53 Pa. Stat. § 13802
Any city of the first class may lay out, widen, extend, or relocate highways and streets connecting with, or used as direct approaches to, bridges crossing streams or tunnels under streams, which form boundaries between this and any other state, and construct the same, either at, above, or below grade, together with such viaducts carrying such highways and streets over other highways and streets and over other property, and such ramps and approaches and such other structures and superstructures in connection therewith, as in the discretion of the council of such city, shall be necessary or convenient: Provided, That any such improvement shall in all cases follow substantially the course of the existing streets of such city which are in the most nearly direct continuous line with such bridge or tunnel.
53 P.S. § 13802