Accurately measuring the magnitude of freight movement is a challenge. No single data source provides complete and timely information on all freight transportation modes for all goods and sectors of the economy. The most comprehensive national picture of freight movement comes from the Commodity Flow Survey (CFS) produced most recently in 1993, 1997, and 2002 by the Bureau of Transportation Statistics (BTS) and the U.S. Census Bureau. As a shipper-based survey, the CFS collects information on how U.S. establishments transport raw materials and finished goods; the types of commodities shipped by mode of transportation; the value, weight, origin, and destination of shipments; and the distance shipped. (By contrast, a carrier-based survey would provide information on shipment route, cost, and time of travel.)
Despite the comprehensive nature of the CFS, important data gaps exist in its coverage of certain industries and commodities and in the domestic movement of imports. BTS estimated that the 2002 CFS covered about 81 percent of the shipment value, 73 percent of the tonnage, and 71 percent of the ton-miles of total U.S. freight movements. To improve the data, BTS made supplemental estimates for farm shipments to processing plants, crude petroleum pipeline shipments, waterborne imports and exports, and imports by surface and air. These supplemental estimates were made for the 1993, 1997, and 2002 CFS. For the 2002 CFS, BTS also filled gaps in shipments of logs and lumber.
Some major differences arise when CFS totals are compared with the supplemental data, especially in relative modal combinations, average shipment distance, and commodity mix. For example, CFS shipments were valued at $733 per ton compared with $470 per ton of shipments in the supplemental data, which has a lower value because it provides better coverage of crude oil and petroleum products. A ton of CFS shipments, on average, traveled about 270 miles, slightly less than the approximate 300 miles for the shipments in the supplemental data, in part because CFS includes large bulk shipments (e.g., sand and gravel), which are mostly local shipments.