motor vehicle
(16) Motor vehicle .— The term “motor vehicle” means a vehicle, machine, tractor, trailer, or semitrailer propelled or drawn by mechanical power and used on a highway in transportation, or a combination determined by the Secretary, but does not include a vehicle, locomotive, or car operated only on a rail, or a trolley bus operated by electric power from a fixed overhead wire, and providing local passenger transportation similar to street-railway service.