49 CFR §383.91

1. (a)Vehicle group descriptions. Each driver applicant must possess and be tested on his/her knowledge and skills, described in subpart G of this part, for the commercial motor vehicle group(s) for which he/she desires a CDL. The commercial motor vehicle groups are as follows:
   1. (1)Combination vehicle (Group A)—Any combination of vehicles with a gross combination weight rating (GCWR) of 11,794 kilograms or more (26,001 pounds or more) provided the GVWR of the vehicle(s) being towed is in excess of 4,536 kilograms (10,000 pounds).
   2. (2)Heavy Straight Vehicle (Group B)—Any single vehicle with a GVWR of 11,794 kilograms or more (26,001 pounds or more), or any such vehicle towing a vehicle not in excess of 4,536 kilograms (10,000 pounds) GVWR.
   3. (3)Small Vehicle (Group C)—Any single vehicle, or combination of vehicles, that meets neither the definition of Group A nor that of Group B as contained in this section, but that either is designed to transport 16 or more passengers including the driver, or is used in the transportation of hazardous materials as defined in § 383.5.
2. (b)Representative vehicle. For purposes of taking the driving test in accordance with § 383.113, a representative vehicle for a given vehicle group contained in § 383.91(a), is any commercial motor vehicle which meets the definition of that vehicle group.
3. (c)Relation between vehicle groups. Each driver applicant who desires to operate in a different commercial motor vehicle group from the one which his/her CDL authorizes shall be required to retake and pass all related tests, except the following:
   1. (1)A driver who has passed the knowledge and skills tests for a combination vehicle (Group A) may operate a heavy straight vehicle (Group B) or a small vehicle (Group C), provided that he/she possesses the requisite endorsement(s); and
   2. (2)A driver who has passed the knowledge and skills tests for a heavy straight vehicle (Group B) may operate any small vehicle (Group C), provided that he/she possesses the requisite endorsement(s).
4. (d)Vehicle group illustration. Figure 1 illustrates typical vehicles within each of the vehicle groups defined in this section.