Performance Evaluation of Two Conceptual Designs for Rail Service to Transbay Terminal Bi-Directional Unidirectional Bi-Directional R. Shiloh AREMA CONFERENCE Tuesday, September 12, Unidirectional Simulation Objectives Examine performance of two different conceptual designs for station approaches. See if either alternative had a fatal flaw on operations Determine if other desirable operational goals could be met. Memory schedules Use of same platform for same train Simulation Objectives (cont d) Determine relative utilization for an initial Strawman schedule. Use of stochastic approach vs. static to improve results. Methodology Arrivals modeled based on a distribution according to train type. Amtrak 9% within 8 minutes. Commuters 95% within 3 minutes.
Reflects real life variances in rail operations where: Trains can arrive early, due to good over the road performance, and there is a pad designed in the schedule. Trains must unload, board passengers, and be serviced. Intercity trains take longer because of baggage, etc. Train performance over the road is subject to many variables: other trains passenger loads dispatching mechanical performance weather infrastructure performance human performance Station is considered as a series of processes Getting trains to station tracks Moving through interlocking Station track availability Dwell times at tracks Passenger unloading and boarding Service Crew changes Departing Moving through interlocking Other trains on lines Key Assumptions Arrival distribution by train type Maximum speed 15 mph because of curvature and turnouts Following headways at 2. minutes Headways of 1. min. for arrivals at station track behind departures Key Assumptions (cont d) Minimum dwell times Amtrak - 15 minutes Commuter - 8 minutes Tripper - 5 minutes cars per train
Key Assumptions (cont d) Used peak cycle of 76 minutes (15 arriving and 15 departing trains) assuming symmetric A.M. and P.M. rush. No storage of equipment at station Arriving and departing train follow FIFO policy (no artificial outside priorities). 4 Amtrak Trains Arrival Distribution from Schedule at Approach Signal 1 35-4 - -2-2 - - 2 2-4 4-6 6-8 8-16 Minutes from Schedule 15 8 11 Tripper Trains Arrival Distribution from Schedule at Approach Signal Commuter Trains Arrival Distribution from Schedule at Approach Signal 25 15 5 25 5 5 5-1 - -.5 -.5 - -.5.5-1 1-2 2-4 4-6 Minutes from Schedule 5 4 45 3 1 1-1 - - 1 1-2 2-3 3-4 4-5 6 - Minutes from schedule Findings Findings (cont d) Both configurations work - no fatal flaws (station design does not worsen On Time Performance Bi-directional slightly superior account fewer delays at entrance interlocking. Arrival delays in less than 2. min. Bi-directional - 9% of trains Unidirectional - 84% of trains Departure delays in less than 2. min. Bi-directional - 98% Unidirectional - 94% Measures subtle differences (trade off between waiting for an interlocking and waiting for track in station)
Findings (cont d) Other operational considerations Can achieve memory schedule but may occasionally trade off other performance parameters. Can achieve putting same train on same track, but will have to accept use of up to two tracks for a particular service. This will impact on platform design. Findings (cont d) Utilization, based on platform occupancy is: Unidirectional - 5% Bi-directional - 54% (%) of Trains % 9% 8% 7% 6% 5% 4% % % % % 75% Arrival Delay Distribution at Approach Signal & Station Track for Unidirectional & Bi-Directional Terminals 9% 84% 13% 8% 4% Arrival Distribution at approach signal (same for both) Unidirectional Terminalarrival at station track Bi-directional Terminalarrival at station track 6% 3% 1% 1% % 1% 4% 5% 3% <=2 2-4 4-6 6-8 > 8 Delay Range in Minutes (%) of Trains 1% % 8% 6% 4% % % Departure Delay Distribution from Station Track for Unidirectional & Bi-Directional Terminals 94% 98% Unidirectional Terminaldeparture from station track Bi-directional Terminaldeparture from station track 2% 3% % 1% 2% % % % <=2 2-4 4-6 6-8 > 8 Delay Range in Minutes Recommendations Recommendations (cont d) Changes in conceptual designs should be reviewed with respect to system performance. Designers should avoid features requiring trains to cross paths at grade May want to check performance at slightly higher volumes May want to check performance at a wider (standard deviation) arrival distribution
Conclusions Conceptual designs can be modeled to highlight even subtle differences. Major changes in conceptual design needs to be reviewed. Modeling reveals potential for trade offs in line schedules versus total performance Conclusions (cont d) Relative performance of a gives design versus another will vary with schedule constraints imposed. (% change in volume may react in a disproportionate change in total performance.)