California is leading a challenge by 17 states and the District of Columbia claiming that EPA’s revised position on model year 2022 to 2025 tailpipe exhaust standards for Light Duty Vehicles was arbitrary and capricious. Clean Air Act regulations required EPA to issue a Mid-Term Evaluation of model year 2022-25 vehicle emission standards by April 1, 2018, to determine whether the standards were still appropriate. EPA issued its evaluation on Jan. 12, 2017, just prior to the change in administrations. It found that the 54.5 mile per gallon standard could be attained, even though it is 10 miles more per gallon than the current standard. More recently, EPA revised its Mid-Term Evaluation, issuing a decision signed April 2, 2018, finding, among other things, that new information on fuel prices and technology meant that assumptions underlying the agency’s January 2017 evaluation had been unrealistically optimistic. Although the revised Mid-Term Evaluation only states that EPA would undertake a new rulemaking with the National Highway Traffic Safety Administration to evaluate setting new standards, the plaintiffs claim that EPA’s decision is a final agency action subject to review under the Administrative Procedure Act. Thirteen of the 18 jurisdictions filing suit have already adopted California’s more stringent 2022-25 standards.