Light straight trucks have a gross vehicle weight (fully loaded maximum weight) of less than 14,000 pounds (6,300 kg). These include panel and pickup trucks and various service vehicles, which are used mainly in local transportation. Medium straight trucks have a gross vehicle weight of 14,000 to 26,000 pounds (6,300 to 11,700 kg). Designed primarily for local transportation, they are sometimes used for intercity purposes. Heavy trucks have a gross vehicle weight of over 26,000 pounds, and they are either straight or tractor-trailer combinations. Many heavy trucks, particularly tractor-trailers, are used for intercity purposes.
Most trucks and tractors are powered by gasoline. The use of diesel power, particularly by larger trucks, has been increasing. Liquefied petroleum gas, propane gas, and butane gas are also used to a limited extent. Trucks powered by gas-turbine engines have been tried experimentally.
The gasoline engine used in trucks and automobiles is a major source of air pollution. The diesel engine, however, causes much less air pollution. Motor trucks also create a noise problem. Various federal, state, and local government regulations have been enacted to control air and noise pollution caused by trucks. Studies show that motor trucks overall are usually less energy-efficient than rail or water carriers, but more energy-efficient than air carriers. For short hauls, however, motor trucks are more energy-efficient than railroads.
