External Urban Truck Trips Based on Commodity Flows: A Model

A procedure is described for incorporating interregional (external) heavy-duty truck trips in a regional travel-demand forecasting model. The procedure was developed as part of a comprehensive truck modeling effort conducted by the Southern California Association of Governments. The procedure is based on commodity flow forecasts and economic input-output modeling techniques. County-level commodity flows are disaggregated to the transportation analysis zone level using employment data, land use data, and commercial facility data. Input-output models are used to determine the portion of each inbound commodity that goes to final demand by consumers and the use of each commodity by industry sectors. Commodity flows then are converted to truck trips using commodity-specific estimates of the portion of tonnage carried in each truck weight class and the average truck payload for each weight class. These estimates are developed using data from the federal Truck Inventory and Use Survey and some truck origin-destination surveys performed at cordon points around the region. The model produces a set of trip tables that can be assigned to the regional roadway network using standard assignment techniques.