16 Pa. Stat. § 2722
After such plans have been adopted and recorded pursuant to law, all applications under the preceding section shall be restricted and shall relate only to the establishing, opening, construction and improvement of the proposed roads of said system or parts thereof and the vacation of roads supplied by the portion opened and improved. The commissioners may relocate, straighten, widen, extend, alter and open, construct and improve, the proposed roads as laid out, surveyed, marked and shown upon the plans of said system, or to originally locate, lay out and establish, construct and improve roads which substantially supply said system or parts thereof which, although not parts of said system, are deemed by the court to be main thoroughfares of sufficient importance to be improved by the county and to be added to said plan, and in such case to vacate so much of the roads of the system and of roads already established as may be rendered unnecessary by the changes or by an entirely new location.
16 P.S. § 2722