Motor vehicles engaged in transporting commodities to or from terminal or port facilities on the Mississippi River may be operated with a total weight and/or size in excess of limitations which may be specified by law, although such size or weight limitations shall never exceed federal limitations for the procurement of federal aid for either maintenance or construction, or the limitations then in force in any state immediately adjacent to the county in which such port or terminal facilities are located, provided that:
The operator of each and every motor vehicle operating under the provisions of this section shall, at all times, carry the permit issued by the said Mississippi Department of Transportation, or a certified copy thereof.
Miss. Code § 63-5-47