Chapter Abstracts
Introduction:
The authors of the "Practical Guide To Railway Engineering" wish to provide the reader
a general overview of the specific disciplines common to railway engineering. Railway
engineering design requires that the engineer approach any modern engineering challenge
with an understanding that encompasses the railway as a system; thereby requiring the
practicing engineer have a general understanding of disciplines other than just their own.
The text hereafter is not intended to supplant the AREMA Manual for Railway
Engineering, the AREMA C&S Manual or other comprehensive texts covering specific
railway engineering disciplines, but rather to provide background enabling the novice
engineer or practicing engineer unfamiliar with railway engineering design to utilize
available resources. Each author and contributor shares a deep love for the industry, and
it is their desire that the pool of collected information be passed on to the next generation
of "railroader" as well.
Chapter 1 – Railway Development
Chapter 1 provides a brief overview of the key occurrences in the history of
transportation leading up to the introduction and implementation of railways and railway
engineering in North America. The goal of this chapter is for the reader to obtain an
appreciation for the reasons behind some of the key current railway engineering practices
based on railway development history. The significant economic role played by
innovations such as CWR, CTC, mechanization of maintenance activities, along with the
evolution of bridge design, materials and construction practices is explored.
Chapter 2 – Railway Industry Overview
Chapter 2 is designed so the reader will gain an understand of the organizational structure
of a railway and to recognize the role played in railway operations by safety, operating
rules, authority of movements, speeds and traffic control systems. Critical issues affecting
railway traffic systems are also considered. Various car configurations and related usage
are identified along with factors governing locomotive utilization including:
• horsepower and tractive effort
• acceleration and balance speeds
• tonnage ratings
• tractive force and adhesion
• ruling grade
• drawbar pull
• momentum grade
• train resistance
• power to stop
• compensated grades
Chapter 3 – Basic Track
Chapter 3 is written for the reader to become more familiar with track components and
terminology and includes over 100 illustrations. The reader will understand the criteria
used to justify maintenance operations and/or capital improvement as well as recognize
the role of track geometry in maintaining and operating today's railway. Specific
maintenance activities along with the function of major production gang activities are
discussed. The role of safety and safety enforcement is also addressed here.
Chapter 4 – Right-of-Way and Roadway
Chapter 4 seeks to explain how right of way is defined and utilized. This chapter includes
typical dimensions, property rights, limitations, utility easements, fencing, and
vegetation. Also addressed are issues concerning; basic soil types, geotechnical behavior
of various types of soils, typical track structure and the loading it imposes on the
subgrade, roadbed failure (landslides and track settlement) causes and remediation, and
ways to identify potential hazards to the roadbed and take appropriate action to mitigate
those hazards.
Chapter 5 – Drainage
Chapter 5 stresses the importance of drainage in maintaining quality track. The primary
hydrology and hydraulic principles are reviewed along with a demonstration of the use of
commonly available resources. Consideration is provided to the impact poor drainage
design can have on railway neighbors as well as the integrity of the railway itself.
Chapter 6 – Railway Track Design
Chapter 6 provides information pertaining to the different design elements of railway
alignments, layout and design. Specific topics include horizontal and vertical alignment
design, turnout geometry, location, and use; railway clearances and vehicular envelope
requirements; typical yard and terminal functions and layouts. Additional considerations
pertaining specifically to design elements of railway alignments and limitations are
discussed as they relate to proposed use (i.e. mainline, branch line, industrial/terminal,
and passenger).
Chapter 7 – Communications and Signals
Chapter 7 is intended as a basic overview of railway signaling. The chapter provides an
appreciation of the historical development of railway signal systems as well as an
understanding of basic signal terminology. An easy to understand approach explains
concepts such as ABS and CTC. Basic types of signals, available energy sources,
lightning and surge protection and basic track circuits including: DC track circuits, Coded
DC track circuits, Style C track circuits, Overlay track circuits and AC track circuits are
addressed here.
An understanding of track switches, components and their
interconnection to the signal system is provided. Crossing warning device theory of
operation and differences between conventional and solid state devices is highlighted.
The basic principles of CTC, sequence of operation and safety checks are explained along
with concepts associated with microprocessor based coded track circuits and solid-state
interlockings. Finally, a description of the common types of defect detectors in use is
provided.
Chapter 8 – Railway Structures
Chapter 8 was prepared to accomplish two primary objectives. For the novice engineer,
the authors wished to provide an overview of the types of railway bridge structures and
their appropriate usage as well as define the primary bridge components and their
functions. Further, drainage structures, retaining walls, tunnels and sheds are classified
by type as well as by common use. For the experienced highway design engineer, the
common design approach differences between highway and railway bridges are
reviewed. Discussion centers on the differences in design loading in Timber Chapter 7,
Concrete Chapter 8 and Steel Chapter 15 of the AREMA Manual for Railway
Engineering. Other critical structure criteria are highlighted such as fatigue, fracture
critical members, structure serviceability, bearings and volumetric changes and
composite design.
Chapter 9 – Railway Electrification
Chapter 9 compares the various alternatives available when considering and designing an
electrified railway. A general overview of the key components and their primary
function is provided for 3rd rail systems and overhead catenary systems (OCS).
Fundamental criteria for selection of style of OCS are discussed along with other design
basics. Finally, the impact that implementation of electrification will have on existing
railroad infrastructure, staff and community is discussed.
Chapter 10 – Passenger, Transit and High-Speed Rail
Chapter10 presents an overview of typical design principles, construction practices and
maintenance considerations applied to passenger rail lines. It describes how basic
railroad engineering principles are applied in specialized ways to accommodate passenger
rail requirements. The chapter notes the key distinctions between railroad and transit
operations and introduces six major types of passenger rail modes. The text then
discusses the service, infrastructure, regulatory (U.S.), maintenance and inspection
considerations associated with each. It concludes with discussion of the special topics of
line capacity and cant deficiency.
Chapter 11 - Environmental Regulations And Permitting
Chapter 11 is a general overview of environmental regulations and permitting in the U.S.,
Canada and Mexico with topics that may be encountered during railway activities
(including construction, as well as operation). This information is general in nature and
the reader is cautioned to contact or use a professional environmental consultant to
prepare an Environmental Assessment. Information is given on wetland issues along
with other topics, such as endangered species, cultural resources, Phase I environmental
assessments, hazardous waste, brownfields, asbestos and air quality. Environmental
information includes: the U.S. Army Corps of Engineers wetland definition, Nationwide
and General permits for proposed construction activities, U.S. Army Corps of Engineers
non-jurisdictional status over isolated wetlands and Best Management Practices (which
mitigate direct and indirect degradation of the environment to the extent possible). Each
topic concludes on where to locate additional information.
Chapter 12 – European Curve & Turnout Mechanics
Chapter 12 serves to provide an appreciation of the European approach design differences
in turnout and curve design from that experienced in North America. The reader will
obtain an understanding of the geometrical and mathematical relationships common to
both North American and European track geometry. The potential for incorporating
European practices in high-speed North American transit initiatives is clearly obvious.
Chapter 13 – Case Studies
Chapter 13 presents four case studies drawn from actual railway design projects using
formatted templates to identify critical stakeholders, identify controlling criteria,
recognize potential problems, and learn from past mistakes. These case studies are
intended to serve as a model for which the templates can be utilized for any railway
design/construction project. It is intended that this will be part of an accessible library of
case study solutions yet to be developed.
Appendix
The Appendix contains a wide variety of useful and related information to the material
presented in the text. Included are articles describing the development of maintenance-ofway practices in the past 40 years from the perspective of a retired Class 1 chief engineer,
geometry solutions for turnout and connection track location, spiral and full body curve
example problem solutions, Bartlett Method of calculating throws for stringlining curves
and a synopsis of one Class 1 railway’s step by step procedures for performing common
maintenance and capital improvement activities.
Glossary
The glossary contains short definitions of the majority of the terms utilized within the
text. Railway engineering terminology common to the industry is often not selfexplanatory. It is essential that the engineer have a clear understanding of the terms in
use.
TABLE OF CONTENTS_______________________________________________________________________
Table of Contents
Introduction
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Chapter 1 - Railway Development
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1.1 Introduction
1.2 Determinants of Transportation Development
1.3 Pre-Railway Transportation in North America
1.4 Physical Determinants of Land Movement
1.5 North American Railway Development and Impacts
1.6 Developments of the Twentieth Century
1.7 Development of Canadian Railways
1.8 Mexican Railway Development
1.9 Institutional Controls
1.10 History of Railway Bridge Engineering
1.11 New Technology – Bridge Developments in the Last Twenty Years
1.11.1 Existing Railway Bridges: Inspection and Assessment
1.11.2 New Railway Bridges: Materials, Design, Fabrication and Construction
1.12 Trade Journals
1.13 Other References
Chapter 2 - Railway Industry Overview
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2.1 Introduction
2.2 Railway Companies
2.2.1 Organization of a Railway Company
Transportation Department
Engineering Department
Mechanical Department
Marketing Department
2.3 Regulatory Agencies and Railway Associations
2.3.1 Regulatory Agencies
United States
Canada
2.3.2 Railroad Associations
AAR and RAC
AREMA
REMSA
RSSI
2.4 Operations of Railways
2.4.1 Safety First in Railway Operations
2.4.2 Bibles of the Railways for Safe Operations
2.4.3 Tracks and Authority of Movements
2.4.4 Speeds
2.4.5 Rail Traffic Control Systems
Radio Communication of Train Orders
Train Spacing and Block Separation
Track Circuit
Signal Block Length
Centralized Traffic Control
Additional Information
2-5 Railway Cars
2.5.1 Freight Cars
Boxcars
Insulated Boxcars and Mechanical Reefers
Intermodal Cars – Piggyback Trailers and Containers
Flat Cars
Auto Rack Cars
Gondola Cars
Hopper Cars
Rotary Gondola/Hopper Cars
Tank Cars
Maintenance-of-Way Cars
Schnabel Cars
2.5.2 Hazardous Commodities
2.5.3 Passenger Cars
2.6 Locomotives
2.6.1 Horsepower (hp) and Tractive Effort
2.6.2 Tractive Force and Adhesion
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2.6.3 Drawbar Pull
2.6.4 Train Resistance
Rolling Resistance
Davis Formula
Starting Resistance
Grade Resistance
Curve Resistance
2.6.5 Compensated Grade
2.6.6 Acceleration and Balance Speed
2.6.7 Tonnage Ratings of Locomotives
2.6.8 Ruling Grade
2.6.9 Momentum Grade
2.6.10 Power to Stop
2.7 Traffic Systems
2.7.1 Priority of Trains
2.7.2 Effects Of Sharing Tracks By Freight And Passenger Trains Vs. Track Of Single Use
2.7.3 Overcoming The Delays That Occur In Freight Yards
Chapter 3 - Basic Track
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3.1 Track Components
3.1.1 Rail
Identification of Rail
3.1.2 Ties
Timber Ties
Concrete Ties
Steel Ties
Alternative Material Ties
3.1.3 Ballast Section
3.1.4 Rail Joints
Standard Joints
Compromise Joints
Insulated Joints
3.1.5 Tie Plates
3.1.6 Rail Anchors
3.1.7 Fasteners
Spikes
Bolts
3.1.8 Specialized components
Derails
Wheel Stops and Bumping Posts
Gauge rods
Sliding (Conley) Joints
Mitre Rail
Bridge/tunnel/overpass guard rails
3.2 Turnouts
3.2.1 Types of Turnouts
Basic Turnout Terminology
3.2.2 Switch
3.2.3 Switching Mechanism
3.2.4 Turnout Rails
3.2.5 Frog
Rail bound manganese (RBM)
Spring Frog
Solid Manganese Self-guarded Frog
Bolted Rigid Frogs
Movable Point Frogs
Determining Frog Number
3.2.6 Switch Ties
3.2.7 Stock Rails
3.2.8 Switch Points
Identifying Left or Right Hand Points
3.2.9 Specialty Components
Switch Clips
Switch Rods
Types of Switch Rods
Connecting Rod
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3.2.10 Special Turnout Plates
Gauge Plates
Switch Plates
Rail Braces
Heel Block Assembly
Turnout Plates
Hook Twin Tie Plates
Frog Plates
3.2.11 Guard Rails
3.2.12 Switch Stands
Spring Switch
3.3 Railway Crossings & Crossovers
3.4 Highway Crossings
3.4.1 Crossing Construction And Reconstruction
3.4.2 Crossing Warning Devices
3.5 Utility Crossings
3.6 Track Geometry
3.6.1 Gage
3.6.2 Alignment
Full Body of the Curve
Transition Spiral of the Curve
Curve Elevation
3.6.3 Surface
3.7 Safety
3-8 Maintenance Activities
3.8.1 Track Disturbance
3.8.2 Track Disturbance Activities
3.8.3 Rail Lubrication
3.8.4 Rail Grinding
3.8.5 Rail Defect Testing
3.8.6 Geometry Cars
3.8.7 Gauge Restraint Measuring System (GRMS)
3.8.8 Vegetation Control
3.8.9 ROW Stabilization & Drainage
3.8.10 Welding
3-9 Production Gangs
3.9.1 Production Rail Gang
3.9.2 Production Tie Gang
3.9.3 Production Undercutting
3.9.4 Production Surfacing Gangs
3.9.5 Road Crossing Renewal Gangs
3.9.6 Turnout Renewal
3.9.7 New Track Construction/Cutout
Track Construction /Cutovers
References:
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Chapter 4 - Right-of-Way & Roadway
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4.1 Introduction
4.2 Right-of-Way
4.2.1 Right-of-Way Width
4.2.2 Fences
4.2.3 Utilities
4.2.4 Vegetation
4.3 Roadway
4.3.1 Soils
Definition
Soil Types
Major Soil Divisions
Soil Texture and Composition
4.3.2 Geotechnical Processes
The Concept of Stress and Strain
Effective Stress
The Effect of Porewater Pressure
Clays
Sand and Gravel
Silt
Soil Behavior Under Rapid Loading
Effect of Shear Strain
Settlement
Seepage
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4.3.3 Track Structure
Historical Background
Components and Functions
Subgrade
Sub-ballast
How Track Fails
4.3.4 Instability
Main Features of Landslides
Slides that Affect the Track
Triggering Mechanisms
Remediation
Soil Improvement
Improved Slope Geometry
Reduce Seepage Pressure
Structural Support
Inspection of Slopes
Monitoring Slope Movements
Areas With the Greatest Hazard
4.3.5 Settlement
Basic Theory
Influence of Construction Methods
Influence of Soil Type
4.3.6 Hazard Identification
Understanding the Factors
Understanding the Mechanisms
Identifying the Hazard
4.3.7 Summary
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Chapter 5 – Drainage
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5.1 Hydrology
5.1.1 Equations and Programs
5.1.2 Rainfall Intensity or Precipitation
5.1.2 Rainfall Intensity or Precipitation
5.1.3 Time of Concentration
5.1.4 Distribution
5.2 Hydraulics
5.2.1 Open Channel Hydraulics
5.2.2 Culvert Hydraulics
5.3 Recommended Procedures
5.3.1 Existing Drainage Study
5.3.2 Proposed Drainage System
5.3.3 Floodplain Encroachment Evaluation
5.3.4 Erosion Control Evaluation
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Chapter 6 - Railway Track Design
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6.1 Stationing
6.2 Horizontal Alignments
Staking Spirals By Deflections
Staking Spirals By Offsets
Applying The Spiral To Compound Curves (Arema 1965)
6.3 Vertical Alignments
6.4 Alignment Design
6.5 Turnouts
6.6 Design Of Yards
6.7 Clearances
References:
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Chapter 7 - Communications & Signal
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7.1 Introduction to Signals
7.1.1 Railway Operation
7.1.2 Timetable Operation
7.1.3 Wayside Signals
7.1.4 Color Light Signal
7.1.5 Signal Terminology
7.1.6 Searchlight Signal
7.1.7 Operating Principle
7.1.8 Automatic Block Signals
7.1.9 Signal Location
7.1.10 Common Terms
7.1.11 Automatic Block Signal System
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7.1.12 Centralized Traffic Control (CTC)
7.2 Energy Source
7.2.1 Batteries
7.2.2 Battery Charging
7.2.3 Lightning Protection
7.3 Track Circuits
7.3.1 DC Track Circuits
7.3.2 Track Circuit Operation
7.3.3 Train Shunting
7.3.4 Coded DC Track Circuit
7.3.5 Style “C” Track Circuit
7.3.6 Overlay Track Circuits
7.3.7 Overlay Track Circuit Operation
7.3.8 Track Coupling Unit
7.3.9 AC Track Circuits and Relays
7.3.10 Apparatus Used with AC Track Circuits
7.4 Track Switches
7.4.1 Hand Operated Switch with SCC
7.4.2 Electric Switch Lock
7.4.3 Dual Controlled Power Switch Machine
7.5 Highway Crossings
7.5.1 Crossing Operation
7.5.2 Crossing Gates
7.5.3 Crossing Motion Detector/Predictor
7.6 Centralized Traffic Control (CTC)
7.6.1 Operation
7.6.2 Sequence of Operation
7.6.3 Microprocessor Based Coded Track Circuits
7.6.4 Theory of Coded Track Circuit Operation
7.6.5 Solid State Interlocking
7.7 Defect Detectors
7.7.1 Hot Box Detector
7.7.2 Hot Wheel Detector
7.7.3 Dragging Equipment Detector
7.7.4 Wheel Defect Detector
7.7.5 Slide Fence
7.7.6 Flood Detectors
7.7.7 Fire Detectors
7.7.8 High/Wide Load Detectors
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Chapter 8 - Railway Structures
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8.1 Introduction to Railway Structures
8.2 Major Bridge Components
8.2.1 Substructure
Investigate Underlying Soil & Geologic Conditions
Piling
Abutments and Piers
8.2.2 Superstructure
8.2.3 Bridge Deck
Open Bridge Decks
Ballasted Decks
Open Deck Vs. Ballast Deck
8.3 Bridge Types
8.3.1 Timber Trestles
Terminology
Caps
Stringers
Timber Connectors
8.3.2 Steel Bridges
Girder Spans
Truss Spans
Steel Trestles
Viaducts
8.3.3 Concrete Bridges
Arches
Rigid-Frame Bridge
Slab Bridges
Concrete Trestles
Concrete Girders
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8.3.4 Moveable Spans
Bascule Bridges
Swing Span Bridges
Vertical Lift Bridges
8.4 Other Structures
8.4.1 Drainage Structures
8.4.2 Retaining Walls
Gravity Retaining Walls
Crib Walls
Sheet Piling
Mechanically Stabilized Earth
Drainage of Retaining Walls
8.4.3 Tunnels
Tunnel Construction Methods
8.4.4 Sheds
8.5 Structural Design Considerations
8.5.1 Introduction
8.5.2 Bridge Loading,
Dead Load
Live Loads
Impact
Centrifugal Load
Lateral Loads
Longitudinal Loading
Wind Loading
Stream Flow, Ice and Buoyancy
Seismic Loads
Combined Loads
8.5.3 Other Structure Design Criteria
Fatigue
Fracture Critical Members (FCM)
Structure Serviceability
Bearings and Volumetric Changes
Composite Design
Bridge Design Assumptions and Constructibility Issues
Recommended Construction Considerations
8.5.4 Retaining Wall Loads
References:
