© apta and arema - 2015 2-d introduction to railway capacity c. tyler dick, p.e. university of...

© APTA and AREMA - 2015

2-DIntroduction to Railway

CapacityC. Tyler Dick, P.E.

University of Illinoisat Urbana-Champaign

© APTA and AREMA - 2015 2

Outline• Introduction• Basic Rail Capacity Concepts• Analytical Models of Railway Capacity• Parametric Models• Simulation Models• Optimization Models• Other Considerations and Expansion Strategies


Fields Related to Capacity• Analytics• Data mining• Network optimization• Queuing theory• Regression modeling• Risk modeling• Simulation• Utility models


Railroad Capacity Over Time• 19th and early 20th century: Great expansion of railroads• World War I: War traffic brought network to standstill due to

insufficient capacity due to inefficient operations • 1920s: Relative balance between capacity and traffic levels• Great Depression: Loss of traffic led to excess capacity• World War II: Congestion from war traffic • After WWII: Overcapacity as passenger and freight

traffic declined• 1990 - Current: Growth in traffic and market power has

permitted railroads to spend substantial amounts to remove choke points


Increasing Demands on Rail Network

ReliabilityIntercity Passenger Trains

Commuter Service

Low CostTransportationFreight Growth

Environment

Cambridge Systematics. (2007). National Rail Freight Infrastructure Capacity and Investment Study.


Problems of Capacity Shortages• Inability to handle more traffic• Decreasing level of service• Diminished ability to recover from a disruption• Limited windows for track maintenance• Increase time in yards, terminals and stations• Increase cycle times• Increase number of trainsets, rolling stock• Increase number of crews (hours of service limitations)• All of the above increase costs


Capacity is an Expensive Resource

• Railway infrastructure is capital intensive and a long-term investment• Capacity lags behind changing demands

Capital Investment as a % of Revenue


Levels of Capacity Analysis• Transportation Network

• Railroad Network• Subdivision or Line• Yards & Terminals• Stations & Platforms• Interlockings & Junctions


Types of Capacity• Practical Capacity: Ability to move traffic at an

“acceptable” level of service• Economic Capacity: The level of traffic at which the

costs of additional traffic outweighs the benefits• Engineering Capacity: The maximum amount

moved before the system ceases to function • Ultimate Capacity: Breakdown conditions at

maximum train density. The system has ceased to function and all signals are red


What Should Capacity Measure?


Railway Capacity MetricsAmount Moved Reliability Utilization

TrainsRailcars

Gross TonsRevenue Tons

PassengersTEUs

(Per Year)(Per Day)

(Per Hour)(Per Peak Hour)

Distribution of Arrival TimesAverage Delay

Standard Deviation of DelayOn Time PerformanceRight Car Right Train

Crew ExpirationsVelocity

Terminal Dwell Blocking TimeSignal Wake

Train Miles/Track MileCycle Time

Trainsets or Railcars On-LineTrack Occupation

Train Density


Unlike highways, there is no standard railroad capacity model• The complex nature of railroad operations and

limited research funding has prevented a universal capacity model from being developed

• Currently several different models are in use


Level of Service to Measure Capacity

• Higher delays correspond to a lower level of service (LOS)

• Maximum theoretical train volumes are never reached due to deteriorated level of service

• Acceptable level of service establishes maximum train volume

Abril, M., Barber, F., Ingolotti, L., & Salido, M. (2008). An assessment of railway capacity. Transportation Research Part E: Logistics and Transportation Review, 44(5), 774-806.


Different Traffic and Track Configurations will Change Delay-Volume Relationship

Acceptable Delay

Volume (Trains/Day)

Del

ay (m

ins)


Track Configuration

• Number of tracks• Siding length• Siding spacing

(distance & time)• Crossover spacing

• Single crossovers• Universal crossovers• Parallel crossovers

• Geometry• Grade• Curvature


Double-Track Operations: Headway

• Common on most transit and some commuter rail operations

• Each track has a dedicated “current of traffic” with trains separated by a minimum headway

• Headway is a function of safe braking distance and signal spacing or control block length

• Very high capacity if all trains in one direction travel at the same speed (i.e. no passing)


Blocking Time Model• Single

direction on double track


Double-Track Analytical Model:Maximum Throughput Calculation• The maximum traffic flow that a rail line can

accommodate under ideal condition

Where: N = Number of trains per day1440 = Number of minutes in a dayHmin = Minimum headway (minutes)


Heterogeneous Train Speeds• Passenger trains travel at higher speeds than freight trains • Speed differential leads to decreased capacity • Passenger train on freight corridor

• Freight train on passenger/commuter corridor

• 1 minority train consumes 3 majority train slots

TimeDist

ance

TimeDist

ance


Overtakes on Double Track

• Passenger or commuter trains may experience additional delay while trailing behind slower trains

• If control system allows, faster trains can use opposite track to overtake slower trains

• Interrupts flow of traffic in opposite direction, decreasing overall capacity

• A passenger train requires over 40 miles to pass a freight at track speed without delay to either train


Single-Track Operation: Meet and Pass

• Single track poses significantly more challenges for practical railway capacity

• No longer simply limited by train spacing• Must consider “meets” of trains traveling in

opposite direction• These impose constraints on schedule


Meets on Single Track


Single-Track Analytical Model: Return Grid Calculation for Meets• Capacity of single track with meets

