Combination trucks, commonly referred to as tractor-trailers, averaged 63,374 miles in 2018, which is more than five times farther than the 11,687 average miles traveled by single-unit trucks. The annual miles for both single-unit trucks and combination trucks increased about 60% from 1970 to 2018, and the ratio of annual miles between single-unit trucks and combination trucks has remained nearly the same.
Note: Data for 2018 are the latest available. Single-unit trucks are defined as trucks with two axles and six tires or more.
Source: U.S. Department of Transportation, Federal Highway Administration, Highway Statistics 2018, Washington, DC, 2020, Table VM-1.