Hybrid scheduling methods for the general routing problem

We study an extension to the general routing problem, which deals with integrating fixed route service with the general pick up and delivery problem to create a hybrid routing problem. The primary application for such a service is a dial-a-ride system used by transit agencies to transport disabled or elderly individuals. The main aim of the integration is to have higher productivity and/or less cost while not significantly reducing the customer service level. Due to the combinatorial nature of the problem, we propose a heuristic approach that provides an approximate solution, which is computationally efficient for solving large sized problems.; Our initial solution is first derived using an Insertion procedure. The solution of the Insertion procedure is fed into an Improvement procedure where we try to identify an alternative path for requests that have multiple hybrid paths that can satisfy the demand. The solution from the Improvement procedure is further improved by two system-wide strategies implemented by a Tabu Search technique, which are Re-sequencing (TABU-S) and Re-assigning (TABU-A).; We tested our heuristics on actual data from a transit agency. The most effective heuristic in terms of the trade-off between solution quality and computation time was TABU-S. The results of the recommended methodology showed that shifting some of the demand to a hybrid service route (18.6% of the requests) reduces the on-demand vehicle distance by 16.6% and the overall customer trip time by 8.7% over the manual schedule provided by the transit agency. However, for these customers who take the hybrid delivery method, their trip time will increase on average by 5.4%.; In addition to developing algorithms to improve the scheduling of a hybrid system, we also develop a model that aids decision-makers in designing a hybrid network. That is, we determine the optimal number of zones in an area where each zone is served by a number of on-demand vehicles which transfer passengers to a fixed route line if the destination is in a different zone or to its final destination if it is within the same zone.