C = Capacity in trains per day1440 = Number of minutes per 24 hourst = Minutes to travel between sidingst/2 = Average dwell time waiting for opposing train to arrivem = Delay for each meet due to braking, entering the siding, running

the length of the siding, leaving the siding and accelerating to speed2 = number of trains per pair


Calculation MethodologySiding A Siding B

Time t

Time 0

Time t+m

Time 2t+m+t/2

Time t+m+t/2


Impact of Different Types of Trains • Differing train operating speeds causes deviations

from regular return-grid model, decreasing capacity

Time

Dis

tanc

e

Inte

rmod

al

Amtra

k

Manife

st

Unit

Time


Overtakes on Single TrackTi

me

T2

Pass Delay


Heterogeneous Operations and Capacity• Simple headway and grid models only work when all trains operate

at the same speed• Actual trains have different

• Operating speed• Acceleration and braking characteristics• Priority• Station stopping patterns

• Particularly apparent where passenger and freight operations share track infrastructure

• From a capacity perspective:1 freight train ≠ 1 passenger train

• These differences decrease capacity and require more complicated capacity analysis tools


Parametric Models• Parametric Models are developed from statistical

analysis of collected operating or simulation data• Key infrastructure and operating parameters are

identified to predict a delay-volume curve• Attributes include

• Average speed• Speed ratio• Priority• Peaking • Siding spacing and uniformity• Percent double track• Signal spacing

• FRA and CN have well-known parametric models


CN Parametric Model Example

Average Speed 44.38Speed Ratio 1.113Priority 0.342Peaking 1.727

Siding Spacing 7.77Siding Spacing Uniformity 0.49Signal Spacing 0.93

Track Outage 0Slow Orders 0% Dbl Track 75

Maintenance 0

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

Volume (Trains per Day)

Del

ay (M

inut

es)

Average Speed 44.4 mph Speed Ratio 1.113

Priority 0.342 Peaking 1.727

Siding Spacing 7.77 miles Uniformity 0.49

Signal Spacing 0.93 % Double Track 50

Krueger, H. “Parametric Modeling in Rail Capacity Planning.” Proceedings of the 1999 Winter Simulation Conference. Phoenix, 1999. 1194-1200. Web. 21 May 2012.


Railway Simulation Tools• Calculate train movements and make decisions

under the same rules as railroad dispatchers• Account for different equipment types, train

consists, train handling characteristics, terrain and track conditions

• Common uses of Simulation Tools:• Develop operating plans• Diagnose bottlenecks and recommend schedule changes• Evaluate various capital improvement scenarios• Assess the impact of adding new trains to a network

• Many simulation models are available depending on the purpose and task of the study


Types of Simulation Tools• Passenger timetable development (passenger)

• OpenTrack• Viriato

• Specify timetable and identify conflicts• RailSYS• RailEval

• Non-timetable (freight) and resolve conflicts with dispatching logic

• Rail Traffic Controller


Optimization Models• Identify required system settings to achieve an

optimal level of performance• Can become computationally complex for large

railway networks with multiple train types• Example applications

• Passenger timetable development• Station platform and track assignment• Rolling stock and crew cycles• Infrastructure investments for running time

improvement on shared corridors


Strategies to Increase Capacity

• Operations options: • Increase average speed• Reduce traffic peaking• Reduce the variability in speed• Reduce number of meets & passes• Increase length & weight of trains• Improved acceleration and braking• Scheduling

• Infrastructure options: • Add or lengthen passing sidings• Additional tracks• Add staging and terminal tracks• Add station platforms• Improve junction design• Grade separations


Passenger Scheduling Strategies• Fleeting

• Train Type: Reduce delays due to different train types operating on the same line

• Train Direction: Reduce delays on single tracks lines by reducing the meet delay

• Express and Skip-Stop scheduling• Decrease travel time by bypassing intermediate station

and terminals• Minimize conflicts with trains in the same direction


Incremental Capacity of Infrastructure Expansion

Volume (trains/day)

Del

ay (h

ours

)

directional running, DT

bidirectional running, DTST, siding every 21.4 miles

Kahn, Ata M. Railway Capacity Analysis and Related Methodology. Ottawa, 1979. Print.


But at what cost?• New passing siding

• $8 million and up

• Second main track• $1 million per mile for rail, ties

and ballast• $4-6 million per mile

depending on embankment, drainage and signals

• Bridges, grade separations and tunnels can quickly increase costs


Other Capacity Factors• Mainline capacity consumed by

• Local service to freight rail customers• Deadhead and repositioning moves• Passenger boarding delays • Locomotive and rolling stock failures• Track inspection• Track maintenance

• Difference between practical and engineering capacity


Rail Capacity Research Needs• Models that capture yard-mainline interaction• Predicting the impact of higher speed passenger

and freight trains on the same corridor• Creating new theoretical & parametric models


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Copyright Restrictions and DisclaimerPresentation Author

C. Tyler Dick, P.E.

Senior Railway research Engineer

University of Illinois at Urbana-Champaign

205 North Mathews Ave

Urbana IL 61801

217-300-2166

[email protected]

Department of Civil and Environmental Engineering

© apta and arema - 2015 2-d introduction to railway capacity c. tyler dick, p.e. university of...

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