Xxx. Integrate Vehicle Routing and Truck Sequencing in Cross-docking Operations

Cross-docking is a an important logistics strategy in which freight is unloaded from inbound vehicles and directly loaded into outbound vehicles, with little or no storage in between. This study considers a crossdocking system which combines the vehicle routing problem with crossdocking (VRPCD) for both inbound and outbound operations and truck sequencing problem at docks. The objective is to minimize the logistics center operation costs and transportation costs. We first formulated the integrated problem with a mixed integer programming model. Since VRPCD and sequencing problems are NP-hard, the integrated problem is also an NP-hard problem. We propose an ant colony optimization (ACO) algorithm to solve the VRPCD and sequencing problem by two independent ant colonies sequentially. The proposed ACO is tested with 15 randomly generated instances. The results show that ACO can obtain the optimal solutions in small size instances. We believe the proposed ACO algorithms can be used for practical use for the cross-docking system.