Section 172(c)(9) of the Clean Air Act (
42 U.S.C. 7502(c)(9)) is amended by adding at the end the following: “Nothing in this Act precludes, with respect to any plan or plan provision, the inclusion and approval of contingency measures that are or may be implemented or take effect prior to the area involved failing to make reasonable further progress or to attain any national primary ambient air quality standard by the applicable attainment date.”.