated by the presence of stationary traffic awaiting
the green signal. A clear zone of 2m from the stop line to the crossing can give
comfort to pedestrians.
*
Secondly, the crossing should be separated by sufficient distance from any
parallel moving traff~cthat a reasonable level of safety can be ensured. Given
that the median nose is set back by a minimum of 0.5m from the edge of the
travelled way, a further setback of 1.5m gives a pedestrian clear zone of 2m from
traffic that is moving while they cross.
Pedestrian crossings of right-turning roadways need to be designed with
considerable care, the following points being important.
Pedestrian crossings of multiple-lane turning roadways should be signalised.
Pedestrian crossings of single-lane turning roadways should be considered
where large pedestrian numbers, lengthy pedestrian delays or excessively
hazardous crossing would result.
At a signalised crossing, the primaty signal must be clearly visible to approaching
drivers, the minimum sight distance being the SSD for the design speed of the
approaching road.
At. an uncontrolled crossing, pedestrians need an adequate view of approaching
traffic so that they can accurately judge the gaps and cross in safety. The minimum
Page 17-3
Safe Crossing Sight Distance(SCSD)from the pedestrian to the approaching vehicle
is set out in Table 17.3.
Table 17.3: Safe Crossing Sight Distance for Uncontrolled Pedestrian Crossing of
Single-lane Right-turning Roadway
17.8
Width of Pedestrian Crossing Facilities
Crossings should normally be 3m in width and should accommodate up to 600
pedestrians per hour. Where higher levels of pedestrian activity are predicted, the
width should be increased as set out in Table 17.4. Crossings wider than 6.0m
should not normally be provided.
fable 17.4: Width of Pedestrian Crossings at Signalised lntenectiona
d7.9
Design Flow
(pedestrianstmin)
RecommendedPedestrian
Crossing Width (m)
up to 10
3.0 (minimum)
12
3.6
15
4.5
20 and above
6.0 (maximum)
Designing for Queue Lengths in Left-turning Lanes
The traffic engineer should provide estimates of the average numbers of left-turning
#vehiclesper cycle of the signal operation in the design peak period in order to
calculate the required storage length. As a general guideline, a minimum storage
length of 120m should be provided.
17.10
Signalised 'Roundabouts
It is possible to improve the operation of roundabouts that are prone to 'locking up' by
the introduction of signals. The design of the signal phasing is critical to the operation
Page 1 7 4
Kuweil Highway Design Menu81
Chepkr 17
Signalised Intersections
and the traffic engineer will need to model the roundabout using a relevant computer
simulation s o h a r e package. Additional useful guidance is available from the UK
Transport Research ~aboratory'. The outcome of the traffic engineer's study may
indicate that geometric modifications would be beneficial. Modifications could include
widening of the external approaches and rationalisation of the layout and pavement
markings on the circulating pavement.
Signalised roundabouts should not be selected for new intersections as they are very
sensitive to traffic volume and are difficult to modify.
17.1 1
U-turns at Signalised Intersections
Many of the considerations set out in Chapter 16 can be applied directly to U-turns at
signals. The designer should decide at the outset whether U-turns are to be
permitted, and if so, whether trucks are to be accommodated. Alternatively, provision
of a free-standing U-turn facility in advance of the intersection should be considered.
Local bulbing is dealt with in a different manner at signals and recommended
arrangements are shown in Figure 17-2and Figure 47.3. The following points should
be noted:
It is rarely necessary to provide local bulbing for buses and trucks. The pavement
should be designed to accommodate the relevant swept path (U-turn diameter
28m).
Local bulbing f ~ private
r
cars is likely to be required only at signalised
installations with a narrow median and two exit lanes. In such instances the
required U-turn diameter of 15m cannot be achieved.
The paved width of the local bulbing should be designed to provide the required
TJ-durn diameter, but should be no wider than 4m. The area should be paved in a
contrasting material (for example red block paving) and bounded by a kerb laid
flat, with an upstand of 50rnrn.
\A
'LKerb Laid Flat
I
\-
Upstand Kerb
Block Paved Area
Figure 47.2: Widening for U-turns at Signalised Intersections
{with right-turning roadway)
Page 17-5
*:
I:,
'12-
'
-P
-(s.:-c:;. -.I:
I
-
?E*57?)
S
' yi1-211 t&z?ELTk?IZI %TI ' X Y N I F - 2
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=Ftl
T ?C f W
:
,
L ~:':&iuc IS: i : i m rixk14,
h&i;- h 1 k . M ;jlh11231;14. * j ~ w T miwhiL~:r;P
.i,*~:-.-I?l~!
a~fir~
W
i.
&I ,.v,lW
.'
k
*-eb&-*
1 l,i~,
+: -z
j.-,:
---------------.
..I+.
i -:
,"I
Block Paved Area
i
a
ut
urn
Figure 17.3: Widening k r U-turns at Slgnalfsed Intersections
(wrth no right-turning roadway)
' Highway Capacity Manual, Transportation Research Board, 2000
Manual on Uniform Traffic Control Devices, Millennium Edition,
US Department of
L r ) w . 7
Transport, 2001
Design Manual for Roads and Bridges, The Highways Agency, Department for
Transport, Local Government and the Regions, UK Government, Various dates
Kuwait Traffjc Signs Manual (Chapter Q), 1988
q
4-71 IF-?
'
l . q . W + l
c1
Use of TRANSYT at Signallsed Roundabouts (Research Repott 274), Transport
Research Laboratory, Crowthome, UK, 1990
t
:
t
'3-
Kuweit HigRwey Design Manuel
Chapier 18
Grade Separetbns end fnterchenges
18
GRADE SEPARATIONS
AND ~NTERCHANGES
18.1
Introduction
This section covers grade separated Interchanges, provides overview of common
types, describes elements of interchanges, and design requirements for each type.
Grade Separations are used to enable two roads to cross each other without
interconnection, using a bridge or underpass.
Fully Grade-separated (or Free Flow) Interchanges are used to vertically separate
some or all of the conflicting streams of traffic, using one or more bridges or
underpasses. Conflicts are eliminated, leaving only merging and diverging
movements, which occur at ramp terminals.
The following factors determine the need for grade-separated interchanges.
(a) Design Designation
When a road is designated to have full access control, grade separation is warranted,
with interchanges at all intersecting roads. Interchanges are the only type of
intersection provided on Special Roads, regardless of traffic volume considerations.
This is to ensure a consistent standard of provision for the users of these longerdistance facilities and to provide the maximum level of safety appropriate to the
higher operating speeds.
(b) Reduction of Intersection Congestion
Grade separations are used when an at-grade intersection is subject to greater
congestion than others along its route. On Primary Roads, interchanges are
appropriate where levels of conflicting traffic are high, but it should be noted that
uniformity of intersection type on this class of road is unimportant. Interchanges will
rarely be warranted on toads of a lower class than Primary Roads.
(c) Safety Improvement
Grade separations are used when a high number of serious or fatal accidents occur
at a particular at-grade intersection. They are only used when cheaper safety
measures are not possible.
Grade separation may offer a more cost-effective solution than an at-grade
intersection in a hilly terrain.
(e) Road User Benefits
Cast-benefit analysis may indicate the provision of an interchange that considerably
reduces delays.
{fj Traffic Levels
An Interchange is warranted where design flows are greater than the capacity of an
at-grade intersection. Lower flows may also be sufficient to justify one, particularly if
the volume of cross traffic is significant.
18.2
Types of Interchange
Table 18.1 shows the different types of interchanges:
Kuwafl Highway Design Manual
Chapter 18
Grade Sepemtim and Intefchanges
Table 18.1: Types of Interchange
Number of
L V
Number of
Bridges
3-leg
Single
Free Flow Interchanges
Trumpet ( 1 d2.j)
Half Cloverleaf (18.2.2)
Other Interchanges
(Some At-grade Elements)
3-leg Compact (I8.2.4)
Multiple 3-leg Direct (1 8.2.3)*
Partial Cloverleaf (1 8.2.8)
4-leg
Single
Cloverleaf (18.2.5)
I
tvlultiple
4-leg Direct (18.2.6)
4-leg Hybrid (1 8.2.7)
4-leg Compact (18.2.9)
Diamond (1 8.2.10)
Dumbbell (18.2.11)
Grade-separated Roundabout (1 8.2.12) ,
The advantages and disadvantages of each type of interchange are set out in the
following sections.
Interchanges can be designed to cater for more than four legs. In such cases,
interchanges should be arranged to cater for the unique circumstances that exist.
Elements within the interchange should conform to relevant guidance given in this
Chapter.
18.2.1
Trumpet Interchange
A: Left-hand trumpet
B: Right-hand trumpet
C: Preferred left-hand trumpet with skew brFdge
Figure 18.q: Trumpet Interchange
Page 18-2
Kuwait Highway Design Manuel
Chapter 76
Grade Separatbns and Interchanges
Arrangement (A) depicts a left-hand trumpet, while arrangement ( 0 ) shows a righthand one. There is no straight-ahead escape route in either layout for a driver
approaching at speed up the stern af the T, often over a crest curve. Arrangement
(A) is slightly preferable in that vehicles have a larger radius curve to negotiate.
Arrangement(C),which is a lefl-hand trumpet, improves on (A) by providing an even
greater radius for the left-hand curve termination of the route approaching up the
stem of the T, although at the expense of a tighter loop for vehicles leaving the
mainline.
Table q8.2: Advantages and Disadvantages of aTrumpet Interchange
Advantages
Requires only one bridge.
Provides relatively high-speed, direct or
semi-direct links for all movements.
Layouts are simple to sign.
Moderate land-take.
Exit precedes entry, sa no weaving
movements.
Disadvantages
Right-hand trumpet (B) unsuitable for
termination of a high-speed route; Lefthand skew trumpet (C)may be
acceptable.
U-turning by emergency and
maintenance vehicles not possible.
I
18.2.2
Half Cloverleaf Interchange
A: Simple
B: W3tI-i C-D road
Figure 18.2: Half Cloverleaf Interchange
The half cloverleaf is a 3-leg Interchange, but has little to commend it over the
trumpet interchange. It introduces unnecessary weaving of the South to West and the
East to South movements. Its sole advantage is the ability to allow the intersecting
road to be extended Northwards at some future date.
Page 18-3
Kuwait HIghwey Design Manuel
Chapter $8
Grade Separations end Interchenpes
Table 18.3: Advantages and Disadvantages of a Half Cloverleaf Interchange
Advantages
Provides moderate-speed, direct or
semi-direct links for all movements,
Layouts are simple to sign.
Only one bridge required.
Moderate land-take.
Permits future expansion into 4-leg
interchange.
Provides U-turning for emergency and
maintenance vehicles approaching on
the stem of the T.
18.2.3
Disadvantages
Not suitable for the termination of a high-
.speed route.
introduces significant weaving
movements. Arrangement (B) with the
link road is preferred, but weaving still
exists.
U-turning not possible for vehicles on the
mainline.
3-Leg Direct Interchange (Delta)
A: Fully conventional
C: Partially conventional
B:Fully conventional 3-level
D: Unconventional
* Unconventional: diverge right to travel left
? Unconventional : mainline turns through 90"
Figure 18.3: 3-leg Direct Interchange
Arrangement (A) is the conventional layout. Traffic on the mainline leaves by a
conventional ramp located on the right side of the road and trafk joining the mainline
does so from the right. Traffic approaching the mainline along the stem of the T
Page 1 8 4
'
Kuwait Highway Design Manual
Chepler l 8
Grede Seperaihs and Interchanges
diverges to the right if wishing to travel to the right along the main line, and similarly
to the left if travelling left.
Arrangement (B) is a conventional layout, but on three levels.
Arrangement (C)is somewhat unconventional, in that trafic approaching along the
stem of the T diverges to the right to travel left along the mainline, and vice-versa.
Such an arrangement might be considered appropriate where there is a heavier flow
in the SE quadrant than the SW quadrant of the intersection, but where both these
flows are exceeded by the through flow on the mainline.
Arrangement (D) is unconventional in that the mainline is designed to turn through 90
degrees in the SE quadrant. This layout could be appropriate in circumstances where
the flow in the SE quadrant is dominant and the flow in the SW quadrant is lowest,
Table 18.4: Advantages and Disadvantages of a 3-leg Direct Interchange
Advantages
Provides high-speed, direct links for all
movements.
Conventional layouts are simple to sign.
Suitable for the termination of a highspeed route.
No weaving movements.
18.2.4
Disadvantages
a
Requires two or three bridges.
Relatively high land-take.
U-Zumifig by emergency
maintenance vehicles not possible.
3-Leg Compact Interchange
Figure 18.4: 3-leg Compact Interchange
Kuwait Highway Design Manual
chapter 18
Grade Separations end Interchanges
3-leg Compact Inte'rchanges can be used in rural or urban locations. They are
simple, low-speed versions of half cleverleaves. A typical compact interchange is
shown in Figure 18.4.
The objectives of compact grade-separation are as follows:
Provide a safe means of crossing a high-speed route.
Reduce the environmental impact of grade-separated interchanges by providing
a compact junction layout.
Regulate and maintain vehicle speed for minor route traffic through the
interchange at a level appropriate to the layout standards.
Remove left turning movements from the major route.
Provide an operationally efficient junction layout.
Provide an economic solution for modifying an existing at-grade intersection to
grade-separated standards.
Compact Interchanges can also be provided on single carriageways.
The only major disadvantage is that high-speed traffic on the major route will exit on
a tight loop radius. Adequate advanced signing, good visibility and chevron signing at
the exit point will reduce the hazard. If all such junctions along a route were the
same, then drivers would be aware of the tightness of the loops and would adapt
accordingly.
Table 18.5: Advantages and Disadvantages of Compact Interchanges
Disadvantages
Advantages
w
Provides low-speed, semi-direct links for
some movements.
,
w
Page 1&6
Layouts are simpbe to sign.
Permits future expansion into 4-leg
interchange.
Requires only one bridge.
No weaving movements.
Less land-take and lower cost than
partial cloverleaves.
Provides U-turning for emergency and
maintenance vehicles on the mainline.
r
Introduces at-grade movements,
normally at signalised intersections.
High-speed traffic on the mainline will
exit on a tight loop radius.
Kuwait Highway Design Manuel
Chapter 18
Grade Separatmns and lnierchanges
18.2.5
Cloverleaf Interchange
A: Simple
B: 1 pair of C-D roads
C: 2 pairs of C-D roads
Figure 18.5: Cloverleaf Interchange
The standard form (A) provides the driver on both main alignments with the following
sequence of elements:
'I. An off-slip (for the leaving right-turn traffic)
2.
An on-slip (for the joining lefl-turn traffic from the loop)
3. A weaving section, often relatively short
4.
An off-slip (for the leaving left-turn traffic to the loop)
5.
An on-slip (far the joining right-turn traffic)
This can' be difficult to sign, because there are two exits in succession and drivers
have to decide in advance on their compass direction (for example, Route South or
Route North). This layout also leads to turbulence in the weaving areas, and even in
through lanes, where vehicles do not theoretically need to change lanes. For these
reasons, a link road is normally provided, as shown in (B) and (C),
This simplifies the
signing oust one exit, fo!lowed by a compass decision) and ensures that all weaving
takes place away from the mainline on a link road where every vehicle weaves.
Chepier 18
Grade Sepemths end Iniemhenges
Table f 8.6: Advantages and Disadvantages of a Cloverleaf Interchange
Advantages
Provides moderate-speed, direct or
semi-direct links for all movements.
Requires only one bridge.
Allows U-turning for emergency and
maintenance vehicles.
Disadvantages
1
Entails significant weaving. Link roads
normally required, as with arrangements
(B) and (C).
Dimcurt to sign.
Left-turning traffic leaves by the second
exit on the right.
Considerable land-take.
18.2.6. 4-leg Direct Interchange
Figure 18.6: 4-leg Direct Interchange
The 4-leg direct interchange provides high-speed connections for all movements.
Layout (A) locates three structures at a single location, which minimises land take but
requires considerable earthworks to achieve the necessary level differences for this
four-level crossing.
Layout (B) restricts all the crossings to two-level, but as a consequence, requires five
structures. Land-take is greater, but earthworks are considerably reduced.
Many other arrangements, symmetrical and asymmetrical, are possible.
Page 18-8
Kuwait Highway Design Manuel
Chepter 18
Grade Seperelions and Interchanges
Table 18.7: Advantages and Disadvantage of a &leg Direct Interchange
1
Advantages
Provides high-speed, direct links for all
movements.
Layouts are simple to sign.
a
Disadvantages
Requires three, four or five bridges.
Relatively high land-take.
4-level layout (A) is dimcult to integrate
into a flat landscape.
U-turning by emergency and
maintenance vehicles not possible.
1.8.2.7 4-leg Hybrid Interchange
Figure 18.7: 4-leg Hybrid Interchange (example)
It is possible to produce designs that incorporate features of several types of
interchange. This figure shows one such hybrid, which uses the direct form, but
replaces two of the direct connections by loops.
It is not possible to comment on the generic advantages and disadvantages of hybrid
junctions, as each will have its unique atlributes,
Page 1 8 9
Kuwaif Highway Design Menual
Chapter f8
Grade Sepsrations and Interchanges
18.2.8
Partial Cloverleaf Interchange
Figure 18.8: Partial Cloverleaf Interchange
Many forms of partial cloverleaf are possible, with one to three loops in various
quadrants. The one illustrated (with two loops in opposite quadrants) eliminates
weaving on the main line, albeit by accepting at-grade left turning on the minor road.
Table 18.8: Advantages and Disadvantages of a Partial Cloverleaf Interchange
Advantages
Provides moderate-speed, semi-direct
links for some movements.
Requires only one bridge.
Can enable the elimination of weaving
(as with the layout shown in Figure
18.8).
Layouts are simple to sign it weaving is
eliminated.
Page 1 8 10
Disadvantages
=
lntrduces at-grade movements,
normally at signalised intersections.
Requires more land than Diamond
Interchanges.
Left-turning traffic leaves the minor road
at the second exit on the right,
Kuwait Highway Design Manual
Chepkr 18
Grede Sepemtrbnsand Interchanges
18.2.9
4-leg Compact Interchange
Figure 18.9: 4-leg Compact Interchange
4-leg Compact Interchanges can be used in rural or urban locations. They are
simple, low-speed versions of partial doverleaves. Typical compact interchanges are
shown in Figure 18.9. the objectives of compact grade-separation are as previously
described in Section 7 8.2.4.
Arrangement (A) might be considered appropriate when the majority of the fraffic on
the minor route wishes to cross the major route, Arrangement (8)should be used
where the minor road traffic movement is primaFily turning onto and off the major
carriageway.
Compact Interchanges can also be provided on single carriageways.
Table 18.9: Advantages and Disadvantages of Compact Interchanges
Advantages
Provides law-speed, semidirect links for
some or all movements.
Requires only one bridge.
=
No weaving movements.
