Optimizing goods assignment and the vehicle routing problem with time-dependent travel speeds

Many mathematical models have been presented for the vehicle routing problem (VRP) in research papers. Most of them assume that the travel speeds are constant, and ignore the fact that travel speeds can change throughout the day. In this research, based on time-dependent travel speeds, an optimization method is proposed for solving goods assignment and vehicle routing problems. Moreover, in the optimization method, the travel time calculation satisfies the ‘‘non-passing” property, which is ignored in most research papers. A real case of a 3C warehousing company and a larger simulated problem are introduced to illustrate the proposed method. The results show that the proposed method is efficient and effective in solving problems.