Vehicle dispatching with time-dependent travel times

Most of the models for vehicle routing reported in the literature assume constant travel times. Clearly, ignoring the fact that the travel time between two locations does not depend only on the distance traveled, but on many other factors including the time of the day, affects the application of these models to real-world problems. In this paper, we present a model based on time-dependent travel speeds which satisfies the ‘first-in-first-out’ property. An experimental evaluation of the proposed model is performed in a static and a dynamic setting, using a parallel tabu search heuristic. It is shown that the time-dependent model provides substantial improvements over a model based on fixed travel times.