Chapter 9 - Railway Electrification
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9.1 Introduction
9.2 Development of Motive Power for Railways
9.2.1 Pioneers of Electric Traction Development
9.3 Rail Operation Classification
9.4 Mainline Railways and Independent Short Lines
9.4.1 Mainline Electrification Studies
9.4.2 Mainline Infrastructure Compatibility
Maintenance
Staff Safety
9.4.3 Impacts of Mainline Railway Electrification on Communities.
9.5 Urban Railways
9.5.1 Impacts of an Urban Electrified Light Rail or Commuter Rail System on the Community
9.6 Existing Electrification Systems
9.7 New Electrification Systems
9.7.1 Sources of Primary Power
9.7.2 Substations
9.7.3 Power Distribution Systems
Feeder Cable Sub Systems
Negative Feeder Cable Sub Systems
Contact System Sub Systems
9.7.4 Current Collectors
Contact Shoe
Trolley Poles
Pantographs
9.7.5 Characteristics Of Third Rail System
Conductor Rail Supports
9.7.6 Characteristics Of An Overhead Contact System
Single Wire System
Catenary Systems
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9.7.7 OCS Style Selection
Location and Environment
Copper Cross-sectional Area
Economics
Cost Factors of OCS Styles
OCS Design Basics
9.8 Electrification Interfaces with Other Rail Elements
9.8.1 Right-of-Way
Track Layout/Realignment
Substations
Supporting Structures for the Contact System
Systemwide Ductbanks
9.8.2 Track Structure
9.8.3 Civil Structures
Tunnels To Be Electrified
Bridges Over Electrified Track
Bridges Under Electrified Track
Station Canopies
OCS Attachments
9.8.4 Signals and Communications
9.9 Interfaces with Project-Wide Staff
Bibliography
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Chapter 10 - Passenger, Transit & High Speed Rail
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10.1 Introduction
10.2 Passenger Rail Modes
10.3 Distinctions between Railway Operations and Transit Operations
10.4 Passenger Rail Service and Vehicle Characteristics by Mode
10.5 Passenger Rail Infrastructure Characteristics by Mode
10.6 Passenger Railway Infrastructure Characteristics
10.6.1 High-Speed Rail (HSR)
Route Alignment Considerations
Regulatory Compliance
10.6.2 Intercity Rail and Commuter Rail
General
Route Alignment Considerations
Track Standards
Regulatory Compliance
10.7 Transit Infrastructure Characteristics
10.7.1 Rapid Transit
Route Alignment Considerations
Track Standards
Regulatory Compliance
10.7.2 Light Rail Transit (LRT)
Route Alignment Considerations
Track Standards
Regulatory Compliance
10.7.3 Streetcar and Vintage Trolley
Route Alignment Considerations
Track Standards
Regulatory Compliance
10.8 Passenger Railway Maintenance Considerations
Maintenance Philosophy
Maintenance Practices
10.9 Transit Maintenance Considerations
Maintenance Philosophy
Maintenance Practices
10.10 Special Topics Associated with Passenger Railway Operations
10.10.1 Passenger Railway Line Capacity
10.10.2 The Impact of Superelevation (Or Cant Deficiency and Why It’s Important)
10.11 Conclusion
Chapter 11 - Environmental Conditions & Permitting
11.1 Introduction
11.2 Environmental Regulations Of The United States
11.2.1 Wetlands Regulations
U.S. Army Corps of Engineers Regulatory Boundaries
11.2.2 Wetland Definition
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11.2.3 Wetland Regulations
Nationwide Permits
General Permits
USACE Non-Jurisdiction Over Isolated Wetlands
11.2.4 Best Management Practices
11.2.5 Endangered Species
11.2.6 Cultural Resources
11.2.7 Phase I Environmental Assessment
11.2.8 Hazardous Waste
11.2.9 Brownfields
11.2.10 Asbestos
11.2.11 Air Quality
11.3 Environmental Regulations Of Canada
11.3.1 Canadian Wetlands Environmental Assessment Guidelines
11.3.2 Endangered Species
11.3.3 Hazardous Waste
11.3.4 Air Quality
11.4 Environmental Regulations Of Mexico
11.4.1 Regulations
11.4.2 Mexico Regulation for Hazardous Waste
11.5 Wetland Case Study
Chapter 12 - European Curve and Turnout Mechanics
12.1 Introduction
12.2 Curves
12.2.1 Curve Definition
12.2.2 Gage
12.2.3 Elevation in Curves
12.2.4 Elevation Transition
12.2.5 Track Warp
12.2.6 Horizontal Transition Curves
12.2.7 Theory of the Transitional Curves
12.3 Gradient Change
12.4 Turnouts and Turnout Design
12.4.1 Measuring the Frog Angle
12.4.2 Turnout Calculations
12.4.3 Clothoidal Turnout
12.5 Speed Raising Improvements
12.5.1 Curve Improvements
12.5.2 Surfacing and Lining
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499
500
502
503
504
504
505
506
507
511
513
514
514
515
517
518
523
524
526
529
531
533
534
537
540
542
543
Chapter 13 - Case Studies
547
13.1 Introduction
#1 – Kasky, KY – Project Survey
#2 – Crestline, OH – Project Survey
#3 – FEC/SFRC Connection, West Palm Beach, FL For Amtrak Service – Project Survey
#4 - Ft. Washington PA – Project Survey
Appendix
549
551
557
561
567
A-1
Applied Science For Railway Tracks
Turnouts, Connections, And Crossings
Turnouts
Location of Turnouts
Turnouts from Straight Track
Turnouts from Curved Track
Connections
From Straight Track
Turnout from the Inside of a Curved Main Track
Turnout from the Outside of a Curved Main - Track
Parallel Tracks - Sidings
Parallel Tracks Both Straight Tracks
Parallel Tracks - Curved Tracks
Parallel Tracks - Crossovers
Crossovers - Straight Tracks.
Crossovers - Curved Tracks
Ladder Tracks
Intersecting Tracks
Intersecting Tracks - Both Tracks Straight
Intersecting Tracks - One Straight and One Curved Track
Intersecting Tracks - Both Tracks Curved
viii
A-3
B-1
B-1
B-1
B-2
B-3
B-3
B-3
B-5
B-12
B-17
B-17
B-18
B-22
B-23
B-24
B-25
B-27
B-27
B-31
B-34
TABLE OF CONTENTS_______________________________________________________________________
Wye Tracks
Wye Track - Straight Main Track
Wye Track - Curved Main Track
Diamond Turnouts
Crossings
Crossing Data
Straight Crossings
Single-Curve Crossings
Double-Curve Crossings
Example Curve Problems With Solutions
PROBLEM 1.
PROBLEM 2.
PROBLEM 3.
PROBLEM 4.
PROBLEM 5.
PROBLEM 6.
PROBLEM 7.
PROBLEM 8.
PROBLEM 9.
PROBLEM 10.
PROBLEM 11.
Spiral Problems & Solutions
Determining Degree Of Curvature
Method Of Determining Degree Of Curvatue
String Lining Curves
Stringlining Of Railroad Curves
Maintenance Processes
Ballast Unloading
Gauging on Wood and Concrete Ties
Mechanical Surfacing of Track
Switch Tie, Yard and Siding Ties & Programmed Maintenance Tie Renewal
Rail Train Rail Pickup
CWR Rail Relay on Wood or Concrete Ties
Mechanized Tie Renewal
Track Abandonment
Track Sledding
Installation of Panelized Turnouts
Unloading Continuous Welded Rail (CWR)
GLOSSARY
ix
B-35
B-36
B-37
B-38
B-39
B-40
B-41
B-42
B-43
C-1
C-1
C-1
C-1
C-2
C-2
C-3
C-4
C-8
C-9
C-13
C-18
D-1
E-1
E-2
F-1
G-1
H-1
H-3
H-7
H-11
H-17
H-22
H-27
H-32
H-37
H-44
H-50
H-57
Glossary-1
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Chapter
Railway Development
1.1 Introduction
History
“Ring Out, oh bells. Let cannons roar
In loudest tones of thunder
The iron bars from shore to shore
Are laid and Nations wonder”
T
his quote from the May 11, 1869 The Chicago Tribune celebrated the
completion in Utah of the first transcontinental railway connection in North
America. By 1885 the Canadian Pacific completed the first single company
transcontinental line and the Atlantic and Pacific were also first linked in Mexico in the
19th century. The exciting impact of a technology that reduced a six-month to a six-day
trip can hardly be imagined today. In the lifetime of anyone reading this, we have seen
nothing with the impact on all aspects of life as the development of the railway.
Only 44 years earlier on October 27, 1825 George Stephenson’s steam locomotive,
“Locomotion Number 1” hauled a 90 ton load consisting of 36 cars carrying more
than 500 passengers and some freight at a sustained speed of 12 mph along the
Stockton and Darlington Railway in northern England. This was the culmination of
decades of imagination, promotion, engineering and experimentation.
What is a railway? A railway can be defined as an engineered structure consisting of
two metal guiding rails on which cars are self-propelled or pulled by a locomotive. In
his book John Armstrong defines a railway as:
“A railroad consists of two steel rails which are held a fixed distance apart on a
roadbed. Vehicles, guided and supported by flanged steel wheels and connected into
trains, are propelled as a means of transportation.” Webster’s Dictionary (1986)
defines a railroad as “1. A road laid with parallel steel rails, along which cars carrying
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passengers or freight are drawn by locomotives, 2. A complete system of such roads,
including land, rolling stock, stations, etc. 3. The persons or corporation owning and
managing such a system.”
The terms railway and railroad are sometimes used interchangeably. However, for
this book, railway will generally refer to the track and other closely associated
items, i.e., signals, crossings, bridges, etc. Railroad will be used where the usage
connotes the bigger system.
In commencing a railway engineering career, you are joining many fellow workers
in a complex and increasingly coordinated activity that is an integral part of any
civilized society. About one-seventh of the workers in advanced economies are
involved in some phase of transportation. Transportation, the movement of
persons and goods, of which railroading is a large and vital part, is tied in with the
location and magnitude of all kinds of human activity which depend on the timely
availability of quality goods and services. This ranges from the necessities of food
and fuel and work to leisure pursuits.
Many of you will be considered as transportation engineers specializing in railway
engineering (not operating trains). We can define railway engineering as that branch of
civil engineering involved in the planning, design, construction, operation and
maintenance of railway land facilities used for the movement of people and goods
serving the social and economic needs of contemporary society and its successors. The
complete railway engineer is active in all aspects of civil engineering practice, surveying,
geotechnics, hydrology, hydraulics, environmental and sanitary and structural design as
well as construction technology.
You will frequently encounter the word “mode” in your railway practice. A mode of
transportation is no more than a particular type of transportation defined in enough
detail for the purpose at hand. It can be as general as the medium through or on which
transportation takes place; for example, air, sea and land modes. The walking or
pedestrian mode involves the moving human. The public transportation mode
includes those systems such as rail commuter lines and public bus and taxi service.
Often, far more detailed descriptions are needed for effective analysis, communication
and understanding. The railway mode is a type of a land transportation mode as
defined above. The light rail transit mode is a further more specifically defined type of
rail service, typically today an urban, electrically powered system operating on its own
right of way with intersections with intersecting public streets. Other terms used in
railway engineering are listed and defined in the Glossary found at the end of this
Manual.
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Flange Out
Grooved
Haunch
Ringwalt
Figure 1-5 English Railways and Freight Cars, as Illustrated in Strickland’s Report, 1826
Railways quickly became a major factor in accelerating the great westward expansion,
as well as tying the older eastern population and industrial centers together, by
providing a reliable, economic and rapid means of transportation. As additional lines
were built, they facilitated the establishment and growth of towns in the West. Except
for the trip from farm to railhead in town, the poor roads and limited canals became
irrelevant. The Federal government and states encouraged and provided financial
support through land grants and loans, which were paid back with reduced rates for
half a century.
Since the first railways, there have been many improvements in all aspects of
railroading. For example, the development of the iron flanged “T” rail was achieved by
1840. (See Figure 1-8 for an early track section) Until mass steel making was
developed, there was a continuing controversy between the use of malleable iron vs.
cast iron for rail. By 1840 wooden ties kept in place by ballast stone had replaced
simple stone surface support.
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Chapter
Railway Industry
Overview
2.1 Introduction
T
he railway industry encompasses not only the operating railway companies and
transit authorities, but also the various government regulatory agencies, railway
associations, professional organizations, manufacturers and suppliers of
locomotives, railcars, maintenance work equipment and track materials, consultants,
contractors, educational institutes and, most important of all, the shipping customers.
The information in this chapter is of a general nature and may be considered as typical
of the industry. However, each railway company is unique and as such it must be
understood what is included in this chapter may not be correct for a particular
company.
2.2 Railway Companies
Government owned freight railways are nowadays limited to some regional lines where
transportation service must be protected for the economic well being of the
communities. Passenger railways, on the other hand, are generally owned by
governments. Transcontinental services, such as the Amtrak or VIA Rail in Canada,
are corporations solely owned by the respective Federal Governments. These
passenger railway companies normally do not own the trackage infrastructures. Except
for certain connecting routes and dedicated high-speed corridors, they merely operate
the passenger equipment on existing tracks owned by freight railways. Local rapid
transit systems are usually operated as public utilities by the individual municipalities or
transit authorities on their own trackage. Commuter services may be operated by
government agencies or private sector on either their own or other railway owned
trackage.
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The tractive effort (in pounds) available from a locomotive can be roughly calculated
as:
Tractive Effort (lbs.) = Horsepower X (308)
Speed (mph)
Where 308 is 82% of 375 lb-miles per hour per hp. For example, a 3000 hp
locomotive will have approximately 74,000 lbs. tractive effort at 12.5 mph.
2.6.2 Tractive Force and Adhesion
It is the tractive force at the locomotive driving wheels (drivers) at the rail that starts
and moves tonnage up various grades. The maximum tractive force that can be
developed at the rail is equal to the weight on drivers multiplied by the adhesion
(coefficient of friction) of the wheels on the rail.
The primary factors, among others, affecting adhesion are rail condition and speed.
Adhesion decreases as speed increases. At about 10 mph, adhesion varies from less
than 10% on slimy, wet rail to about 40% on dry, sanded rail. In general, with the aid
of the sanders, approximately 25% adhesion is usually available.
As all the wheels on most diesel locomotives are driving wheels, the weight of the
locomotives must be about four times the tractive force developed. The HHP (high
horsepower) units for main line service weigh about 195 tons each on 6 axles. The
maximum tractive force is therefore approximately 97,000 lb. per locomotive or 16,000
lb. per axle; that is, if there is enough horsepower at the wheel rims to develop the
tractive effort.
2.6.3 Drawbar Pull
After some of the tractive effort is used to move the locomotive itself, the remaining
effort, in the form of “drawbar pull,” is used to move the rest of the train. As the train
speed increases, the tractive effort from the locomotives decreases and the drawbar
pull available to move the train also decreases.
Due to the limited strength of drawbars and coupler knuckles, the number of
locomotives or motorized axles that can be used in the head end of a train is restricted.
Although rated with a minimum strength of 350,000 lb. (general service coupler made
of Grade B steel), coupler knuckle failure may happen at 250,000 lb. due to age and
wear. Grade E knuckles used on some captive services may have an ultimate strength
of 650,000 lb.
To avoid the risk of drawbar failure enroute, it is recommended to limit the number of
motorized axles in a locomotive consist to 18 (three 6-axle units). If more tractive
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effort is required to move the tonnage of a train, the option of in-train motive power
should be considered.
2.6.4 Train Resistance
Train resistance, the force required to move a train, is the sum of the rolling resistance
on tangent level track, grade resistance and curve resistance of the locomotives and
cars. Other resistances due to wind velocity, tunnels or different train marshalling will
not be discussed here.
Rolling Resistance
Rolling Resistance is the sum of the forces that must be overcome by the tractive effort
of the locomotive to move a railway vehicle on level tangent track in still air at a
constant speed. These resistive forces include:
§
Rolling friction between wheels and rail that depends mainly on the quality of
track.
§
Bearing resistance, which varies with the weight on each axle and, at low speed,
the type, design and lubrication of the bearing.
§
Train dynamic forces that include the effects of friction and impact between the
wheel flanges against the gauge side of the rail and those due to sway, concussion,
buff and slack-action. The rail-flange forces vary with speed and quality of the
wheel tread and rail, as well as the tracking effect of the trucks.
§
Air resistance that varies directly with the cross-sectional area, length and shape of
the vehicle and the square of its speed.
In general, rolling resistance of a train, R (in lb.), can be calculated using an empirical
expression as follows:
R = A + B V + C D V2
where A, B, C & D are coefficients defining the different resistive forces that are either
independent, dependent or affected by the square of the train speed V.
Davis Formula
The first empirical formula to compute rolling resistance was developed by W.L. Davis
in 1926. The original Davis formula provided satisfactory results for older equipment
with journal bearings within the speed range between 5 and 40 mph. Roller bearings,
increased dimensions, heavier loadings, higher train speeds and changes to track
structure have made it necessary to modify the coefficients proposed by Davis. Since
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then, there had been various modifications. Interested readers may refer to Section 2.1
of Chapter 16 in the AREMA Manual for Railway Engineering for more information.
Starting Resistance
The resistance caused by friction within a railway vehicle’s wheel bearings can be
significantly higher at starting than when the vehicle is moving. Depending on the type
of bearings, weight per axle, and the temperature of the bearing, starting resistance can
range from 5 to 50 lb/ton. The ambient temperature and the duration of the stop as
shown below affect temperature of the bearing.
Type of Bearings
Above Freezing
Below Freezing
Journal Bearing
25 lb/ton
35 lb/ton
Roller Bearing
5 lb/ton
15 lb/ton
Starting resistance is generally not much of a problem with the very large tractive effort
available with modern diesel locomotives, except on steeper grades. If necessary, the
locomotive engineer can bunch up the train first, then start the train one car at a time.
The cars already moving will help start the ones to the rear. This is called “taking
slack” to start.
Grade Resistance
Grade Resistance is the force required to overcome gradient and is equal to 20 lb. per
ton per percent grade. This force is derived from the resolution of force vectors and is
independent of train speed. An up grade produces a resistive force while a down grade
produces an accelerating (negative resistive) force. A train moving up a long tangent of
1% grade at 10 mph, a speed that most tonnage trains slow down to at ruling grade
locations, will have a train resistance coefficient of 22.4 to 23.5 lb. per ton with the
grade resistance accounted for over 85% of the total.
Curve Resistance
Curve Resistance is an estimate of the added resistance a locomotive or car must
overcome when operating through a horizontal curve. The exact details of the
mechanics contributing to curve resistance are not easy to define. It is generally
accepted in the railway industry that curve resistance is approximately the same as a
0.04% up grade per degree of curvature (which equals 0.8 lb. per ton per degree of
curvature) for standard gauge tracks. At very slow speeds, say 1 or 2 mph, the curve
resistance is closer to 1.0 lb. (or 0.05% up grade) per ton per degree of curve.
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Chapter
T R A C K
Basic Track
The engineer will frequently work from a set of standardized railway
or transit standards when making his or her selection of track
components for any given design project. However, a basic
understanding of elementary track componentry, geometry and
maintenance operations is necessary if intelligent decisions are to
be made within the options that are typically available.
3.1 Track Components
W
e begin our study with the prime component of the track – the rail.
3.1.1 Rail
Rail is the most expensive material in the track.2 Rail is steel that has been rolled into
an inverted "T" shape. The purpose of the rail is to:
2
•
Transfer a train's weight to cross ties.
•
Provide a smooth running surface.
•
Guide wheel flanges.
Canadian National Railway Track Maintainer’s Course
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Switch Ties
Switch ties (Figure 3-3) are commonly
hardwood species, usually provided in either
6" or 12" increments beginning at 9'-0" up
to 23'-0" in length. Nominal cross-section
dimensions are 7" x 9", although larger ties
are specified by some railways. The primary
use for switch ties is relegated to turnouts
(thus their name). However, they are also
used in bridge approaches, crossovers, at hot
box detectors and as transition ties. Some
railways use switch ties in heavily traveled
Figure 3-3 Switch Timber – Photo by Craig Kerner
road crossings and at insulated rail joints.
