Regions · United States

Since it was amended in 1990, the Clean Air Act requires the Environmental Protection Agency (EPA) to set standards that maximally reduce air pollutant emissions from mobile sources. Fuel economy standards are set by the National Highway Traffic Safety Administration (NHTSA) and, starting in 2009, CO2 standards are set by the EPA. California also has the authority to set its own pollutant emission and CO2 standards and has also implemented requirements for zero-emission vehicles. US EPA emissions standards for model year 2007 and later heavy-duty engines and Tier 3 emissions standards for light- and medium-duty vehicles are among the most advanced national standards in the world, while enforcement of emission and CO2 standards is the best in the world. CO2 and fuel consumption standards apply to model years 2017–2025 light-duty vehicles and model years 2018–2027 heavy-duty vehicles.