Advanced train control systems enabling single-person crews or driverless trains promise to significantly reduce the fixed costs of operating a train, removing a strong incentive for longer trains. For carload freight traffic, operating a given number of railcars in shorter trains enables railroads to improve service quality and revenue through increased train frequencies or more direct trains bypassing intermediate classification yards. However, operating shorter trains increases the total number of trains on existing rail corridors, exacerbating congestion and decreasing network fluidity. Rail Traffic Controller simulation software is used to quantify the potential mainline delay impacts and relative capacity consumption of shorter trains. Different combinations of train length and train type heterogeneity are tested on representative single-track freight corridors. Results indicate that train control systems with moving blocks can mitigate some of the mainline delay impacts of shorter trains, particularly at a high traffic volume, with a mix of train types and a greater proportion of railcars traveling on short trains. Mid-siding crossovers can further boost the effectiveness of moving blocks in managing complex train conflicts caused by train type heterogeneity. Simulation results are used to perform an example railcar transit time estimation illustrating the trade-off between yard connection time benefits and mainline delay disbenefits, and the thresholds at which different operating strategies produce a net transit time benefit. Understanding the mainline delay impacts of shorter trains can assist railroad practitioners formulating long-term capital investment plans, developing future operating strategies, and improving service quality and market share through a short train philosophy.

In response to multiple derailments involving hazmat trains, in early February 2020 Transport Canada released ministerial order (MO) 20-02, imposing speed restrictions of 20 to 25 mph on trains transporting a sufficient quantity of hazardous material. Since much of the North American freight network is used by multiple train types, the extreme speed heterogeneity created by this mandate substantially reduced train performance. Although this order was replaced within 2 weeks by new speed restrictions that were in turn replaced in May, MO 20-02 introduced the most extreme levels of train speed heterogeneity. The research team investigated the corresponding capacity effects to better understand the effects of train speed heterogeneity at low speed and inform agencies on future speed restrictions in this range. Using Rail Traffic Controller and General Train Movement Simulator, we quantitatively investigated the capacity loss from these speed restrictions and found that MO 20-02 can double or triple average train delay and lead to mainline capacity loss in excess of 60% on a representative single-track mainline.