Switch ties ranging in length from 9'-0" to 12'-0" can also be used as "swamp" ties.
The extra length provides additional support for the track in swampy or poor-drained
areas. Some railways have utilized Azobe switch ties (an extremely dense African
wood) for high-speed turnouts. The benefits associated with reduced plate cutting and
fastener retention may be offset by the high import costs of this timber.
Softwood Ties
Softwood timber (Figure 3-4) is
more rot resistant than hardwoods,
but does not offer the resistance of
a hardwood tie to tie plate cutting,
gauge spreading and spike hole
enlargement
(spike
killing).
Softwood ties also are not as
effective in transmitting the loads to
the ballast section as the hardwood
tie. Softwood and hardwood ties
must not be mixed on the main
track except when changing from
one category to another.
Softwood ties are typically used in
open deck bridges.
Figure 3-4 Softwood Timber - Photo by J. E. Riley
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Concrete Ties
Concrete ties (Figure 3-5) are rapidly
gaining acceptance for heavy haul
mainline use, (both track and
turnouts), as well as for curvature
greater than 2°. They can be supplied
as crossties (i.e. track ties) or as switch
ties. They are made of pre-stressed
concrete containing reinforcing steel
wires. The concrete crosstie weighs
about 600 lbs. vs. the 200 lb. timber
track tie. The concrete tie utilizes a
Figure 3-5 Concrete Ties – Photo by Kevin Keefe
specialized pad between the base of the
rail and the plate to cushion and absorb the load, as well as to better fasten the rail to
the tie. Failure to use this pad will cause the impact load to be transmitted directly to
the ballast section, which may cause rail and track surface defects to develop quickly.
An insulator is installed between the edge of the rail base and the shoulder of the plate
to isolate the tie (electrically). An insulator clip is also placed between the contact point
of the elastic fastener used to secure the rail to the tie and the contact point on the base
of the rail.
Steel Ties
Steel ties (Figure 3-6) are often
relegated to specialized plant
locations or areas not
favorable to the use of either
timber or concrete, such as
tunnels with limited headway
clearance. They have also
been utilized in heavy
curvature prone to gage
widening.
However, they
have not gained wide
acceptance due to problems
associated with shunting of
Figure 3-6 Steel Ties
signal current flow to ground.
Some lighter models have also experienced problems with fatigue cracking.
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3.1.4 Rail Joints
The purposes of the rail joint (made up of two joint bars or more commonly called
angle bars) are to hold the two ends of the rail in place and act as a bridge or girder
between the rail ends.6 The joint bars prevent lateral or vertical movement of the rail
ends and permit the longitudinal movement of the rails for expanding or contracting.
The joint is considered to be the weakest part of the track structure and should be
eliminated wherever possible. Joint bars are matched to the appropriate rail section.
Each rail section has a designated drilling pattern (spacing of holes from the end of the
rail as well as dimension above the base) that must be matched by the joint bars.
Although many sections utilize the same hole spacing and are even close with regard to
web height, it is essential that the right bars are used so that fishing angles and radii are
matched. Failure to do so will result in an inadequately supported joint and will
promote rail defects such as head and web separations and bolt hole breaks.
There are three basic types of rail joints (Figure 3-8):
•
Standard
•
Compromise
•
Insulated
Figure 3-8 Conventional Bar, Compromise Bar & Insulated Joint Bar –
Photo by J. E. Riley
6
Canadian National Railway, Track Maintainer’s Course
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Standard Joints
Standard joint bars connect two rails of
the same weight and section. (See Figure
3-9) They are typically 24" in length with
4-bolt holes for the smaller rail sections or
36" in length with 6-bolt holes for the
larger rail sections. Alternate holes are
elliptical in punching to accommodate the
oval necked track bolt. Temporary joints
in CWR require the use of the 36” bars in
order to permit drilling of only the two
outside holes and to comply with the FRA
Track Safety Standard’s requirement of
maintaining a minimum of two bolts in
each end of any joint in CWR.
Figure 3-9 Standard Head-Free Joint Bar – Photo by J. E.
Riley
Compromise Joints
Compromise bars connect two rails of
different weights or sections together.
(See Figure 3-10) They are constructed
such that the bars align the running
surface and gage sides of different rails
sections.
There are two kinds of
compromise joints:
•
•
Directional (Right or Left hand)
compromise bars are used where a
difference in the width of the head
between two sections requires the
offsetting of the rail to align the gage
side of the rail.
Figure 3-10 Compromise Joint Bar – Photo by J. E. Riley
Non-directional (Gage or Field Side) are used where the difference between
sections is only in the heights of the head or where the difference in width of rail
head is not more than 1/8" at the gage point. Gauge point is the spot on the gauge
side of the rail exactly 5/8" below the top of the rail.
To determine a left or right hand compromise joint:
•
Stand between the rails at the taller rail section.
•
Face the lower rail section.
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•
The joint on your right is a "right hand".
•
The joint on your left is a "left hand".
Insulated Joints
Insulated joints are used in tracks having track circuits. They prevent the electrical
current from flowing between the ends of two adjoining rails, thereby creating a track
circuit section. Insulated joints use an insulated end post between rail ends to prevent
the rail ends from shorting out.
There are three types of insulated joints:
•
Continuous
•
Non-continuous
•
Bonded
Continuous insulated joints (Figure 311) are called continuous because they
continuously support the rail base.
No metal contact exists between the
joint bars and the rails. Insulated fiber
bushings and washer plates are used
to isolate the bolts from the bars. The
joint bars are shaped to fit over the
base of the rail. This type of insulated
joint requires a special tie plate called
an "abrasion plates" to properly
support the joint.
Figure 3-11 Continuous Insulated Joint – Photo by J. E. Riley
Non-continuous insulated rail joints
are called non-continuous because these joints don't continuously support the rail base.
A special insulating tie plate is required on the center tie of a supported,
non-continuous insulated joint. Metal washer plates are placed on the outside of the
joint bar to prevent the bolts from damaging the bar.
There are two common kinds of non-continuous insulated joints:
•
Glass fiber.
•
Polyurethane encapsulated bar.
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Chapter
Right-of-Way & Roadway
For this chapter, think of the railway right-of-way as the area from
fence to fence without the track and structures. The roadway is
considered to be any construction within the right-of-way except
the track, bridge structures, signals and crossings.
4.1 Introduction
T
he railway right-of-way (often referred to as the roadway) includes the subgrade
upon which the ballast section and track are built, along with adjacent
improvements and features required to support and maintain the railway track.
The right-of-way is often thought of as the strip of land on which the railway and its
supporting features are built.
The right-of-way typically includes ditches running along the track and related drainage
structures required to divert water past and away from the railway. The issue of
drainage is covered in Chapter 5. It also includes any embankments and cuts on which,
or through which, the railway is built, their side slopes and the vegetation covering the
slopes. It may also include any retaining walls or other earth-supporting structures
required to hold railway embankment and cut side slopes in place. It includes fences,
signs, utilities and outlying structures.
The bulk of this chapter deals with what the railways are built upon, the soil. Just as
concrete and steel are the materials used by the structural engineer, soil is the main
building material for the railway. In the same way as there are various types of steel, or
diverse mixtures of concrete, there are many classifications of soil. Some soils are
suitable for use as ballast and sub-ballast (sand and gravel), some as subgrade materials
(sand, gravel, clay, etc.), while others are totally undesirable for any use in railway
construction (e.g., organic soils).
A major difference between soils and most other construction materials is that soil is a
natural material and is subjected to little or no processing before use. It is therefore
essential to identify the various soils and avoid using those that may give problems,
since it is seldom that soil can be processed to improve its properties. From a
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construction and maintenance over the past 100 years. For instance, it is not unusual
for track that functioned very well for more than 50 years to suddenly develop severe
geotechnical problems.
In solving problems today, the experiences and effects of the last 100 to 150 years of
railway practice must be considered. Not only are the railways dealing with everincreasing loads and ever-increasing traffic, but also a maintenance effort focused on
rails and ties. Ballast, being less visible, receives less attention, and the subgrade, less
still except when problems develop. Nonetheless, knowing the history of a section of
track is an important component of effective track maintenance.
Components and Functions
SUBBALLAST
SUBGRADE
Figure 4-4 The Track Structure
The track structure is made up of subgrade, sub-ballast, ballast, ties and rail as
illustrated in Figure 4-4. Each of these contributes to the primary function of the track
structure, which is to conduct the applied loads from train traffic across the subgrade
safely. The magnitudes of typical stresses under a 50,000 lb axle load are shown in
Figure 4-5. These stresses are applied repeatedly, and each repetition causes a small
amount of deformation in the subgrade. In theory, the track structure should be
designed and constructed to limit rail deflections to values which do not produce
excessive rail wear or rates of rail failure. In reality, cumulative deformation of the
subgrade causes distortion of the subgrade, leading to formation of “ballast pockets"
(Figure 4-6) or outright shear failure.
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Figure 4-5 Stresses Imposed by Train Axle Load
Figure 4-6 Ballast Pockets in Subgrade
Subgrade
The purpose of the subgrade is to support the track structure with limiting deflections.
Every subgrade will undergo some deflection (strain) as loads (stress) are applied. The
total displacement experienced by the subgrade will be transmitted to other
components in the track structure. The stiffer the subgrade (i.e., the higher the
modulus of elasticity), the lower the deflection values will be. It is important that
adequate subgrade strength and stiffness be available on a year-round basis, particularly
during spring thaw and following heavy precipitation events.
The strength, stiffness and total deflection of the subgrade can be improved by:
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§
Carefully selecting materials that are naturally strong (sand, gravel, boulders)
with a high angle of internal friction.
§
Limiting access to water to avoid buildup of porewater pressure and
subsequent reduction of strength.
§
Improving the soil properties, using techniques such as compaction, in situ
densification, grouting and preloading.
§
Maintain good drainage.
§
Maintain stable subgrade geometry.
Sub-ballast
The purpose of sub-ballast is to form a transition zone between the ballast and
subgrade to avoid migration of soil into the ballast, and to reduce the stresses applied
to the subgrade. In theory, the gradation of the sub-ballast should form a filter zone
that prevents migration of fine particles from the subgrade into the ballast. In practice,
insufficient attention has been placed to sub-ballast gradation historically, and much of
the sub-ballast does not adequately perform that function. This notwithstanding, the
number of occurrences of subgrade contamination of ballast are relatively few.
How Track Fails
In a nutshell, track fails when differential rail deflections become excessive. This
differential deflection may be expressed in differential elevation between tracks,
punching of ties, elastic or plastic deformation of the subgrade, or degradation of
ballast.
When the bearing capacity of the subgrade is exceeded, the subgrade will deform
plastically, resulting in a small amount of permanent deformation under each wheel
load. A progressive deterioration of the track begins, as illustrated in Figures 4-7 to 410. It starts with minor deflections and may progress to a fully visible surface heave,
where subgrade material is pushed above the elevation of the rail and ties. Under those
conditions, ballast drainage is impeded, resulting in further softening and degradation
of the subgrade to a point where large, saturated pockets of ballast are trapped in the
subgrade. Frost heave and further degradation commonly follow, leading eventually to
a severe loss of utility of the track structure.
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Figure 4-7 Stable Site
Figure 4-8 Onset of Instability
Figure 4-9 Growth of Heave
Figure 4-10 Surface Manifestation of Heave
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4.3.4 Instability
Instability results when the shear strength of the soil is not sufficient to support the
loads applied to it. Bearing capacity failures discussed in the previous section are one
type of shear failure that occurs when the soil cannot sustain vertical load applied to it
and vertically downward movement results. The term landslide is used to define all
types of mass movement of soil or rock, where the mass moves down slope under the
influence of gravity only. There are many types of landslides, but the distinguishing
feature is that a mass of material is moved and gravity is the driving force.
Main Features of Landslides
The diagnostic features of most landslides include a scarp that forms at the head of the
landslide. This is usually a near vertical wall of soil, usually freshly exposed by
movement. The slump blocks are unique, identifiable blocks of soil, usually bounded
by scarps that show both vertical and horizontal movement. The main body of the
slide is the mass of soil that is pushed ahead by the slump blocks, and may be marked
by numerous tension cracks. Bulging of the soil, and thrusting of the slide debris over
the natural surface usually mark the toe of the slide. The slip plane or shear zone is
usually a distinct and identifiable plane that marks the lower limit of movement and the
upper limit of undisturbed soil. It should be noted that the shear zone is not usually
planar, but rather may be circular, or a composite curvilinear surface that passes
through the weakest zones in the subsurface.
Slides that Affect the Track
Instability that affects the track can be classified according to the impact that it has on
the track. These are described in various illustrations.
§
Figure 4-11 illustrates a slide that encompasses a track and will disrupt the track by
cutting the alignment. Once the track moves out of line, it is no longer serviceable.
Figure 4-11 Slides Cutting Track
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Figure 4-12 illustrates the effect of a landslide upslope where the toe crosses the
track, burying it in under slide debris.
Figure 4-12 Slides Covering Track
§
Figure 4-13 shows the track being heaved up in response to upward movement of
the toe of a landslide.
Figure 4-13 Slides Heaving Track
§
Figure 4-14 illustrates an event where a landslide threatens the track, perhaps by
encroaching on the down slope shoulder.
Figure 4-14 Slides Threatening Track
§
Figure 4-15 illustrates how base failure in fills on soft foundations can cause the fill
to spread and settle. While this may be mistaken as settlement, it is actually a shear
movement involving the foundation soils. It is common on organic terrain and
other soft foundations.
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Figure 4-15 Base Failure
§
Figure 4-16 shows how locations over old landslides may be reactivated due to a
change in stresses within the landslide mass. Many of the ancient landslides are
extremely large, and the limits of the landslides may be difficult to detect.
Figure 4-16 Reactivation of Old Slide
Triggering Mechanisms
The stability of a slope is dependent upon:
§
The shear strength of the soils.
§
Porewater pressure within the soils that make up the slope (this can be roughly
measured by knowing the water table).
§
The geometry of the slope, particularly the slope angle and changes of slope.
§
Any surcharge loading such as fill or bank widening material stored on the slope or
train loads.
Landslides occur either as a result of reduction in soil strength or an increase in the
loading on the slope.
Reductions in soil strength can occur as the result of:
§
An increase in porewater pressure, reducing the available shear strength of the soil.
In the case of moisture sensitive soils, the amount of water needed to cause this
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D R A I N A G E
Drainage
The three most important elements in good track are: #1 Drainage,
#2 Drainage and #3 Drainage – Darrell Cantrell, Engineer Track
(Retired) BNSF
D
rainage is the subject of stormwater behavior as it relates to the properties of
hydrology and hydraulics. This is a subject that is constantly being reviewed
on a regular basis within the regulatory bodies of government and it is
therefore always important to review local requirements to guide the engineer through
the design process. Even though one method of analysis may be appropriate to use in
an area one feels comfortable in, it may not be appropriate in another location. A good
rule of thumb is to contact the local highway department as a starting point and
continue your investigation to local authorities. The other primary source for the
Engineer is the AREMA Manual for Railway Engineering, Chapter 1, Parts 3 & 4.
The engineer needs to be aware that one has to maintain existing drainage patterns and
not increase headwaters upstream or downstream. Adjacent property owners, whether
they are farmers or city dwellers, have certain rights and are protected under common
law concerning storm water conveyance and elevation as it relates to property damage.
5.1 Hydrology
For the purposes of this Guide, Hydrology will be defined as the study of rainfall
events (inches or inches per hour) and runoff (cubic feet per second) as related to the
engineering design of conveyance features such as ditches and culverts. These
conveyance features are typically designed to a particular storm event or storm
frequency. In other words, a storm water conveyance feature is going to be associated
with a certain amount of risk with respect to failure. For instance, a 100 year storm
return period has a 1% probability of occurring in any given year, a 50 year storm has a
2% probability of occurring in any given year, and a 10 year storm has a 10% chance of
occurring in any given year. So it is up to the designer to assign a certain amount of
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5.3 Recommended Procedures
5.3.1 Existing Drainage Study
Before proceeding with the design of the project, it should be realized that it is always
important to visit the actual project site and identify problems that may be
encountered. Existing culverts always seem to be a problem and should be looked at
carefully. Examples of potential problems include excessive ditch scouring and
constant ponding of water along a ditch system. Railway ditches are typically very flat
and do not drain well. However, the designer should always review the situation as if
there is a solution. If it is economically feasible to remedy the situation, then the area
should be regraded and repaired to what is recognized as common engineering
practice.
Below is a recommended approach to an existing consistent drainage study:
•
Utilize a USGS Quadrangle Map or a Hydrologic Atlas (HA) for the area.
•
Plot existing and proposed railway right-of-way.
•
Identify floodplain and floodway boundaries.
•
Identify watershed areas based upon contour interpretation.
•
Identify existing bridges, culverts and problem areas.
•
Identify sheet and concentrated flow.
•
Identify closed drainage systems.
•
Select outlet points for each watershed area.
•
Select the proper hydrology criteria (i.e. rainfall, frequency, formula, etc.).
•
Calculate or run the model and assign flow rates to each of the watersheds.
•
Add flow rates and hydrographs, as necessary, to determine proper flow through
the watershed.
•
Select the proper hydraulic method to determine storm water elevations.
•
Conduct a plan-in-hand field review.
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Remember the existing drainage study is the benchmark study on which all proposed
drainage features are based.
5.3.2 Proposed Drainage System
The proposed drainage system typically addresses impacts to an existing man made or
natural drainage system from a proposed improvement. This can take the form of new
ditches and culverts or it can take the form of improving existing problem areas. Keep
in mind that any improvement to an existing drainage system will more than likely
affect surrounding drainage patterns and elevations on adjacent or downstream
properties. For example, increasing the size of an existing cross culvert introduces
more storm water flow rate to downstream property owners. The designer should
determine whether this situation is going to present a problem.
Below is a recommended approach to the design of a proposed drainage system:
•
Complete and review the existing drainage study.
•
Superimpose the proposed improvements on a copy of the existing drainage study
map.
•
Locate new drainage features such as ditches, bridges and culverts.
•
Are there floodplain and wetland impacts?
•
Never relocate an existing outlet point unless it is absolutely necessary.
•
Try to maintain existing watershed limits (sometimes these do change).
•
Calculate the new hydrology for the watershed.
•
Calculate the new hydraulics for the watershed.
•
Compare the new data with the existing data at the same points.
•
Initiate Permitting process.
For adjacent properties, it is ideal to obtain the same results between existing and
proposed conditions and it may take a few iterations to obtain those results.
Sometimes it is impossible for this to occur. By studying the upstream and
downstream effects, the designer may be able to apply a certain amount of change that
does not harm or cause damage to adjacent property owners. For example, a 0.1’ or a
0.5’ increase in headwater may be acceptable, or a 5% increase in flow velocity may be
acceptable if the surrounding soil conditions are tolerable. There may be more
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considerations to review. However, this is dependent upon the conditions and
regulations unique to that project location.
5.3.3 Floodplain Encroachment Evaluation
The floodplain is identified by criteria established by the Federal Emergency
Management Agency (FEMA) for the 100-year and 500-year storm events or known
depression flood prone areas. Typically, the 100-year base flood elevation is the most
commonly regulated stormwater elevation associated with rivers, streams and
concentrated flow areas. FEMA, State Water Resource Departments, counties and
local communities (that are part of the National Flood Insurance Program) closely
monitor flood plain areas. Any change to the flood plain will generally result in
extensive studies and computer modeling to be submitted for approval.