Less land-take and tower cost than half
cloverleaves.
Provides U-turning for emergency and
maintenance vehicles on the mainline.
Disadvantages
Introduces at-grade movements,
normally at signalised intersections.
WithLayout(A), High-speedtrafficon
the mainline will exit on a tight loop
radius.
Page I&?
I
Kuwait H & M y Design Menuat
Chapter $8
Grede Sepsrai&nsend Iniemhanges
:-
18.2.10 Diamond Interchange
A: Full diamond
*.
,
,..I
.
1
,
B: Split diamond
'J
7
C: Overlap diamond
0:Single-point diamond
Figure 18.10: Dhmond Interchange
The Diamond lnterchange is probably the most common form of grade-separated
intersection, in which the ramps connect to the lower-category road by means of
signalised, at-grade intersections. Arrangement (A) is the conventional full diamond,
with two sets of signals.
Arrangement (B), the split diamond, is sometimes adopted where the spacing of
adjacent cross arterials is too close to allow the ramps to effect the necessary level
difference. This layout, in which there are four sets of signals, is particularfy suited to
situations where the cross-arterials are one-way streets operating in opposite
directions.
Another solution to this situation is the overlapping diamond shown in arrangement
(C). This layout requires two additional bridges but retains the four sets of signals.
Again this works well with one-way cross-arterials.
A major difficulty with arrangement (A) is the fact that all the left turns "hook* to the
right their opposites, rather than "sliding" past them. This can impose a significant
capacity limitation on the intersection, generally necessitating four-stage signal
operation. Arrangement (D), the single point diamond, gets around that difficulty by
allowing all left turns to "slide" to the left of each other, albeit at the expense of a
layout that requires more space and is potentially more prone to driver
.misunderstanding, With such slide turns, the signal operation can be reduced l o
- - -three-stage.
,
.
,
Table 18.10: Advantag-
Cmfw
GredeSeparebknsBndm?mm@s
and Disadvantages of Dlsmond Interchanges
SplIt
Full
DIamond
Diamond
Overlap
Diamond
Single
Pslnt
Diamond
Very small land-take
d
Q
r/
V
Easy to sign
rr
rl
#
#
intersections
V
r/
J
Single bridge only
cf
cl
U-turning possible for
mainline trarffic
ci
#
v
vZ
No weaving sections on
mainline
v
+
*
+
Advantages:
Conventional at-grade
0
'
Maximises spacing
between intersectionson
mainline
#
C,
-
Disadvantages:
tower capcity on minor
road
x
X
x
Left-turns interact
X
XS
Xs
X
X
X
X
X
X
X
X
X
= Weaving on frontage road
Greater possibility of
wrong-way entry fo ramp
= Difficult to expand the
intersection in the future
1 Ssmnd bMge pmbabty requiredIn any avant
2 May be possible, but dffiWlt to sign and c o M
3 Not if crass sire& are one-way
x
Kuweil Highway Design Menlrel
Chapfsr I 8
Grade Separations and I n ~ 8 n ~ e s
18.2.11 Dumbbell Interchange
Figure 18.11: Dumbbell Interchange
The advantages and disadvantages of the dumbbell intersection are similar to those
of the full diambnd. Additionally, the dumbbell scores by eliminating problems arising
from the interaction of left turns, but has the disadvantage that queues may develop
on the off-slip as ather traffic always has priority.
1 8.2.12 Grade-separated Roundabout
A: Simple
B: >Level
Figure 18.12: Grade-separated Roundabout
Page 18-14
Koweif Highwey Design Manual
Chapfer 18
Grade SepamfEwrs and 1nten:hanges
Arrangement (A) is the simple form of this 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.
Table 18.14: Advantages and Disadvantages of a Grade-separated Roundabout
Advantages
8
Easily understood, conventional
layout.
Simple to sign.
Can be signalised to provide additional
capacity or to manage queues on offslips.
18.3
Selection of Interchange Type
18.3.j
General
Disadvantages
Requires two or more bridges.
Higher land-take than diamond or
dumbbell layouts.
Unsignalised layouts can lock up if there
is a lack of capaciiy downstream.
The following paragraphs cover the design procedures for selecting the form of
interchange most suitable for a particular location. Chapters 3 to 6 cover the
geometric design standards for the individual elements within the chosen
interchange.
The designer should prepare a number of preliminary sketch designs, and these are
to be compared and considered before the final selection of the interchange type and
the production of a preliminary design.
18.3.2
System Interchanges
System Interchanges are those that connect a Special Road to another Special
Road. They should always be free-flow interchanges of the types described in Table
18.1.
18.3.3
Service Interchanges
Service Interchanges connect to roads of a lower class than Special Roads. If the
road is a Primary Road, then the full range of interchange options can justifiably be
considered. For Secondary Roads, interchanges that incorporate some at-grade
movements (see Table 18.1) are the norm.
A 8.3.4
Route Strategy
~nterchab~es
in rural areas can be considered independently of each other, since the
spacing of interchanges is most probably very great. Topographical and traffic flow
considerations predominate, but consistency of exit patterns and minimisation of
weaving on the mainline will have a considerable influence on the choice of
interchange.
In urban areas, the selection of interchange type is limited, because of issues of
capacity, weaving and lane balance on the mainline. This is due to the fact the
Page i & i 5
Kuwait Highwey Design Manuel
Ch8phsr 18
Gmde Sepamlionsand Intemhenges
interchanges are closer, and each interchange is likely ta be influenced by the next,
both upstream and downstream.
On a continuous urban route, all the interchanges should be considered together as
a system. Arrangements for the entire corridor can be sketched and alternative
interchange strategies can be developed, analyzed and compared. The designer
should consider the intersecting minor roads and confirm that they are suitable for
the additional traffic that an interchange will transfer on to them.
Due to the amount of land that cloverleaf interchanges occupy, they are the least
suitable for use in urban areas.
Traffic Flows and Design Year
18.3.5
Interchanges are designed using Design Hour Volumes (DHV), as described in
Chapter 2. Of particular importance for interchange design is the volume of traffjc
predicted to undertake each turning maneuver.
,
Interchange Spacing within the Network
18.3.6
The designer should consider the position of the interchange within the entire road
network when selecting the form of grade-separated facility. The aim should be the
provision of a consistent interchange strategy that maximizes safety across the
network.
The indicative minimum spacing of intersections set out in Chapter 13 (Table 13.1) is
aimed at providing adequate lengths of uninterrupted flow appropriate to the road
dass. This length must accommodate any weaving that may occur on the intervening
section of road between !he last on-slip of one interchange and the first off-slip of the
subsequent one. Guidance on the design of weaving sections is given later in this
Chapter.
Initial Information, Requirements and Decisions
Selection of the type of interchange is based on the following:
18.3.7
the class, cross-section and Design Speed of all the intersecting roads.
the DHV.
the location and nature of any engineering constraints to the scheme, such as
Iand ownership, planning constraints, existing and proposed utilities, topography,
dry wadi courses and ground conditions.
The location and nature of any environmental constraints, such as proximity to
dwellings, proximity to buildings of historic or cultural significance, severance of
communities, plants of particular importance, animal habitats, animal tracks and
migration routes, environmentally sensitive buildings (noise I air quality).
The designer must carry out the following before deciding on the type of interchange
to use:
Discuss the overall interchange strategy with the MPW and Kuwait Municipality.
a
Agree the DHV (including turning volumes) with the MPW and Kuwait
Municipality.
Decide which turning movements are to be accommodated.
Decide which movements within the interchange are to be given priority with
grade-separated links and which movements (if any) are to be accommodated
through at-grade intersections.
Confirm the vertical and lateral clearances for structures.
Page I S 1 6
Kuweit Highway Desjgn Manual
Chapter 18
Grad8 Separations end I n t e ~ ~ h a m s
18.3.8
Type of Interchange for Preliminary Design
Before starting the preliminary design, the type of interchange has to be selected
using the guidance given previously in this Chapter. For a given location two or mare
solutions may be worked up into outline designs (usually in sketch form) for
preliminary eva tuation.
The choice of 'over or under' frequently arises, and no firm guidance can be given. In
general, one of the roads is likely to have a higher design speed than the other and
so will require longer verfical curves to achieve the necessary level difference.
Keeping the major route at or near existing ground level may prove more economic.
However, this also implies that the associated at-grade intersections will be
constructed either above or below ground level, where restrictions to forward visibility
may become an issue. Note that any scheme that involves pavement levels below
existing ground levels requires careful design, especially where water table levels are
high, for example near the coast.
8.3.9 Preliminary Design
The following items need to be defined in the preliminary design:
Safety implications for road users.
Number of lanes required for each movement.
Design speed for individual elements within the interchange.
Horizontal radii (especially important for loops).
Vertical clearances for structures.
Maximum pavement gradients.
Lengths of slips, links and loops.
Lengths of weaving sections (between and within interchanges).
Provision for crossing traffic (not wishing to join the mainline).
Provision for pedestrians.
Estimate of construction cost.
-
The designer must also consider:
Method and phasing of construction.
Prevision for and methods of maintenance.
Environmental effects, including landscaping.
Provision for lighting and signing.
Provision for fences and barriers.
The preliminary design will need to be discussed with the MPW and Kuwait
Municipa lily and their approval received before the designer progresses further.
Certain elements of the preliminary design may need to be worked up in greater
detail if requested by the MPW or Kuwait Municipality.
18.4
Lane Provision
Initial estimates of lane prevision are undertaken on the basis that the DHV should be
accommodated, using the Maximum Service Flow Rates fpr pcu per hour per lane
given in Table 2.1. The designer may wish to increase the lane provision above the
Page 18-17
Kuwaa Highway Design Manual
Chapter f 8
Gmde Separetimsand Interchanges
minimum number required to accommodate the predicted future flow, for operational
or lane balance reasons.
Lane balance considerations are important, Three basic principles apply:
1. Entries
The number of lanes beyond !wo merging traffic streams should not be less than the
sum of all the upstream traffic lanes minus one.
2. Exits
The number of approach lanes to an exit should either be equal to or one less than
the number of lanes on the mainline beyond the exit plus the number of diverging
lanes at the exit.
3. Lane Drops
The travelled way of a road should not be reduced 'by more than one lane at any
location.
Mainline lane drops within a junction (3 lanes prior to the diverge, 2 lanes between
the diverge and t h e merge, then back to 3 lanes) are not generally recommended on
operational and safety ground.
Figure 18.13 shows some typical situations.
MERGING
DIVERGING
@
ONE
I LANE UNDER SPECIAL CONDITIONS
OF PRINCIPLE 2
Figure 18.13: Typleal Examples of Lane Balance
Page 18-16
Kuwait Highway Desbn Manual
Chepler i8
Grade Sepemtions and Enterchenges
38.5
Design Speed
The design speed of the connecting roadways needs to be determined after
establishing the design speeds of both the major and minor routes.
Three different conditions are relevant:
Links that are free-flow, connecting the two alignments directly and generally
turning through an angle of 90 degrees.
Slips that connect from a merge or diverge on one alignment to an at-grade
intersection on the other.
Loops that are free-flow, connecting the two alignments directly and generally
turning through an angle of 270 degrees.
Usually, the connecting elements are assigned lower design speeds than those on
the mainline. The stepping-up of design speed on leaving a connecting road causes
no difficulty. The steppingdown of design speed on leaving the mainline should be
handled carefully.
Table 18.1 2: Design Speeds for Connecting Roadways
*
Higher Design Speeds may be appropriak in rural areas.
These design speeds apply to the connecting roadway itself, Merges and diverges
should be designed in accordance with the design speed of the mainline.
78.6
Diverge Design
18.6.1
Selection of Layout Type
The recommended standards for diverging lanes are based on a mainline operating
speed of 100 kmlh, which seems the most appropriate for those roads in Kuwait that
will utilise grade separated junctions. The recommended layouts may be adopted for
lower or higher speeds with suitable adjustment to the proposed standards.
There are two types of exit arrangement available to the designer, namely the direct
type and parallel type. The direct diverging lane, i.e. where the diverging lane exits
via a straight taper, is preferred under normal conditions. The parallel type provides
a greater length over which exiting manoeuvres can take place.
Both taper and parallel layouts can be used with or without a lane-drop on the
through mainline, and both can be used with a single-lane or two-lane off-slip.
Page 18-19
Kuweil Highway Design Manuel
Chapter 18
Gmde deepamtions a d Interchanges
The method of deciding on the most appropriate diverging lane layout to
accommodate design year flows is described in the following paragraphs, It should
be noted that the most suitable layout for a diverge should not be considered in
isolation. The other junctions along the mainline route should also be considered, so
that drivers may be presented with a consistent set of layout features.
The mainline and link flows should be assessed in terms of pculh in the design year,
and the worst combination of these flows, taking account of different peak periods,
used as a base, The base flows should then be adjusted for non-standard traffic
composition and gradient as shown in Table 18.13. The gradient should be
measured over a distance of one kilometre, centred upon the nose of the diverge
lane.
Table 18.13: Percentage Corrections to Predicted Flows for ComposRion and Gradient
Percentage of HGVs on Link or Mainline befng Considered
'
Gradient on
Mainline
5
20
15
20
25
30
35
40
Downhill, Level or
1 % Uphill
-8
-4
0
*4
+8
+I2
*16
*20
- 2% Uphill +2
+6
*I0
+14
+I8
+22 +26
+30
2% - 3% Uphill
+f2
+20
+24
*16
+28
*32
+26
+40
7%
The adjusted design flows should then be plotted on Figure 18.14 to identify the
appropriate flow region,which is indicated alphabetically.
Using Table 18.A4, the types of layout suitable for handling the flow region assessed
as above, are identified. f he shaded diverging lane types are likely to prove the
most acceptable in terms of level of service. Where flow combinations are close ta
boundaries between different flow regions, the layout types indicated for the adjacent
flow region should also be considered.
Page 48-20
K m i t Highmy Design Menus!
Chapter 78
Grade Separetians and Inferehanges
0
1000
2000
3000
4000
5000
Downstream Mainline Flow in pculh
Figure 18.14: Flow Regions for Diverging Layouts
Table 18.14: Type of Diverging Layout Appropriate ta Flow Region
The diverging lane types are shown on Figure 18.15 to Figure 18.18. In conjunction
with Table 18.14, the following notes on each layout type should be considered when
deciding upon the most appropriate layout.
Page 1 &-21
Kuwait Hhhwey Design Manuel
Chapbr l 8
Grade
SeperatMs end InteWnges
18.6.1.1 Type 1 and 3 - Figure 18.15
The direct diverging lane is the most economical layout for single lane links. It is
appropriate up to fiows of approximately 1000 pcuh after correction and where site
conditions are favourable. Where the diverge is situated on a left hand curve, or
where the intersection is an a gradient, the parallel diverging lane layout is more
appropriate.
18.6.7.2 Type 2 and 5 - Figure 18.1 6
The direct diverging lane layout is appropriate for exiting flows around the limit of the.
single lane exit but where site conditions do not favour a single lane. The standard
layout where two exit lanes are required, and where'there is no lane drop, is shown
in the parallel diverging lane layout. The parallel diverging lane layout is particularly
preferred when the diverge is situated on a left hand curve.
18.6.1.3 Type 4 and 6 - Figure 18.17
Where a lane is dropped at the intersection types 4 and 6 layouts are appropriate.
The direct diverging lane may be used in favourable site conditions, whereas the
parallel type layout is more appropriate on left hand curves.
-
18.6.1.4
Type 7, 8 and 9 Figure 18.18
Types 7 and 8 are appropriate along routes with lane drop I lane gain at
interchanges. Type 9 may be used at the divergence of two routes of equal
importance and'carrying equal volumes of traffic, where neither branch is considered
to be the main through route. This type of diverge is also referred to as a Major Fork.
18.6.2
Geometric Parameters for Diverges
A diverge taper shall generally be 1:25. A taper of 1:40 should be adopted, to give
additional space for diverging traffic, at single lane links or at two lane links where
one lane is dropped from a three-lane main line
The length of diverge nose should be a minimum of 70m.
More generous diverging layouts may be required under the following adverse site
conditions:
If the mainline is on a significant right hand curve, a direct taper would result in a
tangential alignment and would be confusing to drivers.
If the main line is on a steep upgrade, a longer distance is needed for the
diverging manoeuvre to enable faster vehicles approaching in the outer lanes to
penetrate through those heavy vehicles that are moving slowly in the right hand
lane.
When the mainline is on a steep downgrade, a problem may arise associated
with the high speed of vehicles on the mainline right hand lane.
In these situations an extra diverging lane 3.7m wide and at least 170111long with a
7Om taper should be provided.
The design parameters are set out in Figure 18.1 5 to Figure t 8.18 on the following
pages.
Page 18-22
Kuwait Highway Design Manual
Chapk?r18
Gnde Sepamtbns and Interchanges
Chapter f8
Grade Separations and lnterchenges
Page 18-24
Kuwait Highwey Design Manual
&8&
Chapter 18
Separations and lnlerchsnges
Page 18-25
Kuwait Highway Design Manuel
Chapter 18
Grade Seaarations and Inkmhanaes
Page f &26
Kuwait Highway Design Manual
Chapter 18
Grade Sepamtbns and Inkrchsnges
18.6.3 Deceleration Distance
Vehicles leaving the mainline need enough distance to enable them to decelerate
clear of the mainline to the design speed that pertains on the connecting roadway.
Design features to the lower design speed standard must not be introduced before
deceleration beyond the tip of the painted nose has occurred.
18.6.4
Forward Visibility
Forward visibility extends over the entire length of a road, therefore might cross into
areas of different design speed.
For the three areas, the following criteria should be used:
Over the taper length
design speed.
- apply
Over the deceleration distance
mainline design.
visibility standards appropriate to the mainline
-
apply visibility standards appropriate to the
-
Thereafter apply visibility standards appropriate to the connecting roadway
design speed.
18.6.5
Superelevation
Normally the main line superelevation continues across the width of the diverging
lane, However, presenting a reversal of the mainline superelevation on the approach
to a right-hand curved off ramp may be essential when the mainline is on a left-hand
curve. In this case the magnitude of the differential between the two falls should not
exceed 4%.
Beyond the painted nose, the vertical profile of the mainline and the off-slip may
diverge, and this effect may be made more pronounced if superelevation is being
developed on the off-slip. Care must be taken to ensure that the fall across the
paved gore is not too great, and a value of 4% should be taken as a working
maximum.
The superelevation across the recovery area (beyond the paved gore) should be the
same as that of the mainline, and the design of the transition from the crossfall
prevailing in the gore area requires careful consideration.
18.6.6
Left Off-slips
Ramps leaving from the lefi (inner) side of the pavement are not recommended. If
they are to be used, they should be treated as major forks (Type 9). Adequate
overhead signing and full Decision Sight Distance must be provided in all cases.
