Clean and Efficient Cars Act of 2018 This bill provides statutory authority for rules concerning corporate average fuel economy (CAFE) standards for automobiles with model years 2021 through 2025 and greenhouse gas emission standards for light-duty vehicles (e.g., trucks) with model years 2017 through 2025. Specifically, the bill provides statutory authority for rules issued in 2012 by the National Highway Traffic Safety Administration (NHTSA) on the CAFE standards and the Environmental Protection Agency (EPA) on the greenhouse gas emission standards. NHTSA and the EPA may not take actions that could reduce the stringency of the standards.