CE 515 Railroad Engineering
CapacitySource: REES Module 6 & An Enhanced Parametric Railway
Capacity Evaluation Toolhttp://ict.illinois.edu/railroad/CEE/pdf/2009%20Papers/Lai%20&%20Barkan%20TRB09-1161-
Final.pdf
“Transportation exists to conquer space and time -”
Factors Affecting Capacity• Infrastructure factors:
– Meet & Pass Planning Point Spacing (MPPPS)– Signal Spacing (SS)– Percent Double Track (% DT)
• Traffic and operating factors: – Traffic Peaking Factor (TPF)– Priority Probability (PP)– Speed Ratio (SR)– Average Speed (AS)– Track Outages (TOs)– Temporary Slow Orders (TSOs)
– The average spacing of locations used to meet or overtake trains, namely siding spacing.
– Locations: bi-directional, mixed priority & different speed trains
– MPPPS for a subdivision is computed as:
• Meet & Pass Planning Point Spacing (MPPPS)
Infrastructure Factors
• Signal spacing (SS)
Infrastructure Factors
http://www.m-a.org.uk/what_use/MathematicsAndRailwaySignalling.doc.
• Percent Double Track (% DT)– Double or multiple track segments have a significant
impact on a track’s ability to move trains– Line capacity rises quickly with properly spaced sections
of double track– Allow for running meets & more than one train in a
segment
– %DT is calculated as the ratio of double track vs. the length of the subdivision
Infrastructure factors
Single Track Bi-directional Running
REES Module 6
Meet delay
Double Track Directional Running
REES Module 6
Bi-directional Running Reduces Capacity
REES Module 6
Directional Running After Merger
REES Module 6
• Traffic Peaking Factor (TPF)– The concentration of traffic within a short time frame (4
hours), often called bunching or peaking– Significant impact on capacity
– Result in traffic levels higher than the subdivision could reliably sustain
– When this occurs the effects are felt for a considerable time into the future as the system recovers from the overload
– TPF is calculated as the ratio between the maximum number of trains dispatched in a 4-hour period vs. the average number of trains for that time length
Traffic Factors
• Traffic Peaking Factor(TPF)– Evaluate the amount of traffic on the entire length of the
subdivision at one time– Designed to be non-directional & include trains in both
directions– Account for the interaction between opposing trains and
the conflict involving overtaking trains
Traffic Peaking Factors Cont.
• Priority Probability (PP)– Dictate which trains will experience delay– Train priorities decrease capacity
– Priority trains are given preferential treatment over lower priority trains, which result in increased delays
– The greater the number of priority classes, the less capacity is available
Traffic Factors
REES Module 6
• Speed Ratio (SR)– Besides PP, speed ratio is another parameter reflecting
the traffic mix over the subdivision
– The speed differential between trains can increase delay on a subdivision by generating overtakes and holding trains in yards to avoid overtaking on line
Traffic Factors
• Average Speed(AS)– A significant parameter affecting capacity is average
train speed– The higher the train speed the lower the delay and
transit time
Traffic Factors
REES Module 6
• Operations options: – Increase average speed– Reduce traffic peaking– Reduce the variability in speed– Reduce number of meets & passes
• Infrastructure options: – Line (links):
– Reduce traffic control block length– Add or lengthen passing sidings– Additional tracks
– Junctions (nodes): – Improve junction design– Grade separation
Options to increase line capacity
REES Module 6
Operations options should generally be considered first because they are typically less expensive and faster to implement than new infrastructure
Questions?