16 Pa. Stat. § 5852
Where, under the provisions of existing laws, a municipality is authorized to construct a bridge or viaduct over a river, creek or stream or other place over which the county is authorized to build bridges, and such municipality is authorized to contract with the county and with railroads, street railways and other companies or parties interested for the building and maintenance of such bridge or viaduct, and for the payment of any damages caused by the location or erection thereof, the county commissioners may contract with such municipality for that part or portion of the bridge or viaduct which crosses any of the places hereinbefore mentioned, including the abutments and piers thereof. Such part shall thereafter be maintained as a county bridge. In lieu thereof, the county commissioners may contract for any part or portion of the whole structure equal to or greater than the part or portion which the county might have built.
16 P.S. § 5852