Below is a summary of possible floodplain permitting reviews.
FEMA:
•
Physical Map Change (Extensive Floodplain Revisions)
•
Letter of Map Revision (Typical Floodplain Revisions)
•
Conditional Letter of Map Revision (Typical Floodplain Revisions done in the
design phase)
•
Elevation Criteria (Typically for building structures)
US Army Corps of Engineers:
•
Excavation below normal water elevation
State Water Resource Department:
•
Floodway (Area within a floodplain that demonstrates conveyance)
County (Some counties may not be involved in the review process):
•
Floodplain
•
Floodway
•
Compensatory Storage (Excavation required to compensate for floodplain filling)
•
Elevation Criteria (Typically for building structures)
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Chapter
Railway Track Design
Basic considerations and guidelines to be used in the establishment
of railway horizontal and vertical alignments.
T
he route upon which a train travels and the track is constructed is defined as an
alignment. An alignment is defined in two fashions. First, the horizontal
alignment defines physically where the route or track goes (mathematically the
XY plane). The second component is a vertical alignment, which defines the elevation,
rise and fall (the Z component).
Alignment considerations weigh more heavily on railway design versus highway design
for several reasons. First, unlike most other transportation modes, the operator of a
train has no control over horizontal movements (i.e. steering). The guidance
mechanism for railway vehicles is defined almost exclusively by track location and thus
the track alignment. The operator only has direct control over longitudinal aspects of
train movement over an alignment defined by the track, such as speed and
forward/reverse direction. Secondly, the relative power available for locomotion
relative to the mass to be moved is significantly less than for other forms of
transportation, such as air or highway vehicles. (See Table 6-1) Finally, the physical
dimension of the vehicular unit (the train) is extremely long and thin, sometimes
approaching two miles in length. This compares, for example, with a barge tow, which
may encompass 2-3 full trains, but may only be 1200 feet in length.
These factors result in much more limited constraints to the designer when considering
alignments of small terminal and yard facilities as well as new routes between distant
locations.
The designer MUST take into account the type of train traffic (freight, passenger, light
rail, length, etc.), volume of traffic (number of vehicles per day, week, year, life cycle)
and speed when establishing alignments. The design criteria for a new coal route
across the prairie handling 15,000 ton coal trains a mile and a half long ten times per
day will be significantly different than the extension of a light rail (trolley) line in
downtown San Francisco.
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curves as D (degrees per 20 meter arc). However, there does not seem to be any
widespread incorporation of this practice. When working with light rail or in metric
units, current practice employs curves defined by radius.
As a vehicle traverses a curve, the vehicle transmits a centrifugal force to the rail at the
point of wheel contact. This force is a function of the severity of the curve, speed of
the vehicle and the mass (weight) of the vehicle. This force acts at the center of gravity
of the rail vehicle. This force is resisted by the track. If the vehicle is traveling fast
enough, it may derail due to rail rollover, the car rolling over or simply derailing from
the combined transverse force exceeding the limit allowed by rail-flange contact.
This centrifugal force can be
counteracted by the application of
superelevation (or banking), which
effectively raises the outside rail in the
curve by rotating the track structure
about the inside rail. (See Figure 6-6)
The point, at which this elevation of the
outer rail relative to the inner rail is such
that the weight is again equally
distributed on both rails, is considered
the equilibrium elevation. Track is
rarely superelevated to the equilibrium
elevation. The difference between the
equilibrium elevation and the actual
superelevation is termed underbalance.
Though trains rarely overturn strictly
from centrifugal force from speed
Figure 6-6 Effects of Centrifugal Force
(they usually derail first). This same
logic can be used to derive the overturning speed. Conventional wisdom dictates that
the rail vehicle is generally considered stable if the resultant of forces falls within the
middle third of the track. This equates to the middle 20 inches for standard gauge
track assuming that the wheel load upon the rail head is approximately 60-inches apart.
As this resultant force begins to fall outside the two rails, the vehicle will begin to tip
and eventually overturn. It should be noted that this overturning speed would vary
depending upon where the center of gravity of the vehicle is assumed to be.
There are several factors, which are considered in establishing the elevation for a curve.
The limit established by many railways is between five and six-inches for freight
operation and most passenger tracks. There is also a limit imposed by the Federal
Railroad Administration (FRA) in the amount of underbalance employed, which is
generally three inches for freight equipment and most passenger equipment.
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Underbalance
limits
above three to four
inches (to as much as five
or six inches upon FRA
approval of a waiver
request) for specific
passenger equipment may
be granted after testing is
conducted.
T R A C K
D E S I G N
EQUILIBRIUM
OVERBALANCE
Center of
Gravity
Gravity
Centrifugal
Force
UNDERBALANCE
Centrifugal
Force
Center of
Gravity
Center of
Gravity
Centrifugal
Force
Resultant
Resultant
Gravity
Superelevation
Resultant
Superelevation
Gravity
Superelevation
Ea + 3
Amount of
Track is rarely elevated to
Vmax =
0.0007 D
Underbalance
equilibrium
elevation
V max = Maximum allowable operating speed (mph).
because not all trains will
Ea
= Average elevation of the outside rail (inches).
be moving at equilibrium
= Degree of curvature (degrees).
D
speed through the curve.
Figure 6-7 Overbalance, Equilibrium and Underbalanced
Furthermore, to reduce
both the maximum
allowable superelevation along with a reduction of underbalance provides a margin for
maintenance. Superelevation should be applied in 1/4-inch increments in most
situations. In some situations, increments may be reduced to 1/8 inch if it can be
determined that construction and maintenance equipment can establish and maintain
such a tolerance. Even if it is determined that no superelevation is required for a curve,
it is generally accepted practice to superelevate all curves a minimum amount (1/2 to
3/4 of an inch). Each railway will have its own standards for superelevation and
underbalance, which should be used unless directed otherwise.
The transition from level track on tangents to curves can be accomplished in two ways.
For low speed tracks with minimum superelevation, which is commonly found in yards
and industry tracks, the superelevation is run-out before and after the curve, or through
the beginning of the curve if space prevents the latter. A commonly used value for this
run-out is 31-feet per half inch of superelevation.
On main tracks, it is preferred to establish the transition from tangent level track and
curved superelevated track by the use of a spiral or easement curve. A spiral is a curve
whose degree of curve varies exponentially from infinity (tangent) to the degree of the
body curve. The spiral completes two functions, including the gradual introduction of
superelevation as well as guiding the railway vehicle from tangent track to curved track.
Without it, there would be very high lateral dynamic load acting on the first portion of
the curve and the first portion of tangent past the curve due to the sudden introduction
and removal of centrifugal forces associated with the body curve.
There are several different types of mathematical spirals available for use, including the
clothoid, the cubic parabola and the lemniscate. Of more common use on railways are
the Searles, the Talbot and the AREMA 10-Chord spirals, which are empirical
approximations of true spirals. Though all have been applied to railway applications to
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6.4 Alignment Design
In a perfect world, all railway alignments would be tangent and flat, thus providing for
the most economical operations and the least amount of maintenance. Though this is
never the set of circumstances from which the designer will work, it is that ideal that
he/she must be cognizant to optimize any design.
From the macro perspective, there has been for over 150 years, the classic railway
location problem where a route between two points must be constructed. One option
is to construct a shorter route with steep grades. The second option is to build a longer
route with greater curvature along gentle sloping topography. The challenge is for the
designer to choose the better route based upon overall construction, operational and
maintenance criteria. Such an example is shown below.
Figure 6-9 Heavy Curvature on the Santa Fe - Railway Technical Manual – Courtesy of BNSF
Suffice it to say that in today’s environment, the designer must also add to the decision
model environmental concerns, politics, land use issues, economics, long-term traffic
levels and other economic criteria far beyond what has traditionally been considered.
These added considerations are well beyond what is normally the designer’s task of
alignment design, but they all affect it. The designer will have to work with these issues
occasionally, dependent upon the size and scope of the project.
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On a more discrete level, the designer must take the basic components of alignments,
tangents, grades, horizontal and vertical curves, spirals and superelevation and
construct an alignment, which is cost effective to construct, easy to maintain, efficient
and safe to operate. There have been a number of guidelines, which have been
developed over the past 175 years, which take the foregoing into account. The
application of these guidelines will suffice for approximately 75% of most design
situations. For the remaining situations, the designer must take into account how the
track is going to be used (train type, speed, frequency, length, etc.) and drawing upon
experience and judgment, must make an educated decision. The decision must be in
concurrence with that of the eventual owner or operator of the track as to how to
produce the alignment with the release of at least one of the restraining guidelines.
Though AREMA has some general guidance for alignment design, each railway usually
has its own design guidelines, which complement and expand the AREMA
recommendations. Sometimes, a less restrictive guideline from another entity can be
employed to solve the design problem. Other times, a specific project constraint can
be changed to allow for the exception. Other times, it’s more complicated, and the
designer must understand how a train is going to perform to be able to make an
educated decision. The following are brief discussions of some of the concepts which
must be considered when evaluating how the most common guidelines were
established.
A freight train is most
commonly comprised of
power and cars. The
power may be one or
several
locomotives
located at the front of a
train. The cars are then
located in a line behind
the power. Occasionally,
additional power is placed
at the rear, or even in the
center of the train and
may be operated remotely
from the head-end. The
train can be effectively
visualized
for
this
Figure 6-10 Automatic Coupler
discussion as a chain lying
on a table. We will assume for the sake of simplicity that the power is all at one end of
the chain.
Trains, and in this example the chain, will always have longitudinal forces acting along
their length as the train speeds up or down, as well as reacting to changes in grade and
curvature. It is not unusual for a train to be in compression over part of its length
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(negative longitudinal force) and in tension (positive) on another portion. These forces
are often termed ‘buff’ (negative) and ‘draft’ (positive) forces. Trains are most often
connected together with couplers (Figure 6-10). The mechanical connections of most
couplers in North America have several inches (up to six or eight in some cases) of
play between pulling and pushing. This is termed slack.
If one considers that a long train of 100 cars may be 6000' long, and that each car
might account for six inches of slack, it becomes mathematically possible for a
locomotive and the front end of a train to move fifty feet before the rear end moves at
all. As a result, the dynamic portion of the buff and draft forces can become quite
large if the operation of the train, or more importantly to the designer, the geometry of
the alignment contribute significantly to the longitudinal forces.
As the train moves or
accelerates, the chain is pulled
from one end. The force at
any point in the chain (Figure
6-11) is simply the force
being applied to the front end
of the chain minus the
frictional resistance of the
chain sliding on the table
from the head end to the
point under consideration.
Figure 6-11 Force Applied Throughout the Train - ATSF Railroad Technical
Manual - Courtesy of BNSF
As the chain is pulled in a straight line, the remainder of the chain follows an identical
path. However, as the chain is pulled around a corner, the middle portion of the chain
wants to deviate from the initial path of the front-end. On a train, there are three
things preventing this from occurring. First, the centrifugal force, as the rail car moves
about the curve, tends to push the car away from the inside of the curve. When this
fails, the wheel treads are both canted inward to encourage the vehicle to maintain the
course of the track. The last resort is the action of the wheel flange striking the rail and
guiding the wheel back on course.
Attempting to push the chain causes a different situation. A gentle nudge on a short
chain will generally allow for some movement along a line. However, as more force is
applied and the chain becomes longer, the chain wants to buckle in much the same way
an overloaded, un-braced column would buckle (See Figure 6-12). The same theories
that Euler applied to column buckling theory can be conceptually applied to a train
under heavy buff forces. Again, the only resistance to the buckling force becomes the
wheel/rail interface.
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Chapter
Communications and
Signals
Types, Theory of Operation and Design Considerations of Train
Control and Railway Communications and Signals Systems.
T
his chapter contains a basic description of the types and theory of operation of
Communications and Signals Systems, their application and design
considerations. Due to the safety sensitive nature of these systems, the
examples and/or sample formulas included should not be incorporated into actual
designs. Readers of this chapter are invited to read the AREMA Communications and
Signals Manual of Recommended Practices for a comprehensive study of the various
elements of signaling, including recommended practices.
7.1 Introduction to Signals
7.1.1 Railway Operation
In the early days of railway operation, there was seldom need for more than one train
to operate on a section of track at any given time. As traffic increased, it became
necessary to operate trains in both directions over single track.
To permit faster and superior trains to pass and provide for opposing trains to meet, it
was necessary to construct sidings. It was then necessary to devise methods to affect
opposing and passing movements without disaster and with a minimum of confusion
and delay. This was achieved by introducing time schedules so that the meeting and
passing of trains could be prearranged. Thus, the "timetable" was born.
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The rails of a track circuit provide the path for the flow of current from the battery.
Bond wires are applied to ensure a path of low and uniform resistance between
adjoining rails.
Insulated joints define track circuit limits. Track circuits vary in length as required.
AREMA definitions of terms commonly applied to track circuit operation are:
Ballast Leakage:
ballast, ties, etc.
The leakage of current from one rail to the other rail through the
Ballast Resistance:
The resistance offered by the ballast, ties, etc., to the flow of
leakage current from one rail of the track to the other rail.
Floating Charge:
Maintaining a storage battery in operating condition by a continuous
charge at a low rate.
Rail Resistance:
connections.
The total resistance offered to the current by the rail, bonds and rail
A low resistance connection across the source of supply, between it and
the operating units.
Shunt Circuit:
Short Circuit:
A shunt circuit abnormally applied.
Shunting Sensitivity:
The maximum resistance in ohms, which will cause the relay
contacts to open when the resistance is placed across the rails at the most adverse,
shunting locations.
7.3.2 Track Circuit Operation
A battery is connected to one end of the track circuit, close to the insulated joints, with
positive energy applied to the south rail “S” and negative to the north rail “N.” The
relay is connected at the other end of the track circuit with one lead of the relay coils
going to rail “S” and the other to rail “N.” With the battery and relay connected,
current has a complete path in which to flow, as indicated by the arrows.
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N
Insulated
Joints
Rails
S
Lightning
Arrestor
Series
Resistor
Limiting
Resistor
Relay
Battery
Figure 7-14 Conventional DC Track Circuit Basics
The track circuit is designed as a series circuit, but because of ballast leakage, many high
resistance paths exist from rail to rail. When an alternate path for current flow exists
from one rail to the other via the ballast, the track circuit becomes a parallel circuit.
The current through each ballast resistance and the current through the relay coils adds
up to the total current drain from the battery during normal conditions.
When a train enters a track section, the wheels and axles place a shunt (short) on the
track circuit. This creates a low resistance current path from one rail to the other and
in parallel with the existing ballast resistance and relay coil. When maximum current
from the battery is reached because of current flow through the relay coils, ballast
resistance and low resistance path created by the train shunt, the relay armature drops.
Most of the current flows through the low resistance shunt path. This reduces the
current in the relay sufficiently to cause the armature to drop, thereby opening the
front contacts. In Figure 7-15, the heavy dark arrows indicate the high current path
through the shunt.
TR
R
G
Figure 7-15 Contacts of a DC Track Circuit Relay Controlling a Lighting Circuit
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In Figure 7-15, the front contact of the relay is inserted in a signal control circuit to
operate a green signal and the back contact to operate the red signal. When a train is
present on that section of track, the relay de-energises and the heel contact makes with
the back contact lighting the red signal. When the last pair of wheels moves off the
track circuit, the current will again flow in the un-shunted track circuit, through the
coils of the relay, causing the front contacts to close and light the green signal.
An appreciation of the effect of ballast resistance is necessary to understand track
circuit operation. When good ties are supported in good crushed stone and the
complete section is dry, the resistance to current flow from one rail to the other rail is
very high. This condition is known as maximum ballast resistance and is ideal for good
track circuit operation.
When the ballast is wet or contains substances such as salt or minerals that conduct
electricity easily, current can flow from one rail to the other rail. This condition is
minimum ballast resistance. With minimum ballast resistance, ballast leakage current is
high. When the ballast resistance decreases significantly, the relay can be robbed of its
current and become de-energized, or fail to pick up after it has been de-energized by a
train and the train has left the track circuit. Because the ballast resistance varies
between a wet day (minimum ballast resistance) and a dry day (maximum ballast
resistance) the flow of current from the battery will vary.
When a train occupies a track circuit, it places a short circuit on the battery. In order to
limit the amount of current drawn from the battery during this time, a resistor is placed
in series with the battery output to prevent the battery from becoming exhausted. A
variable resistor is used in order to set the desired amount of discharge current during
the period the track circuit is occupied. This resistor is called the “battery-limiting
resistor.”
When the battery-limiting resistor is adjusted as specified, higher current will flow
through the relay coil on a dry day due to maximum ballast resistance. If this current is
too high the relay will be hard to shunt. To overcome this condition a variable resistor
is inserted in series with the relay coil at the relay end of the track circuit and is used to
adjust the amount of current flowing in the relay coils.
7.3.3 Train Shunting
Relay drop-away time on train shunt is dependent on the following factors:
•
•
The relay current before the shunt is applied
The effectiveness of the shunt
When a train occupies and shunts a track circuit, the relay will not drop immediately.
The magnetic field that built up around the cores when the relay was energized must
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Motor
Gear train
Hold clear mechanism
Circuit controller
Counterweights are used in conjunction with various lengths of gate
arms for the purpose of off-setting the weight of the gate arm itself, in order that the
motor without excessive current draw can raise the gate.
Counterweights:
The counterweights are adjustable in two ways to provide a sufficient number of footpounds of torque in both the vertical and horizontal positions.
Counterweights are to be installed as per manufacturer's instructions. Gate arms are to
be torqued in the vertical and horizontal position according to the manufacturer's
handbook, which is included with each mechanism. Settings may vary depending on
which type of gate model is used.
The light nearest the tip of the gate arm is at the prescribed distance
from the tip and burns steadily as per the railway’s standards. The other lights are
located to suit local conditions and flash alternately in unison with the lights on the gate
mast.
Gate Lighting:
When positioning the lights on the gate arm, the rightmost light must be in line with
the edge of the roadway and the center light should be placed between the two outer
lights.
7.5.3 Crossing Motion Detector/Predictor
On a crossing equipped with a motion detector, the crossing warning device will
activate as soon as a train is detected. If the train stops or backs up, the crossing
warning device will stop operating. The industry has taken it one step further by
converting the motion sensor into a device that can predict the speed of an oncoming
train to activate the crossing at a pre-determined time. The automatic warning device is
hardware and software driven.
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Termination shunt
TX
RX
Figure 7-30 Bi-directional - Automatic Crossing Warning Device
There are several configurations to choose from. The above example illustrates a bidirectional configuration.
A key function of the transmitter section is to maintain a constant AC current on the
track.
The transmitter wires (TX) send an AC signal:
•
•
•
Down one rail in both directions (bi-directional)
Through the termination shunt at the ends of the circuit
Through the other rail, returning to the AC source
The receiver wires (RX) define the limits of the island circuit and monitor the
transmitter signal.
Track impedance, in the form of inductive reactance (resistance to AC), depends on
the length of the track circuit, which is defined by the termination shunt and the
applied frequency. For this reason, the longer approach circuits should use a low
frequency, while the shorter island tracks should use a higher frequency.
With no train on either approach, the electronic box at the crossing creates a 10-volt
DC signal (distant voltage). When a train comes onto the crossing approach, the
following occurs:
•
•
•
•
Lead axle shunts the track.
Lead axle becomes a moving termination shunt, which shortens the track
circuit as it approaches the crossing.
Track impedance (resistance) decreases as the track circuit shortens.
As the track impedance decreases, the distant voltage (10 VDC) decreases
towards 0 volts at the crossing.