18.7
Merge Design
18.7.1
Selection of Layout Type
As with diverging lanes, a mainline operating speed of 100 km/h has been used in
arriving at fhe recommended standards. The recommended layouts may be adopted
for lower or higher speeds with suitable adjustment to the proposed standards, as
before.
There are two types of entry arrangement available to the designer, namely the taper
type and parallel type. In normal circumstances the direct entry, where the merging
lane joins the main road via a straight taper, is preferred. Situations will occur
however where a more generous layout, including a parallel merging lane plus taper,
will be justified by difficult site conditions. The parallel type provides greater length
for merging the entering flow in to the trafic on the mainline.
Page 18-21
Kuweil Highway Design Manual
Both can be used with or without a lane-gain on the through mainline, and both can
be used with a single-lane or two-lane on-slip.
At higher entry flows, two merging lanes may be required and the resulting layout
may be of the direct or ghost island type.
The method of deciding on the appropriate merge layout that will provide the required
capacity to cater for the design Rows is described in the following paragraphs. It
should be remembered that the recommended layout may require adjustment due to
outside influences, such as a policy decision to provide the same number of lanes
throughout the whole mainline route.
Design year flows in pcuh should be obtained for the'mainline and the entry slip. The
worst combination of these flows, allowing for possible different timing of peaks, is
then used as a base. The base flows are adjusted for non-standard combinations of
traffic composition and gradient as indicated in Table 18.13. The gradient should be
measured over a distance of one kilometre of the mainline, centred on the merge
nose.
The adjusted design year flows in pculh are then plotted on Figure 18.19 to identify
the appropriate flow region, which Is indicated alphabetically.
Having identified the flow region to which the adjusted design year flows correspond,
Table 18.15 should be consulfed to find the merging layout types that will provide the
required capacity. The most appropriate layout types are indicated with shading.
Where flow combinations are close to the boundaries between different flow regions,
the layout types indicated for the adjacent flow region should also be considered.
o
1000
2000
3000
Upstteam Mainline Flow in pculh
Figure 18-19: Flow Reglons for Merging Layouts
a000
5000
Kuwuit Highway Design Menuat
Chapter 18
Grade Separelhs and kfechanges
l a ble d8.15: Type of Merging Layout Appropriate to Flow Region
Diverging Lane Type
I
2
Upstream
Mainline
2
2
3
3
4
5
-
3
4
3
Number
Link
1
21
22
of LanesDownstream
2
3
2
3
Mainline
18.7.2
8
9
-
4
I
2
-
3
2
3
2
Geometric Parameters for Merges
For the direct entry-merging lane a taper of 1:40 is recommended. For single lane
entries, h~wever,this should be increased to I:50 wherever possible.
The length of merge nose should be a minimum of 85m to provide adequate
sideways visibility for merging traffic.
As stated previously, an additional length of parallel merging lane may be required in
the following types of conditions:
Where the main line is on a significant lefi hand curve. In this ease, visibility is
limited and the direct entry is not as effective because the angle of convergence
is too great. By providing a length of parallel lane, drivers are able to observe
conditions on the mainline by using their driving mirrors rather than turning their
heads.
Where the mainline and hence the merging lane are on a steep up-gradient, the
problem is one of matching speeds. A greater distance is required for merging
vehicles to accelerate.
Where the mainline is on a steep down-gradient, there may also be problems
associated with the high speed of vehicles in the near side lane.
In these ,situations, an additional merging lane, 3.7m wide and a minimum of 150m
long, with a 70m taper should be provided.
The merging lane types, showing geometric parameters, are given in Figure 18.20 to
Figure 18.23. The following notes on each type should also be considered in deciding
upon the appropriate layout.
Page 18-29
Kweit Highway Design Menuai
Chapter 18
Grade Sepamfionsend Interchanges
-
18.7.2.1 Types 1 and 4 Figure 18.20
The direct entry is the most economical merging layout for single lane slips. It will
cater for entry flows up to approximately 1000 pcuh, after correction, but should only
be used under favourable site conditions. Where the main line is situated on a right
hand curve, where the main line is on a gradient or where for other reasons it is
necessary to provide greater definition of the merging lane, the more generous
parallel type merging lane layout should be adopted.
18.7.2.2
'
-
Types 2 and 5 Figure 18.21
The direct entry layout is suitable for the higher entry flows near the limit of a single
lane entry but where diverse geometric conditions render a single lane entry
unsuitable. The ghost island layout is the more normal and preferred layout where
entry Rows dictate a two-lane entry but where there is no need for the addition of an
extra lane downstream. The layout permits the left hand traffic on the slip to enter the
mainline early and to dissipate to form gaps for the second merging lane. Both
layouts can accommodate a single Fane slip, widened to a two-lane entry, where
appropriate.
-
18.7.2.3
Types 3 and 6 Figure 18.22
Where an extra lane is required for downstream traffic, these layouts are appropriate.
The parallel entry layout gives the right hand lane of the slip free entry while the left
hand lane of the link merges with the slower traffic on the main line. The ghost island
provides free entry for the faster traffic on the slip and subsequent merging of the
slower traffic and is to be preferred for the higher ranges of traffic in this category.
The ghost island entry is also preferred on right hand curves and uphill slips. In both
layouts, the slower moving traffic on the mainline must eventually merge into the
nearside lane, but there is no immediate necessity to do so.
18.7.2.4
Types 7, 8 and 9 Figure 18.23
Types 7 and 9 are appropriate on routes where lane drop 1 lane gain interchanges
are used. Type 8 is more appropriate in the situation where two routes of equal
status and carrying equal volumes of traffic meet. It is advisable to prevent immediate
weaving by the use of double white lines and such lines, although varying with site
conditions, should be extended for least 50m.
Page t 8-30
-
II
185m
1 :50 TAPER
.I
85m
NOSE
MIN 1:40 TAPER
1
I
DIRECT ENTRY MERGING LANE (TYPES 1 8 4)
F k - p & ~ k Z r p * ]MIN 1:40 TAPER
PARALLEL MERGING LANE (TYPES 1 & 4)
Figure 18.20: Direct and Parallel Merging Lanes Type 1 and 4
K w i t Highwey Design Manuel
Chpter 18
Grade Sepamtions and Inferchanges
Page 18-32
f 85m
1 :50 TAPER
I
NOSE
MINf:4OTAPER
I
DIRECT ENTRY MERGING LANE (TYPES 3 & 61
GHOST ISMHD MERGING LANE (TYPES 3 &A
Ffgurs 18.22: Direct and Parallel Merging Lanes Type 3 and 6
Kuwait Highway Design Manuel
Chapter 18
Grade Sepemfions and Inferchanges
--
Page 18-34
Kuwait Hlghway Design Manual
Chapier 18
Grade S e p a m t h and lnterchenws
3 8.7.3
Acceleration Distance
Vehicles joining the main line need enough distance to enable them to gain enough
speed to be able to merge smoothly into the flow on the main line, and this
acceleration should take place clear of the mainline.
Acceleration distance is measured along the slip road to Ihe point at which the width
of the travelled way of the slip falls below 3.7rn.
18.7.4
Forward Visibility
The forward visibility appropriate to the slip design speed should be provided until the
vehicle reaches the physical nose. Thereafter, the visibility should be in accordance
with the design speed of the mainline.
18.7.5
Superelevation
Similar considerations applying to entries as apply to exits,
18.8
Connecting Roadways
48.8.1
Width
A lane width of 3.7m should be adopted on all connecting roadways, with widening
only being provided where the horizontal curvature requires it.
Due allowance must be made for the consequence of a stalled vehicle on the
connecting roadway. Two-lane facilities provide for passing, but on a single-lane
facility, adequate shoulder width should be provided to allow passing of the largest
design vehicles. The geometric considerations are the same as apply to right-turning
roadways in at-grade intersections. Details can be found in Section 14.1 1.4.
18.8.2
Shoulders and Lateral Clearances
The following advice on shoulders and lateral clearances on slips should be adopted
in Kuwait:
When shoulders are provided on slips, they should have a uniform width for the
full length of slip.
Slips with a design speed of more than 60kmh should have a left shoulder width
of 0.6mto 1.2m and right shoulder width of 1.2m to 3.0m. For other slips, the
sum of the lefl and right shoulder widths should not exceed 3.6m, with a shoulder
width of 0.6m to 1.2m on the left and the remainder on the right.
The single-lane slip widths from Table 14.6 for Case 2 should be modified when
shoulders are provided on the slip. The slip lane width should be reduced by the
total width of both right and left shoulder. However, the slip lane width should
never be less than required for Case 1.
For merges and diverges on Special Roads, where the slip shoulder is narrower
than that on the mainline, the shoulder width of the through lane should be
carried into the diverge, and should begin within the merge, with the transition to
the narrower slip shoulder effected smoothly along the slip road proper. Abrupt
change should be avoided.
Where ramps pass under structures, the total roadway width should be carried
through without change. Desirably, structural supports should be located either
behind a safety barrier or beyond the clear tone (Chapter 8 of this manual gives
guidance on clear tones and the use of barriers).
Page 18-35
Kfmelf Nlghwny Design Manual
Slips on overpasses should have the full approach roadway width carried over
the structure.
18.8.3
Gradient
Gradients of up to 2% more than those relevant to the mainline may be adopted,
giving the maxima shown in Table 18.16.
Table 48.16: Maximum Grades on Connecting Roadways
Main tine Class
Maximum Grade on
Connecting Roadway
Special Roads
Primary Roads
Where a roadway connects a Special Road to a Primar)~or Secondary Road, the
maximum grade for the Special Road (that is, 6%) should prevail.
On loops, the gradient should be uniform throughout the length of the cutve, and is
generally determined by the radius of the loop and the vertical separation of the
roadways.
The maximum superelevation for connecting roadways is normally 4%, but values of
up to 6% may be considered in urban areas.
For loops, however, the maximum value is 8%.
18.8.5
Vertical Alignment - Effect on Horizontal Geometry
The designer should consider the following issues:
What is the likely construction thickness at over bridge decks?
This depends on factors such as the span, the skew, the form of construction
chosen, and whether the bridge has open or closed abutments
What vertical clearance is required between the two road profiles?
This is the construction thickness plus a clearance of at least 5.5~1.AS both
roadways are likely to be super elevated, and possibly on vertical curves, it is
necessary to check all four corners of the structure over the road pavement to ensure
that minimum headroom is maintained at all points.
What vertical alignment should be adopted in order to achieve the
necessary vertical clearance between profiles?
The chosen alignment generally dictates the horizontal location of the nose relative to
the bridge structure.
What slope should be used for the earthworks between the roads?
This figure, which depends on the nature of the material concerned, should be
agreed with the MPW before design begins. It has a direct effect on how close the
connecting roadway can be ta the main line, and so the horizontal geometry should
be checked at all points for compliance with this maximum slope value. Where
physical constraints would require the adoption of steeper slopes, consideration
should be given to the use of retaining walls or elevated viaduct structures, as these
enable the tvvo horizontal alignments to be kept close together.
Kvweit Highwey Design Menuel
Chepler 18
Gmde Separationsand Interchanges
18.9
Spacing of Merges and Diverges
18.9.1
Possible Arrangements
There are four possibilities when considering two adjacent merges or diverges:
Both are exits.
Both are entries.
The first is an exit and the second an entry.
The first is an entry and the second an exit.
These are dealt with in turn below.
18.9.2
Exit 1 Exit
Suitable distances between the noses of successive exits from the mainline should
be adopted to present drivers with simple options. Similarly, having left the mainline,
the driver should not immediately be given a further choice as the slip roads splits
again, This decision should have to be made some distance beyond the mainline
exit nose.
Refer to Table q8.17 to obtain the minimum distances, measured from one painted
nose to the next.
18-9.3
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, and Table 18.17 sets out the recommended
spacing.
18.9.4
Exit I Entry
This is the safest of the four layouts, and this is reflected in the shorter distances set
out in Table 18.14.
18.9.5
Entry 1 Exit
This is the most complex of the four layouts, as weaving of traffic streams will occur.
Only if the slips are sufficiently far apart do they operate as a merge, followed by a
length of open road, followed by a diverge.
Two considerations apply:
7 . There is a minimum distance between the noses to ensure safe operation even
under very light flow conditions - this is the minimum spacing.
2. There is a minimum distance between the noses to permit the traffic streams in
the design year to cross each other safely - this is the weaving length.
Consideration 1 is purely geometric, and is dealt with here. Relevant values are
given in Table 18.17. Consideration 2 is determined by the volumes of weaving
traffic and is dealt with in Section 18.10.
Kuwait Highway Design ManlraE
Cbsprer 18
Grade Separatiwrsand Interchanges
Table 18.f7: Recommended Minimum Spacing Between Successive Entries and l or
Exits
Entry to
or Exit to Exit
Exit to Entry
Entry to ExR
(Weaving)
Turning Roadways
NOT APPLICABLE TO
CLOVERLEAF LOOP W P S
Special
Road
Primary
Road
Special
Road
Primary
Road
System
Inter-
change
Service
Interchange
System to Service
Interchange
Special
Road
Primary
Road
Service to Service
Interchange
Special
Road
-
18.10
Primary
Road
Weaving
A weaving section is the section of a carriageway where there is movement of traffic
in the same general direction, but where vehicles within hrvo or more traffic streams
intersect at a small angle so that the vehicles from one stream can cross into another
stream gradually. If all vehicles are to cross each other safely, then there must be
both sufficient width on the road, and sufficient length between the relevant entry and
subsequent exit points. Both of these elements depend directly on the volume of
traffic in each stream, and must to be calculated by the traffic engineer.
These calculations are outside the scope of this manual, and the designer is referred
to the Highway Capacity ~ a n u a l ' .In essence, the length of the weaving section
depends on the weaving traffic volumes (ignoring the non-weaving flows) and the
operating speed. The width depends on the total flow on the weaving section, with
weaving streams being given an appropriate additional weighting factor over nonweaving streams.
Where weaving volumes are high, and non-weaving volumes are relatively low, the
designer should consider carefully whether the amount of weaving could be reduced,
for example by reversing the ramp arrangements.
Weaving at cloverleaf interchanges is generally best handled on link roads. Without
these, the turbulence generally interferes with the smooth Row of traffic on the
mainline and safety can be jeopardised. Weaving calculations must always be
undertaken, as the outcome may well influence the design of the loops, or indeed
dictate that another form of interchange be used.
18.11
tink Roads
Link roads can be 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. Link roads are at least two lanes
in width, and generally adopt a design speed IOkmh lhto 20kmfh less than that of the
Kuwait Highwey Design Manual
mainline. Decision Sight Distance to the downstream exit point should normally be
provided for drivers on a link weaving length.
Link roads should be considered for all cloverleaf interchanges, which inherently
generate significant weaving movements. When weaving volumes exceed
IOOOpculh, link roads should always be provided.
Although the provision of link roads increases the land take through an interchange,
the lower design speed may enable smaller loop radii to be adopted, thus offsetting
this disadvantage.
Where a continuous length of link road is provided, transfer roads are provided to link
it te the main line at suitable intervals. Both ends of the transfer road are designed as
dip merges or diverges of the appropriate standard.
18.1 2
Other Design Considerations
18.12.1 Abnormal Load Requirements
The designer should seek guidance from the MPW and Kuwait Municipality to
ascertain whether any additional clearance or headroom is required at specific
structures in order to accommodate the movement of abnormal loads.
f 8.12.2 Superelevation
The relevant recommendations in Chapter 5 of this manual should be used to design
the superelevation and crossfall, making sure that the entire pavement drains
effectively and that there is no risk of long vehicles grounding at changes of
superelevation.
18.12.3 Pedestrian Crossings
Provision for pedestrian crossing at grade-separations and interchanges should also
be grade-separated from main line traffic.
18.12.4 Safety Barriers
Special consideration should be given to the safety barrier treatment at the physical
nose of off-slips. High-speed vehicles that stray into the gore area are at particular
risk, and the ends of safety barriers at these locations should be given special
treatment to reduce the dangers of head-on impact. Consideration should also be
given to the provision of energy absorbing terminations for these locations,
particularly if bridge piers or other massive elements are located in the gore area.
Chapter 8 gives further information.
Direction and warning signs for interchanges may be large and possibly gantrymounted. The need for protection of isolated signs supports and gantry legs should
be carefully assessed.
In addition to safety barriers, consideration should be given to provision OF barriers to
prevent unauthorised movements within an interchange. Movements across verges
between slips or links and the mainline are highly dangerous and must be strongly
discouraged.
18.12.5 Signing
Effective and clear signing is essential for the safe operation of any intersection, This
is particularly true for interchanges, where vehicle speed and traffic volumes are
high. Signs are large and frequently gantry-mounted, and adequate space must be
allowed for the large foundations and clearances required.
Kuwait Highway Design Manuel
C h ~ p l a18
r
Gmde Separationsand hterchanges
Detailed guidance on signing is provided in the Kuwait Traffic Signs Manualz. The
designer should consider the signing requirements at the preliminary design stage.
At this early stage the designer can also identify suitable locations for signs and
check that visibility is not likely to be obscured, for example by a preceding
overbridge.
18.12.6 Lighting
The potential for accidents throughout the road nehvork c a n be reduced by
appropriate lighting. The lighting requirements must be considered during the
preliminary design stage, keeping in mind that special attention is required for the
bases of tall lighting supports.
18.12.7 Utilities
Information about existing or proposed sewices must be obtained from the Utility
Authorities at an early stage in the design process. Diversion or modification to
services can have a major impact on the cost of an interchange. Utility Authorities
may also request the provision of services reservations through the interchange to
accommodate future provision. Chapter 8 gives further information,
18.12.8 Emergency Vehicles
During preliminary design, the Designer should consider how emergency vehicles
would teach the scene of an incident. Provision of additional clearance width
beneath structures could be considered, along with emergency median crossovers
with demountable safety barriers. The potential advantage of an interchange that
permits U-turns by emergency vehicles should also be borne in mind.
18.12.9 Maintenance Provisions
Maintenance of the pavement and the structures will be required during the life of the
scheme, and the designer should consider the implications of maintenance strategies
and traffic management on the layout of his proposed interchange. The designer
must ensure that the interchange can be safely maintained and that traffic
movements can be reasonably accommodated while maintenance operations are
taking place.
18.12.10 Environmental Issues
The designer should attempt to overcome any unacceptable environmental impacts.
Any impacts that remain should be minimised as far as possible.
The main impact of interchanges is visual intrusion due to their sheer size. Careful
landscaping can reduce the impad of large structures above ground level and a
combination of hard and soft landscaping often achieves the best results. The
designer should use materials in keeping with the surroundings and should carefully
consider colours, textures and styles. In proposing soft landscaping, the designer
must consider how the planting can be safely maintained thro~~ghout
the year and
define an appropriate watering regime.
Landscaping cannot be allowed to interfere with the operational requirements of the
interchange, and in particular, landscaping features must not interfere with sight
distances, obaruct visibility of signs, or reduce the effectiveness of road lighting.
