For the purpose of this chapter "commercial motor vehicle" means a self-propelled or towed vehicle used on a highway in interstate or intrastate commerce to transport passengers or property, when the vehicle:

(1) Has a gross vehicle weight rating or gross combination weight rating or gross weight or gross combination weight of 4,536 kilograms or more (10,001 pounds or more); or

(2) Is designed or used to transport more than eight passengers, including the driver, for compensation; or

(3) Is designed or used to transport more than fifteen passengers, including the driver, and is not used to transport passengers for compensation; or

(4) Is used in transporting materials found by the secretary of transportation to be hazardous under 49 U.S.C. Sec. 5103 and transported in a quantity requiring placarding under regulations prescribed by the secretary under 49 C.F.R., subtitle B, Chapter I, subchapter C.

A recreational vehicle used for noncommercial purposes is not considered a commercial motor vehicle. "Recreational vehicle" includes a vehicle towing a horse trailer for a noncommercial purpose.