The table in TMC 10.75.130 shall not apply to truck tractor and dump semitrailer or truck-trailer combinations, when such are used as a combination unit exclusively for the transportation of sand or salt for highway maintenance operations, gravel, slag stone, limestone, crushed stone, cinders, blacktop, dirt or fill material, when such vehicles are used for transportation to a highway or road construction site or highway maintenance project or facility, except that such vehicles or combinations of vehicles shall not be exempted from any application of the table as may be required to determine applicable axle weights for triple and quad axles. As used in this section, the term “dump semitrailer” means any semitrailer designed in such a way as to divest itself of the load carried thereon. (Code 1981 § 43-683. Code 1995 § 142-752.)