36 Pa. Stat. § 655.2
It shall be the plan of the parkway to avoid congested areas, if possible. The highway shall have as light grades as possible, and shall be designed primarily for tourist traffic and passenger vehicles. No intersecting highways carrying more than three hundred vehicles per day shall enter at grade level, nor shall any public driveways of any sort be permitted to enter thereon at intervals more frequent than five miles apart, at such points as the Secretary of Highways shall designate. No advertisements of any sort shall be permitted to be erected along said highway or within five hundred feet thereof under any circumstances, and no notices, signals or directions, other than those erected by the Department of Highways. Bridle trails and pedestrian foot paths may be constructed and maintained as their prospective use may seem to warrant. Landscaping and plantings shall be so planned that the Commonwealth's native plant life be utilized, and in such a manner that trees, high shrubbery or plantings will not obstruct the view of the valley side of the parkway. The parkway shall be constructed wherever possible over and through lands now owned by the Commonwealth as State forest, game or fish lands.
The commission hereinafter created may from time to time as it sees fit prohibit the use of the parkway by any commercial vehicle, and it shall so prohibit the use thereof during the months of June, July, August and September, by any commercial vehicles except for forest fire protection, local deliveries, maintenance or emergency work involving service lines or military purposes.
36 P.S. § 655.2