Comparison of Capacity of Single- and Double-Track Rail Lines

Abstract

Single-track line capacity is limited by the need for trains to decelerate, stop, and accelerate out of sidings to allow other trains to use the intermediate single-track sections. Meeting at these sidings is the largest cause of train-interference delays on single tracks (3). Doubletrack configurations largely eliminate this dynamic and allow the line to operate at a significantly higher capacity. Because of these inherent efficiencies, double-track lines can run more trains at higher average speeds than a single-track configuration. In the absence of meetings, passing conflicts and train spacing become key capacity constraints for a double-track line.For both single-and double-track configurations, previous research has determined that simultaneous operation of different train types consumes more capacity than homogeneous operations. Vromans et al. used simulation to investigate options to improve passenger operations (4). Leilich and Dingler et al. used simulation analysis to determine the delay caused by the interaction of unit trains and intermodal trains and found a capacity loss due to heterogeneous operations (5,6). Harrod used integer programming to show that it can be feasible to run higher-speed trains in a single-track freight network provided there is a lane available (7). Petersen and Taylor used simulation analysis of where to locate sidings in single track to accommodate higher-speed trains (8). Sogin et al. used simulation analyses to show that there is a larger increase in delay to freight trains by adding a passenger train instead of a freight train in both single-(9) and double-track networks (10). METHODOLOGYFour key factors (Table 1) were considered in the simulation experiments. The different permutations of Table 1 can represent various shared-corridor conditions. Traffic volume is defined as the total number of trains per day (TPD). Traffic mixture (heterogeneity) is the percentage of these that are freight trains and describes the traintype heterogeneity of the corridor. The parameters of total TPD and percent freight are also described interchangeably by number of passenger trains and number of freight trains per day. The subsequent analyses use both pairs of parameters. The maximum speed of the passenger train was analyzed at 79 and 110 mph with intermediate speeds used in a correlation analysis. The fourth factor was the number of main tracks on the line.The full factorial of Table 1 was simulated. Each simulation run featured a unique combination of the four factors described in Table 1. RTC was used to simulate a dispatcher making decisions regarding the train movements across a particular line. RTC is commonly used by railroad capacity planners in North America to simulate train traffic. Each simulation outputs the performance of trains over a 3-day period. This simulation was then repeated four times Federal, state, and regional transportation authorities have shown an increased interest in adding or increasing passenger rail service between many city pairs. The most commonly prop...

Transitioning from flexible to structured heavy haul operations to expand the capacity of single-track shared corridors in North America

“…Subsequent heterogeneity research included randomized train departures but did not include schedule flexibility as a factor in the experimental design. 15,16…”

Relative train length and the infrastructure required to mitigate delays from operating combinations of normal and over-length freight trains on single-track railway lines in North America

“…Related research conducted by the coauthors and colleagues have examined the overall distribution of train delay under various North American single-track operating conditions. 24–26 Differences in average train delay by train type will be considered in “Relative delay to short and long trains” section.…”

Comparison of Passenger Rail Energy Consumption with Competing Modes

“…As incremental higher-speed rail projects are completed and train speeds increase to 90 and 110 miles per hour (mph), the efficiency of passenger trains in these corridors will be affected as additional energy is required to overcome aerodynamic drag. Research has shown that on shared corridors, as the speed differential between passenger and freight traffic increases, both passenger train delay and run time variability also increase on both single-track and double-track lines (Sogin et al 2011, Sogin et al 2013. Increased delay and variability in run time can result in extended schedules to maintain reliability, which comes at the expense of increased idle time and less-efficient operations.…”