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 Capacity Constraints and Remedies  Curves  Grades  Station stops  Bridges  Diamonds  Track maintenance and renewal 22 September 2010 SCORT/TRB.

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Presentation on theme: " Capacity Constraints and Remedies  Curves  Grades  Station stops  Bridges  Diamonds  Track maintenance and renewal 22 September 2010 SCORT/TRB."— Presentation transcript:

1  Capacity Constraints and Remedies  Curves  Grades  Station stops  Bridges  Diamonds  Track maintenance and renewal 22 September 2010 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida1

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3 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

4  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

5 W W W RR R FF F Direction of curve Relative forces on rails (a) Speed < Balanced Speed(b) Speed = Balanced Speed(c) Speed > Balanced Speed

6  V max = maximum allowable train speed, mph  E a = outside rail elevation, inches  E u = allowable cant deficiency, inches  3 inches for conventional equipment  4 inches for certified equipment  higher where approved by FRA  D = degree of curve

7 4½” superelevation Intermodal Freight Passenger (conventional eqpt.) Passenger (tilt eqpt.)

8  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

9  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 G1G1 G2G2 PVC PVT L L/2 x y PVI

10  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%

11  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

12  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

13  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

14  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

15  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

16  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 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida16

17  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 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida17

18  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

19  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

20  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

21  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

22  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 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida22

23  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

24  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

25  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

26 22 September 2010 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida26 Track Class Max. Freight Speed (mph) Max. Passenger Speed (mph)

27  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

28  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

29  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 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida29

30  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 SCORT/TRB Rail Capacity Workshop - Jacksonville Florida30


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