No person shall operate on a highway any motor vehicle or combination of vehicles having a licensed gross weight in excess of 40,000 pounds unless the motor vehicle or combination of vehicles is equipped with rear fenders, flaps, or guards of sufficient size to substantially prevent the projection of rocks, dirt, water, or other substances to the rear. Vehicles used exclusively for hauling logs and tractor trucks shall be exempt from the provisions of this section.
Va. Code § 46.2-1083