A Commercial Driver License allows people to operate heavy-duty vehicles. Generally speaking, there are 3 Classes of CDL: Class A, Class B and Class C
A Class A license is required to operate the big trucks that pull long trailers. A big truck that pulls a long trailer is called a Combination Vehicle because it is a combination of 2 vehicles (1 truck and 1 trailer). a fully-loaded trailer can weigh as much as 65,000 pounds. The trucks can weigh between 15,000 and 20,000 pounds. These big trucks can also have as many as 18 speeds! Most cars have just 5 or 6 speeds.