p-REES 1: Module 1-B Introduction
to Railway Infrastructure
William T. Thomsen, PE
Senior Vice President
Urban Engineers
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Presentation Author
William T Thomsen, PE
Senior Vice President
National Infrastructure Services
Urban Engineers, Inc.
530 Walnut Street
Philadelphia, PA 19106
215-922-8080
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Presentation Overview
During this module we will cover elements of Railway
infrastructure to include:
• Track
• Drainage
• Turnouts
• Bridges
• Tunnels
• Stations
• Trains
• Terminals
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Track Structure
• Primary Track Functions:
• Support
• Guidance
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Track Structure
• The weight of the train is transferred from the steel wheels
to the steel rail where it is distributed by the beam action of
the rail to several crossties.
• Crossties further
redistribute the load,
passing it on to the ballast.
• The ballast redistributes
the load again and passes
it on to the subballast and
ground.
• Guidance for the train is
provided by the wheel
flange and the rail.
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Track Types
Ballasted
Embedded
Direct Fixation Track
(DFT)
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Track Types: Ballasted
• Ballast is the stone, cinders, slag, shells or other
granular material placed between the crossties, down
to and on top of the subballast or subgrade.
• The term is derived from
gravels and other materials
carried by ships to properly
balance or weigh them
down.
• It was readily available
and suitable material to
use in constructing the
early railroads.
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Ballast Purpose
• Prime function is to spread the wheel loading from
the base of the crossties to the subgrade at
pressures that will not cause subgrade failure.
• Functions:
• To provide structural support
for the track
• To distribute the load evenly to
the subgrade
• To provide for stability of track,
holding it in true line and grade
• To provide for drainage
• To help prevent growth of weeds
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Ballast Requirements
• Requirements for suitable ballast material has changed
overtime due to heavier loads being hauled.
• Cinder is no longer available due to its tendency to
crush under heavy loads
• Technological improvements in rock crushers and
mechanical automatic tamping equipment have made
it easier to obtain and install good ballast.
• Today, ballast is hauled long distances from quarries
and evenly distributed along the track, and tamped by
machinery.
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Types of Ballast
• Cinder – during the steam
locomotive era
it was almost always available
and its higher
sulfur content discouraged
weed growth
in the track. Over time, cinder
ballast begins
to break up and become fouled
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Types of Ballast
• Washed gravel – used successfully on light tonnage lines.
It is less stable than stone and tends to become muddy if
its clay content is high
• Slag, shells and coral – used in
lighter tonnage
tracks
• Stone ballast (trap rock) –
suited for heavy
service
• Examples: Granite, quartz,
feldspar
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Ballast Testing
• Typical laboratory tests for determining the quality of
ballasts:
• Sieve analysis – used to determine
the size and gradation of
individual stones
• Absorption –used to determine
the blotter characteristics of the
stone and how well it will resist
repeated freezing and thawing
• Soundness (Sodium sulfate soundness) – measures how
well the stone will resists freezing/thawing.
• Deval Abrasion and Los Angeles Abrasion
• Both tests are used as a measure of soundness and ability
to resist wear
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Subballast
• Purpose:
• Provide better drainage
• Prevent upheaval by frost
• Better load distribution over roadbed
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Subballast Qualifications
• 6 inches or thicker
• Spread on top of finished subgrade
• Placement should be made in layers not exceeding 8
inches in uncompact thickness
• Material is bladed off and compacted to a tolerance
+/- 0.1 feet.
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Subballast Materials
Crushed stone sand
Crushed slag
Gravel/sand, pit run
Cinder
Screening from ballast
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Track Types - Embedded
• A track structure that is completely covered – except
for the top of the rails – within pavement.
• Flangeways can be
provided either by
using grooved head
girder rail or by
forming a flangeway
in the embedment
material.
• Standard for light rail
transit routes constructed
within public streets, pedestrian/transit malls, or
anywhere where rubber-tired traffic must operate.
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Embedded
• Types of track structures:
• Concrete slab track structure
• Continuous single-pour concrete slab with two rail
pockets or troughs
• Two-pour concrete slab with cold joint between the two
pours located at the base of the rail
• Three-pour concrete slab with a bathtub design providing
stray current protection below and beside the concrete
track slab.
• Conventional ballasted track with embedment
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Rail Embedment Materials
• Extruded elastomeric Trough Components
• Cast-in-place resilient polyurethane components
• Concrete fills
• Asphaltic bituminous mortar
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Track Types – Direct Fixation Track (DFT)
• A track using a plate-type assembly to hold the rail
in place on a support
• Concrete support, steel or other superstructure
material.
