Those persons wishing to drive a tractor-trailer (a.k.a. semi) are required to have CDL training and to hold a valid Class A commercial driver’s license, commonly referred to as a CDL. The CDL was created by an act of Congress known as The Commercial Motor Vehicle Safety Act of 1986 which was signed into law on October 27, 1986.
"The goal of the Act is to improve highway safety by ensuring that drivers of large trucks and buses are qualified to operate those vehicles and to remove unsafe and unqualified drivers from the highways. The Act retained the State's right to issue a driver's license, but established minimum national standards which States must meet when licensing CMV drivers." - Federal Motor Carrier Safety Administration website, April 2006
The CDL ensures the truck driving schools meet the minimum requirements for the safe operation of a tractor trailer through testing and licensing standards. The Act also makes it illegal for a driver to hold more than one type of license. Although the Act is a Federal law, each state, from California all the way to Texas, retained the right to license drivers with the adoption of the standards. A CDL has been required to drive a tractor trailer since April 1, 1992. To obtain a CDL, the truck driver must pass a knowledge and driving skills test administered by their state – they initially train for this in a truck driving school. The skills test must be the type of vehicle which the driver intends to be licensed.
Truck drivers need a class A CDL in order to drive a tractor trailer. The class A vehicle type has been designated as "any combination of vehicles with a GVWR of 26,001 or more pounds provided the GVWR of the vehicle(s) being towed is in excess of 10,000 pounds.” – Federal Highway Administration (FHWA)