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•
As the train leaves the crossing, the distant voltage rises again towards 10
VDC.
The rate of voltage drop is dependent on the speed of a train. From this, you can
probably see that with a little creative programming, the box can predict the speed of a
train and activate the crossing at the appropriate time or stop the crossing operation if
the train stops or backs up.
For this configuration (bi-directional), no insulated joints are required. However, if
there are insulated joints because of the presence of a DC track circuit, bypass couplers
can be used to allow the AC signal around the joints while blocking DC.
Output terminals from the crossing predictor provide 12 volts DC to the crossing
control circuits. The crossing control circuits are either relay logic control circuits or
solid-state control circuits. Crossing control circuits operate the bell, flashing lights and
gate arms.
7.6 Centralized Traffic Control (CTC)
Centralized Traffic Control (CTC) permits both opposing and following moves of
trains on the same track by the indication of block signals. CTC allows for more than
one train to be in a block, travelling in the same direction at the same time and
eliminates the need for train orders and timetable superiority.
Control point circuitry, controlled block signals, dual control power operated switch
machines, electric locks in conjunction with switch circuit controllers and advanced
communications systems are all integral parts of a CTC system.
Signal indications authorize train movement in CTC. Once a train is allowed into a
block by the dispatcher (control signal often referred to as home signal), the train is
controlled by automatic block signals (intermediate signals).
Important Note: The sequence of operations described below is a typical model only.
For compliance to FRA requirements and regulations refer to Parts 235 and 236.
7.6.1 Operation
Many existing CTC systems are relay based. Modern installations are microprocessor
based with solid-state support circuits and advanced communication links. For this
discussion, we will consider a relay-based system. A later section of this chapter will
introduce solid-state systems.
Control and indication codes rely on step-by-step operation of relays and mechanisms
at the field location, working in synchronism with step-by-step operation of relays at
the control office.
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CTC systems are controlled by a dispatcher with code and carrier systems, which
provide communications to the field control points with two line wires and/or by
microwave signals, regardless of the number of control points.
To transmit a control, the dispatcher positions the necessary levers
and buttons on the control machine. Next, he pushes the appropriate start button that
causes a code to be transmitted. All field locations connected to the code line see the
control code, but only the one called is selected. At the selected location, the control
portion of the code is delivered through field application relays to cause the function
relays to operate switches, signals, etc.
Control Codes:
When a field change occurs in the position of a switch, the aspect
of a signal, or the condition of a track circuit, an indication code is set up at the field
location, which in turn automatically transmits the indication back to the control office.
When the indication code is received at the control machine, the appropriate
indications light up on the dispatcher’s panel to show the conditions existing at the
field locations.
Indication Codes:
Control Points may consist of a single switch or a cross-over between
tracks, or various combinations of switches and crossovers with associated signals.
From the control machine, the dispatcher remotely controls the power switch
machines. A network of signals is associated with each power switch to ensure that
train movements are made safely. CTC is basically a series of controlled switches and
signals at wayside locations, connected with automatic signalling.
Control Point:
Control Office:
Each train dispatcher is responsible for the operation of traffic on
his/her assigned territory. A dispatcher's duties require that he set up routes and
signals for traffic, arrange meets of trains and provide protection for roadway workers.
Railways have implemented computers to assist with train control systems. The
computers are equipped with mass storage devices on which train and signal activity
are archived for future reference. This information is accessed for purposes ranging
from accident investigation to train delay reports.
The dispatching computers are located in a special room. This room contains an air
conditioning system to keep the environment at a constant temperature and humidity,
and a fire protection system to safeguard against fires in and around the computer
room. As well, the system is equipped with an un-interruptible power supply (UPS) to
keep it up and running in the event of a commercial power failure. The uninterruptible
power supply is made up primarily of storage batteries and a diesel generator. The
generator is used to keep the batteries fully charged if the power failure persists.
The computer duplicates all of the interlocking checks performed by the field circuitry,
safeguarding against any potentially unsafe requests by any of the system users.
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This chapter contains a basic description of the types of railway structures and their
design considerations. The purpose is to inform engineers of design considerations for
railway structures that are different from their non-railway counterparts. Due to
variations in design standards between the different railways, consult the controlling
railway for their governing standard before starting design.
8.1 Introduction to Railway
Structures
Railway structures encompass a wide array of construction intended to support the
track itself or house railway operations. Common examples of track carrying structures
are bridges, trestles, viaducts, culverts, scales, inspection pits, unloading pits and similar
construction. Examples of common ancillary structures are drainage structures,
retaining walls, tunnels, snow sheds, repair shops, loading docks, passenger stations and
platforms, fueling facilities, towers, catenary frames and the like.
While the design of ancillary structures for the railway environment may introduce
considerations not found in their non-railway counterparts, these considerations are
usually well defined in the governing railway’s standards. Accordingly, this chapter will
focus primarily on track carrying structures.
When designing railway
structures, the various
sources of their loads
must be considered, as
they would be with any
other similar, nonrailway structure. In
addition to the dead
load of the structure
itself, there are the usual
live loads from the
carried traffic. To these
are added the dynamic
components of the
traffic such as impact,
centrifugal, lateral and
Figure 8-1 Typical Railway Bridge - Courtesy of Metra
longitudinal
forces.
Then there are the environmental considerations such as wind, snow and ice, thermal,
seismic and stream flow loads. Finally, because railway structures must perform under
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heavier loads, have longer service lives, and dissimilar maintenance constraints
compared to their highway counterparts, other factors, including fatigue and
maintenance issues, tend to influence railway structure design more than roadway
structures.
Once the designer has established the first pass at the load environment for the subject
structure, the primary difference between a highway structure and a railway structure
should become obvious. In the typical railway structure, the live load dominates all of
the other design considerations. For the engineer accustomed to highway bridge
design, where the dead load of the structure itself tends to drive the design
considerations, this marks a substantial divergence from the norm. Specifically, the
unacceptability of high deflections in railway structures, maintenance concerns and
fatigue considerations render many aspects of bridge design common to the highway
industry unacceptable in the railway environment. Chief among these are welded
connections and continuous spans.
8.2 Major Bridge Components30
In general terms, the major components of track carrying structure are very similar to
their non-railway counterparts. In addition to the types of construction, the engineer
must also choose from among the available material alternatives. Generally, these are
limited to timber, concrete and steel, or a combination of the three. Exotic materials
can also be considered, but they are beyond the scope of this book. Each material has
its specific advantages. Timber is economical, but has strength and life limitations.
Structural timber of the size and grade traditionally used for railway structures is getting
more difficult to obtain at a price competitive with concrete or steel. Concrete is also
economical, but its strength to weight ratio is poor. Steel has a good strength to weight
ratio, but is expensive. The material chosen for the spans will generally determine the
designation of the bridge. For instance, steel beam spans on timber piles will be
considered a steel bridge.
The point where one form of construction with a certain type of material becomes
advantageous over another is a matter of site conditions, span length, tonnage carried
and railway preference. While initial cost of construction is a major point in the
decision process, the engineer must keep in mind such additional factors as
construction under traffic and the long-term maintainability of the final design.
Selected materials from “Railway Track & Structures Cyclopedia,” 1955 Edition, Simmons-Boardman
Publishing Company
30
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The nature of the obstacle being crossed will drive most superstructure design
decisions with the ultimate goal to achieve the least overall lifecycle cost for the
structure. For short (height) structures, trestle construction is favored due to the
economies of pile bents. Conversely, taller structures over good footing are likely to be
viaducts with longer spans supported by towers. Where there is insufficient clearance
over navigable waterways, moveable spans may be necessary. The addition of longer
or moveable spans to clear main channels does not significantly affect the design of the
balance of the structure. However, as the structure becomes taller, the economies of
pile bents are diminished due to the need to strengthen the relatively slender
components.
The alternative to conventional trestle construction is trestle on towers, otherwise
known as viaducts. Trestle on towers can offer a significant reduction in footprint for
only a moderate increase in span requirements. It is customary for the spans to be of
alternating lengths, with the short span over the tower equal to the leg spacing at the
top of the tower. This ensures that each span remains a simple span with full bearing
at the ends of the span. Of course, trestle construction represents the typical site
conditions. More demanding site conditions may require exotic solutions. For
example, very tall, very short (length) conditions may lend themselves to arch
construction, whereas for transit operations, very long main span requirements may
lend themselves to suspension type construction and some trestles on towers may be
better constructed as a series of arches.
8.2.3 Bridge Deck
The bridge deck is that portion of a
railway bridge that supplies a means of
carrying the track rails. In comparison
to the rest of the superstructure design,
bridge deck decisions are relatively simple.
The choices are open deck and ballast
deck. On open deck bridges (Figure 85), the rails are anchored directly to
timber bridge ties supported directly
on the floor system of the
superstructure. On ballasted bridge Figure 8-5 Open Deck Structure - Courtesy of Canadian
decks, the rails are anchored directly National
to timber track ties supported in the
ballast section. The ballasted bridge
decks require a floor to support the ballast section and such floors are
designated by their types, such as timber floors, structural plate floors, buckle
plate floors or concrete slab floors, all of which transfer loads directly to the
superstructure.
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Variations from the two general types of bridge deck construction consist of track rails
anchored directly to steel or concrete-slab superstructures (direct fixation) and the
several types of concrete-encased beam spans or concrete-filled steel-trough
superstructures on which the ballast section is placed. The latter types of structures
have many examples still in service today, but are not generally cost-effective for new
construction.
Some might consider the notion of bridge railings to be an odd bridge design
consideration. Railway bridges traditionally have not been designed for the conveyance
of anything other than railway traffic, which does not in and of itself, require any sort
of railing whatsoever. Recently, however, a greater focus upon railway worker safety
has resulted in railings being widely incorporated.
Open Bridge Decks
Many different considerations enter
into the choice of open or ballast
decks, and the selection usually is
governed by the requirements of
each individual structure. Open
decks are less costly and are free
draining (Figure 8-6), but their use
over streets and highways requires
additional measures such as
canopies, plates or wooden flooring
Figure 8-6 Open Deck Bridge - Courtesy of Metra
to protect highway traffic from
falling objects, water or other materials during the movement of trains.
Open-deck construction establishes a permanent elevation for the rails. Normal
surfacing and lining operations, particularly in curves, eventually result in line swings
leading into the fixed bridge. The grade frequently is raised to the extent that the
bridge eventually becomes low. The bridge dumps are of a different modulus than the
rigid deck. Thus, it becomes difficult to maintain surface off of the bridge as well.
This equates to extensive maintenance costs that shortly will surpass the first cost
savings gained by installing an open deck bridge over a ballast deck bridge. In welded
rail, tight rail conditions can occur at the fixed ends of an open deck bridge, thus
requiring an increased level of surveillance in hot weather.
Requirements for Ties
For ballast deck structures, bridge ties are no different than those found in traditional
track construction. However, in track constructed with concrete ties, the track is often
times transitioned to timber ties before crossing the structure. Some railway companies
and agencies have had difficulty with fouled ballast, track alignment and deck surface
damage resulting from the use of concrete ties on bridges. Individual railway
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fastened with metal straps to the bottoms of bridge ties to bring all ties to the required
surface. Procedures for dapping and/or shimming ties for superelevation are covered
in Chapter 7 of the AREMA Manual for Railway Engineering, Section 1.14.7.
Ballasted Decks
A ballasted deck (Figure 8-7)
provides a better riding track. The
track modulus is consistent on the
dumps of the bridge as well as
across the bridge. Thus, one is
unlikely to have surface runoff
problems on the bridge dumps.
Surfacing and lining operations can
continue across the bridge
unimpeded. However, care must be
exercised to maintain a permanent
grade line in the vicinity of and over Figure 8-7 Ballast Decked Bridge. – Courtesy of Canadian National
a ballasted deck bridge to be certain
that excessive quantities of ballast are not accumulated on the bridge structure through
track raises during successive reballasting operations.
Ballasted decks (Figure 8-8), irrespective of the type of bridge floor, afford a
considerable measure of protection to the steel floor system against damage from
derailed car wheels traveling across the bridge. Over roadways, vehicles and the public
are protected from dropping ballast and material off of the cars.
Ballast
The depth of ballast contributes to
the satisfactory functioning of
ballasted decks on railway bridges.
It is generally agreed that 6 inches
to 12 inches of ballast under the
ties is adequate and that more than
12 inches is undesirable because
of the potential of overload
involved, except when provision is
made in the design for a greater
load. Many designers calculate the
dead load on the basis of 18
inches to 24 inches of ballast to
accommodate future raises.
Figure 8-8 Ballast Decked Structure - Courtesy of Metra
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8.5 Structural Design
Considerations
8.5.1 Introduction
With the exception of larger bridges, most highway structures designed for a 50 to 75year service life often begin to reach their practical service life at about 30 years of age.
Though this is commonly a result of increases in traffic or higher safety standards, the
ability to perform major repairs or upgrades of highway structures by temporary
removal of the bridge from service is generally not a significant concern. Railway
bridges, on the contrary, are designed to have a significantly longer life, and indeed, a
considerable number of railway structures in service today are in the neighborhood of
100 years old.
Detour routes resulting from failure or significant repair/maintenance efforts are
expensive and may not be viable. Though the design criteria within AREMA reflect
this consideration, the operating impact and expense must be called to mind when
considering the replacement of an existing structure. Often times a designer will have a
proposed design solution rebuffed by a railway for this reason. Though the solution
offered may be widely accepted in highway design, the permanence required by the
railway environment may not have been yet proven to the railway.
Railway structures require a much greater consideration of longitudinal loading than a
typical highway bridge. This is the result of two environmental variables. Vehicle and
individual wheel loads of railway vehicles are many times greater than roadway vehicles.
Likewise, unlike roadways, the vehicle running surface (the rail) is continuous between
the bridge structure and the adjacent roadbed. The track structure by its very nature is
moderately flexible, distributing loads in all directions over a length of track. The
introduction of a fixed object (e.g. end of bridge) concentrates this loading to specific
points of distribution.
When comparing railway bridges to roadway, pedestrian, and other sorts of bridges, the
live loading relative to the dead load is much greater and more consistent. This
consistent loading and unloading over a greater stress range results in fatigue
considerations more prevalent in railway bridge design than other types.
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8.5.2 Bridge Loading32, 33
In the design of any structure, the designer must consider several different load types,
including, but not limited to, dead load, live load, wind, weather (snow, ice, etc.),
earthquake or any combination there of. Like other governing codes and design
organizations including ACI, AISC and AASHTO, AREMA sets forth guidelines for
both allowable stress for steel (Chapter 15) and timber (Chapter 7) and load factor
design guidelines for concrete (Chapter 8) to be used in the design of structures subject
to railway loading. Many of these guidelines are consistent in character, if not identical
to other codes. However, there are many distinctions, which are the result of the
different service demands of railway structures as well as railway practice or preference
developed over the past 150 years.
The designer must be cognizant of the fact that each chapter is effectively independent
of the others, and not all handle similar design considerations in the same fashion.
Where a single structure may incorporate several different types of materials (e.g. a
composite structure with steel stringers and a concrete deck), both Chapters 8 and 15
must be referenced throughout the design process. Some other chapters of the
AREMA Manual for Railway Engineering may reference one of the structural chapters
when addressing structural issues.
The reader is also cautioned that the Manual for Railway Engineering is always under
revision. The following material is current as of the date this text was published and is
provided herein only for general informational understanding. Referencing the latest
issue of the Manual for Railway Engineering is essential before undertaking any design
activity.
Dead Load
The dead load consists of the estimated weight of the structural members, plus that of
the tracks, ballast and any other railway appendages (signal, electrical, etc.) supported by
the structure. The weight of track material (running rails, guard rails, tie plates, spikes
and rail clips) is taken as 200 pounds per lineal track foot. Ballast is assumed to be 120
lbs per cubic foot. Treated timber is assumed to be 60 lbs per cubic foot.
Waterproofing weight is the actual weight. The designer should allow for additional
ballast depth for future grade or surfacing raises (generally 8” – 12”). On ballasted
deck bridges, the roadbed section is assumed to be full of ballast to the top of tie with
no reduction made for the volume that the tie would include.
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Composite Design
The design and use of composite steel and concrete spans for railway bridges is
addressed in Section 5.1 of Chapter 15 of the AREMA Manual for Railway
Engineering. This type of superstructure comprises a steel beam or girder and a
concrete deck slab. The connection between the two materials is designed and
constructed to transfer adequate shear force, such that the two materials behave as a
single, integral unit under load.
The theory of composite design, governing the recommendations in the AREMA
Manual for Railway Engineering, is very similar to that found in the working stress
method in AASHTO and allowable stress methods in various building codes. Some of
the important issues include:
§
Selection of the effective flange width of the concrete as a function of slab
thickness, steel beam spacing or span length;
§
Proportioning of the cross-section by the moment-of-inertia method;
§
Application of the dead load forces to the non-composite or composite section,
depending on construction sequencing and methods;
§
Considering the effect of creep due to long term dead loads acting on the
composite section.
Shear connectors may be either steel channels or headed studs welded to the top flange
of the steel and embedded in the concrete deck. Reference is made to the AREMA
Manual for Railway Engineering or engineering textbooks for specifics on the
preceding items.
Additional consideration is warranted for railway bridges in other aspects of design,
however. One issue to address in composite design is the magnitude of live load to be
resisted. Although not specifically addressed in the AREMA Manual for Railway
Engineering, railway companies generally require that the steel beams or girders be
proportioned to carry without contribution from the concrete deck slab, a Cooper’s
live load of only a slightly reduced magnitude than that of the entire structure. For
example, a bridge with a composite design load of E-80 is often required to have the
steel section alone provide support for an E-60 or higher, and maybe as much as E-80
as well, depending upon the railroad and the type of structure considered. This ensures
that if the concrete deck is damaged during a derailment, the steel section will be
sufficient to carry rail traffic, even if the concrete must be torn out and an open deck
installed.
If the steel alone is sized for the design load, the cost savings through efficient use of
materials is somewhat less for railway structures than it is for highway and building
structures that make full use of the composite section to resist live load and impact.
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The limitation on deflection due to live load plus impact also can usually be waived
when considering the steel only for railway bridge design. The full composite section
should be designed as being sufficiently stiff to meet the deflection limitations.
Even if the steel section is adequate to carry the final design loading without
contribution from the concrete slab, composite action still must be investigated. The
neutral axis of the composite section will be higher on the cross-section than that for
the non-composite section. This will increase the stress range in the material below the
neutral axis, and fatigue details should be checked for this increased range.
While composite steel and concrete spans provide a stiff design with the benefits of a
ballasted-deck bridge, they are unlikely to be used to replace existing structures on
existing alignments. Compared to precast concrete deck panels, the additional time
required to form, place and cure the cast-in-place concrete deck of a composite span
requires off-line construction to minimize impact to rail operations. Parallel
construction of a composite span with a lateral roll-in during a train free window is one
way to work around this problem. Additionally, since the deck concrete is not under
compression from prestressing or post-tensioning, the use of a waterproofing system
to protect the deck may be warranted.
Where structure depth is limited by vertical clearances below the structure, a steel plate
may be used instead of a concrete deck. The steel plate may or may not be included in
the beam design, depending on the connection to the beam.
Bridge Design Assumptions and Constructibility Issues
When planning railway structures, it is imperative to be mindful of the factors that
frequently control design and construction. Many in the railway industry would agree,
that the driving factor of design and construction is track time. Operations are key,
and with greater traffic demands on an ever-aging infrastructure, track time is at a
premium. It is important for railways to balance time for operations,
maintenance/repair and new construction. The designer is challenged with producing
plans and specifications that will yield the best structure in the shortest amount of time.