1
Highway Capacity Manual (Special Report 209),Transportation Research Board,
National Research Council, Washington DC, 1997
Kuwaif Traffic Signs Manual, 1988
Page 1840
Ministry of Public Works
Roads Administration
PART 2
Kuwait Bridges and Highway Structures
Design Manual
Edition 1
March 2004
Kuwait Bridges and Hkhwey Stmtums Design Manual
TabC of Contents
TABLE OF CONTENTS
2.1 Vertical Clearance
2-1
--
2.2
Approach Slabs---
2.3
Deck Drainage
2.4
Architectural Consideration
3.1
Design Live Loading
-
2-1
2-1
-
-
-------
2-2
--
--
3-1
- 3-1
3-2
3.2 Dead toads
3.3 N n d Loads
3.4
Thermal Forces
3-2
3.5
'Uplift
3-2
3.6
Seismic Loading
3-2
---
3-7 Movement Rating
---
3.8 Bearing Friction Forces
3.9
3-3
-
Differential Settlement
-3-3
3.10 Distribution of Loads-----
3-3
--4-1
------
4.7
Design Method
4.2
Superficial Soils-
4.3
Ground Water and Sulfates-
3-2
4-1
---
4-1
-.
------
5.2
Factors of Safety
5.3
Expansion and Contraction Joints
7.1
Live Load Surcharge
8.7
Concrete-
5-1
5-1
--
7-1
--
8.2
Concrete Protection Against Aggressive Soils--
8.3
Reinforcement ---------------
8.4
Slab Design
---
--
8-1
8-1
8-2
8-2
Kuweit Bridges and Highway Slrvctures Design ManusE
Table of Contenfs
8.5
--
Slab Thickness
8.6
Protection Against Corrosion
8.7
Design Method
8-2
--
---
--
83
8-5
-
9.2 Allowable Stresses
--
9-1
------
9-1
9.3
Shear
9.4
Concrete
9-2
9.5
Precast Pre-tensioned I-beams
9-2
9.6
Post-tensioned Box Girder Bridges ---
9-3
9.7
Prestressed Voided Slab
96
9.8
Prestressed Box Beams
9-7
-
---
10.1 Design Method -
10.2 Materials
--
10-1
10-1
-
10.3 Allowable Fatigue Stresses
10-1
10.4 Load Cycles---
-10-1
10.5 Charpy V-Notch Impact Requirement
10-1
-----
10.6 Stiffeners and Connections
10-1
I 1.? Movement Criteria
11-7
12.1 Movement Rating ---
12-1
12.2 Common Deck Joint Types
-
12-2
--------
13-1
--
13.1 Movement Criteria---
73.2 Types of Bearings Recommended -------------------
13-1
73.3 Bearing Schedule-
13-5
14.1 Vertical Fixed Restrainers
14-1
14.2 Vertical Expansion Restrainers
14.3 Shear Keys14.4 Keyed Hinge
-----
---
14-1
-
14-1
14-1
Kuwait Bridges and Highway SInrctums Design Manual
Jabfe of Contents
18.1 Design Loads
16.2 Design Details
--
---
iii
--
j6-1
16-1
Kuwait Bndges and Highway Structures Design Manual
Bridges and highway related structures shall be designed and constructed in
accordance with The American Association of State Highway and Transpadstion
Officials ((AASHTO) Publication, "Standard Specifications for Highway Bridges" and
all active Interim Specifications up ta date of commencement of the design
agreement.
The following chapters describe design requirements stated by the Ministry of Public
Works, prov~deguidance on the interpretation of AASHTOs requirements and list
specific requirements related to local conditions.
These design criteria are not intended to replace AASHTO but to be used as a
supplement. The designer shall be aware of other constraints, exercise judgment
on the application of these guidelines.
The purpose of this design portion of this manual is to list the MPWs criteria and
provide guidance on the interpretation and application of AASHTO Design
Standards. This portion shall be read in conjunction with other chapters of this
manual. Any conflicting requirements shall be raised to MPW and resolved prior to
completion of design.
This manual should be used as a guide only. It will always be the responsibility of
the designer to ensure that the guidelines offered in this manual are applied
properly and modified as needed to suit particular project's requirement.
The Designer may propose variations if, in hislher judgment, such criteria are
required. However, all deviations from the criteria must be justified and approved in
writing from MPW.
Page 1-1
KuwaH Bridges and Highway Structures Design Manual
Chapter2
Gene& Features of Design
The general features of design shall be as specified in Section 2 of AASHTO except
as clarified or modified in this manual.
Vertical Clearance
The following are recommended design minimum vertical clearances for structures:
Structure Type
Highway Traffic Structures
passing over Motornays,
Expressways, Rural and Urban
Arterial)
Minimum Clearance
(m)
Posted Clearance
(m)
5.5 minimum*
6.0 preferred*
over the entire roadway
width
5.2
Pedestrian Overpasses
6.0
5.2
Tunnels
5.5
5.0
Sign Structures
6.0
-
* The preferred Vertical Clearance under highway bridges is 6.0rn. However, in
urban areas where it is difficult to physically provide this clearance, 5.5m shall
be the absolute minimum
Other structures may be identified by Ministy of Public Works for special clearance
requirement.
Approach Slabs
Concrete approach slabs shall be used on all structures, Approach slabs sewer a
dual purpose of providing a transition structure from the bridge to the approach
roadway should the roadway embankment settle and of eliminating the live load
surcharge of the abutment back wall when the conditions specified in AASHTO
3.20.4 are satisfied. Approach slabs are to be designed using the Service Load
Design Method and shall cover the entire roadway width including the shoulders,
from wing wall to wing wall.
Deck Drainage
On grade separation structures, roadway drains shall not discharge water into
unprotected embankment slopes or within 5rn of the traveled roadway below, nor
shall drains be located less than 1.5m from the centerlines of abutments or piers. In
urban areas collection of deck drainage in a pipe system may be required, with
down drains in or on pier columns discharging into storm drainage collecter
systems. Consideration should always be given to provide collector drains and
discharge systems on the approach roadway gutter rather than on the bridge.
For bridges with sidewalks, expansion joints shall be turned up at the curb line to
prevent roadway water from entering sidewalk areas. Appropriate means shall be
taken to ensure that sidewalk drainage does not pond and that the water does not
escape around the wing walls and erode the embankment.
Page 2-1
K w i t BrEdges and Highway Structures Design Manual
Chapter 2
General Feeturns of Design
2.4
Architectural Consideration
Bridges shall be designed to be slim in appearance, be in harmony with the
surroundings and respect local culture. Architectural treatment, which is simple and
elegant, shall be used when appropriate.
It is vev important to provide uniformity of design for structures in same interchange
and along a particular route.
Page 2-2
Kuwait Bridges and Highwey S h c l u t ~ sDesign Manual
Chepter 3
Loads shall be as specified in Section 3 of AASHTO except as clarified or modified
in this manual.
Design Live Loading
Highway Load (AASHTO Section 3.7): Loading on Interstate Highway
Bridges (HS20) multiplied by the factor of 1.5 (49 Tonnes).
-
Overload (AASHTO Section 3.5.2): In addition to the above, design shall
be adequate to carry infrequent "overload" of 90 Tonne, 5-axle Military
Vehicle.
One single Military Vehicle in one direction only shall cross the bridge at any one
time, occupying any traffic lane without concurrent loading in the rest of this lane (no
other normal Zraffrc). The rest of the bridge (all other lanes) can be loaded with
normal traffic in both directions. Military Vehicles in convoys shall be spaced a
minimum of IOOm.
Loading combination for overload shall be Group If3 of AASHTO with 10% value for
Maximum Unit Stress over Allowable Basic Unit Stress.
Overload Vehicle
(Dimensions in mm, Weight in Tonnes)
Dead Loads
Dead loads and dead load combinations shall be as per AASHTO. However, all
bridges shall be designed for additional load:
-
Future Wearing Surface: I . 2 k ~ l r n *applied over the entire width of roadway
from curb to curb to allow for future wearing surface. This load is in addition
to any wearing surface applied at time of construction. However, the weight
of Future Wearing Surface shall be excluded form deflection calculations.
Utilities: shall be as per specific bridge requirements. The design shall allow
for a SkNllinear metre of bridge for future utilities distributed over all the
beams uniformly.
When concrete deck slabs are used as wearing surface, the top 15mm shall
not be considered part of the structural member when computing strength
but it shall be included in dead load computation.
Page 3-1
Kuwait Bridges and Highwey Structures Design Manual
3.3
Wind Loads
Wind loads shall be applied to structures as per AASHTO. To compute wind load
intensities, wind speed shall be taken as 3 IOkph with gusts of 150kph.
3.4
Thermal Forces
Thermal forces shall be considered in accordance with AASHTO using the following
parameters:
Ambient temperature range from + 5% to + 55%
Assuming a construction temperature range of 15 "Cto 39 OC
Temperature rise (I
5 OC to 55 OC)= 40°C
Temperature fall (39 'C to 5 OC) = 34'C
Mean relative humidity: 20% to 60%
3.5
Uplift
Provisions shall be made to attach the superstructure to the substructure 'by
ensuring that the calculated uplift is resisted by tension members capable of
resisting the largest force developed under the following conditions:
100% of calculated uplift caused by combination of loadings in which live
load plus impact loading is increased by 100%.
150% of the calculated uplift at working level.
100% of calculated uplift at Load Factor level.
3.6
Seismic Loading
As a minimum, bridges have to be designed to AASHTO Section Division I-A
Seismic Design for Acceleration of Coefficient Less than 9% or 0.09 and Importance
Classification [I.
3.7
Movement Rating
Provisions shall be made in the design of structures to resist induced stresses or to
provide for movement resulting form the variation in temperature and anticipated
shortening due to creep, shrinkage or pre-stressing.
Accommodation of thermal and shortening movements will entail consideration of
deck expansion joints, bearing systems, restraining devices and the interaction of
these three items.
The required movement rating is equal to the total anticipated movement. The
calculated movements used in determining the required movement rating shall be
as per AASHTO except as modified below:
Mean Temperature: 2792.
To allow for the effect of long-term creep and shrinkage in pre-cast concrete
members, additional shortening shall be considered. For joints, 20mm per
IOOm is recommended. For bearings, 40mm per TOOm is recommended.
To allow for the effect of long-term creep and shrinkage in post-tensioned
box girder bridges, additional shortening shall be considered. For joints,
40mm per 100m is recommended. For bearings, 80mm per 100m is
recommended.
Kuwait Bridges and Hlghwey Sfnrctures Design Manual
Chapfer3
Losds
t
3.8
Bearing Friction Forces
Friction forces due to elastorneric bearing pads or TFE surfaces shall be based on
the manufacturers' data for the bearing used.
3.9
Differential Sefllernent
Differential settlement shall be considered in the design when indicated in the
Geotechnical Report. The Geotechnical Report should provide the magnitude of
differential settlement to be used in the design.
Differential settlement, if required, shall be considered the same as temperature and
shrinkage farces and included in Group IV, V and VI load combinations.
3. I 0
Distribution of Loads
The Designer shall determine distribution of Live Loads in accordance with Section
3 Part C of MSHTO.
Page 3-3
Kuwaif Bridges and Highway Sinrcbms Deslgn Menual
Chapter 4
Foundations
Foundation design shall be based on soil investigation specific to the location under
design. An Interpretive Geotechnical Report should be submitted as part of design
calculations.
Soil suwey test results shall be included with contract documents.
Design Method
Service Load Design method shall be used for designing foundations. If Load
Factor method is to be used by the Consultant, prior written permission is required
form MPW.
4.2
Superficial Soils
In most areas, the geology of Kuwait City comprises of Eocene Limestone at depth
completely obscured by superficial deposits.
The superficial deposits comprise of a lower marine sand, known locally as Gatch,
overlain by windblown sands, made ground or a combination of both. This
superficial windblown sandstmade ground was found to extend to depths of up to
6m though generally in the range f.5m to 2m.
These materials are highly variable with recorded SPT *Nnvalues in the range from
4 to in excess of 50. Due to the generally weak and variable nature of these
materials, no structures are to be founded in them.
Ground Water and Sulfates
Ground water is present at many locations at shallow depth depths. If dewatering
will be required during the construction of such structures, the designer shall
address the issue of the effect of dewatering on soil and adjacent foundation.
Remedial measures shall be specified to protect adjacent structures.
The groundwater is generally sulfate rich due to the presence of gypsum and other
minerals within the soils, and will therefore be aggressive towards concrete. Thus it
will be necessary to design any concrete structure below or close to the
groundwater to withstand sulfate attack. The designer shall refer to recognized
codes of practice to address this important issue. See Chapter 8 (Reinforced
Concrete) for additional details.
Page 4-1.
Kuwait Bridges and HMhway Structures Design Af81?l18/
Chapier 5
Retaining Wells
5. $
General
On the Kuwait Motorway System, two types of retaining walls have been
successfully used:
Non-Gravity Cantilevered Walls (reinforced concrete)
Mechanically Stabilized Earth
For mechanically stabilized earth, if proprietary systems are to be specified, the
supplier shalt be requested to submit full documentation of successful application of
the system in similar conditions. Relevant material test results shall be requested.
As a minimum the following should be included in shop drawing:
The minimum factor of safety against overturning
The minimum factor of safety against sliding
Maximum coefficient of friction against sliding
Phi angle of the backfill
Allowable bearing pressure
Minimum design life
Water table level
Elevation of footing bottom
Maximum tolerable deflection
Where utilities are to be placed near the retaining walls, the mechanically stabilized
earth using reinforcement strips or bars shall be carefully detailed to ensure that
access to such utilities is provided without having to cut the reinforcement.
Factors of Safety
Retaining Walls shall be designed for a minimum Factor of Safety as follows:
Sliding:
1.5
Overturning:
2.0
For Mechanically Stabilized Earth Wall:
Sliding:
1.5
Overturning:
2.0
Pullout Resistance:
1.5 for wall heights equal or less than 1Im
2.0 for wall heights over 11m
Bearing Capacity:
3.0
Slope Stability:
T .5
Expansion and Contraction Joints
For reinforced concrete walls, construction joints shall be provided at a distance not
exceeding 9m and expansion joints at a distance not exceeding 27m. All joints shall
be filled with appropriate joint filler.
Page 5-1
Kuwaif Bridges and Highway StrucfuresDesign Menuel
Chapter 6
Culverts
Culverts shall be designed in accordance with Section 6 of AASHTQ using similar
live loading specified for bridges in Chapter 3 of this Design Manual.
Selection of concrete and concrete protection measures shall take into account the
particular ground conditions. Because there are several areas in Kuwait with high
sulfate content combined with varying ground water depth, underground concrete
structures wilt require additional protection measures. See Section 8 (Reinforced
Concrete) for additional details.
Page 6-1
Kuwait Bridges end Highway Structures Design MBnual
Chapter 7
Su~stmtwre
The substructure shall be designed to allow easy inspection
Abutments on mechanically stabilized earth shall not be allowed except with prior
permit in writing form the MPW.
7.1
Live Load Surcharge
Where live load is present near retaining walls or abutment, a live load surcharge
load equivalent to I m of soil as a minimum shall be added.
Kuwait Bridges snd Highw~yStructrrws Design Manrrd
Chapter 8
Rehfomd Concrete
8
REINFORCED CONCRETE
Reinforced concrete design criteria shall be as specified in Section 8 of AASHTO
except as clarified or modified En this manual.
Concrete
Concrete for highway structures shall have, as a minimum, the following 28 day
Cylinder Strength:
Decks and Barriers
f ' c = 30MPa
Abutments
f ' c = 20MPa
Pier Columns and Shafts f ' c
= 30MPa
Drilled Shafts
f ' c=3OMPa
Retaining Wall Stems
f ' c = 24MPa
Footings
f1c=20MPa
For design, Cube Strength and Cylinder Strength can be assumed as follows unless
specifically listed othenvise in the design calculations:
Concrete Protection Against Aggressive Soils
Ground water is present at many locations at shallow depth. The groundwater is
generally sulfate rich due to the presence of gypsum and other minerals within the
soils, and will therefore be aggressive towards concrete. Thus it will be necessary
to design any concrete structure below or close lo the groundwater to withstand
sulfate and other chemical attack.
Concrete mix design and concrete protection requirements shall be in accordance
with BRE Special Digest (Parts 1 to 4) CONCRETE IN AGGRESSIVE GROUND
requirements. This guide is published in the UK by ConsEruction Research
Communications Limited.
The designer has to specify in design calculations the following:
Structural Performance Level SPL
Kuwait h+dges end Highway S1Nclures &sign M8nUaf
DS Class for the Soil
Aggressive Chemical Environment for Concrete (ACEC) Class for the
Ground
Concrete Grade and Cement Type
8.3
Reinforcement
When epoxy coated bars are deemed necessary by the designer, the specifications
should indicate that fusion bonded epoxy coated reinforcement steel conforming to
AASHTO M 31M (ASTMA615M) Grade 400.
All reinforcement shall be Grade 400 as a minimum.
8.4
Slab Design
Slabs shall be designed in accordance with the criteria specified in Section 3 of
AASHTO except as clarified or modified below.
All reinforcing bars shall be straight bars top and bottom, The use of truss bars will
not be permitted.
For skews less than or equal to 20 degrees, the transverse bars shall be placed
parallel to the skew. For skews greater than 20 degrees, the transverse bars shall
be placed normal to the girders.
Use of steel stay-in-place forms is discouraged and should be considered only in
special conditions and after obtaining written approval from MPW. Some
circumstances that warrant such use include: bridges over heavily traveled roads
that cannot be closed for traffic for a reasonable period and bridges with extremely
difficult access. A discussion on their use shall be made in the design concept
report. If use of steel stay-in-place forms is not recommended during design, they
will not be allowed during construction due to the extra dead load. Contractor
requests for usage during construction will not be approved.
8.5
Slab Thickness
The thickness of new deck slabs shall be designed in 5mm increments with the
minimum thickness as shown below, unless othewise directed by the MPW. Design
span shah be as defined in AASHTO. This table does not pertain to slab on grade.
Minimum Slab Thickness
Span m)
Page 8-2
fhi~kness
Imm)
0.000
to
2.100
190
2.tOV
to
2.400
200
2.401
to
2.700
2 10
2.701
to
3.000
220
3.001
to
3.300
230
3.301
to
3.600
240
3.60T
to
3.900
250
Kuwait Bridges and H ~ h w a yStructures Design Manual
CRaprer 8
Reinfoad Concrete
8.6
Protection Against Corrosion
The minimum clearance for top reinforcing in new decks shall be 55mm. For bottom
steel, 25mm is adequate.
8.7
Design Method
All reinforced concrete members that are entirely below grade such as footings, but
not ceiurnns or members that are intended to retain water, shall be designed using
AASHTO's Service Load Design method (ASD).
Deck slab transverse reinforcement shall be designed using AASHTO's Service
Load Design method (ASD).
