Large combination trucks1 made up only 5 percent of traffic volume in urban areas, but accounted for 76 percent of loadings in 2003 (figure 13-3). On rural segments of the Interstate Highway System, these trucks represented 14 percent of traffic volume and 83 percent of loadings in 2003 (figure 13-4). As the heaviest category of highway vehicles, large combination trucks may cause more pavement damage, a measurement that is estimated in terms of vehicle loadings (box 13-A).
Between 1993 and 2003, large combination truck traffic volume declined from 18 percent to 14 percent on rural Interstate highways and also declined from 6 percent to 5 percent on urban Interstates. Concurrently, their share of loadings decreased on rural roads and increased on urban Interstate highways. Passenger cars, buses, and light trucks, which the Federal Highway Administration aggregates into one category, followed a different trend-representing an unchanged percentage of loadings but a growing portion (from 90 percent to 91 percent) of traffic volume in urban areas .
1. U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 2003 (Washington, DC: 2004), table TC-3.
1 Large combination trucks weigh more than 12 tons and have 5 or more axles.