Whenever the Department of Highways shall adopt any existing street parallel to any State highway in any borough as a State highway, and such parallel street has been improved and constructed by the borough according to the standards of the department for the construction of streets forming parts of State highways and under plans prepared by the department, the Department of Highways shall reimburse the borough for the amount expended by such borough for the improvement and construction of such street, to be determined by the councils of such borough and the Department of Highways; and any moneys appropriated to the Department of Highways for the construction and/or maintenance of State Highways shall be available therefor, and for such purpose so much thereof as may be necessary is hereby specifically appropriated.