Ala. Code § 32-9-1
Trailers, when used in a truck tractor-semitrailer-trailer combination may be operated on the national system of interstate and defense highways and other highways upon designation by the Director of Transportation and final approval by the Governor. The Director of Transportation shall, at a minimum, designate those highways necessary to cause the State of Alabama to be in compliance with the Federal Surface Transportation Assistance Act of 1982.
Except as provided above, no person shall operate any trailer, as defined in this title, on any highway unless such trailer is operated for the purpose of constructing highways or other facilities of the state or a political subdivision thereof. The Department of Transportation is authorized to regulate the movement of such trailers from one job to another by special permits issued in the same manner as permits are issued under Section 32-9-29. No trailer or semitrailer of any kind shall be used for the hauling of passengers for hire except as provided by Article 2 of this chapter.
The provisions of this article relating to trailers shall not apply to the movement over the highways of trailers manufactured, reconditioned, or repaired in this state when reasonably necessary for the delivery of such trailers to the owners or purchasers thereof outside the state; provided, that such movement shall be subject to special permit to be issued by the Director of the Department of Transportation. Such permits may be issued and may be renewed upon such terms and conditions, in the interest of public safety and the preservation of the highways, as the Director of the Department of Transportation may in his or her discretion require, and he or she may designate the route over which such trailers may be moved and the hours of movement thereof.
Ala. Code § 32-9-1 (1975)