Optimizing inbound and outbound door assignments in less-than-truckload crossdocks

This study is concerned with inbound and outbound trailer-to-door assignments in crossdocks, which are used by many transportation companies as a redistribution point. A Simulated Annealing (SA)-based heuristic procedure to determine the door assignments in order to minimize the overall material handling workload in a rectangular crossdock is presented. The SA heuristic addresses congestion concerns as well as robustness concerns in a worst-case sense. Using internally generated data, and square versus narrow shapes, the SA heuristic is evaluated against optimal solutions (with up to 20 doors) and solutions obtained from a pairwise exchange, steepest-descent procedure (with up to 96 doors). The SA heuristic performs well in all problems tested. A linear mixed-integer program formulation for the general rectilinear-quadratic assignment problem is also presented. Lastly, the SA heuristic is applied at a 118-door crossdock operated by Con-way. The door assignment obtained with the SA heuristic outperforms the current door assignment by approximately 35% on data sets provided by Con-way.