The highways embraced within the Interstate System shall be established, constructed, and maintained by the Commonwealth under the direction and supervision of the Commissioner of Highways with state funds as may be appropriated and made available for such purposes, together with such appropriations as may be made by any locality in the Commonwealth and funds as are now available or that may be derived from the federal government for such purposes. State funds for repayment of federal construction advances may be raised by toll facilities, if approved by the Federal Highway Administration.