Many times the design efficiency is sacrificed for a shorter construction period. Let’s
briefly examine one simple scenario: the superstructure replacement of a short, singlespan bridge. In it’s nearly 100-year life span, the steel superstructure had been raised
while being converted from a ballasted deck to an open deck. This conversion
included the use of what is known as a grillage. A grillage (also known as cribbing) is a
temporary steel support, usually in the form of short sections of steel H-piles, welded
together side-by-side to form a shallow (1-2 foot) bearing seat.
The steel is subsequently encased in concrete. This technique is most common to
rehabilitation projects. When replacing this superstructure, the most efficient design
might include cutting the backwall, removing the grillage (thus lowering the beam seat)
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Chapter
RAILWAY ELECTRIFICATION
9.1 Introduction
D
espite the competition
of airplanes, buses,
trucks and cars, trains
still play a major transportation
role in society, filling specific
markets such as high-speed and
non-high-speed
intercity
passenger service, heavy haul of
minerals and freight, urban light
rail systems and commuter rail.
This chapter presents an
Figure 9-1 Overhead High Speed Catenary - Courtesy of LTK, Inc.
introduction to electrification of
rail systems. It is intended to provide a historical perspective and an overview of
typical design principles, construction practice, and maintenance considerations. Those
interested in learning more are invited to review AREMA’s Manual for Railway
Engineering, Chapter 33, Electrical Energy Utilization, and Chapter 17, High Speed
Rail Systems, which contain sections devoted to electrification power supplies, traction
power systems studies and guidelines for the design of overhead contact systems.
9.2 Development of Motive Power
for Railways
The earliest recorded tramway served a mine in Germany, beginning in about 1550.
The tramway was developed because the rolling resistance of wheels on rails was much
less
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Does not create possible electrical safety hazards to the public due to the presence
of the bare conductors of the contact system.
When the cost of diesel fuel was 9 cents a gallon and the supply seemed unlimited,
United States railways were not interested in alternative methods of propulsion.
Railway electrification interest peaks during times of uncertainty in the energy industry.
When fuel rose to 34 cents per gallon and the oil embargos occurred, much effort was
expended studying alternatives to hydrocarbon fuels. Studies showed that "an
estimated 34% savings in energy could be achieved by using electric power.
Electrification of just 10% of the (then) present rail trackage (in the densest traffic
corridors) could result in a 40% reduction in railway diesel fuel consumption.”
Studies made in the 1970’s also showed that approximately 6 years after electrifying a
route, the operating cost would break even when compared to the operating cost of
diesel service. At 30 years, the annual operating cost of an electrified system would be
one-third that of diesel service. In other words, over the effective life of a railway, the
cost to operate a diesel-electric system far exceeds that of an electric system. These
increased costs mainly come from the price of fuel and maintenance. Diesel
locomotives average 3 to 10 gallons or more of fuel per mile and three times the
amount of maintenance of straight electric locomotives.
The most significant aspect arising from these studies is that in order to realize the
long-term savings, a huge capital investment is needed. Even when engineering
economic studies show that an electrified system would be beneficial, raising enough
money to perform the capital upgrade is a daunting challenge. Private railways would
most likely require government assistance or financing from the utilities.
9.4.2 Mainline Infrastructure Compatibility
The electrification of a section of existing mainline cannot be undertaken without
considering the requirements that the electric locomotives, substations, overhead or
third rail power distribution systems and traction return system will place on the
existing rail infrastructure.
The more significant issues are noted below:
§
Tracks may need to be upgraded, including new track work or re-alignment. Sites
must be found and real estate acquired for substations. In rights-of-way with
restrictive width, the location of the system-wide ductbank requires coordination
with track drainage, the foundations for OCS poles and emergency walkways. In all
cases, maintenance access must be provided.
§
If DC traction is used, the effects of electrolytic corrosion due to leakage (stray)
currents must be mitigated.
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§
Additional clearance may need to be provided in tunnels and at bridges. Existing
civil structures may have insufficient clearance to accommodate the proposed
electrification system. It may be necessary to lower tracks through overhead
crossing bridges. New bridges resulting from grade-crossing elimination will need
to be built with adequate electrical clearance. Future widening of existing
overhead bridges must be considered.
§
Tunnels may be suitable for electrification, or may require costly remedial work,
enlargement or “daylighting.”
§
Integration of the electrification support structures with existing station canopies
must be considered. Station canopies that project over platform edges may need
modification.
§
Where OCS poles cannot be
installed for lack of clearance,
attachments, such as wall
brackets, will need to be added
to civil structures. Pictured at
the right is an example of an
OCS cantilever attachment to
an overhead structure.
§
Signals and communication
systems will need to be replaced
or upgraded. Because electric
Figure 9-4 OCS Cantilever Attachment - Courtesy of LTK, Inc.
traction systems use the same
running rails for traction return current, it is necessary for the two electrical
systems to be electrically isolated. The signal circuits need to be “immunized”
from the traction power circuits.
§
Grounding and bonding of exposed metals is necessary to protect the public from
electrical hazards, as well as insuring that there is no interference with the signals
and communications systems.
§
A central location will be needed to supervise the power system. SCADA, pilot
wires or a relaying system must send information to a central point to insure
power is being supplied to the system when necessary.
Maintenance
More details on these and other aspects impacting the railway route are given later.
The advent of electrification increases the level of overall maintenance on the right-ofway. The traction power distribution system, comprising substations, feeder cables,
OCS or third rails, lineside disconnect switches, impedance bonds and rail bonds
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urban areas, the structures are often relegated to sidewalks. To help the structures fit
into the urban environment, the structures will often serve double duty by acting as
light poles, traffic signal poles, etc. On straight or slightly curved track, either
cantilevers or cross-spans support the trolley wire such that it is placed over the center
of the track. When the track requires tight curves, the trolley wire is held in place with
cross-spans, pull-offs and back bones. Although trolley poles pivot at the base, the
trolley harp does not pivot so that the trolley wire must be placed towards the center of
the curve on sharp curves to allow the trolley shoe to track efficiently. The trolley shoe
must be drawn tangentially along the trolley wire, thereby not rubbing against the
‘cheeks’ of the groove. Only by using rigid harps can the trolley shoe diverge onto the
correct trolley wire at turnouts, as the pole operates passively being positioned only by
the direction of the streetcar on its tracks.
Catenary Systems
Two-wire systems are referred to as
simple catenary and utilize a contact
wire and above it, a messenger wire.
The messenger wire serves two
purposes (1) to support the contact wire
vertically between structures by use of
hangers and (2) to provide more
electrical conductivity.
Variations of simple catenary exist, such
as low profile simple catenary, which
can be considered as a three-quarter- Figure 9-19 Two Cross-span Wires with Full Simple Catenary scale version of the most economic Courtesy of LTK, Inc.
simple catenary style. The low profile
simple catenary has reduced visual impact by virtue of requiring only one cross-span
wire for support between poles compared to the necessary two cross-span wires with
full simple catenary as pictured (Figure 9-19). Structure spacing is, however, reduced,
thus increasing the pole count by about 30%.
Nevertheless, it is still only about half the cost of a single contact wire system with
parallel underground feeders, which would be electrically equivalent. Twin contact
wires are also commonplace on light rail systems in Europe. Other systems using
three conductors called compound catenary are operating, but are more costly and are
generally not considered necessary for new installations. Compound catenary utilizes
three or more conductors, with a main messenger being the top conductor, the contact
wire serving as the bottom conductor, and an auxiliary messenger located between the
two. Other styles, which have been installed in the past, include stitched catenary,
triangular catenary and ‘hanging beam’ catenary, and all continue in use today.
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Inclined catenary exists to the present day in the Northeastern United States and
requires the use of the messenger, and on severe curves, an auxiliary messenger to align
the contact wire around curves. This is accomplished by inclining the OCS so that the
messenger wire is moved to the outside of the curve while the contact remains close to
the track centerline. Sloping hangers support the contact wire at a carefully calculated
angle to provide the lateral restraint. Inclined catenary has fixed terminations, which
means that the contact wire moves up and down relative to the track surface as
temperatures change. Thus greater clearances are required under structures and over
grade crossings. Because of the special techniques needed to align inclined catenaries,
the trend today is to replace them with chordal (simple) catenary, where the messenger
is located directly above the contact wire.
Catenary systems are designed to allow the contact
wire to operate satisfactorily over the full extent of
the carbon-rubbing strip of the pantograph.
Careful calculations are performed to determine the
extent that the wire can be staggered at the OCS
registrations (supports) and to ensure that the
pantograph does not dewire in a combination of
adverse operating conditions, including strong
winds, maximum vehicle sway and poor quality
track.
These calculations are then used to
determine how much the contact wire can be
allowed to be placed off the centerline of the track
and still allow safe operations. On tangent tracks,
the wire is intentionally staggered from one side of
the track centerline to the other at successive poles
to prevent grooves from forming in the middle of
the pantograph carbons.
Figure 9-20 Contact Wire Placement in a
Curve - Courtesy of LTK, Inc.
All overhead contact systems exhibit the characteristic of increased sag between
supports and loss of tension when conductor temperatures rise due to solar gain
and/or current heating. Although small variations to sag and tension do not adversely
affect current collection, also called ‘commutation,’ large variations, say over 6 inches,
can be unacceptable. In order to control conductor sag between supports, two options
are available:
§
Limit span length (length between poles)
§
Tension compensation (described later)
Both options apply to Single Contact Wire (SCW) systems and to multiple conductor
catenary systems to be described later.
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9.8 Electrification Interfaces with
Other Rail Elements
When an established railway is to be electrified, there can be significant engineering and
operational impacts on the existing infrastructure. The more significant impacts
involve:
§
Right-of-Way
§
Track Structure
§
Civil Structures
§
Signaling and Communications
9.8.1 Right-of-Way
Track Layout/Realignment
It is desirable that track alignment and modifications to track crossovers and turnouts
be completed before route electrification occurs. Additionally, track renewals and track
lowering measures, as described below, should have been finished. Future track
improvements may need to be accelerated to avoid the need for later changes. Old
redundant track should be removed before initiating electrification so that cranes are
not impeded by the presence of high voltage catenary wires, conductor rails or cables.
Substations
Typically, 25kV substations require a site area of about an acre in size, with road access
suitable for trucks delivering the largest piece of substation equipment. DC substations
are smaller, ranging in size from 2000 to 5000 square feet, but are generally more
numerous than AC substations.
Supporting Structures for the Contact System
On existing main line routes, particularly those with more than two tracks, there will
probably not be enough room between tracks to install OCS pole foundations.
Therefore, the poles will be allocated to the outside of the line. The right-of-way needs
to be examined to insure that structures and any supporting back guys fall within the
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ROW without impeding drainage. Since third rail is attached to the end of the ties,
ROW limits are not as critical for third rail systems as for overhead systems.
Systemwide Ductbanks
Ductbanks are required for power distribution cables and should be designed to
accommodate new signal or communication cables, should existing aerial signal and
communication cables need replacement. The location of parallel track and cross-track
ductbanks will need to be coordinated with drainage pipes, foundations for signals and
OCS poles, and emergency walkways.
9.8.2 Track Structure
On rail lines, the area extending from
track centerline in which no wayside items
can be placed is known as the structure
clearance envelope. On non-electrified
lines, this envelope is based on the
dynamic envelope of the vehicle along
with passing clearances. For electrified
lines, this envelope has to be increased to
allow for the electrical clearance envelope.
This increased envelope insures that no
wayside structures come close enough to
any “live” part of the vehicle to create an
electrical hazard. One way to provide the
requisite vertical clearance at overhead
bridges is to lower the tracks. However, if
significant lowering is required, the track
subbase may need to be excavated first,
which may be a prohibitive operating precondition.
Figure 9-23 Clearance Envelope - Courtesy of LTK, Inc.
Because the running rails will be carrying the high currents of the traction return
system, it is necessary that all bolted rail joints be paralleled with traction bonding
cables to carry the 1000 amps or more of traction current. Defective bonds can give
rise to severe arcing between the rails and cause enough damage to curtail normal train
operations.
The possible effects of electrolytic corrosion due to leakage (stray) currents from the
track rails, especially with DC power must be addressed. With AC systems, the effects
of leakage currents is considered to be minimal, but still needs to be checked. Leakage
currents can cause and/or accelerate corrosion in underground piping, steel
reinforcement in concrete structures and may damage underground utilities.
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Chapter
Passenger, Transit & High
Speed Rail
INTRODUCTION TO PASSENGER RAILWAY
INFRASTRUCTURE
“Form ……follows function”
Louis Henri Sullivan, Architect, “Lippincott’s Magazine,” March 1896
10.1 Introduction
T
he above quotation, while originally written to describe the practice of
architecture, nonetheless provides useful insight into the practice of passenger
railway engineering. In particular, the concept concisely describes how
fundamental differences in design can arise between a railway built for passenger
service and one built for freight, as their functions (and hence their forms) may be
radically different. However, while a passenger line and a freight-only line may look
very different, the same engineering principles apply to each -- sound railway
engineering is still sound railway engineering. The applications of these basic
engineering principles will vary, however, to reflect the different functions each type of
infrastructure must support.
This chapter presents an introduction to passenger rail infrastructure requirements. It
does not dwell on basic railway engineering concepts. Instead, it expands upon the
materials presented elsewhere in this Practical Guide as necessary to provide an overview
of typical design principles, construction practices and maintenance considerations
applied to passenger rail lines. The emphasis here is on the typical. The authors’
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acknowledge that North American passenger experience is rich with exceptions to the
“typical,” and while a few exceptions have been noted herein, no attempt has been
made to include them all. Instead, the intent is to provide a basic understanding of
typical North American practice.
Those interested in learning more are invited to review Chapter 12 (Rail Transit) and
Chapter 17 (High Speed Rail Systems) of AREMA’s Manual for Railway Engineering. The
reader is also referred to the Track Design Handbook for Light Rail Transit, published by
the Transportation Research Board.
10.2 Passenger Rail Modes
Passenger rail operations in North America serve a wide variety of functions, from
long distance intercity travel to daily commuter trips to local urban transit services.
These operations encompass a diversity of vehicle types, operating speeds, right-of-way
requirements and service frequencies. The characteristics of each type of operation are
so different from one another that it is useful to think of each as a separate rail-based
transport mode. For purposes of this chapter, the various types of passenger rail
operations will be divided into six categories:
•
High-Speed Rail (“HSR”)
•
Intercity
•
Commuter Rail
•
Rapid Transit (“RT”)
•
Light Rail Transit (“LRT”)
•
Streetcar and Vintage Trolley (“Streetcar”)
These terms will be utilized throughout the chapter in describing the various rail modes
and their infrastructure characteristics. People mover operations (such as found in
airport terminals) are not addressed here, as these typically use proprietary vehicle and
systems technologies, and are often based on rubber tire/concrete paving guideway
systems.
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10.3 Distinctions between Railway
Operations and Transit Operations
The types of operations noted above can be separated into two major subgroups.
High Speed Rail, Intercity and Commuter Rail may be considered “railway” operations
while Rapid Transit, LRT and Streetcar may be considered “transit” operations.
Characteristics, which distinguish between railway operations and transit operations,
are discussed in general terms below.
Passenger railway operations are conducted over portions of the North American
freight rail network, or on dedicated passenger lines that are contiguous to this network
and which share compatible technical standards. (In the United States, Part 213.1 of
the FRA regulations defines this as the “general system of railway transportation.”)
These systems generally utilize AREMA (or AREMA-compatible) technical standards
for trackwork and AAR (or AAR-compatible) technical standards for vehicles. As
such, these systems represent passenger adaptations of North American freight railway
practice, and inter-operability with the freight network is maintained. Intercity and
Commuter services are generally compatible with freight infrastructure practice, while
HSR will employ more stringent standards for dedicated high-speed territories while
retaining compatibility with freight infrastructure for conventional speed operations.
Transit operations are conducted on trackage that is dedicated to passenger service, not
open to freight operations, and not part of the “general system of transportation.”
Technical standards are not based on interoperability with the North American rail
network, but rather the stand-alone requirements of each operator. Trackwork and
vehicle standards may be AREMA- and AAR-based, but more typically reflect transit
practice with use of sharper track curvature and specialized track appliances, and
lightweight vehicles with narrower wheels and smaller flanges. For the “traditional”
systems (those built in the late 19th and early 20th centuries), track and wheel practice
may still reflect the standards in effect at the time of construction. “New start” LRT
systems (those built after approximately 1975) may utilize European transit track and
wheel practices.
There is one hybrid type of operation that should be noted – LRT and freight services
operating on shared trackage. In these systems, LRT and freight operations are
typically “time separated,” with LRT running during the day and freight running at
night. Each service has exclusive use of the system during its designated operating
period. In these systems, LRVs utilize wheel standards compatible with standard
railway trackwork. Examples of such operations include San Diego and Baltimore.
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§
Curve Maintenance: The sharp curves found on transit properties can create the
need for significant maintenance work. This work can involve gauging, fastener
tightening and rail replacement. It is typically done with small equipment adapted
to working in close confines.
§
Special Track Appliances: As noted previously, transit properties make use of
unique turnout designs, extensive check rail installations and other track features,
which require maintenance. As these appliances typically require close control of
dimensions (such as guard faces and back-to-back distances), significant attention
is needed to keep them in adjustment.
§
Maintenance Access: Physical access to conduct maintenance can be difficult,
particularly for elevated structures and tunnels. Work processes and machinery
must be adapted to deal with the available access and working space.
§
On some properties, alignment imperfections in small bore tunnels caused by
construction tolerances translate to deliberate imperfections in track geometry
necessary to keep track centered within the tunnel.
10.10 Special Topics Associated
with Passenger Railway
Operations
10.10.1 Passenger Railway Line Capacity
Unlike highways, which measure unlinked trips over individual route segments, rail
line capacity fundamentally must be considered as a network evaluation. The type of
train service, where it begins, and where it is destined are equally important
components, along with the infrastructure itself. Whether it is through or local
operations, routine maintenance or seasonal impacts, operators must consider events
that have the potential for creating cascading effects on a given route’s performance,
even though they may happen many miles away.
Capacity analysis begins with an evaluation of the physical route. The length of the
line, terrain it operates through (curvature, gradient, etc.), number of tracks and type of
train control exercised over the line all set the stage for determining some of the most
basic components of line capacity. Train performance characteristics in terms of
maximum speeds, acceleration (HP/ton) and deceleration rates are critical to
determining throughput rates for unopposed trains. Equally as critical is the mix of
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train types, as there will be pronounced differences in end-point transit times when
comparing passenger, intermodal, manifest and unit freight train types. Distance
between terminals, capacities of the terminals, local switching enroute, performance
variability and day-of-week variability are key factors to be considered.
Where passenger trains operate over a freight route, the difference in running times
becomes even sharper. Besides the criteria typically considered for freight service, the
number of station stops, dwell times at each station, and distances between stations
must be considered. Passenger trains typically are permitted to operate at higher
maximum speeds and through curves at higher speeds by employing greater levels of
cant deficiency when compared to freight trains. The effect of both is to further
reduce transit times. Terminal operations must also be factored into a line capacity
analysis, as trains typically follow a different route or multiple routes at slower overall
speeds compared to operations on the main line.
If every train operated in the same direction, at precisely the same speed and assuming
a relatively sophisticated method of controlling train movements, line capacity over a
single track would be very high. If this same group of trains were split evenly so one
half operated in the opposite direction and uniform length passing sidings were evenly
distributed, line capacity would drop proportionate to siding distance and to reflect the
time required to reset routes through interlockings and for trains to accelerate and
decelerate for siding entry and exit. Overall capacity would remain relatively high,
however.