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DFT Uses
• Minimize the track envelope in tunnels and to
reduce the dead weight on aerial structures,
compared to other forms of tracks
• Train washes and areas prone to spills
• Locations where track to station platform
relationships are important
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DFT Uses
• Locations where at-grade slab track has lower
life cycle cost than ballasted track
• Transitions to structures
• Adverse soil conditions
• Locations requiring high track
reliability
• Locations with poor
maintenance access
• High density routes
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Concrete Ties
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Concrete Ties
• Ties transfer loads to the ballast and subgrade
and hold the rails upright and keep them
spaced as designed
• Wood ties are popular, but concrete ties have
advantages
• Longer service life
• Greater strength
• Lower maintenance
costs
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Concrete Ties
• Can be used for:
• Heavy-haul main lines
• Mass transit
• Industrial sidings
• Guidelines
• AREMA (American Railroad
Engineering Maintenance-ofWay Association) Chapter 30
maintenance access
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Rail and Rail Fasteners
• Rail: one of the pair of Rolled Steel Rail on which
a train travels
• Track consists of two steel rails
• Secured with ties
• Bolted with Joint Bars
• Continuously Welded Rail
(1440 foot strings)
• Rail Fasteners:
• Affix rail to ties
• Includes anchors, tie plates, chairs
and track fasteners – part of
the entire rail fastening system.
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Rail and Rail Fasteners
• Rail Section: Common rail Section known as T
Rail varies in size and dimension
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Rail and Rail Fasteners
• Spikes and screws
• Rail spike, screw spike,
spring spike
• Fang bolts
• Rail Supports
• Chairs
• Tie plates
• Clips
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Turnouts
• The part of the track structure used to divert rolling
stock from one track to another.
• It consists essentially of an arrangement of a switch
and a frog with closure rails.
• Turnouts require special material, such as switch
timber ranging in length from 9 ft. to 16 ft., special
plates, and special rails.
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Turnouts
• The hand is determined by standing in the gage of
the track at the switch points facing the frog.
• Right-Hand (RH) – diverting move to the Right
• Left-Hand (LH) - diverting move to the Left
• Facing point – traffic entering
the turnout from the switch
point
• Trailing point – traffic entering
from the frog
(Left Hand Turnout)
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Turnout Classes
• High speed turnouts
• Necessary to enable faster diverting
movements of present day trains
• Operated remotely from interlocking
towers by compressed air or electrical
impulses
• 300 to 400 foot distances are required
from the switch point to the clearance
point
• Main line or common turnouts
• Yard turnouts
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Turnout Switches
• Types
•
•
•
•
•
Stub switch
Plate switch
Three-way switch
Wye switch
Double slip switch
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Turnout Challenges
• A turnout presents a considerable discontinuity in
the wheel/rail running surface
• The wheel/rail interaction may cause highfrequency impact loads on the turnout system and
its components
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Bridges
• Freight – Cooper E 80 capable of handling heavy
loading
• Passenger – Commutes rail same as freight
• Light rail uses lower loading regiment similar to highway
loading
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Freight Rail Bridges
• Freight rail bridges are designed to carry heavier
loads than passenger rail bridges
• Bridges for passenger rail are designed for freight
rail loadings and conditions, as the rail bridge
should be able to carry both types of loads
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Passenger Rail Bridges
Bridges for passenger rail carry less loading than freight
bridges
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Bridge Types
• Stone Arch
• Wood Trestle
• Steel Truss
• Through Girder
• Deck Girder
• Open Deck
• Ballasted Deck
• Movable Bridges
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Tunnels
• Bored tunnels
• Cut and Cover Tunnels
• Pedestrian Tunnels
• Subaqueous Tunnels
• Other
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Stations
• Passenger safety is the most important design
criterion
• Platform width is one of the most important factors
• Station exits and entrances
• Side platform station
• Island platform station
• Elevated stations
• Underground
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Yards
• Yards take in freight, typically from all different
directions, sort it out and send it on its way to
either the next yard of final destination.
• Smaller yards have a few tracks used for storage
• Designated locomotive (switch engine or yard goat)
used to properly sort yards
• Inclined plane that allows cars to roll down hill onto the
appropriate sorting track
• Maintenance Facility
• Mid-Day Storage
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Yards
• Yard Layout
• Double-Ended
• Stub Ended
• Main line at one end of the yard
• Once a train has entered the yard limit
speeds are restricted to 5 or 10 mph
• Engine terminal can usually be found
from one of the main tracks
• Yard office or yard tower
• Yard master controls all movements within the yard
• Trainmaster controls the actual movements of the trains
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Terminals
• Passenger Terminals
• Where passengers can embark and disembark and a common
area for ticket purchase, waiting, and for activities servicing
large volumes of passengers
• Freight Terminals
• Where freight can be transferred
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Thank you!
Questions?
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