36 Pa. Stat. § 670-907
It shall also be lawful for the local authorities and department to provide by agreement that the department may advertise and receive bids for the construction of any part or portion of a highway, or any structure forming part thereof, or to provide that cities of the first class may advertise and receive bids for similar construction within the limits of such cities, whenever, in the judgment of the secretary, such arrangements are desirable and such construction may be done in conjunction with construction by the department or not interfere therewith. Such advertising, when done in accordance with the laws applicable to advertising for bids by the department shall be the only advertising necessary, any law to the contrary notwithstanding.
36 P.S. § 670-907