a hierarchical multimodal hub location model with maximum allowable delay (case study: iran)

in this study, a hierarchical hub location problem by considering different modes of transportation and maximum allowed delay is investigated. this study is done on iran’s express postal service with 2 days maximum delay in delivery considering ground and airport hubs. the problem is of the type of location and single allocation for collection, transfer and distribution of the shipments. all the hubs are of limited capacity and there is a penalty for violation of the maximum allowed delay. the strategic goal of the model is to determine the location of ground and airport hubs and the allocation of links to these hubs by which the delay is minimized and the total cost of the system is optimized. the model is linear mixed-integer programming. finally, a case study to implement the model in iran’s postal service is conducted, and a sensitivity analysis is done using gams software.