HEURISTIC ALGORITHMS FOR THE HANDICAPPED PERSONS TRANSPORTATION PROBLEM

We examine the problem of determining an optimal schedule for a fleet of vehicles used to transport handicapped persons in an urban area. Th e problem is a generalization of the well-known advance-request Pickup and Delivery Problem with Time Windows. Due to the high level of serv ice required by this kind of transport, several additional operational constraints must be considered. The problem is NP-hard in the strong sense, and exact approaches for the solution of real-life problems (ty pically with hundreds of users to be transported) are not practicable. We describe a fast and effective parallel insertion heuristic algorit hm which is able to determine good solutions for real-world instances of the problem in a fete seconds on a personal computer. We also prese nt a Tabu Thresholding procedure which can be used to improve the star ting solution obtained by the insertion algorithm. The application of the proposed procedures to a set of real-life instances for the city o f Bologna, involving about 300 trips each, is also discussed. The heur istic algorithms obtain very good results compared with the hand-made schedules, both in terms of service quality (all the service requireme nts are met) and overall cost.