Ala. Code § 32-5A-30: Uniform Marking of Highways and Erection of Traffic-Control Devices.

(a) The Department of Transportation is authorized to classify, designate, and mark both interstate and intrastate highways lying within the boundaries of this state.

(b) The Department of Transportation shall adopt a manual and specifications for a uniform system of traffic-control devices consistent with the provisions of this chapter and other state laws for use upon highways within this state. Such uniform system shall correlate with and so far as possible conform to the system set forth in the most recent edition of the Manual on Uniform Traffic-Control Devices for Streets and Highways and other standards issued or endorsed by the federal highway administrator.

(c) No local authority shall place or maintain any traffic-control device upon any highway under the jurisdiction of the Department of Transportation except by the latter’s permission.