Path Optimization Model for Intra-City Express Delivery in Combination with Subway System and Ground Transportation

Combined conventional ground transport with a subway system for line-haul transport for intra-city express delivery is a new transportation mode. Subway transportation can be used in the line-haul transportation of intra-city express delivery services to reduce cost, improve efficiency, raise customer satisfaction, and alleviate road congestion and air pollution. To achieve this, we developed a path optimization model (POM) with time windows for intra-city express delivery, which makes use of the subway system. Our model integrated the subway system with ground transportation in order to minimize the total delivery time. It considered the time window requirements of the senders and the recipients, and was constrained by the frequency of trains on the subway line. To solve the POM, we designed a genetic algorithm. The model was tested in a case study of a courier company in Shanghai, China. Meanwhile, based on the basic scenario, the corresponding solutions of the four different scenarios of the model are carried out. Then, we further analyzed the influence of the number of vehicles, the frequency of trains on the subway line, and the client delivery time window on the total delivery time, client time window satisfaction, and courier company costs based on the basic scenario. The results demonstrated that the total delivery time and the total time outside the time window decreased as the number of vehicles increased; the total delivery time and the total time outside the time window decreased as the delivery frequency along the subway line increased; the total delivery time and the total time outside the time window decreased as the sender's time window increased. However, when the sender's time window increased beyond a certain threshold, the total delivery time and the total time outside the time window no longer decreased greatly. The case study results can guide courier companies in path optimization for intra-city express delivery vehicles in combination with the subway network.