In accordance with the CMVSA, all drivers of commercial motor
vehicles must possess a valid CDL in order to be properly qualified
to operate the vehicle(s) they drive. In addition to passing the CDL
general knowledge and skills tests required for the basic vehicle group, all
persons who operate or expect to operate any of the following
vehicles, which have special handling characteristics, must obtain
combination vehicle endorsement.
(a) Double/triple trailers;
(b) Tank vehicles;
(c) Tank and Hazmat combo vehicles;
(d) Vehicles required to be placarded for hazardous materials.
These are all Class A commercial vehicle types. The Class A CDL is obtained
by passing the General Knowledge, Combination Vehicles and Air Brakes tests.