36 Pa. Stat. § 2712
Whenever any county of the Commonwealth, by its county commissioners, has heretofore agreed in writing with any borough to defray a portion of the cost of improving and reconstructing any road or street within the limits of such borough, lying on the route of a State highway, and where such road or street has been heretofore duly improved and reconstructed by such borough with the understanding that a portion of the cost of such improvement and reconstruction was to be paid by the county, and where the county has failed to pay its due proportion of the cost of such improvement and reconstruction for the reason that no legal authority for such payment existed by law, such agreement on the part of the county is hereby validated and made as binding upon the county as if full legal authority existed therefor at the time such agreement was entered into; and the county commissioners of the county are hereby authorized to draw their warrant in favor of, and to pay to, such borough, out of the funds of the county, the portion of the cost of improving and reconstructing such borough road or street agreed upon in the agreement by them entered into; and upon making such payment to such borough the county commissioners shall be relieved from all further liability.
36 P.S. § 2712