Neither of the above situations occurs often in real life. Geography, community
development, and the markets served can, and do, greatly affect the design and
configuration of a rail line. Much more typical would be sidings of varying lengths,
with unequal distances between them. Ruling grades frequently bring average speeds
of freight trains down to very slow speeds or require adding helper locomotives to
negotiate grades. Dispatchers must carefully plan meets between opposing trains of
varying types around the physical infrastructure capable of accommodating them.
Intermodal and passenger trains will “overtake” slower trains along the route and
dispatchers must stage passes between trains running in the same direction in order to
allow the faster trains to proceed without delay. Locals and work trains occupy main
line tracks for extended periods of time while performing their duties. The net effect
of all of these operations is to reduce rail line capacity.
Rail line capacity is not easily determined. In addition to differences in the types and
numbers of trains, their speeds and their overall reliability, capacity is constrained by
the number of tracks, interlockings and their spacing, types of train control and signal
systems in place, FRA track class, moveable bridges, permanent slow orders, grade
crossings, etc. Each of these elements may contribute to, or reduce, the handling
capability of a route.
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Undertaking an operations simulation of the line is one accepted method to determine
line capacity. This is generally performed through the development of representative
operating plans, for both existing and future scenarios, and testing them against the
available fixed plant. Iterative variations of plans can lead to identification of optimal
operating plans that maximize use of the line. Most simulations are now performed
through use of computer software programs, the more sophisticated of which
accurately emulate actual operating conditions. These programs also provide a
powerful set of decision-making tools to help determine infrastructure improvements.
They may be used to identify chokepoints on a line that constrain growth, to adjust
fixed plant investment in response to traffic changes, or to assist in programming
maintenance activities. Computer simulation technology continues to advance,
reducing set up and evaluation procedures, and making its use progressively more
valuable in a quickly changing environment.
North American railways already operate among the most efficient rail systems in the
world (in terms of ton-miles per route-mile). This status has been achieved by a variety
of means to balance fixed-plant investment against operating requirements. As
projected rail traffic levels continue to grow, greater use of the existing infrastructure
will place ever-higher emphasis on maximizing its use. Understanding and being able
to utilize each line’s capacity will be key to success.
10.10.2 The Impact of Superelevation (Or Cant
Deficiency and Why It’s Important)
Chapter 3 introduced the concept of unbalance or underbalance in operation through
horizontal curves. In passenger rail terminology, this same concept is generally
referred to as “cant deficiency.” The term is drawn from British and European
practice where superelevation is referred to as “cant” and the term “cant deficiency”
describes the circumstance where a vehicle operates through a curve with insufficient
cant to achieve equilibrium.
Superelevation (banking or track cant) is a necessary ingredient for safe and
comfortable curve negotiation. Superelevation is used to counteract the effects of
centripetal acceleration (centrifugal force) on the vehicle and the occupants. The
amount the outer rail is elevated is determined by the sharpness of the curve and the
speed the vehicles operate through it.
Some definitions are in order:
§
Balance Speed: The speed at which the combination of curvature and
superelevation exactly balance the centripetal acceleration and the resultant force
vector is normal to the track plane.
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orders have followed, for example, the Clean Water Act, Pollution Control Standards
Act, etc.36
11.2.1
Wetlands Regulations
Jurisdictional wetlands are part of a classification recognized by government agencies
known as “waters of the United States.” The term “waters of the United States” is:
•
All waters which are currently used, or were used in the past, or may be susceptible
to use in interstate or foreign commerce, including all waters which are subject to
the ebb and flow of the tide;
•
All interstate waters including interstate wetlands;
•
All other waters such as intrastate lakes, rivers, streams (including intermittent
streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows,
playa lakes or natural ponds; the use, degradation or destruction of which could
affect interstate or foreign commerce including any such waters:
i.
Which are or could be used by interstate or foreign travelers for recreational or
other purposes; or
ii. From which fish or shellfish are or could be taken and sold in interstate or
foreign commerce; or
iii. Which are used or could be used for industrial purpose by industries in
interstate commerce;
•
All impoundments of waters otherwise defined as waters of the United States
under the definition;
•
Tributaries of waters;
•
The territorial seas;
•
Wetlands adjacent to waters (as discussed later in this chapter).
“adjacent” means bordering, contiguous or neighboring.
The term
The traditional definition of a wetland is the transitional land between the terrestrial
and aquatic environment where the water table is usually at or near the surface, or the
land is covered by shallow water. Wetlands must have the following attributes:
1) At least periodically, the land supports predominantly hydrophytic vegetation;
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2) The substrate is predominantly undrained hydric soil; and
3) The substrate is nonsoil and is saturated with water or covered by shallow water at
some time of the growing season each year.37
Since European settlement began in the United States, millions of acres of wetlands
were drained, dredged or filled so that by the mid-1980’s, almost 53% of the lower 48
states’ wetlands had been eliminated. At that time, an estimated 104 million acres of
wetlands remained, which amounts to approximately 5% of the country’s land
surface.38
Traditionally, wetlands have been viewed as wild places, teeming with mosquitoes,
venomous snakes and disease, while in reality they provide a number of valuable
benefits. Some of these include:
1)
2)
3)
4)
5)
6)
Flood storage and conveyance,
Groundwater recharge,
Erosion reduction and sediment control,
Pollution control,
Wildlife habitat,
Recreation and education.
This listing only highlights a few of the many functions wetlands provide. The Illinois
Department of Natural Resources (IDNR) Wetlands Program considers the full range
of wetland functions and values when administering its wetland protection
responsibilities.39
The United States Army Corps of Engineers (USACE) has been involved in regulating
activities in navigable waterways through the granting of permits since the passage of
the Rivers and Harbors Act of 1899. This program was meant to prevent obstructions
to navigation. By the early 20th century, the USACE had regulatory authority over the
dumping of trash and sewage. Passage of the Clean Water Act in 1972 greatly
broadened the USACE’s role by giving them authority over dredging and filling in the
“waters of the United States,” including many wetlands.40
Chinn, R., 1998, Wetland Delineation and Management Training Manual and References, Richard Chinn
Environmental Training, Inc., Pompano Beach, FL.
38 Dahl, T.E., 1990, Wetland losses in the United States 1780s to 1980s, United States Department of the
Interior, Fish and Wildlife Service, Washington, DC.
39 Illinois Department of Natural Resources, 2000, A Field Guide to the Wetlands of Illinois, Second Edition,
Illinois Department of Natural Resources.
40 U.S. Army Corps of Engineers, Undated, Services for the Public-US Army Corps of Engineers,
http://www.usace.army.mil/public.html.
37
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Permit Number 1, Category II, impacts 0.25 to 2 acres of waters of the United States
or impacts high-quality aquatic resources. Individual Permits may be required for
impacts over 2 acres. Mitigation is required for impacts over 0.25 acres at a minimum
of 1.5:1 replacement.
In addition, some local regulations may apply. For example, in DuPage County,
Illinois, the County regulates all activities in wetlands, and mitigation is required for all
impacts. The County’s jurisdiction supercedes the USACE’s jurisdiction. While a
USACE permit is still required, if the County’s permit is approved, the USACE’s
permit will be approved.
USACE Non-Jurisdiction Over Isolated Wetlands
On January 9, 2001, the U.S. Supreme Court issued its opinion in the Solid Waste
Agency of Northern Cook County (SWANCC) v. U.S. Army Corps of Engineers
(USACE). The Court ruled 5-4 against the USACE and EPA and in favor of
SWANCC, overturning the USACE’s requirement for a Clean Water Act Section 404
permit for the construction of a landfill involving the fill of isolated wetlands at a
former gravel mining site.46 As a result, the primary effect of the decision is that the
Migratory Bird Rule, under which the USACE asserted jurisdiction over isolated
wetland areas, non-navigable and completely intrastate waters based solely on the
presence or potential presence of migratory birds, is no longer valid. Therefore,
isolated wetlands are no longer jurisdictional to the USACE. All tributaries to Waters
of the United States (such as interstate waters, tidal waters, etc.) as well as wetlands
contiguous to and adjacent to those tributaries are still regulated. To be contiguous or
tributary, there must be a continuous surface water connection between the two
aquatic areas. This surface water connection can be either surface flowing water at
regular intervals of time, or a continuum of wetlands between the two areas.
Groundwater, surface overflow of extreme precipitation events, or tiling do not
constitute surface water connections. A culvert under a road fill connecting two
aquatic areas would constitute a surface water connection, provided the culvert is not
excessively long. Excessively long piping between two aquatic areas would not
constitute a surface water connection. The term “excessively long” is defined on a
case-by-case basis by the USACE reviewer. In addition, any natural stream that is
placed in a culvert for extended lengths, with waters on each end, would continue to be
considered a tributary.
States are moving fast to regulate isolated wetlands (non-jurisdictional to the USACE).
For example, recently Lake County, Illinois has adopted an ordinance, which regulates
all wetland areas that are not regulated by the USACE. If a wetland is identified on the
site and is considered isolated, a permit by the USACE is not required, however, a Lake
County Watershed Development Permit is required.
Miller, Z.C. and C. Kamper, 2001, Memorandum, Regarding Supreme Court Decision in SWANCC,
http//www.dgslaw.com/articles/347951.html.
46
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11.2.4 Best Management Practices
Best Management Practices (BMPs) are policies, practices, procedures or structures
implemented to mitigate the direct and indirect degradation of surface water quality
from an activity. BMP’s are required for all permits, to the extent possible. BMPs
include non-structural elements, such as the preservation of existing natural areas
(floodplains, streams, wetlands, prairies, woodlands and native soils) and drainageways,
and structural elements. Structural elements include vegetated swales, filter strips and
infiltration trenches, which are designed to remove pollutants, reduce runoff rates and
velocity, and protect aquatic resources. Another BMP is to limit the amount of
impervious surface area through practices such as reducing road widths and clustering
developments designed around open space.
In addition, a project should use the following structural BMPs, if appropriate, both
individual lots and the overall site to the maximum extent practicable:
1) Lot controls: grassed swales, underground sand filter, infiltration trenches,
vegetated filter strips, vegetated natural buffers, level spreaders, dry wells or
roof downspout systems, rubber rooftops.
2) Site controls: wetland detention, wet bottom detention, grass swales,
infiltration basins, vegetated swales, vegetated natural buffers, level spreaders,
curb cuts, leaky berms.
Applicants who protect water quality and minimize run-off by designing and
implementing a comprehensive and coordinated use of BMPs throughout the project
site may receive partial compensatory wetland mitigation credit.
For additional BMP’s, please refer to the Illinois Urban Manual.47
11.2.5 Endangered Species
Section 10 of the Endangered Species Act is designated to regulate a wide range of
activities affecting plants and animals designated as endangered or threatened, and the
habitats upon which they depend. The Act prohibits many activities affecting these
protected species unless authorized by a permit from the United States Fish and
Wildlife Service or the National Marine Fisheries Service. Parts of the Act make it
unlawful to take (which includes harm, harass, pursue, hunt, shoot, wound, kill, trap,
capture or collect any wildlife within the United States); remove and reduce to
possession any plant from areas under Federal jurisdiction; maliciously damage or
U.S. Department of Agriculture, Natural Resource Conservation Service, 1995, Illinois Urban Manual, A
Technical Manual Designed for Urban Ecosystem Protection and Enhancement, Illinois Environmental
Protection Agency, Springfield, IL.
47
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destroy an endangered plant on areas under Federal jurisdiction; and remove, cut, dig
up, or damage or destroy any endangered plant in knowing violation of any state law or
regulation or in the course of a violation of a state criminal trespass law. These
prohibitions apply equally to live or dead animals or plants, their progeny (seeds in the
case of plants), and parts or products derived from them.
An “endangered species” is any animal or plant that is in danger of extinction. A
“threatened species” is any animal or plant that is likely to become endangered in the
near future. “Critical habitat” is a geographic area which maintains biological/physical
features essential to conservation of the species and which may require special
management, consideration or protection.
A take permit allows for the taking of listed species that may result from a lawful
development activity. Take permits are issued by the United States Fish and Wildlife
Service and/or the National Marine Fisheries Service. Applying for a take permit
requires a completed application form, any necessary supporting materials and an
application fee.48
Coordination should occur as early as possible and usually occurs in conjunction with
other project permits or authorizations such as Corps of Engineers or Coast Guard
Permits, Bureau of Land Management Easements and NPDES (construction)
Permits.49
In addition, no activity is authorized under any NWP, which is likely to jeopardize the
continued existence of a state or federally listed threatened or endangered species or a
species proposed for such designation, as identified under the Federal Endangered
Species Act, or which will destroy or adversely modify the critical habitat of such
species.
U.S. Fish and Wildlife Service, Undated, Permits for Native Species, Under the Endangered Species Act,
U.S. Department of the Interior and the U.S. Fish and Wildlife Service.
49 AREMA Committee 13, 2001, Environmental Permitting Issues on Railroad Construction Projects,
Conference Notes, Overland Parks, KS, AREMA, 8201 Corporate Drive, Suite 1125, Landover, MD 207851420.
48
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•
Native American Graves Protection and Repatriation Act
•
Archaeological Resource Protection Act.
In addition, check with local authorities in your area. For example, Illinois has several
other acts to protect cultural resources: the Illinois Archaeological and Paleontological
Resources Protection Act; the Human Skeletal Remains Protection Act; and the
Revised Illinois State Agency Historic Resources Preservation Act. As of 1990, the
State Agency Historic Resources Preservation Act requires the same for all private or
public undertakings.
Some examples of cultural resources are: historic buildings/districts, burial sites,
campsites, spiritual sites, churches/cemeteries, trails, tunnels, towers, bridges and
miscellaneous structures.
11.2.7 Phase I Environmental Assessment
The Phase I Environmental Assessment is an essential first step in determining
whether contamination exists on a property. It is important that a Phase I
environmental assessment is completed before proceeding with additional site
investigation activities.
A Phase I Environmental Assessment is a report that includes record reviews,
interviews and physical property inspections to identify areas of potential hazardous
substance contamination. The following is an example of details that may be included
in a Phase I environmental assessment:
1) Property overview: Property information, geographic features and potential
receptors/environmentally sensitive areas.
2) Property history: Site specific conditions (past and present): Products (for
example, abandoned drums of pesticides, etc.), waste inventory, waste disposal
processes and recycling or reuse, bulk storage tanks, chemical and waste
storage areas, disposal sites.
3) Regulatory history: Present activities of owner/operator, permits, inspections,
hazardous substance/hazardous chemical inventory and regulatory compliance
history.
4) Environmental investigations and cleanups:
environmental assessments.
Environmental cleanups,
5) Physical reconnaissance: Investigators investigate by conducting interviews
and a field reconnaissance, and evaluating current and past site activities.
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Chapter
European Curve and
Turnout Mechanics
Railroading is railroading, although the methods that we use to get
to the end product may vary significantly.
An in-depth
understanding of the geometrical relationships that are common to
all railway configurations is essential, whether designing, building
or maintaining a high-speed passenger line or a 40 mph drag coal
line.
12.1 Introduction
T
he purpose of this chapter is to examine mathematically some key components
of the track structure, curves and turnouts, but from a European perspective.
The European railway, in many ways, is significantly different than the typical
railway of North America. High-speed rail plays a very significant role in not only
Western Europe, but also in Eastern Europe as well. In Europe, curves are built broad
and long, favoring high-speed operations. The approach in North America is entirely
different. Privatized North American railways were built to keep construction costs
down and to bridge great distances as quickly as possible. This translates into sharp
curvature and heavy grades, even for heavy haul activities. The need to move bulk
commodities over great distances favored the loading and design approach used by
North American railways. The excellent road system developed over the vast majority
of the populated segments of North America has relegated the majority of passenger
rail travel to a limited few heavily populated corridors. In Europe, the exorbitant cost
of fuel, a very high population density within countries the size of states or provinces,
along with a nationalized system of railways, has necessitated and enabled the
development of an extensive passenger rail based system.
Naturally, the European and North American rail networks evolved in two very
different directions. The one system is based solely on the reliable movement of heavy
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tonnage at the lowest cost. The other on pure speed. Vehicle and truck/suspension
development also took diverging paths between the two continents. European trucks
are set much further in than their North American counterparts. Truck (bogey)
suspensions handle track anomalies much differently in Europe. Europeans do not
stagger joints as is done in North America. Rock-off is unheard of in jointed territory.
On the other hand, vehicle bounce can be accentuated.
Today though, the North American engineer may need to take a new look at how our
counterparts "across the pond" have surmounted the problems of dealing with
operating at high speeds within existing alignments. North American railways are
looking for ways to operate faster at lower costs. European tangential turnouts have
been successfully installed in a number of heavy-haul territories. There is renewed
interest in high-speed inter-city passenger trains with a number of feasibility studies
underway. A new 110-mph Amtrak/IDOT service between Chicago and Springfield,
Illinois will soon initiate service.
This chapter does not pretend to cover all the significant design approaches used by
European railways in the handling of curvature and turnouts, particularly at high speed.
Nor does it present itself as being totally inclusive of European practices. There is
wide variance between systems in Western and Eastern Europe. But the reader
hopefully will get an appreciation of why Europeans have taken the approach they
have to these two topics. In addition, the commonality will also be apparent and
hopefully, the reader will secure a better appreciation of why we in North America
have developed the standards that we have.
12.2 Curves
12.2.1 Curve Definition
Prior to discussing curve engineering, one must have a common method of defining a
curve. There are two ways of describing curvature in common practice. In North
America, a railway curve is described by the angle in degrees subtended by two radii,
whose end points on the curve form a chord of 100 feet in length. In other parts of
the railway world, the length of the radius described above, measured in meters,
describes the curve.
The circumference of a complete circle is 2 ⋅ R ⋅ Π . Since the full body of a curve is
theoretically circular in construction, each degree of curvature will describe 100 feet of
chord (at relatively small degrees of curvature, the arc distance is approximately equal
to the chord distance). Thus, the circumference for such a circle made up of 100 foot
chords, each describing 1° of curvature, would for practical purposes, be 3600 feet and
the radius would be:
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dh
= n ⋅V
dt
The maximum permissible rate of elevation increase will vary with different railway
companies. The SNCF network permits up to 70mm/sec on the DB (Deutche Bahn)
network up to 35mm/sec and on the JNR (Japanese National Railroad) up to
42mm/sec.
According to Prof. A. Prud’homme, a rate of elevation increase of 100mm/sec. is
theoretically possible for high-speed trains, but is not the practice of the European
railways.56
If the rate of elevation increase on the ramp is 28mm/sec, we can get the horizontal
component length of the ramp by:
l = 10 ⋅ V ⋅ h
The value determined is generally rounded to the nearest 5m or so.
For heavy curvature or gradients, the permissible rate of elevation of increase is
increased to 35mm/sec. or:
l = 8 ⋅V ⋅ h
For high-speed rides, Deutche-Bahn AG recommends:
l = 12 ⋅ V ⋅ h
Shock (Jerk)
In Europe, a parameter called shock (jerk) is utilized to determine the configuration of
the ramp. The magnitude of the vertical jerk is defined as a change in the vertical
acceleration within a given time span:
Ψ=
da æ m ö
ç ÷
dt è s 3 ø
The maximum jerk value is set at by experience at:
Ψ = 1 .0 m
s3
and the common range of values of the jerk is:
56
Professor A. Prud’homme, “General Revue for French Railroad,” November 1976, Paris, France.
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Ψ = 0 .3 − 0 .5 m
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s3
The curved ramp is the second type of ramp configuration used in Europe to
transition in superelevation and is shown in Figure 12.7.
