Rolling stock scheduling with maintenance requirements at the Chinese High-Speed Railway

Efficient rolling stock schedules have always been the focus of railway companies. At the Chinese High-Speed Railway, rolling stock scheduling is usually done manually by dispatchers. Such an approach often makes it difficult to quickly obtain an optimal rolling stock schedule that can be used to operate the proposed timetable and which is also feasible with respect to the rolling stock maintenance requirements. In this paper, we consider the problem of rolling stock scheduling with maintenance requirements and propose a heuristic approach that decomposes the problem into two main stages. In the first stage, the maintenance restrictions are ignored and a conventional Mixed Integer Programming model is used to generate multiple candidate rolling stock schedules. In the second stage, we check to see whether any of the candidate rolling stock schedules are feasible when maintenance restrictions for the individual rolling stock units are also considered. Checking a candidate rolling stock schedule can be performed using an assignment problem. To provide some structure to the search, candidate rolling stock schedules generated in the first stage are sorted in descending order according to their objective values. The two stages can be iteratively performed to avoid generating all schedules in the first stage before proceeding to the second stage. We analyze the performance of the proposed approach on real-life instances provided by the Chinese High-Speed Railway. These instances focus on the railway network within the Zhengzhou Group, which is one of the busiest transportation networks in China. Comparisons with the manual approach that is currently used in practice show that the proposed approach yields far superior schedules. The optimized schedules improve rolling stock efficiency and lead to a reduction in operating cost of approximately 10.5%.