The federal commercial vehicle maximum weight standard on the interstate highway system is 80,000 pounds gross vehicle weight, unless a higher maximum weight existed on the state level before July 1, 1956.
Off the interstate highway system, states may set their own commercial vehicle size and weight standards. In most states, the maximum permitted length for a single trailer is 53 feet. Tractors pulling two 28-foot trailers are known as twins or western doubles.
Trucks that are even bigger than western doubles are allowed to travel on some roads. These trucks, called longer combination vehicles, sometimes have three trailers. In other cases, they have two, but one of them exceeds 28 feet, or the combined weight of the rig exceeds 80,000 pounds.
Two U.S. Department of Transportation agencies plus individual states oversee large truck safety. The National Highway Traffic Safety Administration (NHTSA) sets standards for new truck equipment. The Federal Motor Carrier Safety Administration (FMCSA) oversees the safety of commercial vehicles in interstate commerce (vehicles operating across state lines) and has some jurisdiction over equipment standards for trucks currently on the road. FMCSA regulations cover equipment, licensing, hours of service and vehicle inspection and maintenance.
States regulate trucks that operate only within their borders, and state personnel conduct roadside inspections of trucks and drivers to enforce federal rules for equipment, hours of service and vehicle maintenance and inspection. Federal and state personnel also conduct reviews of carriers' compliance with these regulations. Carriers with high rates of crashes and inspection violations are subject to interventions including warning letters, offsite investigations, onsite investigations and suspensions of service.
Licensing drivers is a state matter, but since 1992, federal law requires states to meet licensing standards for commercial driver's licenses (CDLs). Prior to 1992, a few states allowed any driver licensed to drive an automobile to drive a large truck or bus, and other states had weak testing and licensing standards for commercial drivers. Since 1992, federal law has established testing, licensing and health standards for issuing CDLs.
Both interstate and intrastate commercial drivers must obtain CDLs if they operate trucks with gross vehicle weight ratings of 26,001 pounds or more, if they transport 16 or more passengers, or if they transport hazardous materials. A national database of all CDL holders helps to deter truckers from obtaining licenses in more than one state and then "spreading" their traffic convictions over more than one license to avoid sanctions for multiple violations. The database also prevents disqualified drivers from being licensed.
If large trucks cross state lines or carry hazardous materials, their drivers must be 21 or older. States can permit drivers ages 18-20 to operate large trucks within the state.
Multiple studies indicate that truck drivers younger than 21 and in their 20s have a higher rate of involvement in both fatal and nonfatal crashes than older drivers (Campbell, 1991; Blower et al., 1990; Blower, 1996; Frith, 1994; Teoh et al., 2017).