Whenever Federal emergency funds and city or county funds are available therefor, the department is hereby authorized to construct, replace or repair bridges in cities of the third class, whether such bridges are owned and maintained by such cities or by the counties in which located, which bridges form connecting links on State highways which have been or may be designated by any Federal agency or department as essential to National defense. No such bridge shall be constructed, repaired or rebuilt without the consent of the public authorities responsible by law for the maintenance of such bridge.
36 P.S. § 670-712