Multi-trip vehicle routing and scheduling problems

This research is inspired by a variety of transportation industries' problem of letting vehicles make more than one trip each day to effectively use their resources. This study defines the problem as the multi-trip vehicle routing and scheduling problem (MTVRSP). The objectives of the MTVRSP are to minimize first the number of vehicles and then the total travel time by allowing vehicles to make multiple trips during a planning period, while satisfying not only the constraints to the basic vehicle routing problem but also delivery time windows. Despite its practical importance, there exist very few the MTVRSP-related studies in the literature. The MTVRSP is NP-hard; therefore, the objectives of this research are to first model the problem and then develop an efficient and effective heuristic solution algorithm to the problem. Empirical testing is used to evaluate the effectiveness of the solution algorithm.