Capacity Constraints and Remedies Curves Grades Station stops Bridges Diamonds Track...

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

D

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

DEE

V 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

Ma

xim

um

Tra

ck

Sp

ee

d (

mp

h)

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 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

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 15

2 25 30

3 40 60

4 60 80

5 80 90

6 110 110

7 125 125

8 160 160

9 200 200

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

productivity22 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

Capacity Constraints and Remedies Curves Grades Station stops Bridges Diamonds Track...

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