Four court of appeals have now considered the validity of the Environmental Protection Agency's attempt to compel the states to administer and enforce transportation controls under the Clean Air Act. The split in judicial authority which the first three decisions produced was analyzed in a previous ELR Comment.¹ The D.C. Circuit's recent ruling,² while kinder to EPA's regulatory approach than were the Fourth³ and Ninth⁴ Circuit decisions which preceded it, still leaves the law on this point very uncertain and the viability of the whole idea of transportation controls under the Clean Air Act open to serious question.