Exact and heuristic solution methods for time-constrained vehicle routing

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Time-constrained vehicle routing problems consist of determining least-cost vehicle routes to cover a set of tasks such that each task is executed within a predefined time window and vehicle capacity is respected for each route. Several problem variants exist, arising from different applications in freight transportation. In this proposal, we develop mathematical optimization models and methods to help the planners in determining the best possible vehicle routes. The optimization methods can be classified into two categories: an exact method seeks an optimal solution and can require substantial computational time; a heuristic method is much faster but provides a good-quality solution that may not be optimal. We explore three research directions for exact methods and one for heuristics. Furthermore, we develop optimization methods for two specific vehicle routing problems: the split delivery vehicle routing problem with time windows and synchronization constraints that allows multiple visits to each customer if they occur simultaneously; and the pickup and delivery vehicle routing problem with time windows and last-in, first-out constraints that consists of picking up merchandise at customers to deliver it at specific locations in the reverse order of the corresponding pickup operations. From a scientific point of view, the results of this research are rather methodological and will be applicable to a wide variety of vehicle routing problems in different mode of transportation and even to certain problems arising in other domains. From a commercial point of view, these results will help the freight companies to better manage the utilization of their vehicles and will therefore contribute to increase the productivity of Canadian companies. Finally, from an academic point of view, this research will provide financial support and training to three PhD students and two MSc students that will be in demand by the Canadian optimization software development companies after completing their studies.