All other members shall be designed In accordance with the applicable provisions of
AASHTO, the Strength Design method (LFD).
Page 8-3
Kuwait Bridges end Highway Structures Design Manual
Chapter 9
Prestressed Concrete
General
Prestress design criteria shall be as specified in Section 9 of AASHTO except as
clarified or modified in this manual.
Members shall be designed to meet both Service Load Design and Strength Design
(Load Factor Design) criteria as specified in AASHTO.
Prestressing steel for precast prestressed members and cast-in-place posttensioned members shall be 12.7mm diameter "Uncoated Seven-wire High Tensile
Cold Drawn Low Relaxation Strand for Prestressed Concrete" as specified in ASTM
A416, Grade 270.
Use of 15.2mm diameter strand is allowed for cast-in-place post-tensioned
members only.
The yield point stress of prestressing steel fy, may be assumed equal to 0.90 fc for
low relaxation strand.
Section properties shall be based on gross area of members. Use of the
transformed area of bonded reinforcement shall only be used for unusual structures
and only when approved.
Web reinforcement for shear shall consist of rebars, not welded wire fabric.
The minimum top cover for slab reinforcement shall be 55mm.
Allowable Stresses
The maximum allowable tensile stresses in a pre-compressed tensile zone at
service load affer losses have occurred shall be in accordance with AASHTO except
as modified below:
Allowable tension in concrete shall be based on Severe Corrosive Exposure
conditions.
For overload group, the allowable tension can be increased up to 0.5 dfc (metric
units) under service loads.
Shear
Shear design shall be in accordance with Ultimate Strength Design Method
contained in the latest M S H T O Specifications.
Prestressed concrete members shall be reinforced for diagonal' tension stresses.
Shear reinforcement shall be placed perpendicular to the axis of the member with
spacing not-to-exceed three-fourths the depth of the member.
The critical sections for shear in simply supported beams will usually not be near the
ends of the span where the shear is a maximum, but at some point away from the
ends in a region of high moment.
For the'design of web reinforcement in simply supported members carrying moving
loads, it is recommended that shear be investigated only in the middle half of the
span length. The web reinforcement required at the quartet points should be used
throughout the outer quarters of the span if the critical shear section is included
within the design section.
For continuous bridges whose individual spans consist of precast, prestressed
girders, web reinforcement shall be designed for the full length of interior spans and
Page 9-1
K u W W g e s end H @ h y Shcfures Design Manuel
for the interior three-quarters of the exterior span and based on the critical shear
design section.
9.4
Concrete
The following concrete strengths are the acceptable. Use of higher strengths may
require prior approval of MPW.
= 35MPa
Maximum Fc = 41MPa
Minimum f'c
9.5
Precast Pre-tensioned I-beams
9.5-d
Live Load Continuous Beams
To minimize the number of deck joints, girders shall be designed as composite
section, simple supported beams for live load plus impact and composite dead load.
The superstructure shall be constructed continuous with the negative moment
reinforcing designed considering continuity over intermediate supports for live load
plus impact and composite dead loads. The positive moment connection may be
designed using the method described in the PCA publication 'Design of Continuous
Highway Bridges with Precast, Prestressed Concrete Girders". In determining the
positive restraint moment, use 30 days as the length, of time between casting the
girders and deck closure. The development length of the strands may be based on
the criteria contained in Report No. FHWA-RD-77-14, 'End Connections of Pretensioned I-beam Bridges" November 1974. In determining the number and pattern
of strands extended, preference shall be given to limiting the number of strands by
increasing the extension length and alternating the pattern to increase contractibility.
9.5.2
Debonded Strands
When using strands to pretension, precast beams, the use of de-bonded strands
shall be limited to end blocks.
9-5.3
Deflection
The Release Deflection equals the deflection the prestress girder undergoes at the
time of strand release. The Release Deflection includes the dead load of the girder
and the release prestressing force (including the effects of elastic shortening).
The Initial Deflection equals the deflection the prestress girder undergoes at the
time of erection prior to the diaphragm or deck pours. The Initial Deflection includes
the deflection due to the dead load of the girder, the initial prestressing and the
effects of creep and shrinkage up to the time of erection. The time of erection
should be assumed to be 60 days after release.
The Final Deflection equals the deflection due to the dead load of the deck slab,
diaphragms and barriers and the effects of long term creep on the composite
girders. The effects of the future wearing surfaces shall be excluded from deflection
calculations.
Minimum build-up (Haunch) at the edge of Type 111 girders and smaller shall be
15rnrn. For Type IV, V and VI girders the minimum build-up shall be 25mm. This
minimum build-up at the critical section will ensure that the flange of the girder will
not encroach into the gross depth of the slab.
The tops of the erected girders shall be surveyed in the field prior to placement of
the deck forming. If the tops of the ereGded girder elevations are higher than the
Page 9-2
Kuweif Bn-dges and Highway Slmtures Design Manual
Chapter 9
Prestressed Concrete
finish grade plus camber elevations minus the deck slab and buildup thickness,
adjustments will have to be made in the roadway profile or in the girder seat
elevations. Encroachment into the slab of up to 15mm will be allowed for random
occurrences.
9.5.4
Shear
The value of 'd" to be used in shear calculations shall equal the depth of the beam
plus the effective depth of the slab with a minimum d = 0.80 times the overall depth.
The shear shall be calculated assuming full continuity for composite dead load and
live load plus impact.
For single span structures, use the shear design spacing at the X point for sections
from the end of the beam to % point. For continuous multi-span structures, use the
shear design spacing required from the % point to the pier for the section from the %
point to the abutment end to obtain a symmetrical reinforcing pattern for all girders.
9.5.5
Method of Analysis
The dead load shall be assumed to be unsupported and carried by the girders only.
The location of the harped point of the strand should be located as required by
design with the preferable locations being near the 1110 of the span as measured
from the midspan of the girder.
9.5.6
Bearing Pads
Laminated neoprene bearing pads should be used for relatively light reactions and
moderate superstructure movements.
Pot type bearings should be used for heavy reactions large superstructure
movements and superstructure on horizontal curve alignment.
Allow an extra 40mm movement per 100m of girder length for long-term creep and
shortening due to prestressing.
Elastomeric bearing pads will be a maximum width of 50mm less than the normal
width of the botdorn flange to accommodate the 20rnrn side chamfer and should be
set back 50mm from the end of the girder to avoid spalling of the girder ends,
9.5.7
Creep Factor
Use a creep actor of 3 when calculating long-term deflections.
9.5.8
Oifferentiai Shrinkage
Differential shrinkage should be considered in the design when the effects become
significant and when approved by the Project Manager.
9.5.9
Method of Analysis
AASHTO Type V and Type VI modified girders should be used in place of type V
and type VI regular girder whenever possible.
The theoretical build-up depth shall be ignored for calculation of composite section
properties.
Post-tensioned Box Girder Bridges
Post-tensioned Box Girder Bridges shall be designed in accordance with AASHTO
specifications. Girders shall be designed by Working Stress Method and checked
Page 9 3
K m i t Bddges and Highway Sh-ucturas Design Menual
by the Ultimate Stress Method (Load Factor Design). The deck slab is to be
designed by the Working Stress Method. Concrete strength to be used is similar to
previous section.
9.6.1
Bearing Pads
Allow an extra 80mm movement per 7OOm of girder length for long-term creep and
shortening due to post-tensioning.
9.6.2
Creep and Shrinkage
For restrained members in continuous bridges where shortening due to posttensioning induces moments and shears, a shrinkage and creep coefficient of 1.5
shall be used for design of substructure elements with the total movement equal to
1.5 times the initial shortening. For superstructure elements, no creep factor should
be applied except for long-term deflection considerations.
9.6.3
Flange and Web Thickness - Box Girder
Minimum top slab thickness shall be 19Omm. Minimum bottom dab thickness shall
be 150mm. Minimum web thickness shall be 300mm (measured normal to girder
for sloping exterior webs). Interior webs shall be constructed vertical.
9.6.4
Diaphragms
A single 250mm thick intermediate diaphragm shall be placed at the mid-span for all
bridges. Special consideration for additional diaphragms should be given to box
girders with large skews, curved boxes and boxes over 2m in depth. Diaphragms
shall be placed parallel to abutments and piers for skews less than or equal to 20
degrees and normal to girders and staggered for skews over 20 degrees.
Diaphragms shall be cast integral with girder webs.
9.6.5
Deflections
The deflection shall be calculated using dead load including barriers, but no the
future wearing surface, a modulus of elasticity Ec = 4800 df c (MPa), gross section
properties and calculated final losses. The additional long-term deflection shall be
calculated by multiplying the deflection by b o .
An additional parabolic shaped deflection with a peak equal to 30mm per IOOm
should be added to the total deflection for simple spans.
The final long-term deflection shall be the sum of the dMection, the additional longterm deflection and the additional deflection for simple spans. The camber shown
on the plans shall be the final long-term deflection.
9.6.6
Allowable Stresses - Prestressing Steel
In calculating the stress in the Prestressing steel after seating, the friction and
anchor set losses only should be included. For post-tensioned members,
overstressing for short periods of time to offset seating and friction losses is
permitted but the maximum allowable jacking stress for low relaxation strand shall
be limited to 0.78 f s.
9.6.7
Allowable Stresses - Concrete
In calculating the temporary stress in the concrete before losses due to creep and
shrinkage, the friction, anchor set and elastic shortening losses should be included.
Page 9-4
KrrweH Bridges and Highway Stwctures Design Manual
Chapter 9
Prestressed Concrete
Special consideration shall be given to bridges supported on false work with large
openings where deflections could be harmful to the structure. Unless false work
requirements are strengthened or other means taken to ensure the bridge does not
form tension cracks prior to tensioning, the maximum allowable tension in a precompressed tensile zone shall be limited to zero.
9.6.8
Loss of Prestress
For multi-span bridges, the cable path should have its low point at the mid-span.
If the information of actual system to be used in post-tensioning is not available, the
design should be based on usage of galvanized rigid ducts with K = 0.00066 (per
metre) and p = 0.25. Anchor set losses should be based on 16mm set.
For creep of concrete, the variable fcds should be calculated using the total dead
load applied after prestressing, including the 1.2 k ~ l r future
n ~ wearing surface.
9.6.9
Flexural Strength
In determining the negative ultimate moment capacity, the top layer of temperature
and shrinkage and bottom layer of distribution reinforcing may be used. In
determining the positive ultimate moment capacity, the longitudinal flange
reinforcing may be used.
9.6.10
Shear
Girder webs will be designed for shear using the Ultimate Strength Method.
The maximum girder web stirrup spacing will be 300mm within 6m from the front
face of the abutment diaphragms. This will eliminate the need for re-spacing the
web stirrups at the point of web Rare if the post-tensioning system requires flaring,
The value of "d"to be used in shear calculations shall be the larger of the calcutated
"dl'value or 0.8 times the overall effective depth.
Horizontal shear shall be investigated in accordance with the provisions of AASHTO
9.20.4.
Calculations shall include the shear due to secondary moment and cable shear. For
curved box girder bridges, the shear due to torsion shall be included.
9.6.11
Flange Reinforcement
Reinforcing in the bottom slab of box girders shall confom to the provisions of
AASHTO 8.17 except that the minimum distributed reinforcing in the bottom flanges
parallel to the girders as specified in AASHTO 8,17.2.3.T shall be modified to be
0.30percent of the flange area.
9.6.12
Method of Analysis
The superstructure may be designed using the system as described below:
The bottom slab, in the vicinity of the intermediate support, may be flared to
increase its thickness at the face of the support when the required concrete
strength exceeds 320 kglcm2. When thickened, the bottom slab thickness
should be increased by a minimum of 50 percent. The length of the flare
should be at least one-tenth of the span length (measured from the center of
the support) unless design computations indicate that a longer flare is
required,
Page 9-5
Kuwaft Bridges end Highwey SMures Design Manual
Chapter9
Prestressed Cancrefe
Section properties at the face of the support should be used throughout the
support; i.e. the solid cap properties should not be included in the model.
Negative moments should be reduced to reflect the effect of the width of the
integral support.
Dead load forces should not produce any tension in the extreme fibers of the
superstructure.
For box girders with severe doping webs or boxes over 2m deep, transverse flange
forces induced by laterally inclined longitudinal post-tensioning shall be considered .
in the design,
Single span structures should be jacked from one end only. Symmetrical two span
structures may be jacked from one end only or jacked from both ends.
Unsymmetrical bridges should be jacked from one end or both ends as required by
the design. Three span or longer structures should be jacked from both ends.
Several prestressing systems should be checked to verify that the eccentricity and
anchorage details will work. In determining the center of gravity of the strands, the
Z factor, the difference between the center of gravity of the strands and the center of
the ducts, shall be considered.
For structures over 120m in length, in determining the c.g. of the strands, the
diameter of the ducts should 'be oversized by 13mm to allow for ease of pulling the
strands.
For horizontally curved bridges, special care shall be taken in detailing stirrups and
duct ties. Friction losses should be based on both vertical and horizontal
curvatures. In designing for horizontal curvature, the exterior web with the smallest
radius shall be used. Consideration to the -1- 5% variation allowed per web shall be
included.
,
9.7
Prestressed Voided Slab
9.7.1
End Blocks
End Blocks should be 380mm long with sufficient steel provided to resist the tensile
forces due to concentrated prestressing loads.
9.7.2
Diaphragms
Diaphragms shall be cast within the slab at midspan for spans over 12m.
9.7.3
Lateral Ties
One lateral tie shall be provided through each diaphragm located at the mid-depth
of the section.
9.7.4
Shear Keys
After shear keys have been filled with an approved non-shrink mortar, lateral ties
shall be placed and tightened.
9.7.5
Barriers
Barriers shall have a 6mm open joints at the mid-span to prevent the barrier from
acting as an edge beam and causing long-term differential deflection of the exterior
beam.
Kuwait Bridges end Highway Stmtures Design Menual
Chepfer 9
P~stressedConcrete
9.8
Prestressed Box Beams
9.8.1
End Blocks
End Blocks 450mm long shall be provided at each end and sufficient steel shall be
provided in the end blocks to resist the tensile force due to the prestressing loads.
9.8.2
Diaphragms
Diaphragms, cast within the beam, shall be provided at the midspan for spans up to
15m, at the third points for spans from 15m to 22m and at quarter points for spans
over 22m.
9.8.3
Lateral Ties
One lateral ties shall be provided through each diaphragm located at the mid-depth
of the section. However, for the 990rnrn and 1065rnrn deep sections, when adjacent
units are tied in pairs for skewed bridges, in lieu of continuous ties, We ties shall be
provided, located at the third points of the section depth.
9.8-4
Shear Keys
After shear keys have been filled with an approved non-shrink, low slump mortar,
lateral ties shall be placed and tightened.
Page 4 7
Kuweif Bridges and Higtnwy SImtures Design Manuel
Chapter 10
Sfmturel Steel
'to
Structural steel design criteria shall be as specified in Section 10 of AASHTO except
as clarified or modified in this manual.
10.1
Design Method
The Service Load Design Method (allowable stress design) shall be used except
that the strength design method (load factor design) may be used for major or
unusual structures when approved.
Materials
Material shall conform to the requirements of AASHTO article 10.2 with the
selection based on stress requirements and over all economy.
The preferred maximum thickness of tension flanges is 50mm. Tension flanges
thicker than 50mm shall be normalized.
Allowabfe Fatigue Stresses
Splices stiffeners, shear connectors and bracing details shall be designed
categories. A through C details in order to limit the fatigue stress.
using
Category E details shall not be used.
Load Cycles
The stress cycle case to be used in AASHTO, Table 10.3.2shall be Case 1.
Charpy V-Notch Impact Requirement
M e r e applicable, the Charpy V-Notch impact requirements for structural steel shall
be for temperature Zone I.
Stiffeners and Connections
Intermediate stiffeners shall be placed only on the inside face of exterior girders.
The number and the location of the girder shop and field splices shall be determined
so as minimize fabricated and erected mst of the girders.
All connections except field connections shall be welded. ASTM A325M high
strength bolts shall be used for field connections.
Page 10-1
Kuwait Bridges and Highway Shuctums Design Manual
Chapter II
Expansion wd Contraction
'l
11
EXPANSION AND CQNTRACTION
1?.I Movement Criteria
Provisions shall be made in the design'of structures to resist induce stresses or to
provide for movements resulting from variations in temperature and anticipated
shortening due to creep, shrinkage or prestressing. Accommodation of thermal and
shortening movements will entail consideration of deck expansion joints, bearing
systems, restraining devices and the interaction of these three items.
The main purpose of the deck joints is to .seal the joints opening to obtain a
watertight joint while allowing for vertical, horizontal and or/ rotational movement.
The bearings are required to transmit the vertical and lateral loads from the
superstructure to the substructure units and to allow for movement in the
unrestrained directions.
Restraining devices are required to limit the displacement in the restrained
directions. Improper design or construction of any of these devices could adversely
affect the operation of the other devices.
The required movement rating is equal to the total article movement (i.e. the
difference between the widest and the narrowest opening of a joint). The calculated
movements used in determining the required movement rating shall be as specified
in AASHTO except as modified below:
Mean temperature and temperature ranges shall be as specified in this manual.
f o allow for the effects of the long term creep and shrinkage in precast prestressed
concrete members, the following additional shortening shall be considered:
Joint:
20mm per IOOm
Bearings:
40mm per 100m
To allow for the effects of long term creep and shrinkage in post-tensioned box
girder bridges, the following additional shortening shall be included:
Joints:
40mm per IOOm
Bearings:
80mm per 100m
Kuwait Brjdges and Highrey Stm1ums Design Manual
Chapter f2
Deck Joints
Kwait rnotonvay system has utilized several types of joints. Many joints have
exhibited problems with mortar infill adjacent to asphalt pavement. Therefore, for
shod span bridges, joints at piers shall be eliminated as much as possible by using
continuous deck construction.
When deck joints are used, they shall be designed properly and durable deck joints
shall be specified.
Movement Rating
The movement rating for joints for steel structures shall be based primarily on the
thermal expansion and contraction characteristics of the superstructure, while for
concrete structures the effect of shortening due to creep and shrinkage and where
applicable, prestressing shall also be based on the temperature variations as
measured from the assumed mean temperature.
Published movements ratings are usually based on the difference between the
maximum and minimum opening without consideration to the required minimum
installation width. In determining the movement rating, consideration must be given
to the installation width required ta install the seal element.
Other factors, which should be considered in the determining the required
movement rating, include consideration of the effects of any skew, anticipated
settlement and rotations due to live loads and dead loads, where appropriate.
Items requiring attention include:
The type of anchorage system to be used.
The method of joint termination at the ends.
The method of running joints through barriers, sidewalks andIor medians.
Physical limit of size of joints.
Susceptibility of joint to leakage.
Possible interference with post-tensioning anchorages.
Selection of appropriate modular proprietary systems that meet design
requirements.
