The Intermodal Trailer Assignment Problem

The problem of optimally assigning highway trailers to railcar hitches in intermodal transportation is studied. An integer-linear programming formulation is constructed. The problem is formulated using set covering. The resulting formulation is very small, and possesses in practice a tight linear programming relaxation. This allows it to be solved effectively by a general purpose branch-and-bound code. This formulation also provided the basis for the development of a Greedy Randomized Adaptive Search Procedure (GRASP). This heuristic is observed to be extremely fast. Empirically, it finds the optimal solution to all of the problem instances furnished over a two year period by Consolidated Rail Corporation.