An unpaired pickup and delivery vehicle routing problem with multi-visit

This paper studies an unpaired pickup and delivery vehicle routing problem allowing for multi-visit. The problem consists of two interacted decisions: the pairing of supply and demand and the vehicle routing. Given the complexity of the problem, a novel unified model is formulated to decouple the interactions between the two decisions. Based on the unified model, some valid inequalities are derived and a tabu search algorithm is proposed. The computational results show that the tabu search algorithm can provide high quality solutions to the problem under investigation and the closely related problem studied in Chen et al. (2014).