(1) "Auxiliary power unit" means a mechanical or electrical device affixed to a vehicle that is designed to be used to generate an alternative source of power for any of the vehicle’s systems other than the primary propulsion engine.

(2) "Commercial diesel vehicle" means a self-propelled diesel motor vehicle licensed for use on a public roadway to transport passengers or property when the vehicle has a gross vehicle weight rating or gross combination weight rating, or gross vehicle weight or gross combination weight of ten thousand and one pounds or more, whichever is greater.

(3) "Passenger bus" means a vehicle designed to carry sixteen or more passengers.

(4) "Vehicle" means a commercial diesel vehicle.