rail capacity workshop

SCORT/TRB Rail Capacity Workshop - Jacksonville Florida

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Rail Capacity Workshop Capacity Constraints and Remedies

Curves Grades Station stops Bridges Diamonds Track maintenance and renewal

22 September 2010

Curves

Curve Components

TC CT

PI

M

E

100 ft

D

X

Y

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

Spiral

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 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

W W W

R R R

F F F

Direction of curve

Relative forces on rails

(a) Speed < Balanced Speed (b) Speed = Balanced Speed (c) Speed > Balanced Speed

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

DEEV ua

0007.0max

Train Speeds Through Curves (Unconstrained)

0

20

40

60

80

100

120

140

160

1 2 3 4 5 6 7 8 9 10

Degree of Curvature

Max

imum

Tra

ck S

peed

(mph

)

4½” superelevation

Inte

rmod

alFr

eigh

tPa

ssen

ger (

conv

entio

nal e

qpt.)

Pass

enge

r (tilt

eqp

t.)

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 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

G1 G2

PVC PVT

L

L/2 L/2

x

y

PVI

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 gradesImpact 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 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 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

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 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


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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

22 September 2010


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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

22 September 2010

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

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 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

Flangeway

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


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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

22 September 2010

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

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

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


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Track Classes

22 September 2010

Track ClassMax. Freight Speed (mph)

Max. Passenger

Speed (mph)1 10 152 25 303 40 604 60 805 80 906 110 1107 125 1258 160 1609 200 200

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


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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

22 September 2010


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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

22 September 2010

rail capacity workshop

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