The Center for the American Future represents a coalition of Plaintiffs suing the EPA for exceeding its delegated authority under the Clean Air Act. The federal Clean Air Act preempts states from regulating air emissions from mobile sources, such as cars and trucks, because these sources are capable of traveling from state to state unimpaired. If each state could enact its own emissions standards for cars and trucks, commerce could come to a halt at the state line. However, California has been given special dispensation under the Clean Air Act. It is permitted to apply to the EPA on a case-by-case basis for a waiver from federal preemption if it can demonstrate that it has a compelling and extraordinary need for a more stringent state standard because of its unique geographic location and population density.