Forces applied to the surrounding concrete by the joint.
Available types of joints include compression seal strip seals, and nodular joints.
Compression seal joints and strip seal joints are generic and should be detailed on
the plans, by standards and or/ covered in the special provisions. Modular joints are
proprietaty and require that the designer specify allowable joint types and style in
the special provisions. Information concerning specific design parameters and
installation details of modular joints should be obtained from literature supplied by
the manufacturer of the system. It is the responsibility of the designer to review the
proprietaw joint literature and related manufacturer' specifications to ensure that the
selected joints types are properly specified and compatible with the design
requirements.
The following features of joints should be shown on the plans or shop drawings:
Blockout details showing a second pour, including blockout dimensions and
additional reinforcing required,
Page 12-1
Kuwait Bridges and Highway Structures Design Manual
Chapter 12
Deck Joints
Required end treatment in barriers or curbs, including enough details or
explanation to accommodate each of the proprietary systems selected (i.e.
cover plates, etc).
Consideration to traffic control in determining section pattern lengths.
Movement rating.
Assumed temperature and opening at time of installation with temperature
correction factors.
Actual horizontal length of joint measured from in side of the barrier face to
inside of barrier face corrected foe skew.
For modular joints, the joints style, gland type, steel edge beam material
shall be specified.
'I2.2
Common Deck Joint Types
12.2.1
compression Seals
The compression seal element should have a shape factor of I:Itwidth to height) to
minimize sidewall pressure. The size of the compression seal shall be specified on
the plans.
Effective movement ratings for this type of joint range up to 50rnm, Advantages for
this type of join include its low cost, proven performance and acceptance for use on
pedestrian walkways. However, this type of joint cannot be unbolted and easily
raised, generates pressure and it is not good for high skews or horizontal direction
changes.
12.2.2
Strip Seals
Effective movement ratings for this type of joint range up to 100mm. This type of
joint is best used when the movement rating is beyond the capacity of compression
seals and for large skews. Strip seals joints will require cover plates for pedestrian
walkways.
12.2.3
Modular Joints
Modular joints are very complex joint systems. Effective movements ratings range
from 100mm up to 750rnrn. Modular joints are the best choice for movement's
ratings over 100mm.
Page 12-2
Kvweit Bridges and Highway SImtures Design Manuel
Kuwait motorway bridges built in the early 1980's have exhibited severe bearing
deterioration such as excessive bulging, tearing, and separation of laminated pads.
The fojlowing recommendations shall be addressed in design and detailing of
bearings for new bridges.
Bearings shall be accessible and easily inspected by providing enough
vertical and lateral clearances.
Pot bearings should not be covered and should have permanent marking
indicating initial position (rotation and displacement) and height (when
loaded) of bearing.
Bridge seat and beam end diaphragms shall be detailed to allow jacking of
bridge from bridge seat whenever is practical in case of bearing replacement.
Design of fixed bearings should avoid using elastomeric pads with holes for
anchor rods as this makes bearing replacement extremely dimcult.
r
Cln-reinforced elastomeric bearing pads shall not be used unless for very
light leading.
Reinforced elastomeric pads shall be of neoprene (not natural rubber) and
used only for short span precast beams.
Movement Criteria
Because bearings must be designed to install at temperatures other than the mean
temperature, the movement rating should be based on the full temperature range
and not the rise or fall from a mean temperature. Calculation of the movement
rating shall include:
Thermal movement, shortening due ta creep, shrinkage and prestressed
shortening.
For cast-in-place post-tensioned concrete box girder bridges both the elastic
and long term prestress shortening effects shall be considered.
An initial offset of the top sliding surface from the centerline of bearing should be
calculated and shown on the plans or shop drawings so that the top sliding surface
will be centered over the bottom sliding surface and the centerline of bearing afler
all shrinkage, creep and post-tensioning shortening has taken place in the
superstructure.
Types of Bearings Recommended
Permissible beating types include, elastomeric bearing pads, steel bearings, sliding
elastomeric bearings and high- laad multi-rotational bearings (pot, disc or spherical).
Because of previous problems with existing bearings, all bearings types including
electrometric bearing pads shall be designed for impact.
Elastomeric Bearing Pads
Elastorneric bearing pads shall conform to the requirements of AASHTO. Bearing
pads shall be designed and to be constructed using steel laminates. If fiberglass
laminates are needed, this has to be indicated. The following data should be shown
on the plans or shop drawings:
Length, Width and Thickness of Pad
Page 13-3
KWH
Bridges and Highway
Stnretures Design Manual
Chapter $3
Beerings
Owrometer Hardness
1
Design Methods (A or B)
Design Load
Low temperature tone (A, B or C)
Elastomer Grade (0,2 or 3)
Shear Modulus
Generally, bearing pads shall be Durometer 60-Elastomer with steel reinforcement.
Design Method A shall be used for design. If space constraints require smaller
bearings and Design Method B is used to justify smaller bearings, the specifications
shall dearly indicate the required testing and quality control procedure required.
Pads shall have a minimum thickness of 25mm and generally with maximum
thickness around t OOrnm. Holes will not be allowed in the pads.
Where possible, width and length dimensions shall be detailed in even 50mm
increments.
Where used with prestressed I-girders, pads shall be sized a minimum width of
50mm less than the nominal width of the girder base to accommodate the 20mm
side chamfer and shall be set back 50mm from the end of the girder to avoid
spalling of the girder ends.
Elastameric pads should not be used in cases where deck joints or bearings limit
vertical movements, such as in holder style sliding steel plate joints or widening
where existing steel bearings are !to remain.
Where elastomeric bearing pads with greased sliding plates are used on posttensioned box girder bridges to limit the required thickness of the pad, the pad
thickness should be determined based on temperature movements only, with the
initial and long term shorfening assumed to be taken by the sliding surface.
Elastameric bearing pads are the preferred bearing type for new steel girders,
precast prestressed girders and short span post-tensioned box girder bridges.
Steel Bearings
Steel bearings may consist of rockers or fixed or expansion assemblies, which
conform to the requirements, specified in Section 1 Q of AASMTO.
Steel bearings are not a preferred bearing type and their use should normally be
limited to situations where new bearings are to match the existing bearings type on
bridge widening projects,
Sliding Elastomeric Bearings
Sliding elastomeric bearings consist of an upper steel bearing plate anchored to the
superstructure, a stainless steel undersurface and an elastorneric pad with Teflon
coated upper surface. The Teflon surface shall be attached to a IOmm minimum
thick plate, which is vulcanized to the elastorneric pad. The bearing accommodates
horizontal movement through the Teflon sliding surface and rotation through the
elastomeric bearing with the thickness of the elastomeric bearing determined by the
rotational and friction force requirements. Keepers may be used for horizontal
restrain of the pads. Anchor bolts with slotted keeper plates may provide vertical
restraint or individual vertical restraint as appropriate. The pad dimensions and all
Page 1 9 2
:, ) -
Kuwait BrEdges and Highwey Stuetutes Design Manual
Cheprer if3
Beatims
details of the anchorage and restraint systems shall be shown on the plans. The
special provisions should allow for proprietary alternates.
Sliding elastorneric bearings should be considered for applications where regular
elastomeric bearing pads would exceed 100mm in height or where special access
details would be required for other proprietary bearings in such places as hinges.
13.2.4
High Load Multi-Rotational Bearings
High load multi-rotational fixed bearings consist of a rotational element of the Pottype, Disc-type or Spherical-type. High-load. multi-rotational expansion bearings
consist of a rotational element of the Pot-type, Disc-type or Spherical-type, sliding
surfaces to accommodate translation and guide bars to limit movement in specified
directions when required.
Pot bearings consist of a rotational element comprised of an elastorneric disc totally
confined within a steel cylinder. Disc bearings consist of a rotational element
comprised of a polyether urethane disc confined by upper and lower steel bearing
plates and restricted from horizontal movement by limiting rings and a shear
restriction mechanism. Spherical bearings consist of a rotational element comprised
of a spherical bottom convex plate and mating spherical top concave plate.
These design criteria were prepared for the broad range of normal applications and
the specified limits of loads, farces and movements. The design and manufacture of
multi-rotational bearings relies heavily on the principles of engineering mechanics
and extensive practical experience in bearing design and manufacture. Therefore, in
special cases where structural requirements fall outside the normal limits, a bearing
manufacturer should be consulted.
13.2.4.1
Rotational Requirements
he' rotational requirements of these bearings are treated in a new way.
Rotational requirements of the bearings, Rb, are determined by:
Rb= Rs+Rc
Where
Rb = Rotation capacity designed info the bearings.
Rs = Anticipated rotation of the structure in service. (Includes live loads and
rotations induced by constructionIerection sequences).
Rc = Rotation induced in the bearing by construction tolerances, 0.02 radians
maximum.
13.2.4.2 Use
-
Use of mufti rotational bearings is especially indicated where:
Low profile, high load bearings are required.
.
Long span, curved, or skewed bridges and other similar structures of
complex design are required.
Long slender columns or light frames and members exhibit minimum
stiffness or rigidity.
Settlement of the substructure is anticipated.
Self-aligning capabilities are required.
Large movements are anticipated.
Kuweit Brfdges and Highway Slnrctures Design Menuat
Chapter 73
Economical, long life, or low maintenance bearings are desirable.
Regular eiastomeric bearing pads would exceed 100mm in height.
7 3.2.4.3 Design Criteria
Since special details are required to allow for access of inspection, repair or
replacement of the bearings, the replacing of joints to eliminate the need for use
these bearing types should be considered.
Some structural considerations in use of multi- rotational bearings are listed
below. Reference to "this specification" refers to the design criterja below.
1. Vedical and horizontal loads shall be assumed to occur
simultaneously. All loads are service loads. Minimum vertical laads
are dead loads and superimposed dead loads excluding the future
wearing surface, and live loads and impact.
2. The total recommended clearance between all guiding and guided
sliding surfaces is 1.5mm in order to limit edge stress on guiding
interfaces.
3. Avoid specifying total spacing of more than 1.5mrn between guides
and guided components where possible.
4. In specifying the horizontal force capacity of bearings, i is
recommended only one fixed or guided expansion bearing shall be
assumed to resist the sum of all the horizontal forces at each
abutment. Bent, column, hinge or pier.
5. Where feasible provide at last two fixed or guided expansion bearings
each able to resist all horizontal forces at each abutment, column,
hinge or pier far design redundancy.
6. Some press-fit guide bar details in common use have proven
unsatisfactory in resisting horizontal loads. When analyzing these
designs, consideration should be given to the possibility of rolling of
the bar in the recess.
7. Multi-rotational bearings should not be used at vertical loads less
than 20% of their vertical capacity. Bearings for less than 20%
vertical capacity require special design.
8. Special consideration in bearing design shall be given where high
horizontal to vertical load (above 0.30)is anticipated.
9. Frictional resistance of bearing slide surfaces should be neglected
when calculating horizontal load capacity.
do. The installed alignment of bearing guiding systems relative to the
anticipated movement direction of the structure should be carefully
considered to avoid bearing guide system failure. Special studies or
designs may be required on curved or skewed structures to ensure
correct installation.
11. The substructure and superstrwcture should be designed so as to
remain rigid under all service conditions in areas around and in
contact with the bearings, paying particular attention to the use of
stiffness at extreme points of movements.
Kuwslt Btiuges and HIQ~?W@YShuctums Desjgn MenueE
A2. The substructure and superstructure design should permit bearings to
be removed for inspection or rehabilitation by minimum jacking of the
structure. Jacking points shall be provided in the structural design.
13, The minimum structure rotational, Rs, of bearings covered in the
specification is 0.01 radians. Rs comprise live loads and rotations
induced by constructionlerection sequences.
14. The maximum construction rotation, RG (rotation induced by
construction tolerances), is 0.03 radians but is cautioned to
investigate the cost and practicality of the changes contemplated.
15. Recommended coefficients of friction for structure design follows:
Untilled sheet or woven fiber
PTFEfstainless steel 0.04
Filled PTFE sheetlstainless steel 0.08
The above coefficients of friction are based on he average stress and
limits of edge stress of PTFE in this specification. Out of level
installations within the limits of this specification and normal in service
oxidation of the stainless steel mating surface. Service conditions,
where exceptional corrosion of the stainless steel mating surface may
occur, will require special assessment of the long-term coefficient of
friction.
16. Pot, disc and spherical multi-rotational bearings should not be mixed
at the same expansion joint or bent. The differing deflection
characteristics and differing rotation characteristics may result in
damage to the bearings and 1 or structure.
17.
Contract drawings and documents should contain a bearing
schedule.
18.
Some bearing tests are very costly to perform. Other bearings tests
cannot be performed because of the unavailability of test equipment.
The following test requirements should be careful'ly considered before
specifying them:
Vertical toads exceeding 2,250,000kg.
Horizontal loads exceeding 225,000kg.
The simultaneous application of horizontal and vertical loads
where the horizontal loads exceeds 75% of the vertical loads.
Xriaxial test loading.
The requirement for dynamic rotation of the test bearing while
under vertical loads.
13.3
Bearing Schedule
A bearing schedule shall be included in the contract drawings or as built documents
and shall contain the following as minimum:
A schedule of all minimum and maximum vertical and horizontal service
loads.
Minimum structure and construction rotation requirements.
Magnitude and direction of movements at all bearing support points.
Page 13-5
Kuweit W g e s and Highmy S f m f u ~Design
s
ManuaE
Chapfer f3
Bearings
Quantity, type (fixed, expansion or guided expansion).
Plan view, alignment and location of all bearing units.
Allowable upper and lower bearing contact pressure.
Fixing or anchorage details and I or requirements.
9
Grades, bevels and slopes of all bearings.
Allowable coefficient of friction of slides surfaces.
Surface coating requirements and the appropriate specifications.
Seismic requirements, if any.
Uplift details, temporary attachments or other requirements.
Installation scheme.
Bearing preset details, if required.
Design rotation movement and other requirements in the bearing schedule should
only refer to the requirements of the structure where the bearings are to be used.
Page $ 3 6
Kuwait E w e s and Highway Shretures Design Manual
Restraining devices are meant to prohibit movement in a specified direction.
Restraining devices shall be designed to resist the imposed loads including
earthquakes as specified in AASHTO and as modified in this manual.
Restraining devices could include concrete shear keys or end blocks, horizontal or
vertical cable restrainers or mechanical restraining devices that would be an integral
part of bearing or a separate system. Restraining device to prohibit vertical
displacement at expansion ends shall be designed to allow for inspection and future
replacement of bearings.
Allowable restraining devices include, but are not limited to the following: vertical
fixed restrainers, vertical expansion restrainers, external shear keys, internal shear
keys and keyed hinges.
14.1
Vertical Fixed Restrainers
Vertical fixed restrainers consist of cable and appropriate hardware and are
designed to allow rotation but no translation in either horizontal directions.
14.2
Vertical Expansion Restrainers
Vertical expansion restrainers consist of cable and appropriate hardware and are
designed to allow rotation and longitudinal translation but no transverse translation.
Some limited vertical displacement is allowed to permit replacement of bearing if
required.
14.3
Shear Keys
Shear keys are reinforced blocks designed to limit transverse displacement while
allowing longitudinal and rotational movements. External shear keys are preferable
to internal restrainers since they are more accessible for repairs and easier to
construction.
94.4
Keyed Hinge
A keyed hinge is a restraining device, which limits displacements in both horizontal
directions while allowing rotation.
For a typical expansion seat abutment where restraining devices are required, the
restraining devices will consist of vet-tial expansion restrainers and external shear
keys.
For a typical seat abutment for a post-tension box girder bridge, restraining devices
will consist of vertical fixed restrainers and external shear keys. For a typical pinned
seat abutment for a prestressed girder bridge, restraining and external or internal
shear keys.
For a typical pinned pier, restraining devices will consist of vertical expansion,
restrainers and internal shear keys.
For a typical pinned pier, restraining devices will consist of vertical fixed restrainers
and internal shear keys or a keyed hinge.
Page 14-1
Kwsit Bfidges end Highway Structures Desfgn Manual
Chapter f5
Sign SuppoH Structures
Sign support structures shall be designed in accordance with AASHTO1sStandard
Specifications for Structural Supports for Highway Signs, Luminaries and Traffic
Signals.
Page 15-1
Kuwait Bndges and Highwey Stmchms Design Manual
Chap& 16
Pedestrian Bridges
Pedestrian bridges shall be designed in accordance with AASHTO's Guide
Specifications for Design of Pedestrian Bridges except as clarified or modified in this
manual.
16.1
Design Loads
16.1.3
Pedestrian Live Load
Pedestrian Live Load shall be as per Section 1.2.1 of AASHTO1s Guide
Specifications for Design of Pedestrian Bridges. However, Live Load shall not be
less than 4.3kPa for walkway area,
16.1.2
Vehicle Load
When ramps are used the b~idgeshall be designed for a maintenance vehicle. If not
specified by MPW, the maintenance vehicle shall be:
When the bridge dear deck width is less than 3.00rn, H-5 x 1.05 truck shall
be used with total weight of 47kN.
When fhe bridge clear deck width b larger than 3.00m, M-10 x 1.05 truck
shall be used with total weight of 94kN.
All bridges regardless of width shall be designed for a single load equal 25kN
placed at location to produce maximum stress.
16.2
Design Details
In addition to the requirements of Section 1.3 of AASHTO's Guide Specifications for
Design of Pedestrian Bridges, the following shall apply:
16.2. t
Stairs and Ramps
Where necessary or as directed by the owner, ramp type approaches shail be
provided in addition to auxiliary stairways.
The ramps shall be 2.5m wide with a maximum grade of 8.33%. The preferred
grade is 5%, which shall be used where possible.
Where the total rise of a ramp exceeds 3.5n-4, horizontal landings shall be provided
at equal intervals along the length of the ramp. Each section of ramp shall not have
a rise more than 3.5m. The length of the landing shall not be less than 2m.
When ramps are provided, auxiliary stairnays width shall be no less than 1.Elm. For
auxiliary stairways, the stairs shail have 280mm treads and 180rnrn risers. Non-slip
nosing shall be provided on stairs with Intermediate platforms.
In special circumstances where provision of ramps and auxiliary stairs is not
possible, stairs only or ramps only can be provided. This will require prior approval
MPW.
Where stairs only are used:
The number of steps in single flight of stairs shall not be more than 20.
The risers and treads of each step in a single flight shall be uniform.
The riser shall not be more than 150mrn and the treads shall not be less than
30Omm.
Page 16-1
KuwsH Bndges and Highway Stnrdutes Design Manuel
Chepter 36
Pedestrien Bridges
Completely open risers are not acceptable.
16.2.2
Handrails
Handrails shall be provided on both sides of stairs, ramps and ramp approached.
16.2.3
Walkway
The width of walkway shall be no less than 2.0rn. When the bridge is covered or a
canopy is provided the minimum headroom for all walks shall be 2.3m.
