Intermodal and international freight network modeling

The authors describe the development and application of a single, integrate d digital representation of a multimodal and transcontinental freight trans portation network. The network was constructed to support the simulation of some five million origin to destination freight shipments reported as part of the 1997 United States Commodity Flow Survey. The paper focuses on the routing of the tens of thousands of intermodal freight movements reported i n this survey. Routings involve different combinations of truck, rail and w ater transportation. Geographic information systems (GIS) technology was in valuable in the cost-effective construction and maintenance of this network and in the subsequent validation of mode sequences and route selections. H owever, computationally efficient routing of internodal freight shipments w as found to be most efficiently accomplished outside the GIS. Selection of appropriate intermodal routes required procedures for linking freight origi ns and destinations to the transportation network, procedures for modeling intermodal terminal transfers and inter-carrier interlining practices, and a procedure for generating multimodal impedance functions to reflect the re lative costs of alternative, survey reported mode sequences. (C) 2000 Elsev ier Science Ltd. All rights reserved.