36 Pa. Stat. § 668.18
When all bonds, notes or other obligations and the interest thereon shall have been paid, or a sufficient amount for the payment of all bonds, notes or other obligations and the interest to maturity thereon shall have been set aside in trust for the benefit of the holders of such bonds, notes or other obligations and shall continue to be held for that purpose, the turnpike and the connecting roads, tunnels and bridges shall become a part of the system of State highways and shall be maintained by the Department of Highways free of tolls; and thereupon, the Commission shall be dissolved, and all funds of the Commission not required for the payment of the bonds, notes or other obligations, and all machinery, equipment and other property belonging to the Commission, shall be vested in the Department of Highways.
36 P.S. § 668.18