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Rail Capacity Workshop. Capacity Constraints and Remedies Curves Grades Station stops Bridges Diamonds Track maintenance and renewal. Curves. Y. D. X. Curve Components. Spiral. Curve whose degree changes uniformly with distance from origin Used to:

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rail capacity workshop
Rail Capacity Workshop
  • Capacity Constraints and Remedies
    • Curves
    • Grades
    • Station stops
    • Bridges
    • Diamonds
    • Track maintenance and renewal

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

curve components

Y

D

X

Curve Components

Spiral

  • Curve whose degree changes uniformly with distance from origin
  • Used to:
    • transition from tangent alignment to curve or between consecutive curves
    • introduce curve superelevation

Circular Curve

  • Curve of constant degree (radius)
  • Used to change alignment direction
  • May connect to tangents or other curves
  • Introduced by spirals in higher-speed track
  • Mild curvature: D ≤ 2º
  • Medium Curvature: 2º < D ≤ 8º
  • Sharp Curvature: 8º < D ≤ 12º
  • Extreme Curvature: D ≥ 12º
impacts of curvature
Impacts of Curvature
  • Restricted train speed
  • Increased train resistance
    • 0.08 lb per train ton per curve degree
    • Affects acceleration time, power requirements
  • Increased maintenance
    • Track alignment and elevation
    • Rail and wheel wear
  • Greater potential for derailment
curve forces
Curve Forces

Direction of curve

R

R

R

F

F

F

W

W

W

(a) Speed < Balanced Speed

(b) Speed = Balanced Speed

(c) Speed > Balanced Speed

Relative forces on rails

curve speed limit
Curve Speed Limit
  • Vmax = maximum allowable train speed, mph
  • Ea = outside rail elevation, inches
  • Eu = allowable cant deficiency, inches
    • 3 inches for conventional equipment
    • 4 inches for certified equipment
    • higher where approved by FRA
  • D= degree of curve
train speeds through curves unconstrained
Train Speeds Through Curves (Unconstrained)

4½” superelevation

Intermodal

Freight

Passenger (conventional eqpt.)

Passenger (tilt eqpt.)

mitigating delay due to curves
Mitigating Delay due to Curves
  • Increase curve elevation
    • FRA maximum for track classes 3-5 is 7 inches
    • Generally requires spiral length adjustment
    • Consider effect on clearances, structures, crossings
  • Provide proper spiral design
    • Rate of elevation change limits speed
  • Qualify equipment for greater cant deficiency
  • Realign track
    • Reduce curve degree
    • Reduce number of curves
  • Extend sidings to reduce length of single track
    • Reduces meet delay in speed limited territory
vertical alignment
Vertical Alignment
  • Consists of grade tangents connected by parabolic vertical curves
  • Grade tangent has uniform change in elevation over distance (expressed as percent)
  • Smooth transition between grade tangents provided within length of vertical curve

PVI

G1

G2

y

x

PVT

PVC

L/2

L/2

L

impacts of grades
Impacts of Grades
  • Grade force is 20 lb per train ton per percent
  • Grades can severely affect:
    • Maximum sustained train speed (upgrade)
    • Acceleration (upgrade)
    • Train speed control (downgrade)
    • Stopping distance
    • Train buff and draft forces
  • Curves add resistance and limit speeds, further increasing impact of grades

Impact potential of sustained grades:

Low G ≤ 0.25%

Moderate 0.25% < G ≤ 0.75%

High 0.75% < G ≤ 1.5%

Very High G> 1.5%

types of grades
Types of Grades
  • Ruling grade: train with minimum P/W ratio can crest at crawl speed within motive power short-time limits
  • Momentum grade: train with minimum P/W ratio will crest with some speed reduction from track speed
  • Helper grade: train gets temporary additional power added to help crest grade
  • Riprap territory: undulating profile requires care to control buff/draft forces in long trains
reducing grade impacts
Reducing Grade Impacts
  • Raise P/W ratio on freight trains
    • May increase speeds on ascending grades
    • Reduce need for capacity consuming helper and doubling operations
  • Increase power and tonnage on freight trains
    • Longer trains can reduce train volume, free up slots
    • Especially useful with distributed power
  • Avoid stopping train on severe upgrades
    • Provide operating authority to pass restricting signals at low speed
    • Provide power switches at sidings
engineering approaches to grade management
Engineering Approaches to Grade Management
  • Change alignment to reduce grade
    • Typically involves major capital investment
    • May increase track length, curvature
    • Potential complications, delays from R-O-W acquisition, permitting
    • Tunneling, large cuts can introduce additional maintenance issues
    • Requires careful assessment of economics
  • Lengthening vertical curves
    • Improves train handling
    • Increases ride comfort at speed
engineering approaches to grade management1
Engineering Approaches to Grade Management
  • Provide multiple main tracks on long grades to permit passes and overtakes of slow trains
  • Provide auxiliary tracks at top and bottom of grade to:
    • Clear helper movements
    • Reduce delay by trains requiring setup/release of retainers
    • Prevent blockages while doubling
  • Electrification
    • Allows increase in train power, regenerative braking
    • Major capital investment, economics sensitive to fuel prices
impacts of station stops
Each stop requires time for deceleration, station dwell, and acceleration

