Section: New Results

Vehicle routing for dial-a-ride problems

Static and deterministic vehicle routing problems cannot be used in many real-life systems, as input data are not reliable and revealed over time. In [11] , we study a pickup and delivery problem with time windows accounting for maximum ride time constraints – the so-called dial-a-ride problem – in its static and dynamic variant, and we make specific proposal on robust optimization models for this problem. To solve the static model, we develop a branch-and-price approach that handles ride time constraints in the process of generating feasible vehicle routes in the course of the optimization procedure. The work is focussed on the pricing problem solver and acceleration techniques for the branch-and-price approach. Our numerical results show that the method is competitive compared to existing approaches that are based on branch-and-cut. In the dynamic context, where some input data are revealed or modified over time, we apply our branch-and-price algorithm for re-optimization in a rolling horizon approach.