Integrated optimization and simulation models for the locomotive refueling system configuration problem

This paper introduces the locomotive refueling system configuration problem, which arises when railroad companies aim to improve efficiency in refueling yards through new technologies or policies. Refueling speed is important to freight railroad operational efficiency; faster refueling can increase rail network capacity without the infrastructure cost associated with new terminals or tracks. We propose a method that integrates integer programming and discrete event simulation to inform these decisions, and we demonstrate the method on data derived from industry. Specifically, the models determine the best location (denoted the "strike line") to align trains at the refueling platform and measure the impact on refueling yard throughput associated with adopting the optimal strike lines in combination with new refueling equipment. Results using realistic parameters demonstrate a statistically significant improvement over intuitive policies.