N.J. Stat. § 39:3-79.1
No person shall operate or cause to be operated any bus, truck, full trailer or semitrailer of registered gross weight exceeding three tons on any public highway unless the same is equipped with suitable metal protectors or substantial flexible flaps on the rearmost wheels, and, in case the rear wheels are not covered at the top by fender, body or other parts of the vehicle, the rear wheels shall be covered at the top by protective means, of such standard type or design and installed in such manner as shall be approved by the Director of the Division of Motor Vehicles in the Department of Law and Public Safety and as shall conform substantially to any requirements of the Interstate Commerce Commission governing similar subject matter, in order to prevent, as far as practical, such wheels from throwing dirt, water or other materials on the windshields of the following vehicles, except in cases in which the motor vehicle is so designed and constructed that the above requirements are accomplished by reason of fender or body construction or other means of enclosure; provided, however, this act shall not apply to pole trailers, dump trucks, tanks, or other vehicles where the construction thereof is such that complete freedom around the wheel area is necessary to secure the designed use of the vehicle.
N.J.S. § 39:3-79.1