The slope of this ramp varies along the
curve and the greatest slope is located in the
middle of the ramp, at point S in Figure
12.6. It follows:
1 : ns =
2h
1000 ⋅ l
Figure 12-6 JZ (Yugoslavian) Superstructure Regulations
The curved ramp (spiral) is longer than the linear ramp and thus, it is more suitable for
higher speeds. The curved ramp is used for speeds up to V=180 km/h (112 mph) and
its length is defined by:
Lcurve = 1.41 ⋅ Lstraight
where Lstraight is the length of the associated linear ramp (i.e., about 41% longer)
The greater the rate in acceleration change, the longer the required ramp must be. In
the sinusoidal ramps (utilized in the Tokaido Railroad), the length of ramp is calculated
by:
Lsin = 1.60 ⋅ Lstraight
In the case of the curved ramps, the resultant curve and the slope increase in the form
of two squared parabolas touching, but whose slope constantly changes.
In the case of sinusoidal ramp, the largest curve is at the beginning and at the end of
the ramp, while the vertical velocity is continual.
Sinusoidal Ramp
Sinusoidal ramps are longer in length than the other forms of transition ramps and
allow higher speeds. For
V ≤ 180km / h
max .n s = 4V and n s = 400
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12.4.2 Turnout Calculations
Conventional European turnout calculations are based on a geometric projection of
the length and the relative direction at the points where the connections are made.
This method assumes that kinematic forces rather than dynamic forces determine
vehicle response.57 To determine the essential equations, one uses one of the
projection methods.
The open polygon method option is shown on Figure 12-23 and the closed polygon
method is shown on Figure 12-24. Elements of the turnout are projected on a
convenient coordinate system. From the geometric length relations, the equation can
be written as:
The equation representing the open polygon of Figure 12-23 is:
A ′E ′ = a ⋅ cos α + b ⋅ cos β + c ⋅ cos γ − d ⋅ cos δ
Figure 12-23 – Courtesy of University of Zagreb
Figure 12-24 – Courtesy of University of Zagreb
The equations representing the closed polygon in Figure 12-24 are:
a ⋅ cos α − b ⋅ cos β − c ⋅ cos γ = 0
a ⋅ sin α + b ⋅ sin β − c ⋅ sin γ = 0
On the European Railway network, the tangent of an angle rounded off to the nearest
degree expresses the diverging angle.
Mejgyeri, J., Geometric Movement in Turnout Development, Austrian Railway Archive Volume 40, Pages
59–65, 1985.
57
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For example:
(
)
(
)
1 : n = 1 : 10 ∴ α = 50 42'38" or
1 : n = 1 : 14 ∴ α = 4005'08"
The maximum permissible lateral acceleration is 0.8m/sec2. Thus, one could develop a
curve in the closure rail with a radius that, for a desired diverging speed, generated a
lateral acceleration of a = V2/R, not exceeding 0.8m/sec2. This curve would be
independent of the frog number utilized. In effect, Europeans will utilize a variety of
turnout closure rail curves with the same movable point frog in order to secure
different diverging speeds. The resultant turnout, obviously lengthens significantly as
the radius of the curve grows. This is in direct opposition to the turnout practices of
North American railways, that utilize one given closure rail curve for a given turnout
number.
The effective radius is performed by calculating the offset at the switch heel, based on a
chord (12.2m or 40’) centered about the switch heel. The calculated offset will provide
the effective radius ( R ) at the switch heel by using:
C2
R=
8 ⋅V
On the JZ (Jugoslavian Railroad), the chord length of 12.2m is the shortest distance
between wheel set centers (truck centers currently in service).
Thus, for example, in high-speed operations, the diverging angle can be:
α = 2°29'22"∴ (tan α = 1 : 23.5)
and the permissible diverging radius is R=1390m (4,560 ft.). This permits a diverging
speed of 80 km/h in 120 km/H territory.
For 100km/h in a diverging route, we need a curve with a radius of 1500m.
As determined by the following equation:
Vmax = 2.91 R1/2
This radius is coupled with a tan α = 1:18.5 or diverging angle α = 3º05’38.4”.
For Turnout Model EW (1:40.154) (DB Railroad), α=1º12’ 7.5” (tan α=1:40.154)
with a radius of 6100m (20,013 ft), which allows a diverging speed of 200 km/h.
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#1 – Casky, KY – Project Survey
Project Summary
Location
• Casky, Christian County, Kentucky
Description
• Construct new mainline in order to create new 5,600 TF stub ended
industrial lead track.
Railroad(s) involved
• CSX Transportation, Inc.
Construction Cost
• $1.47 Million
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Construction Duration
• Proposed - Spring 2001 to Fall 2001
• Actual – Summer 2001 to Spring 2002
Statement of Need
•
The traffic flow along this corridor is high density and high speed.
Switching industries off the main track has caused transportation delays
for through trains and impacted switching operations for five industries.
In addition, future industrial growth in this area is suspended. This
location is the fastest growing industrial area for the CSXT. Five
industries were installed in the last five years. The benefits gained from
the new construction will allow CSX to increase velocity of trains
operating in this corridor and increase the opportunity for future growth
in the Hopkinsville Industrial Park.
Project
Understanding
(Definition)
•
A new main track, west of the existing line, will be constructed. The old
main track will be used as an industrial lead with access on the south end
only. Industrial Development gains the opportunity to grow the business
on the north side by future extension of the industrial lead. When fully
developed, this industrial lead will connect to the south end of “Casky
Siding,” providing CSX with a 20,000 foot siding when the industrial lead
is not in use.
The rate of return is 18% for $1.47 Million
•
Identify
Stakeholders
Railroad
Train Operations
•
CSX Transportation, Inc.
•
Train Operations, Design & Construction, Industrial Development,
M/W, Train Control, Real Property, Inc. and Outside Railroad
Contractors (Design, Grading and Track) were main players from the
railroads approach to the project.
Planning Department
(Critical
Dependencies)
Train Operations/Industrial Development Dept.
•
Defined project scope and provided funding for construction.
•
Design and Construction performed preliminary design, prepared estimate
for the track, performed project inspections, managed budget expenditures,
employed track and grading contractors, monitored construction progress,
ordered track materials, coordinated curfews & track time and coordinated
with the County for local road closing.
Design & Construction
Engineering Department
•
•
MOW – performed track inspections, scheduled work trains and provided
track protection for the project.
Train Control – performed all work associated with signals.
Real Estate Department
•
Real estate group researched property issues and negotiated price sales with
local landowners. In addition, handled deed records for new acquisitions.
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Design Contractor
•
Provided detailed design engineering and construction quantities.
•
Constructed roadbed in accordance with CSX specifications.
•
Constructed all track and performed track shifts in accordance with CSX
specifications.
Identify
Stakeholders
•
Non-Railroad
•
(Critical
Dependencies)
•
Christian County – the county transportation officials reviewed road crossing
approach design and helped coordinate road crossing closing. Advance
warning signal protection remained flashing lights only.
WorldCom – fiber optic company relocated fiber optic cable outside project
limits to allow the start of construction.
5 Industries – Sun Chemical Corp., Budd Talent Co., Seimer Milling,
Continental Mills, and Free Flow Pkg. gain better switching operations.
Coordination with Sun Chemical to relocate switch out of mainline and
install in new industrial lead. Track was out of service for 1 week.
Grading Contractor
Track Contractor
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Feasibility Assessment
•
Construct new main line on west side of existing main track and realign
existing main track, at each end, into the new main. Will need to purchase
property from adjoining property owners in order obtain enough area to
build roadbed in accordance to CSX specifications.
Alternative Analysis
•
Build new industrial lead track on east side and relocate all industrial switches
out of the main and into the new lead track. Will need to construct roadbed
and realign all industrial tracks for 5 industries. No new property needed,
right of way is sufficient to support roadbed according to CSX specifications.
Rejected this alternative because all 5 industrial tracks would require substandard curvature.
Design
•
•
•
•
•
All construction according to CSX specifications.
Roadway materials to be built in accordance with KYTC specifications.
Maximum degree of curvature for industrial tracks is 12 degrees. (Should
never exceed 17 degrees)
All railroad construction is to not interfere with the wetland area.
All track work and grading work to be performed by outside contractors.
Operating Criteria
•
•
•
Time table speed to remain at 60 mph for this segment of track with
temporary slow orders as the work was in process.
Curfew times would only be available on Mondays and not to exceed 8
hours. Maximum allowable track time for any other day would not exceed 4
hours.
Road crossing could be closed for a period of 1 week.
Project Management
•
Key Project
Elements
Overall project management falls with the Project Engineer from Design &
Construction. The Roadmaster will schedule track protection during the
work and schedule work trains to dump ballast. In addition, the Roadmaster
will provide final inspection of the track construction. Train Control will be
responsible with progressing along with the track construction and manage
all signal-related issues.
Operating Parameters
•
The railroad operates approximately 40-45 trains per 24-hour period.
Mondays generally have one scheduled critical train, UPS, which runs during
morning hours.
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Schedule
•
Critical Design
Considerations
Project to start early Spring 2001 and be completed prior to Thanksgiving,
due to UPS peak season. In addition, asphalt plants close in early November.
Property Acquisition
•
Need to acquire two adjoining parcels of land in order to construct roadbed
according to CSX specifications.
Utility Service Availability
•
Utility service for crossing protection and industrial switch is not an issue.
The 5 industrial switches are dispatch controlled and already have electrical
service. Industrial lead switch required one pole drop and power was fed by
a nearby electrical line.
Grade-Crossing Considerations
•
Asphalt approaches for new road crossing shall fall off at a minimum of 1%,
for a distance of 28 feet from the outside edge of rail. Extending further
away, approaches can fall off no greater than 8% until it ties into the existing
road.
Construction Phasing
Project Challenges
•
Grading construction will start after fiber optic cable has been relocated.
Train Control will install buried signal wire in roadbed prior to subballast
installation. Track contractor will start track work after subballast is installed
and all material delivered. Train Control will work along with track
contractor schedule in order to keep signal protection for the railroad. Track
and Grading contractors will coordinate road crossing installation in order to
minimize road crossing closure time.
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Complete project prior to CSX-UPS peak season, which begins November
23rd and ends December 25th.
Start grading work prior to having all property acquisitions under contract.
In addition, Fiber Optic company was waiting on final property lines to
determine which side of track to relocate fiber optic cable.
Completing grading work within 45 days was not attainable. Contractor
experienced 20 days of weather related delays.
Redirect waterway for pipe outlet after grading contractor built pond for local
property owner. Waterway originally exited into wetland/tree line area.
Local property owner, as part of his construction contract with grading
contractor, instructed the contractor to build a pond near the CSX property
line and direct all ditch lines to the north to empty into pond. The pond
elevation was higher than outlet end of pipe, causing water to pond up in
water channel and soak into roadbed. CSX had grading contractor to close
south water channel to pond and redirect waterway for the pipe in opposite
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direction.
Providing a location to spot 8 ribbons of rail prior to grading work being
completed.
Finding a staging area to receive and distribute track material onto roadbed.
Track contractor did not have same construction easement with local
property owner.
Dump ballast on the new main and surfacing the track prior to the track
shifts. Project had limited access and trucking in ballast was not an option.
Our original proposal was to construct the industrial lead up to the first track
shift location on the south end, then shift the main on to the industrial lead
and run trains through the industrial lead switch for 3 days. This meant that
this section of corridor would operate without signals for 3 days. A week
prior to cutover, Transportation rescinded their original plan of approval.
We then decided to install a temporary turnout on the north end in order to
dump ballast and surface track. Track shifts on the north and south ends
would both occur during the same curfew.
Need property acquisition to occur prior to construction season starting.
Property acquisitions for project caused 2 months delay, preventing the
Grading Contractor from starting in April.
Provide language in construction contract where Contractor will be penalized
for not meeting the construction schedule. Granted, 20 days of delay was
attributed to weather delays but other outside interferences caused additional
delays.
Be firm with outside contractors. Remember that contractors are working
for you. In addition, cover the general conditions during the pre-bid
meetings and after the contract has been awarded. Contractors sometimes
forget their responsibilities and play stupid when told of them.
Instruct Contractors to complete a daily progress report and provide this to
you on a daily/weekly basis. This will allow you to keep up with days
worked, activities performed on each day and can be used as a tool for future
references.
Preach the importance of Safety from the pre-bid meeting up until the
contractor completes the job.
Watch the finances from the beginning and complete budget forecasting
every few weeks to determine if project is on budget.
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STRINGLINING OF RAILROAD CURVES
1995 ROADMASTERS & MAINTENANCE OF WAY ASSOCIATION
COMMITTEE REPORT
Chairman: A.M. Charrow, Asst. Dir. - Mtce., Santa Fe
Co-chairman: B. Jamison, Tech. Instr., Norfolk Southern
In this age of automatic tampers, computers, geometry cars and, of course, reduced
forces, why bother teaching the traditional methods of stringlining? The answer to that
question is that the traditional methods of stringlining will allow the practitioner to
rapidly field determine curvature and, if necessary, line track with low-tech hardware.
Railroad track is a dynamic structure, and there are many causes of its movement from
design alignment to one of irregular alignment, particularly on curves. Train operations
impart forces to the track structure, which, over time, tend to change the alignment.
Our predecessors who discovered that as speeds increased, the alignment entering and
leaving simple curves became distorted recognized this early, which in turn lead to the
development of transition curves between the tangents and simple curves and spirals.
However, even with perfectly designed curves with the correct superelevation and
spiral length for the associated curvature and track speed, lateral forces will still occur as
not every train will be operating at design speed. Running traffic at an unbalanced
condition is a compensation for this, but lateral forces will still be imparted to the track
related to directional tonnage, grades and current of traffic operation.
Therefore, alignment should be expected to change or deteriorate as time goes by
through normal operations, eventually requiring surfacing and lining. Compounding
the above, there exist locations not blessed with perfectly designed or constructed
subgrades, which for various reasons, poor original location, poorly constructed fill,
slides or high water, the alignment changes.
Another type of track instability relates to thermal expansion and contraction, primarily
the dreaded sun-kink, which can make the alignment most irregular, possibly leading to
catastrophic results. Less dramatic changes in alignment will occur also, as I am sure
most of you have seen curves gradually shift in and out during the different seasons,
especially where insufficient ballast exists.
Another cause of irregular curve alignment, or at least alignment different from what
was originally designed, is previous lining. Years of smoothing and surfacing without
staking will result in a curve that while perhaps not particularly bad looking or poor
riding might be off alignment. Likewise, normal maintenance operations, such as tie
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G L O S S A R Y
GLOSSARY
GENERAL RAILWAY DEFINITIONS
AND COMMON RAILWAY TERMS
“A” End:
In a railway freight car, the end that does not
have the brake handle; opposite to the “B” end –
SEE “B” End.
A
AAR:
See Association of American Railroads
Adjacent Track:
In relation to excepted track and for the purposes
of the Track Safety Standards, any track or tracks
next to a track that is designated as an excepted
track. Any tracks or tracks with centerlines that
are 30 feet or closer to the excepted track in
question are considered as adjacent and speeds on
those tracks must not exceed 10 m.p.h.
Adjustment, Rail:
A process whereby the neutral temperature of
continuous welded rail (CWR) is raised or
lowered through the removing or adding of rail.
Administrator:
The chief officer of the Federal Railroad
Administration. That person has the authority to
issue safety regulations and other emergency
directives.
Advanced Signal:
A fixed signal used in connection with one or
more signals to govern the approach of a train or
engine to such signal.
Advanced Train Control System: (ATCS)
Term referring to the next generation of train
control. Aspects of control include accurate train
location, train and locomotive monitoring and
reporting, computerized analysis and track orders,
and automatic order enforcement.
Adzing Machine:
Portable power-operated machine designed to adz
(smooth) the rail seat on ties to provide proper
bearing for rail or tie plates.
AEI:
See Automatic Equipment Identification System
Air Dump Car:
Hopper Car with air dumping capabilities.
Alinement [or alignment]:
The position of the track or rail in the horizontal
plane expressed as tangent or curve.
Angle Cock:
An appliance used for the purpose of opening or
closing brake pipe on ends of cars, rear ends of
tenders, and front ends of switch engines so
equipped. Provision is made for the supporting
hose at proper angle.
Antisplitting Iron:
A piece of steel strip, beveled on both sides at
one edge, and bent to a desired shape, for
application by driving into the end (cross section)
of a tie or timber to control its splitting.
Approach Track:
In signaling, the section of track on the approach
side of a signal which is equipped with a circuit to
detect the arrival of a train and transmit its
presence to the controlling circuits of the signal
and its associated route. Used to lock a route and
prevent it from being altered once a train has
approached within a safe braking distance, known
as approach control. This prevents the route
being changed at a time when the train could run
onto it and be derailed.
Also use to clear signals normally maintained at
danger until a train has approached within a given
distance. This distance is calculated to ensure the
locomotive engineer sees a red signal as he
approaches. This has the effect of causing the
locomotive engineer to reduce train speed to a
required level, at which point the signal will clear.
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Unbalanced:
The superelevation in a curve that is less than a
calculated value that will otherwise equally
distribute onto both rails the dynamic force of
trains that are traveling at the maximum
authorized speed.
territorial seas, and (6) wetlands adjacent to
waters.
Warp:
See Difference-in-cross-level
Welded Rail:
Two or more rails welded together.
Unbalance Speed:
Traveling through a curve faster than balance
speed. This may also be expressed as the curve
being under elevated for the speed. The amount
of reduction in elevation from balanced can be as
much as 3 inches for conventional equipment.
Wetlands:
The transitional land between the terrestrial and
aquatic environment where the water table is
usually at or near the surface, or the land is
covered by shallow water.
Undercutter:
Production machine that removes the ballast
from the track in one continuous operation.
Wheel Impact Load Detector (Wild):
A device found in some Hot Box Detectors or as
stand alones, which measure excessive wheel
impact on rail.
Under balanced:
See unbalanced.
Uniform Code of Operating Rules:
An operating rules book formerly used in the
U.S.A.
Unit Train:
A freight train consisting of carloads of the same
commodity moving from origin to one
destination, on one day from one shipper to one
consignee on one bill of lading.
V
V-max:
The maximum speed, based on a mathematical
formula, permitted on a curve based on the
average curvature and average superelevation.
Variation (Crosslevel):
The change in crosslevel between two points
exactly 31 feet apart in a “short spiral.” [see
definition of short spiral]
W
Waivers:
See exemption.
Waters of the U.S.:
Regulated by the U.S. Army Corps of Engineers
and sometimes state and local authorities they
include: (1) Waters used for interstate or foreign
commerce, (2) all other waters including lakes,
rivers, streams, mudflats, sandflats, wetlands,
sloughs, prairie potholes, wet meadows, playa
takes, or natural ponds, (3) impoundments,
(4) tributaries of waters of the U.S., (5) the
Wig Wag:
A reference to the motion of lights on railway,
vehicle-crossing signals.
Willful Violation:
To intentionally circumvent or ignore a regulatory
safety requirement.
Wing Rail:
See “Frog: Wing Rail.”
Wing Wheel Riser:
See “Frog: Wing Wheel Riser.”
Wood Trestle:
A wood structure composed of bents supporting
stringers, the whole forming a support for loads
applied to the stringers through the deck.
Work Train:
A train engaged in railway maintenance or repair
work.
Written Authorization:
The formal procedure where a person is
designated in a document generated by a railroad
to conduct certain safety related functions such as
track inspection or maintenance of track under
traffic conditions.
Wye Track:
See “Track: Wye.”
Y
Yard:
A system of tracks within defined limits provided
for making up trains, storing cars, and other
purposes, over which movements not authorized
by time table or by train-order may be made,
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