In 1903 the Automobile Club of America staged the first U.S. commercial vehicle contest to test the economy, reliability, durability, speed, and carrying capacity of the truck. At the time, the truck was the newest mode of hauling freight. Stimulated by results of the contest, the use of motor trucks flourished. More than 4,000 trucks were in use in the United States by 1908.

By the beginning of World War I in 1914, more than 300,000 trucks were in use; by the end of the war, more than a million trucks were being used. The first kind of modern trailer used was the full trailer, defined as a towed trailer. Its entire weight rests on its own axles. The semitrailer, whose front end rests on the rear of the hauling truck tractor, gained popularity by 1920. Early trucks were powered either by steam or internal combustion engines. The first tractors powered by diesel engines were built in the early 1930s. Diesel engines burned fuel oil instead of gasoline.