Excluding gas pipelines, all modes of freight transportation, combined, generated nearly 4 trillion domestic ton-miles in 2000, 20 percent more than in 1990. This represents an average growth rate of almost 2 percent per year during the decade .
Domestic ton-miles for all modes, except water, grew during this decade (figure 7). On an average annual basis, air grew the fastest (5 percent per year), followed by rail and truck (4 percent each). Rail and truck accounted for the majority of domestic traffic, representing 39 percent and 30 percent of domestic ton-miles, respectively, in 2000 (figure 8). Truck data, however, do not include retail and government shipments and some imports and, therefore, understate total truck traffic.
Water transportation and oil pipelines1 accounted for 16 and 15 percent of domestic ton-miles, respectively, in 2000. Although domestic waterborne ton-miles decreased 23 percent between 1990 and 2000, waterborne vessels continued to play a prominent role in international trade [1, 2]. Ships transported 78 percent (by ton) of U.S. imports and exports in 2000.
Air freight tends to transport high value, relatively low weight goods. Thus, on a ton-miles basis, air freight accounted for less than 1 percent of domestic freight in 1998, whereas on a value basis, this mode accounted for 12 percent of domestic freight2.
Ton-miles is the primary physical measure of freight transportation output. A ton-mile is defined as one ton of freight shipped one mile and, therefore, reflects both the volume shipped (tons) and the distance shipped (miles). Ton-miles provides the best single measure of the physical volume of freight transportation services. This, in turn, reflects the overall level of activity in the economy.
1. U.S. Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 2002 (Washington DC: 2002), table 1-44, also available at http://www.bts.gov/.
2. _____, U.S. International Trade and Freight Transportation Trends (Washington, DC: 2003).
3. U.S. Department of Transportation, Federal Highway Administration, The Freight Story (Washington, DC: 2002).
1 The Bureau of Transportation Statistics developed data for gas pipelines in 2003 but not in time to include in this report.
2 The most recent year for which freight value basis data are available is 1998.