Tennessee Code Title 55. Motor and Other Vehicles § 55-8-188

(1) “Emergency vehicle” means a vehicle of a governmental department or public service corporation when responding to an emergency, a vehicle of a police or fire department, or an ambulance;

(2) “High occupancy vehicle” means a public transportation vehicle; privately owned bus; motorcycle; private passenger motor vehicle, including vans and pick-up trucks, carrying no fewer than two (2) passengers; or as otherwise determined by the commissioner of transportation; and

(3) “HOV lane” means a lane or set of lanes on a highway facility of any class, so designated by signing, pavement delineation or markings, or other means of positive guidance, that is reserved for the exclusive use of high occupancy vehicles during specified hours of specified days of the week, in order to provide preferential service over traditional, mixed vehicles on that remaining part of the same highway facility.