According to the Department of Motor Vehicles (DMV) in the United States, there are three main types of commercial drivers' licenses, although each of these classes is often broken up into additional designations. Most people have a Class C driver's license, which allows them to drive any single vehicle as long as the weight falls under 26,000 pounds (11,793 kg). Class A licenses allow drivers to operate a combination tractor-trailer truck weighing 26,000 lb (11,790 kg) or more. A Class B license, which can be quite difficult to obtain, allows the driver to operate straight vehicles weighing over 26,000 pounds (11,793 kg) in addition to any of the vehicles contained in Class C.
Class B license also allows the holder to drive buses, farm labor vehicles, and any housecar or trailer over under 45 feet (14 m). With this license, a driver is not allowed to pull a trailing unit weighing over 10,000 pounds (4,536 kg); with an A license, he can.
To obtain a Class B license, a person must already possess a C license. He or she must be at least 18 years old and pass a special visual acuity test and a road/skill test. For commercial driving across state lines, a Class B driver must be over 21. This class of license is also required to drive a single fire fighting vehicle; this is special kind of license known as "Restricted Class B Fire Fighter License." While the license is valid for five years, a new medical test must be submitted every two years in order to keep the license updated.
Certain types of Class B licenses may require special endorsements. This includes drivers who will be transporting hazardous materials, pulling double or triple trailers or tank vehicles, driving school buses, and handling vehicles not equipped with air brakes.