Integrated scheduling and assignment of trucks at unit-load cross-dock terminals with mixed service mode dock doors

Scheduling trucks and assigning them to dock doors are two major operational decisions at cross-dock facilities. Including flexibility by operating (part of) the dock doors in a mixed service mode is known to make cross-dock operations more efficient (i.e., when both inbound and outbound trucks can be processed at these mixed-mode doors). However, the literature and practice often consider the truck scheduling and dock-door assignment problem sequentially, or only for either inbound or outbound operations. When combined with mixed-mode dock doors, such a sequential approach results in suboptimal or even infeasible solutions. In this paper, we study an integrated approach to solve the two problems simultaneously for cross-dock terminals where dock doors can operate in a mixed service mode. We propose an adaptive large neighborhood search algorithm to solve the integrated problem and find good solutions within a reasonable amount of computational effort. Extensive computational experiments demonstrate that the operational costs at a cross-dock terminal reduce on average 12% compared to the best solution with a sequential approach (and even 20–30% compared to the results of the metaheuristics from the literature). Moreover, with the integrated approach, we study what percentage of dock doors to operate in a mixed service mode and where to position these flexible doors in U-shaped cross-dock terminals. Numerical results indicate an average cost savings of 9.7% when 60% of the dock doors are used flexibly, and the savings increase to 12.3% when these doors are centrally located in the cross-dock facility.