(a) Except as provided by Subsections (b) and (c), a vehicle combination operating under a permit under this subchapter may operate on a federal interstate highway or a state, county, or municipal road, including a frontage road adjacent to a federal interstate highway, if the truck-tractor displays a sticker required by § 623.422 and the vehicle combination does not exceed the maximum axle or gross weight applicable to the combination under the terms of the permit.
(b) 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.

(c) A permit issued under this subchapter does not authorize the operation of a truck-tractor and semitrailer combination on a county road or bridge for which a maximum weight and load limit has been established and posted under § 621.301.