Large combination trucks1 represent a small portion of traffic on the U.S. Interstate Highway System . Because they are heavier, they may cause more pavement damage, a measurement that is estimated in terms of vehicle loadings (box 4-A). In urban areas, these trucks made up only 6 percent of traffic volume, but accounted for 77 percent of loadings in 2002 (figure 4-2). These trucks also make up a greater portion of the vehicles on rural segments of the Interstate Highway System, representing 18 percent of traffic volume and 89 percent of loadings in 2002 (figure 4-3).
Between 1992 and 2002, large combination truck traffic volume grew from 16 percent to 18 percent on rural roads, while declining from 7 percent to 6 percent on urban Interstate highways. Concurrently, their share of loadings decreased on both rural and 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 traffic volume but a growing portion (from 1 percent to 3 percent) of loadings in urban areas .
1. U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 2002, table TC-3, available at http://www.fhwa.dot.gov/policy/ohim/hs02/pdf/tc3.pdf, as of February 2004.
1 Large combination trucks weigh more than 12 tons and have 5 or more axles.