Influence of mainline schedule flexibility and volume variability on railway classification yard performance

Abstract

Single-railcar shipments of freight transported by multiple freight trains and sorted at several classification (marshalling) yards between origin and destination remain an important source of traffic and revenue for North American railways. To aid railroads in making business decisions regarding train operating plans and efficient use of yard capacity, this research investigates the influence of inbound traffic volume variation and schedule flexibility on classification yard performance. Simulation experiments using YardSYM, a discrete-event simulation model developed for hump classification yard analysis, quantify the interaction of these factors through different yard performance metrics. Simulation results suggest increasing schedule flexibility causes classification yard performance to decline while increasing volume variability has a less pronounced effect. For the simulated yard, the combined effect of train arrival time and volume variability increased average railcar dwell by over 3 h, and reduced railcar connections achieved by ten percent. Bunching train departures increased dwell by nearly 2 h and cut on-time train originations in half. To better understand the implications for network performance, additional analysis of the propagation of schedule flexibility and volume variation through classification yards demonstrates how schedule flexibility is amplified and dampened to medium values related to the consistency of the train assembly process.