A parallel two-phase metaheuristic for routing problems with time windows

This paper describes the parallelization of a two-phase metaheuristic for the vehicle routing problem with time windows and a central depot (VRPTW). The underlying objective function combines the minimization of the number of vehicles in the first search phase of the metaheuristic and the minimization of the total travel distance in the second search phase. The parallelization of the metaheuristic is based on the concept of cooperative autonomy, i.e., several autonomous two-phase metaheuristics cooperate through the exchange of solutions. The parallelized two-phase metaheuristic was subjected a comparative test on the basis of 356 problems from the literature with sizes varying from 100 to 1000 customers. The derived results seem to justify the proposed parallelization concept.