Where the Secretary of Highways proceeds under the authority of this act, he shall have authority to construct and maintain any tunnel, bridge, culvert, drainage structure or other structure or appurtenances incidental thereto, other than sanitary sewers, as may be necessary in the construction of the limited access highway: Provided, however, That the Secretary of Highways shall have authority to replace, reconstruct or restore existing sanitary sewers.
36 P.S. § 2391.5