Whenever the county commissioners shall deem it expedient , they may cause to be purchased, located, constructed, operated and maintained roads, tunnels, subways or underground roads anywhere within the county, either wholly or partly within the boundaries of any municipal corporation. Any road, tunnel, subway or underground road, purchased or constructed under the provisions of subdivision (a) 3 of this article, shall forever thereafter be a county road, tunnel, subway or underground road, and the duty of maintaining and keeping the same in repair shall devolve upon the county. The expense thereof shall be paid by the county as hereinafter provided.
16 P.S. § 2730