Miss. Code Ann. § 63-5-47: Miss. Code Ann. § 63-5-47

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:

(a) Said movement is wholly within a county which has therein a bridge across the Mississippi River.

(b) The operation of such vehicle or vehicles with such gross weight shall first be approved by the Mississippi Department of Transportation, and a permit issued by said department specifying the roads, highways or streets within such county over which such vehicle or vehicles may be operated.

(c) Said commodities have been received at such terminal or port facilities by water transportation and are destined for delivery across the bridge or said commodities have been received by movement across the bridge and are to be shipped from such terminal by water.

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.