CE 515 Railroad Engineering Capacity Source: REES Module 6 & An Enhanced Parametric Railway Capacity Evaluation Tool http://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 tracks 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
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