A person shall not operate on a highway in this State a pleasure car, pleasure car with trailer coach attached, motor truck, truck-tractor in combination with a trailer or semi-trailer, motor bus, or school bus registered in Vermont, manufactured or assembled after January 1, 1955, unless such vehicle is equipped with directional signal lamps, of a type approved by the Commissioner, on front and rear of such vehicle or combination. (Amended 1971, No. 228 (Adj. Sess.), § 32.)