Average train speed decreases as number and spacing of stations increases

Close spacing may not permit train to accelerate to track speed between stations

Inefficient platform configuration may increase dwell

Stopping trains may delay other traffic

Through trains may have to slow at stations to reduce risk to passengers

Impacts of Station Stops
mitigating factors for station stops
Mitigating Factors for Station Stops
  • Provide train P/W ratio to achieve performance goals considering desired dwell time and station spacing
  • Provide for meets and passes at stations where warranted by traffic demands
    • Sidings
    • Multiple main track
  • Optimize platform configuration to minimize dwell time
    • Adequate length to match access points with demand
    • High-level fastest loading/unloading

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

operational impacts of bridges
Operational Impacts of Bridges
  • Reduced train speed due to bridge design or condition
  • Restrictions on traction/braking due to bridge design or condition
  • Equipment restrictions due to bridge design or construction
  • Restricted train speed approaching movable bridge
  • Delays imposed by open movable bridges

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

reasons to speed restrict bridge
Reasons to Speed Restrict Bridge
  • Bridge condition or structural design inadequate to withstand
    • Speed related impact loads
    • Speed related lateral loads
  • Reduce load effects on critical structures
  • Remediate track condition defects
  • Permit train crew verification of movable bridge position
  • Reduce derailment risk at movable span
movable bridges
Movable Bridges
  • Types
    • Lift bridge
    • Bascule (draw) bridge
    • Swing bridge
  • Open/close cycle time influences delay
  • Can be significant capacity constraint with heavy water traffic
  • More to go wrong than conventional designs
track crossings
Track Crossings

Flangeway

  • Track capacity reduced by crossing movements
  • Approaching train must be protected against conflicting movement
    • May limit speed, increase occupancy time
  • High maintenance location due to impact loading
    • Problems increase with speed
crossing improvements
Crossing Improvements
  • Reduce maintenance requirements
    • Provide premium components
    • Replace with One-Way Low Speed (OWLS) design
  • Replace with turnouts
    • Improves reliability, operational flexibility
    • Realignment of track costly, particularly for right-angle crossings
    • Crossing movements still consume capacity
  • Provide interlocking with distant signals to reduce approach delay
    • Automatic-first come, first served
    • Dispatcher/operator controlled-can prioritize traffic
  • Grade separate
    • Costly, uses more real estate
    • Permanently solves capacity issues
track maintenance
Track Maintenance
  • Railroads must inspect and maintain track
  • Track must comply with federal Track Safety Standards (49 CFR Part 213)
  • Track maintenance workers and machinery must be protected from train traffic in accordance with 49 CFR Part 214
  • The impact of these requirements on track capacity must be considered

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

maintenance activities
Inspect track

Service and adjust special trackwork and track appliances

Replace or repair worn track components

Replace failed track components

Keep track in proper gage, alignment, and surface

Maintain stormwater drainage elements

Correct ballast drainage problems

Address subgrade problems

Control vegetation

Manage thermal loads in CWR track

Distribute materials for projects

Repair storm or derailment damaged track

Reconstruct track to higher standards

Maintenance Activities
factors influencing track maintenance needs
Characteristics of track system

Rail and rail fasteners

Crossties

Ballast

Track horizontal and vertical alignment

Effectiveness of track drainage

Nature of track subgrade

Traffic volume and mix

Maximum train speed

Maximum wheel loading

Climate

Factors Influencing Track Maintenance Needs
speed and track condition
Speed and Track Condition
  • Owner sets train speed limits (pax, freight)
  • Speeds establish federal track class
  • Track condition must meet requirements for class
  • If track condition does not meet requirements, owner must take immediate remedial action
    • Repair
    • Reduce track class to make defect compliant
    • Remove track from service
track classes
Track Classes

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

categories of defects
Categories of Defects
  • Class specific
    • Defect may become compliant by reducing track class (slow ordering)
    • Examples: gage, alignment, mismatch
  • Non-class specific
    • Defect is non-compliant regardless of track class
    • Examples: drainage, vegetation
  • Speed defined
    • Defect type requires specific limiting speed
    • Example: rail defect, minimum curve elevation
track maintenance approaches
Working under traffic conditions

Practical for many types of work

Trains may pass through work site while work is in progress

Typically requires speed reduction

Need to clear on-track equipment adds delay

Workers must have protection per Part 214

Taking track out of service

Necessary for some times of work

May simplify Part 214 compliance

Capacity unavailable until work complete

Track Maintenance Approaches
mitigating capacity impacts
Mitigating Capacity Impacts
  • Limit duration of slow orders for defect remediation on main tracks
  • Address root causes of maintenance problems
  • Minimize on-track time for forces
    • Employ hi-rail equipment where practical
    • Provide nearby clearance location for on-track equipment
    • Prefabricate track panels and pre-position materials
    • Use high-production equipment and techniques
  • Schedule work during off-peak periods
    • Have close liaison between operations and engineering
    • Consider need to provide for night work, lower productivity

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

mitigating maintenance impacts
Mitigating Maintenance Impacts
  • Consider life-cycle costs of track components
    • Premium components can reduce maintenance needs
    • Include operating cost impacts of maintenance
  • Employ “blitz” approach
    • Plan all possible work in zone, perform during shutdown
  • Design to reduce impacts of maintenance on operations
    • Increase spacing between main tracks and sidings
    • Provide crossovers in multiple track territory
    • Consider maintenance in design of yards and terminals

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida