Nothing contained in sections 1391-1398 of this title, shall restrict the weight of snow plows, road machines, oilers, traction engines, tractors, rollers, power shovels, dump wagons, trucks, or other construction or maintenance equipment when used by any town, incorporated village, city, or state in the construction or the maintenance of any highway, provided that such construction or maintenance is performed by persons employed by or under contract with such town, incorporated village, city, or the State for this purpose. However, any operation of motorized highway building equipment or road making appliances used in construction work contracted by a town, incorporated village, city, or the State shall be unrestricted as to weight only within a construction area. Nothing contained in sections 1391-1398 of this title shall restrict the weight of municipal and volunteer fire apparatus. (Amended 1991, No. 121 (Adj. Sess.).)