Each record also contained information on the type of commodity moved, its weight, dollar value and whether containerized or a hazardous material. Export shipments were also identified on the records, along with data on U. S. port of exit and foreign destination city and country. In this manner many shipmentspecific data problems encountered by ORNL in their routing procedures were reported back to census in a timely fashion, allowing census to call back some shippers and thereby confirm, correct, or recover missing or otherwise unusable data. The ORNL system computed mileages, by mode, for all single modes and for any reported multimodal sequence. Mileages between origin- destination ZIP Code centroids were computed by finding the minimum impedance path over mathematical representations of the highway, rail, waterway, air, and pipeline networks and then summing the lengths of individual links on these paths.
Impedance is computed as a weighted combination of distance, time, and cost factors.
The ORNL multimodal network database is composed of individual modal- specific networks representing each of the major transportation modes highway, rail, waterway, air, and pipeline. The links of these specific modal networks are the representation of line- haul transportation facilities. The nodes represent intersections and interchanges, and the access points to the transportation network. To simulate local access, test links are created from each five- digit ZIP Code centroid to nearby nodes on the network. For the truck network, local access is assumed to exist everywhere.