Optimization on Railway Empty Wagon Allocation Based on Robust Connecting Time

Empty wagon allocation is the key link in railway transportation. The scheme of empty wagon allocation should have robustness to avoid the influence of uncertain factors. Based on the fixed technical operation time of stations and travel time between stations, the connection time relationships between arrival and departure trainsin supply stations, and between departure trainsin supply stations and in demand stations are identified. To maximize the revenue of empty wagon allocation, an empty wagon allocation model involving vehicle type substitution is established. On this basis, the fluctuation rate is introduced to describe the uncertainty due to the technical operation time of stations and travel time between stations, and the lower limit of fluctuation is set to adjust the model robustness. A robust optimization model is established for empty wagon allocation under uncertain conditions. Combined with model properties, a fast algorithm for solving the robust optimization model is designed in terms of the change of traffic flow relationship, and the nonlinear problem is transformed into a robust equivalent model that is easy to solve. The results show the empty wagon allocation scheme can accurately obtain the empty wagon flow and vehicle type substitution, and the fluctuation rate and lower limit of uncertain factors affect the revenue of the scheme. Under absolute robustness, compared with the certain model, the revenue of the scheme is decreased by 16.2%, 12.1% and 28.1%, respectively, due to the uncertain factors, including the travel time between stations, technical operation time of supply stations and technical operation time of demand stations.