Here are the federal requirements:
Commercial Drivers License--Commercial Motor Vehicle Traffic Enforcement--DOT HS 809 422, July 2002
The Commercial Motor Vehicle Act of 1986 (The Act) was designed to remove unsafe and unqualified drivers of heavy trucks and buses from the nation痴 highways. The Act required the Secretary of the U.S. Department of Transportation to issue regulations establishing guidelines and standards for the testing and licensing of CMV drivers. These guidelines and standards were established in the Code of Federal Regulations (CFR) Chapter 49, Part 383.
All states adopted these licensing guidelines and standards in April 1992. The commercial driver痴 license requirements are applicable to drivers transporting persons or property in both interstate or intrastate commerce. The commercial driver痴 license has three classes covering the following vehicle classification groups:
Class A -- Required for a combination vehicle with a gross combination weight rating (GCWR) of 26,001 pounds or more and towing a vehicle with a gross vehicle weight rating (GVWR) of more than 10,000 pounds.
Class B -- Required for a single unit vehicle with a gross vehicle weight rating (GVWR) of 26,001 pounds or more, or any such vehicle towing a vehicle not in excess of 10,000 lbs. GVWR.
Class C -- Any vehicle, regardless of weight rating, transporting hazardous material in any amount requiring the display of placards by 49 CFR, part 172, subpart F, or designed to transport 16 passengers or more, including the driver.
Individual states may, at their discretion, issue restricted, specific use CDLs to allow operation of specific vehicles, or exempt specific occupational fields, such as farmers and emergency response vehicles, from the CDL requirements. Refer to your State code for State-specific requirements.