Missouri Revised Statutes Title XIX. Motor Vehicles, Watercraft and Aviation § 307.015. Certain motor vehicles, mud flaps required--violation, penalty

1. Trucks, semitrailers, and trailers, except utility trailers, without rear fenders, attached to a commercial motor vehicle registered for over twenty-four thousand pounds shall be equipped with mud flaps for the rear wheels when operated on the public highways of this state.  If mud flaps are used, they shall be wide enough to cover the full tread width of the tire or tires being protected;  shall be so installed that they extend from the underside of the vehicle body in a vertical plane behind the rear wheels to within eight inches of the ground;  and shall be constructed of a rigid material or a flexible material which is of a sufficiently rigid character to provide adequate protection when the vehicle is in motion.  No provisions of this section shall apply to a motor vehicle in transit and in process of delivery equipped with temporary mud flaps, to farm implements, or to any vehicle which is not required to be registered.

2. Any person who violates this section is guilty of an infraction and, upon plea or finding of guilt, shall be punished as provided by law.