All unexpended balances of any appropriation, heretofore or which shall hereafter be made to the Department of Highways for the construction of State-aid highways, in accordance with the provisions of the act of May thirty-first, one thousand nine hundred and eleven (Pamphlet Laws, four hundred sixty-eight), and its supplements and amendments, shall be consolidated with and become a part of any current appropriation for a similar purpose.
72 P.S. § 3446