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?