© apta and arema - 2015 2-d introduction to railway capacity c. tyler dick, p.e. university of...
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© APTA and AREMA - 2015
2-DIntroduction to Railway
CapacityC. Tyler Dick, P.E.
University of Illinoisat Urbana-Champaign
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Outline• Introduction• Basic Rail Capacity Concepts• Analytical Models of Railway Capacity• Parametric Models• Simulation Models• Optimization Models• Other Considerations and Expansion Strategies
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Fields Related to Capacity• Analytics• Data mining• Network optimization• Queuing theory• Regression modeling• Risk modeling• Simulation• Utility models
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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
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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.
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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
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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
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Levels of Capacity Analysis• Transportation Network
• Railroad Network• Subdivision or Line• Yards & Terminals• Stations & Platforms• Interlockings & Junctions
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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
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What Should Capacity Measure?
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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
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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
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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.
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Different Traffic and Track Configurations will Change Delay-Volume Relationship
Acceptable Delay
Volume (Trains/Day)
Del
ay (m
ins)
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Track Configuration
• Number of tracks• Siding length• Siding spacing
(distance & time)• Crossover spacing
• Single crossovers• Universal crossovers• Parallel crossovers
• Geometry• Grade• Curvature
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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)
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Blocking Time Model• Single
direction on double track
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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)
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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
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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
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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
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Meets on Single Track
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Meets on Single Track
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Meets on Single Track
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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
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Calculation MethodologySiding A Siding B
Time t
Time 0
Time t+m
Time 2t+m+t/2
Time t+m+t/2
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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
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Overtakes on Single TrackTi
me
T2
Pass Delay
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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
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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
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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.
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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
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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
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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
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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
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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
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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.
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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
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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
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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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It is the author’s intention that the information contained in this file be used for non-commercial, educational purposes with as few restrictions as possible. However, there are some necessary constraints on its use as described below.
The materials used in this file have come from a variety of sources and have been assembled here for personal use by the author for educational purposes. The copyright for some of the images and graphics used in this presentation may be held by others. Users may not change or delete any author attribution, copyright notice, trademark or other legend. Users of this material may not further reproduce this material without permission from the copyright owner. It is the responsibility of the user to obtain such permissions as necessary. You may not, without prior consent from the copyright owner, modify, copy, publish, display, transmit, adapt or in any way exploit the content of this file. Additional restrictions may apply to specific images or graphics as indicated herein.
The contents of this file are provided on an "as is" basis and without warranties of any kind, either express or implied. The author makes no warranties or representations, including any warranties of title, noninfringement of copyright or other rights, nor does the author make any warranties or representation regarding the correctness, accuracy or reliability of the content or other material in the file.
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
ctdick@illinois.edu
Department of Civil and Environmental Engineering
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