Minimizing Trailer-on-Flat-Car Costs: A Network Optimization Model

This paper discusses the mathematical and computational underpinnings of an optimization model that reduces United Parcel Service, Inc.'s trailer-on-flat-car (TOFC) usage costs by $4 million per year. It includes an informal statement of the TOFC problem, an integer linear program (ILP) formulation, and a transformation of this ILP into a pure minimum cost network flow program, whose software implementation provides the TOFC planner with a rich set of practical features.