(a) General rule.--The provisions of this title apply upon any turnpike or highway under the supervision and control of the Pennsylvania Turnpike Commission unless specifically modified by rules and regulations promulgated by the commission which shall become effective only upon publication in accordance with law. A copy of the rules and regulations, so long as they are effective, shall be posted at all entrances to the turnpike or highway for the inspection of persons using the turnpike or highway. This section does not authorize the establishment of a maximum speed limit greater than 55 miles per hour, except that a 65-miles-per-hour or 70-miles-per-hour maximum speed limit for all vehicles may be established where the commission has posted a 65-miles-per-hour or 70-miles-per-hour speed limit.

(a.1) Posting.--No maximum speed limit established under subsection (a) shall be effective unless posted on fixed or variable official traffic-control devices erected after each interchange on the portion of highway on which the speed limit is in effect and wherever else the commission shall determine.