(1) Except for such legally and specifically authorized vehicular traffic as may be necessary for the operation and maintenance of public airports, or the operation and maintenance of business activities conducted upon or adjacent to such airports, it shall be unlawful to operate any vehicle, device or contrivance other than aircraft upon the runways, taxiways, or aprons of any public airport in the state of Montana. Motor vehicle racing or any motor vehicle contest or test shall not, within the meaning of this regulation, be considered to an activity, which may be legally authorized upon the runways, taxiways, or aprons of any such airport. The term "aircraft" shall not include free flight model airplanes.