A METHODOLOGY FOR ESTIMATING DETAILED INTERAREA COMMODITY FREIGHT FLOWS FROM CENSUS OF TRANSPORTATION DATA

The most widely used data available on U.S. interarea commodity freight flows comes from the public use tapes of the Census of Transportation Commodity Transportation Survey. This data set provides data on flows of specific commodities between states, as well as major production and market areas. Unfortunately, the completeness of this data is limited by the statutory requirement that the Census Bureau not release data which might reveal information about the operations of individual firms. As a result of this non-disclosure requirement, data are withheld on shipments of a particular commodity group whenever there were only a few firms sampled which made shipments in that commodity group. Since there is no way to determine the volume of flow for each of these unreported commodity groups directly from the Census data, the data are inadequate for freight transportation planning studies conducted at a detailed commodity level. This report presents an algorithm which has been developed for estimating the volume of each unreported area to area flows among specific commodity groups in proportion to the flows of these commodity groups in nationally aggregated data. The algorithm has been programmed. A listing of the program and necessary documentation is included as an appendix.