On different formulations for the multi-period vehicle routing problem with simultaneous pickup and delivery

In this paper, we extend the vehicle routing problem with simultaneous pickup and delivery (VRPSPD) with a consideration of multiple planning horizons. We propose three alternative mathematical formulations for Periodic-VRPSPD (P-VRPSPD) based on the available formulations for VRPSPD in the literatures, namely the three-index commodity flow formulation, four-index commodity flow formulation, and three-index vehicle flow formulation. We perform comparison analysis by conducting extensive numerical experiments on a set of instances with various complexities in order to evaluate the performance of these formulations. Overall, it is observed that the three-index commodity flow formulation returns the best results.