The surfacing of walkways shall be have a slip resistant finish which has a skid
resistance against rubber, leather or composition of sole material of not less than 65
units under wet conditions.
f 6.2.4
Railing
Railing for pedestrian bridges must comply with the geometry and strength
requirements of current AASHfO's Standard Specifications for Highway Bridges
Section 2.
Pedestrian railing openings between horizontal or vertical members must be small
enough that a 150mm sphere cannot pass through them.
Railing can be metal or concrete or combination of the two materials.
Where the walkway is near residential areas or where people would be present
around the bridge, consideration shall be given to providing a solid railing, which
provides visual barrier and protect the privacy of users of bridge and nearby
residences.
16.2.5
Enclosed Walkways
Enclosure may be required to protect users from direct sunlight or to prevent users
of the bridge from dropping objects on highway. Enclosure will only be needed
when specified by the MPW.
16.2.6
Lighting
Pedestrian bridges shall be illuminated adequately.
Page 16-2
Ministry of Public Works
Roads Administration
PART 3
Kuwait Highway Drainage
Design Manual
Edition 1
March 2004
Tabk of Contents
TABLE OF CONTENTS
1.1
Planning and Coordination
2.1
Design S torn----------
2.2
Catchment Areas
2.3
Rational Method
3.1
Pavement Drainage
---
1-7
2-1
--
--
2-7
3-1
3.2 Storm Drains
6
2-6
3-4
3.3
Roadside Channels
3-7
3.4
Storage Facilities-
3-7
3.5
Stormwater Pumping Stations
3.7
Subsurface Drainage
3.8
Highway Crossing Culverts
3-9
4.1
Utilities
4-7
4.2
Right-of-way-
4-1
4.3
Service Life
4.4
Environmental Issues -
5.1
Hyd~+ology
-
5-1
5.2
inlets
5-1
5.3
Conduits--
5.4
Other
-
3-7
-3-8
-4-1
-
4-1
---
-5-1
Losses
5-2
5.5 Cost Estimating
5-2
DOCUMENTATION, CONSTRUCT~ON
AND MA IWNAHCE---------------------------
6-1
6.1 Documentation6.2
6-1
--
Construction
6.3 Maintenance
-
---
6-1
6-2
Kuwaif Highway Wrainege Deslgn Manuel
Stormwater drainage for Kuwait highway systems shall be designed in accordance
with Highway Drainage Guidelines, AASHTO. The Kuwait Highway Drainage
Design Manual is not intended to replace AASHTO. It is a supplement that gives
guidanoe on the interpretation of AASHTO's requirements as they relate to local
conditions in Kuwait.
Highway drainage should be designed to be compatible with existing drainage
patterns and facilities. It should also protect the highway and the road user from the
hazards of flooding. The purpose of highway drainage is threefold.
To prevent adverse interference to existing drainage systems.
To protect the travelled roadway from design flood events.
To provide for the removal of storm water from the roadway sub grade and
the embankment.
This manual is primarily concerned with stormwater from rain falling within the rightof-way and from adjacent overland flow. Guidance is given on how to design
drainage systems that collect, convey and discharge stormwater runoff. Stormwater
drainage systems may include the following elements:
Pavement drainage
Inlets
Storm drains
Roadside drainage channels
Stormwater storage facilities
Pumping stations
Subsurface drainage
Highway crossing culverts
Advice is also given on culvert design for cross drainage provision at wadi crossings
or open channels, computer modelling, and system construction and maintenance.
1.q
Planning and Coordination
Planning and coordination should begin early on in the project with a
comprehensive study of the existing drainage patterns and facilities, followed by an
examination of the potential impacts of the proposd highway.
Close
cemmunicartion and coordinate with all agencies that have interests E
n drainage
matters will help the designer provide a drainage system that will benefit both the
highway user and the local residents or businesses. Agencies include MPW, EPA
and Kuwait Municipality.
Page 1-1
K m i t Hbhway Dminage Design ManuaE
Stormwater drainage design is dependant on an estimate of magnitude, voiurne and
distribution of stormwater runoff. An overestimate of run-off may result in excessive
expenditure of construction funds. An underestimate may result in storm damage
and traffic disruption due to poor performance of the drainage system.
Kuwait is located in an arid region and experiences very little rainfall. When rain
occurs, it is generally characterised by severe thunderstorms of limited geographic
extent. An instantaneous peak flow rate, such as that determined by the Rational
Method, is therefore considered sufficient for use in the design of highway drainage
systems in Kuwait.
Complex drainage systems employing pumping stations and storage facilities may
require the use of hydrographs. Techniques applied should be commensurate with
cost, risk and importance of the system. The designer is referred to Hydrology,
Highway Drainage Guidelines, AASMTO.
Given the lack of rain in Kuwait and the length of most projects, it may be
impractical or even impossible to calibrate or validate either hydrologic or hydraulic
data. If required, methods for calibrating data should be agreed with MPW.
2.1
Design Storm
In order to calculate peak flow rates, it is necessary to identify the relationship
between rainfall intensity, frequency and duration.
Rainfall intensity for a given duration and frequency shall be selected from the
cunres developed by MPW. Rainfall intensity I frequency / duration curves for
Kuwait have been prepared by MPW for frequencies of 2, 5, 10, 25, 50 and f 00
years, as shown in Figure 2.1.The rainfall data is given in Table 2.I.
Page 2-1
Kuweif Highway Drainege Design Menual
Page 2-2
Table 2.1 Rainfall Intensity I Duration I Frequency
intensity (Vslha)
Duntion
2-Y.ar
Return
Period
6-Year
R-rn
Period
90-Year
Return
Period
26-Year
R a m
Period
50-Year
Return
Period
100-Year
R a M
Pedod
5
129.4
209.5
257.9
314.0
352.4
387.9
6
123.5
200.1
246.8
301-7
339.6
375.0
7
117.8
190.7
235.8
289.3
328.8
362.1
8
111.8
181.5
225.1
277.5
314.5
3.48.8
Q
106.3
172.9
215.1
266.4
303.1
338.4
10
101.1
164.8
205.8
256.2
292.7
328.2
11
96.3
157.6
197.5
247.2
283.8
319.4
12
92.0
152.O
190.0
238.2
275.7
311.9
13
88.0
145.1
183.2
232.0
268.6
305.2
84.3
139.5
1n.o
225.3
282.0
299.1
15
80.9
134.4
171.7
219.0
255.8
293.4
18
77.8
129.8
165.5
212.9
249.7
287.6
77
75.0
125.0
160.2
207.4
243.8
281.9
18
72.4
120.8
155.2
201.§
238.1
276.4
19
70.0
116.8
150.5
198.3
232.8
271.3
20
67.9
113.3
146.2
191.5
227.9
266.6
21
65.9
110.1
142.4
187.2
223.5
262.4
22
64.1
107.2
139.0
183.3
219.6
258.7
23
62.4
104.5
t 35.8
179.7
215.9
255.2
24
60.8
101-9
132.7
17B.4
212.5
251.3
25
59.3
99.5
129.8
173.1
209.2
247.7
26
57.7
97.0
126.9
169.8
205.9
244.8
14
-
Dun'0n
2-ye.r
Return
Period
5-Year
Return
Period
10-Year
Return
Period
26-Year
Return
Period
SO-Year
Retwrn
Period
100-Year
Redurn
Period
27
56.2
94.6
124.0
166.8
202.6
241.2
28
54.7
29
53.3
90.0
118.5
160.3
196.2
234.7
30
52.0
87.9
116.0
157.4
193.1
231 .I
31
50.9
86.0
113.7
154.7
190.2
228.2
--
32
49.9
84.3
111.6
152.0
t 87.3
225.0
.
33
49.0
82.7
109.5
149.5
184.4
221.8
34
48.1
81.2
107.6
147.1
181.7
218.9
35
47.3
79.7
105.7
144.7
178.9
216.0
38
46.4
78.3
103.8
142.3
176.2
213.1
92.2
121.2
199.4
163.4
238.3
-
-
- :
3
h
.A
7.1
c
I
I
4
,
. ..>.
-
!, s.:> ;
38
44.7
75.4
100.1
137.6
170.7
207.4
:P.
30
43.9
73.9
98.2
135.2
168.0
204.8
40
43.0
72.4
96.3
132.8
165.2
202.3
41
42.2
71.0
94.4
130.4
162.5
199.4
42
41.4
69.6
92.6
128.1
159.9
196.9
43
40.6
68.2
90.9
f26.0
157.4
1M.7
44
40.0
67.2
89.6
124.2
155.4
192.2
45
39.3
66.1
88.2
122.5
153.5
790.0
50
37.0
62.4
83.5
110.5
146.3
181.5
80
331
56.2
75.6
106.1
133.9
166.9
4
A
-
.
I.:
.I ..a.
I
37
45.6
76.8
102.0
140.0
173.4
210.2
-
- - &
.
14
-
-
,.
r
,.L
-.
-
Pape 2 4
70
29.7
50.8
08.6
98.8
122.8
153.5
-
80
26.8
46.0
62.3
88.2
112.1
140.7
Kuwait Hi~hwayDdnage Design Manual
Intensity (Ilslha)
Duration
(mins)
SO-Year
Return
Period
-
-
- - - - - - - -
Period
f 00-Year
Return
Period
p
p
90
24.5
42.2
57.3
81.3
103.5
130.2
100
22.6
38.8
52.6
74.8
95.3
f20,l
I10
20.8
35.7
48.4
68.9
87.8
110.7
120
19.3
33.0
44.7
63.6
81.1
102.3
130
18.0
30.8
41-7
59.2
75.5
95.2
140
16.8
28.6
38.6
54.8
69.9
88.1
150
16.0
27.0
36.4
51.6
65.8
82.9
160
15.1
25.5
34.4
48.7
62.0
78.1
170
14.7
24.7
33.3
47.0
f 80
14.0
23.5
31.7
44.7
75.3
59.9
I
56.9
71.5
For local roads in residential areas, a minimum storm duration of 15 minutes should
be used. Storm durations for other areas should be agreed with MPW early on in
the design process.
The design storm frequency, or return period, should be selected according to the
importance of the road, expected traffic volumes, anticipated development in the
area and the potential for damage to adjacent facilities. For highway drainage
systems,the frequencies are as follows:
Road Classification
Design Frequency (yr)
Special Road Network
0
Primary Road Network
10
Secondary Road Network
10
Local Road Network
5
Atypical situations may require further consideration. The drainage of a depressed
roadway, for example, may warrant a higher design frequency than that of an atgrade roadway.
K w f t Highway Drainage D e a n MBRWB~
Acceptable frequency limits for crossing culverts where roads cross watercourses
(wadis) or open channels are as follows:
Road Classification
Design Frequency (yr)
Special Road Network
50
Primary Road Network
50
Secondary Road Network
50
Local Road Nehnrork
25
Certain land uses may require additional protection from overland flow.
Frequencies for these areas are as follows:
Land Use
Design Frequency (yr)
Hospitals, Airport
100
KOC
50
Higher frequencies may also be required where adjacent facilities need additional
protection. These facilities include fresh water storage reservoirs, electricity
substations and foul or stormwater pumping stations or treatment plants.
Frequencies at these locations should be agreed with MPW.
Catchment Areas
A catchment area is usually surrounded by an easily discernable topographic divide.
This divide is the line that separates the rainfall onto two adjacent wtchrnent areas,
ensuring the runoff is directed into one or the others collection system. Determining
the size of the catchment area that contributes flow to the drainage system is an
important step in hydrologic analysis.
Field inspections should be undertaken to confirm the boundaries of catchment
areas, as topographic maps are not always current. Plans of existing stormwater
drain systems may also be a valuable source of drainage boundary information.
Once the boundaries of contributing areas have been established, they should be
delineated on a base map.
Rural catchment areas should include the areas within the right-of-way subject to
direct precipitation and the broader natural catchment areas within which the road
runs.
Urban catchment areas shall incorporate the areas within the right-of-way subject to
direct precipitation and any adjacent contributing areas assessed from development
plans or topographic maps.
The shape of the area affects the rate at which water is supplied to the storm drain
narrow watersheds may have lower runoff rates than fan or pearshaped watersheds.
system. Long
The slope of the catchment area is also related to surface runoff. Steeper basins
yield a quicker response time than flat basins.
Kuwait H @ M yDmlnage Design Manuel
Chapter 2
HvdmFosy
For further information on drainage areas, refer ta Hydrology, Highway Drainage
Guidelines, AASHTO.
Rational Method
There are a number of methods for estimating flood peaks, storm durations and
runoff volumes. One of the simplest, the Rational Method, is an empirical formula
that expresses a relationship between rainfall intensity, catchment area and runoff,
as follows:
Where:
Q = Peak discharge (11s)
C = Average of the runoff coefficients assigned to different contributing areas
I = Rainfall intensity for the selected frequency and time of concentration (Ilslha)
A = Catchment area (ha)
Discharge, as computed by this method, assumes that the discharge has the same
frequency as the selected rainfall intensity. Because of the assumption that rainfall
is of equal intensity over the entire watershed, and because its frequency is not truly
related to flood frequency, it is recommended that this method be used only for
estimating runoff from areas of 80ha or less on highway drainage schemes.
Rain failing on the earth's surface is either retained where it falls, passes through
the soil surface as infiltration, or finds its way into the storm drain system. The
amount of infiltration varies for differing surfaces. Runoff coefficients are used to
determine the percentage of the runoff that will reach the storm drain system. The
following runoff coefficients should be used in Kuwait:
Surface Type
Pavement
Runoff Coefficient
0.90
Residential single family
0.70- 0.90
0.50 - 0.80
0.50 - 0.70
0.40 - 0.60
Lawns, parks or green areas
0.T 0 - 0.20
Commercial development
Industrial development
Residential multiple family
Undeveloped desert areas
0.15
The use of average coefficients for different kinds af surfaces assumes that the
coefficient does not vary. The designer should be aware that, in practice, the runoff
coefffcient for any particular surface varies with respect to the length of time of prior
wetting.
Page 2-7
K w / t HbbWRy Dminage Design MBRUB~
For guidance on other methods of estimating flood peaks, durations and volumes,
refer to Hydrology, Highway Drainage Guidelines, AASHTO.
Kuwait Highway Drainage D
e
w Manual
The function of the drainage system is to collect, convey and release stormwater
runoff, generally from within the highway corridor, The collection elements include
the roadway pavement, channels and inlet structures. The conveyance and release
of stormwater can be achieved by using closed conduits or open channels. All of
these elements are discussed in detail in this section.
3.1.
Pavement Drainage
Pavement drainage occurs in two different ways. The first involves sheet Row
across the pavement surface. The second occurs where kerbs contain and channel
the runoff within the gutter until it can be removed via an inlet.
3.1.1
Surface Drainage of Pavements
Effective surface drainage of the road pavement is essential for effective
maintenance of the roadway and for the safety of vehicular and pedestrian traffic.
Water on the pavement can interrupt traffic, reduce skid resistance, increase
potential for hydroplaning, reduce visibility due to spray and cause dificulty in
steering. In addition, accelerating, braking or cornering forces may cause the driver
to lose control.
The accumulation of stormwater runoff on the pavement is dependant on the
longitudinal slope, crossfall, width, surface texture and rainfall intensity. Potentially
hazardous locations include curves, superelevation and associated transitions, wide
pavements, bridge decks or anywhere where excess water may accurnu!ate. For
information of pavement surface properties and methods of calculating resuttant
flow paths and water depths, refer to Stom Drain Systems, Highway Drainage
Guidelines, AASHTO.
The water depth required to produce a sufficient loss of friction to present a major
driving hazard is in the range of 1.5mm to 5mm. Unfortunately, it is virtually
impossible to prevent water from exceeding these depths on wide pavements during
high intensity rainfall similar to that experienced in Kuwait. It is therefore considered
the driver's responsibility to exercise caution when driving during wet conditions.
3.1.2
Kerbs and Gutters
A limited right-of-way within an urban environment wit1 often precludes the use of
roadside ditches to collect and convey runoff. In these situations, kerbs and gutters
are commonly used. Kerbs vary in shapes and sizes.
Gutters begin at the intersection of the pavement surface and base of the kerb.
They extend from the kerb toward the roadway centreline. Gutters are generally
between 0.3m and 1.8m wide. Gutters need not necessarily have the same
crossfall or be constructed of the same material as the road pavement. Care should
be taken alongside flush or dropped kerbs, where there may be little or no gutter
available for runoff conveyance. Gutters may also be positioned on inverted
crowns, where flush kerbs delineate between a travelled way and a parking bay, for
example.
Page 3-1
Kuwait Highway Dmiage De&n Manuel
Chapter 3
System Design
The kerb and gutter form a triangular channel that c a n convey runoff from low
intensity storms events without interruption to traffic. However, when the design
storm occurs, the width of runoff may spread to include parking bays,shoulders or a
certain section of the travelled way. The limits of allowable water spread should be
set after considering the following:
Volume and speed of traffic
Number of lanes
Presence of gutters, shoulder or parking bays
Extent of roadway width that can be sacrificed in a design storm
Safety
The allowable water spread, or ponded width, shall be limited to an absolute
maximum of 2.5m.
A modified Manning's equation can be used to compute the spread of flow in s
triangular gutter if the rate of discharge, pavement crossfall, longitudinal slope and
Manning's roughness coefficient are known, as follows:
T
Q = ( 0.376 1 n ) s:.~~
~
.
~
~
or
7 = 1.443 [( Q n ) 1 ( s:."
SO.'
and
d=TS,
Where:
Q = Rate of discharge (m3/s)
n = Manning's roughness coefficient (for asphalt pavements n = 0.013 to 0.017)
S = Longitudinal slope ( d m )
S, = Crossfall (mlm)
T = Top width of water surface (m)
d = Depth of flow at deepest point (m)
The maximum surface water depth, or ponded depth, shall be limited to 150rnm and
the minimum longitudinal slope for a gutter shall be 0.3%,
Inlets
Inlets enable the stormwater to be removed from the roadway area. Inlets must be
properly located and sized so that kerb and gutter drainage is effective. Several
types of inlet are available for intercepting water flow and these include:
Grate inlets - horizontal gullies (including Motorway Type E gullies)
1
Kerb opening inlets - vertical gullies
Combination inlets - combined gullies (including Motorway Type A gullies)
Slotted drain inlets
The following information is needed in order to properly locate the inlets:
Plan and profile of the road
f opographic plans of the adjacent area
Typical road cross section
Superelevation information
There are a number of locations where inlets should be provided regardless of
contributing drainage areas. These include:
Sag points in the gutter profile
-
=
Immediately upstream of median breaks or mergeldivergesnoses.
Immediately upstream of bridges
Immediately upstream of crossfall reversals
Immediately upstream of pedestrian crossings
At the end of channels in cut sections
On side streets immediately upstream of intersections
Behind kerbs, shoulders of footpath to drain low areas
In locations where significant ponding may occur, such as on sag curves, it may be
necessary to place flanking inlets on each side of the inlet at the low point of the
sag. For further information on Ranking inlets, refer to Storm Drain Systems,
Highway Drainage Guidelines, AASHTO.
