Upon the taking over for construction and maintenance by the Commonwealth of any of the highways or sections thereof, bridges, tunnels, viaducts or approaches thereto specified in this act, the Commonwealth shall thereafter assume all rights, obligations and liabilities of the county, except for any outstanding construction or reconstruction obligations and liabilities in effect at the time of such transfer relating to said highways or sections thereof, bridges, tunnels, viaducts or approaches thereto, whether the same arise by virtue of any order of the Public Service Commission, the Pennsylvania Public Utility Commission, by contract or otherwise, with respect to those highways, bridges, tunnels, viaducts and approaches thereto designated in section 101 , which are located in cities of the second class and third class. This article is not intended and shall not be construed:
The rights, powers, duties, obligations and responsibilities set forth in this section which are not placed upon or transferred to the Commonwealth and which will or would be placed upon or transferred to cities of the second and third class by existing law shall become and/or remain the rights, powers, duties, obligations and responsibilities of said cities: Provided, however, That said cities may contract with counties of the second class for an assumption by said counties of any or all said duties, obligations and responsibilities.
36 P.S. § 1758-103