There shall be exempt from this article as to length, detachable wind deflection devices which have been approved by the State Department of Transportation, loads of poles, logs, lumber, laminated wood building materials, structural steel, piping, and timber, and vehicles transporting same. Trucks, trailers, and semitrailers which are constructed and used exclusively for the hauling of livestock, shall also be exempt from the restrictions of this article as to length, but shall not exceed 65 feet in length.