Concentrated runoff from large area adjacent to the road should be intercepted prior
to reaching the pavement. Large volumes of water can be collected more efficiently
in channels rather than being allowed to flow onto pavements and into pavement
inlets.
inlet sire and location are interrelated. For example, the use of lower capacity inlets
rquires more inlets, the use of higher capacity inlets allows for fewer inlets. It
should also be noted that the use of more, lower capacity inlets enables a decrease
in the allowable spread in the gutter.
The inlet capacity is a fundion of the inlet types, the geometry of the opening, the
longitudinal slope and the crossfall. The MPW has established standard inlet
lengths and sizes in order to facilitate design and control constructian costs, as
shown on the MPW Standard Detail Drawings.
Carryover represents the portion of the total flaw that is allowed to bypass an inlet
and flow on to the next. Inlets sized to allow some carryover optirnises the number
of inlets by making more efficient use of the allowable spread in the gutter.
However, inlets that are provided regardless of contributing drainage areas, as
listed above, should be sired to intercept 100% of the design flow. All sag inlets
should be sized to accommodate the total design flow. Calculations for inlet
spacing should be submitted to MPW for approval.
Further information on different types of inlet, such as grate inlets, kerb opening
inlets, combination inlets, slotted drain inlets and bridge deck inlets, can be found in
Storm Drain Systems,Highway Drainage Guidelines, AASHTO.
MPW prefers the use of Motorway Type A and E inlets. However, other types of
inlets may be used if appropriate.
Page 3-3
Kuwait Highway Drainage Design Manual
Chapter 3
System Design
3.2
Storm Drains
The storm drain is part of the highway drainage system that receives water through
inlets and conveys the water through conduits to an outfall. The storm drain is
made up of pipes, boxes and other closed conduits, inlet structures, manholes and
other miscellaneous structures. It is important to understand the hydraulics of stem
drains in order to select the correct criteria, to develop a sound design process and
to design the appurtenant structures. The hydraulics of storms drains is further
explained in Storm Drain Systems, Highway Drainage Guidelines, AASHTO.
3.2.1
Design Criteria
Design criteria describe the limiting factors that produce an acceptable design.
These factors include:
Flood frequency (see Chapter 2)
Allowable high water at inlets and manholes
Minimum flow velocities to prevent deposition
Clashes with other utilities
Soil conditions
Future expansion of the system
Future land development
r
Other Government ciieria
Maxjmum high water is the maximum allowable elevation of the water surface
(hydraulic gradient) in the storm drain. This is especially relevant at inlet and
manholes where there is access from the storm drain to the ground suhce.
Maximum high water should not interfere with the functioning of an inlet or reach a
manhole cover.
A minimum slope of 0.1% shall be used for stormwater drains. A generally
accepted self-cleansing velocity is 0.9mls. The absolute minimum actual velocity of
the design flow shall be 0.75mJs.
MPW requires that minimum pipe diameter for single inlet connections shall be
250mm (30Omm for concrete pipes) and the minimum slope shall be 1%. The
minimum pipe diameter for double inlet connections shall be 300rnm, the minimum
slope shall be 1% and the maximum slope shall be 12%. The maximum length for
an inlet connection shall be 25m.
Pipes used in stormwater drain systems can be concrete, HDPE or any other
material approved by MPW. The minimum pipe diameter shall be 300mm (400mrn
for the Special Road Network). The following pipe diameters are available in
Kuwait: 250, 300, 350, 400, 450, 500, 600,700,800,900,1000,1200, 3400, 1600,
1800 and 2000mm. Pipe details are shown on MPW Standard Detail Drawings.
MPW prefers a maximum design flow velocity of JmEs for unreinforced concrete
pipes and 5nils for reinforced concrete pipes.
A minimum cover depth of 1.5m to all conduits is recommended by MPW.
However, the minimum cover to pipe connections for grate inlets may be reduced
1.15m, if required. The minimum cover for kerb opening or combined inlets may be
reduced to 1.dm.
Page 3 4
Kuweit Highway Drainage Design Menuat
Chap& 3
System Design
3,2.2
Design Process
The design process is the compilation of all the activities discussed in this manual.
There is no fixed order in which these activities must be performed, nor are all the
activities required on every project. The designer must select the steps that are
most appropriate. The design process is one of trial and error. The design will
continue to change and adjustments will be required as the design progresses..
Data acquisition is the first step, followed by the pavement drainage design. This
yields information such as road crossfalls and longitudinal slopes, inlet locations and
catchment areas. Having accumulated this information, the designer then prepares
a storm drain system plan, which delineates main and lateral drainage runs, whilst
ensuring that all inlets are efficiently connected and directed to an ouffall. The
following aspects should be addressed.
Minimum and maximum conduit sizes should be determined
Conflicts with utilities should be avoided
Deep trenches should be minimised
Alternate main and lateral runs should be compared for cost and efficiency
The outfall should be low enough to provide an efficient conduit dope
The layout should enable construction with minimum disruption to traffic
Alteration to existing drainage patterns should be minirnised
The storm drain network must be arranged so that all lines have gravity access to
an ouffall, othenrvise a pumping station will be required. The designer then sizes the
conduits and checks the hydraulic adequacy and efficiency of the system. This is
done by computing the hydraulic gradient for all the main and lateral lines in the
system. Computing the hydraulic gradient for more onerous flood frequencies will
also enable the designer to evaluate the risks associated with larger floods.
The designer should then review the entire design before final acceptance and
inclusion in the highway project. At this stage, the following items should be
considered:
Elimination of over design
Improving compatibility with other construction processes
Opportunities for better satisfying the drainage needs
The following equations shall be used in the calculation of pipe capacities. Average
velacity shall be calculated using the Manning's equation:
and
R=AIP
Where
V = Average velocity (rnls)
n = Manning" coefficient of roughness (for concrete pipes n = 0.013)
R = Hydraulic radius (m)
Page 9 5
Kuwait Hthway Dtainage Dedgn Menuel
Chepter 3
System Design
S = Pipe slope (mlm}
A = Cross-sectional area of flow(m2)
R = Wetted perimeter (m)
Flow rates shall be calculated using the continuity equation:
. Where
'
Q = Flow rate (m3/s)
V = Average velocity (mls)
A = Crass-sectional area offlow (m2)
Appurtenant Structures
Drain runs are connected by appurtenant structures such as inlets and manholes.
Manholes enable access for inspection and maintenance purposes. Junction
chambers within manholes join two or mare drain runs together or connect conduits
of different types, sires or shapes.
Manholes are positioned at changes in direction, slope and storm drain size
changes, as well as at conduit intersections or where inlet connections are made.
Manholes should also be placed at intervals along lengthy sections of conduit. The
maximum length of conduit between manholes shall be 50-70m for pipes of
1400mm diameter or less and 700-200m far pipes of greater diameter.
Manholes in Kuwait are usually constructed of reinforced concrete and should be
designed to withstand both live and dead loads that may be imposed on them.
Manholes should be provided with corrosion resistant access steps. Details of
various types of typical manholes are shown on the MPW Standard Detail
Drawings. Typical manholes are considered to have pipes entering and leaving at
either angles of 0° (&5' ) or 90° (W).
Manholes losses should be considered as part of the design process and conduits
passing through manholes should have good hydraulic properties in order to
minimise these losses. If possible, the slope of storm drain should be continued
through the manhole. If the conduit size is increased on the downstream side of a
manhole, then the soffit levels of the inlet and outlet conduits shall be matched. If
this is not possible, a minimum drop of 50mm is recommended. If, for some reason,
the height of the conduit on the downstream sire is lower than that of the upstream
conduit, the invert levels of the conduits should be matched.
Manhole necks are required where the depth kom ground level to invert level
exceeds the fallowing values for the corresponding pipe diameters.
Depth (mm)
Pipe Diameter (mm)
2800
300-1600
3000
1800
3230
2000
K m i S Highway Oreinwe Design M~nuel
chapter3
System Design
'$
The manhole frame and cover should be made of cast iron and must be designed to
support the expected loads. It is preferable to locate manholes away from traffic.
Surface topography shall also be considered when locating manholes.
Junction chambers of different types are also shown on the MPW Standard Detail
Drawings. For further information on methods of calculating head losses in
manholes or junction chambers, refer to Design of Urban Highway Drai~age,
FHWA.
Roadside Channels
Roads located within an extensive right of way or within a rural environment may be
better drained using roadside channels or ditches. Roadside channels senre the
following functions:
Drain the roadway surface
Drain the roadway base and sub grade
=
Prevent surface runoff from reaching the roadway
Channels may also be used to direct flow to or from a stom drain conduit. Further
details can be found in Hydraulic Analysis and Design of Open Channels, Highway
Drainage Guidelines, AASHTO.
Storage Facilities
Temporary storage or detention of excess stormwater runoff may be required to
prevent the overloading of existing downstream storm drain systems. The storage
and regulated release of stormwater can reduce the frequency and extent of
downstream flooding, soil erosion, sedimentation and water pollution. For further
design details, refer to Storm 'Drain Systems, Highway Drainage Guidelines,
AASHTO.
Stormwater Pumping Stations
Stormwater pumping stations remove water from highway facilities that cannot be
drained by gravity. Because of the costs and potential maintenance problems, a
pumping station should only be used when no other system is feasible.
Some of the general considerations involved in the design of pumping stations
include:
a
Location
Hydrology
Wet well or dry well station
Number and capacity of pumps
Types of pumps
Types of power
Storage to reduce peak flow rates
Maintenance requirements
Emergency backup systems
Page 3-7
Kuwea Highway Dminage Demn Manual
Chapter 3
System DeMn
For further information, refer to Storm Drain Systems, Highway Drainage
Guidelines, AASHTO and the Manual for Highway Stormwater Pumping Stations,
FHWA.
Outfalls transfer collected water to an acceptable point of release, usually referred
to as the "receiving waters". In Kuwait, these may include the sea, overland flow
(wadis), percolation areas or other storm drains. An outfall may be an open channel
or a closed conduit. St is the most downstream element of the storm drain system.
Ouifalls can range from a few meters to several kilometres in length, and as such
may extend well beyond the limits of the highway corridor. Additional right-of-way
requirements may have a significant bearing on the location of the outfall.
Open channel outfalls are less expensive than closed conduit outfalls and provide a
safety factor against storms in excess of the design storm. However they require
more maintenance and are often used as dumping grounds.
Closed conduits should be used where the right of way is too narrow far an open
channel or there is a risk of flooding to adjacent property. Closed conduits are
difficult and expensive to enlarge, therefore provision for the future should be
accommodated in the design.
For Kuwait, sea outfall invert levels shall equate to a Mean Lower Low Water level
of +0.50m.
Specific considerations should be given to environmentally sensitive receiving
waters. Contamination due to the discharge of untreated stormwater can be
mitigated by incorporating interceptors into the system or by relocating the outfaH.
Subsurface Drainage
Subsurfam water in generally collected in a separate system that is connected to
the main storm drain system. Water trapped beneath the pavement surface but
within the roadbed structure or foundation can cause a rapid deterioration af the
pavement. Subsurface drainage systems are designed to remove or prevent water
from reaching the roadbed. There are several sources of water that can enter sub
grades or pavement layers. These are:
Surface water infiltrating through porous or cracked pavements or unsealed
joints
Lateral seepage into the edges from a saturated median or shoulders
Upward seepage from groundwater
Capillary action from underlying groundwater
Accumulated water vapour from temperature variations and humidity
Water can be removed from embankment slopes, pavement layers and sub grades
using a number of different systems. These include:
Horizontal drains
Pipe underdrains
Vertical wells
Sub grade drainage systems
Edge drain cotlector systems
KuwaB Highway Dminage DersEgn Menuel
Chapter 3
Syslem Qesfgn
S
for further design details, refer to Storm Drain Systems, Highway Drainage
Guidelines, AASHTO.
Highway Crossing Culverts
The function of a culvert is to convey surface water across or from the highway
right-of-way. In addition to its hydraulic functions, if must also carry construction
and highway traffic, and earth loads. Culvert design involves both hydraulic and
structural design. For information on the hydraulic aspects of culvert design, refer to
Hydraulic Design of Culverts, Highway Drainage Guidelines, AASHTO. For
information on the structural aspects of culvert design, refer to the Kuwait Bridges
and Highway Structures Design Manual.
Page 3-9
Kuwea Hbhway Dreinege D e a n Manual
Chapter 4
Other Factom Affecting &s@n
7
The drainage aspects of highway design are affected by many factors that are only
peripherally related to hydrology and hydraulics. Some of these are discussed in
the following section.
Utilities
Since highways and utilities often share the sdme right-of-way, coordination with the
service authorities is necessary to accommodate their current and future needs.
Widening an existing highway may incur problems due to a restricted right-of way
and numerous existing utilities that lie within it. When storm drains and utilities are
in conflict, there are three options:
Relocate the utility
Relocate the storm drain
Provide a structure to accommodate both the stom drain and the utility
Approval for relocation of utilities should be sought from the relevant utility authority.
Placing the storm drain under the roadway in order to avoid utility conflicts is not
recommended for the following reasons:
Manholes may be required in the roadway
Maintenance operations will interfere with traffic flow
Settlement problems can result from poor backfilling, infiltration or pipe
failure
Right-of-way
It may be necessary to buy additional land to accommodate drainage features.
Approval far purchase of additional right-of-way should be sought from MPW and
Kuwait Municipality early on in the design process.
Sewice Life
Service life is generally defined as the number of years of relatively maintenancefree life of the conduit material. The design service life should be based an:
a
Service life of the facility
lrnportance of the facility
Difficulties associated with repair or replacement
Future demands on the facility
'
Service design life for the different elements of the storm drain system should be
agreed with MPW early on in the design process.
Environmental bsues
Erosion and sedimentation can be very visible, particularly on urban projects.
Etosion control features should be carefully designed, installed and maintained in
Page 4-1
K m i t # & h e y Dtwinep Design Manual
Chapter 4
Other Factors Alfectng DesQn
sensitive surroundings. Refer to Erosion and Sediment Control in Highway
Construction, Highway Drainage Guidelines, AASHTO.
Hazardous spills occurring on the highway may be transported through the storm
drain system to the outfall. Interceptors may be required if the receiving waters are
deemed sensitive to pollutants.
At several locations in Kuwait, contaminated groundwater has been encountered.
Dewatering of excavations during construction may lead to the release of harmful
gases into the atmosphere. Water removed from the ground during dewatering
procedures should be treated in accordance with EPA requirements.
KrmsrY Highway Dmlnaga Cwign Manusf
Storm drain modelling s o h a r e mathematically models the occurrence of a storm in
a storm drain system. This section gives an overview of the desirable features and
functions ofmodelling software.
Variables such as runofl rates, storm patterns, profile elevations and inlet locations
are input into the model. The model can then be used to evaluate the performance
of an existing system or identify the geometric requirements of a new system.
There should be no limit to the size of the system that can be anatysed in a single
nm. It may be necessary to evaluate extensive existing systems in order to obtain
input for a smaller proposed highway system.
The software should allow for the systematic entry of design data in a logical order
and format. It is also essential that the storm drain model be modular in structure.
5.1
Hydrology
Hydrologic methods in storm drain modelling software fall into two categories, peak
discharge determination and surface hydrologic simulatian.
Peak discharge procedures, such as the Rational Method, are common, easy to use
and applicable to most highway storm drain systems in Kuwait. Using computer
software greatly simplifies the tedious, repetitive and time-consuming calculations
required. It also provides well-organised hydrologic documentation.
Surface hydrological simulation attempts to model the rainfall-runoff process. The
software can madel synthetically formulated design storms or actual historical
storms, accounting for all the water that falls on a land segment. The software
establishes a hydrograph that represents the amount of rain falling during specified
time steps of a set length. Hydrographs are only required for the design of highly
complex storm drain systems.
Inlets
The computer model should assist the designer in determining optimum spacing
and siring of inlets, and should allow for the selection of different inlet types such as
grate, weir, slot or any combination of these. The software should also be capable
of dividing gutter flow into two components, the flow intercepted by the inlet and the
carryover flow.
Conduits
The model should be able to simulate a variety of flow conditions in the conduit
system and appurtenances. Flow conditions may be affected by conduit type,
manholes or angular changes in profile or alignment.
The model should allow the designer to select a variety of conduit shapes (circular,
box, arch, elliptical or oval) and roughness values (rnaterjal, lined or unlined).
The model should be able to compute and display hydraulic gradients. Supercritical
flow introduces complexities into gradient analyses. Pipe runs encountering
supercritical flow must be clearly identified within the model so that the designer can
provide the necessary high velocity facilities and to ensure that the hydraulic
gradient computations are reasonable,
Page 5-1
K m f t HhInuay Drainags Design Manlral
chapter 5
Computer Mod@!liing
5.4
Other Losses
The model should have the ability to compwte energy losses, such as those at
manholes, bends or transitions, and adjust the energy gradient accordingly.
5.5
Cost Estimating
A desirable feature of the software is the ability to select the best alternative, taking
into account financing, operating and maintenance costs. The model should also be
able to calculate the cost of a stem drain system with sufficient accuracy so as to
be used in the final cost estimate.
'
Chapter6
DocumenZafion. Cdnshiefkm and Meinfenam
6
DOCUMENTATION, CONSTRUCTION AND MAINTENANCE
6.1
Documentation
Documentation is an important feature of design and facilitates the incorporation of
proposed systems into existing systems. Knowledge of the methodology and
criteria used in past designs is necessary for the accurate interpretation of design
data.
A design drainage manual should accompany the design drawings and should
include the following:
Design criteria
Photographs
a
Contoured survey plans showing catchment boundaries and flow directions
Records of existing drainage systems
Drawings from previous projects
Proposed drainage details
Documentation of hydrologic and hydraulic data in the f o m of drawings, notes,
correspondence and calculations should be included in the appendices.
As-built records offer the best documentation of drainage features. These
should include:
Plan and profile drawings showing drainage structure sizes
Invert levels
Detail drawings of structure types
* Design drainage plans showing flow quantities, flow directions and
catchment boundaries
Drainage calculations
6.2
Construction
Different personnel may perform the design and construction functions. Adequate
communication between these two groups of personnel should be maintained
throughout the construction period. The designer should always be consulted when
construction changes occur as these changes may affect the performance of the
drainage facilities.
The designer should aim to achieve a proper balanoe between material and
construction costs. For example, the least expensive material may not be the
proper choice because the constructions costs may be greater than for a more
expensive material.
Changes in land use or utilities added after the design is complete may bring about
an extensive redesign of a storm drain system. This reinforces the need for full
cooperation with MPW, Kuwait Municipality, service providers, developers and any
other interested parties during the design phase.
Temporary traffic detours should include provision for temporary drainage.
Page 6 1