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

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 proposed approach has been to operate passenger trains on existing freight railroad infrastructure. However, operation of passenger and freight trains on the same infrastructure poses a variety of challenges because of their different performance characteristics. In addition, track configuration—single versus double track—can significantly influence the interaction effects between trains. The maximum speed of passenger trains has little impact on the performance of freight trains on single-track lines. However, in double-track configurations, the speed of the passenger train has a major impact on freight train delays. Single-track operation can show an asymmetrical delay distribution centered on an average run time, with very few trains arriving close to the minimum run time. A double-track configuration can result in a delay distribution shaped similarly to an exponential distribution with many trains maintaining their minimum run times. In both single- and double-track operations, a higher passenger train maximum speed can lead to a greater range of possible travel times. These analyses can help transportation authorities further understand the interactions between passenger and freight trains for current and future shared-corridor operations.