(1)    Vehicle classes. For purposes of this chapter, motor vehicles are divided into the following classes:

      (a)    Class A. A “Class A” motor vehicle is any combination of vehicles with a gross vehicle weight rating, actual gross weight or registered weight of over 26,000 pounds, if the aggregate total gross vehicle weight rating, actual gross weight or registered weight of the vehicle or vehicles being towed is in excess of 10,000 pounds.

      (b)    Class B. A “Class B” motor vehicle is any single vehicle with a gross vehicle weight rating, actual gross weight or registered weight of over 26,000 pounds, and any such vehicle towing a vehicle or vehicles with an aggregate total gross vehicle weight rating, actual gross weight or registered weight of 10,000 pounds or less.

      (c)    Class C. A “Class C” motor vehicle is any single vehicle with a gross vehicle weight rating, actual gross weight and registered weight of 26,000 pounds or less, including any such vehicle towing a vehicle with a gross vehicle weight rating, actual gross weight and registered weight of less than 10,000 pounds, if any of the following applies:

         1.    The vehicle is designed to transport 16 or more passengers, including the driver.

         2.    The vehicle is transporting hazardous materials requiring placarding or any quantity of a material listed as a select agent or toxin under 42 CFR 73.

      (d)    Class D. A “Class D” vehicle is any motor vehicle not included in par. (a), (b), (c) or (e).

      (e)    Class M. A “Class M” vehicle is any motorcycle.

   (2)   Vehicle types. For purposes of this chapter, certain vehicles intended to carry school children or other passengers, or having special operating characteristics, are divided into the following vehicle types specified in pars. (a) to (f):

      (a)    Hazardous materials transporter. Hazardous materials transporter vehicles are vehicles transporting hazardous materials requiring placarding or any quantity of a material listed as a select agent or toxin under 42 CFR 73.

      (b)    Full air brakes equipped. Full air brakes equipped vehicles are commercial motor vehicles equipped with a braking system operating fully on the air brake principle.

      (bm)    Partial air brakes equipped. Partial air brakes equipped vehicles are commercial motor vehicles equipped with a braking system operating partially on the air brake principle and partially on the air over hydraulic brake principle.

      (c)    Tanks. Tanks are commercial motor vehicles which are tank vehicles.

      (d)    Passenger carrying. Passenger-carrying vehicles are motor vehicles designed to carry, or actually carrying, 16 or more passengers, including the driver.

      (e)    School buses. All school buses, including those which are commercial motor vehicles.

      (f)    Vehicles towing double or triple trailers. Vehicles towing double or triple trailers are commercial motor vehicles with double or triple trailers.