(a) A permit issued under this subchapter does not authorize the operation of a truck-tractor and semitrailer combination on:
(1) the national system of interstate and defense highways; or
(2) load-restricted roads or bridges, including a road or bridge for which a maximum weight and load limit has been established and posted by the Texas Department of Transportation under Section 621.102 or the commissioners court of a county under Section 621.301.
(b) Subject to Section 623.406, a permit issued under this subchapter authorizes the operation of a truck-tractor and semitrailer combination only on highways and roads approved by the Texas Department of Transportation.