Federal Law. The federal Clean Air Act (CAA) preempts state governments from adopting their own air pollutant emission standards for new motor vehicles and engines. The CAA expressly permits the State of California to apply to the United States Environmental Protection Agency (EPA) for a waiver from preemption. Since the late-1960s, California has received over 100 federal preemption waivers. In recent years, EPA granted California waivers to, among others, implement its Advanced Clean Cars II (ACC II), Advanced Clean Trucks (ACT), and Heavy-Duty Omnibus Low NOx (Omnibus) rules. In January 2025, California withdrew a waiver request relating to implementing its Advanced Clean Fleets rules.
The CAA permits other states to either adopt the federal vehicle emissions standards or adopt California's, under certain conditions. To date, 17 states have adopted at least some of California's vehicle emissions standards.
California Vehicle Emissions Standards. California's motor vehicle emission standards include, in part, low-emission vehicle (LEV) and zero-emission vehicle (ZEV) requirements. LEV requirements establish that all vehicles sold in states subject to California's standards must exceed emissions performance standards for certain criteria air pollutants and for greenhouse gases. Specific performance requirements vary depending on the vehicle's model year, weight, and type.
ZEVs, including battery-electric vehicles and hydrogen fuel cell engine vehicles, must produce zero exhaust emissions of air pollutants and greenhouse gases. ZEV requirements specify that a certain percentage of vehicles delivered for sale in the state by manufacturers must be ZEVs. Manufacturers must either deliver the required percentage or obtain credits. Credits may be earned by either delivering vehicles for sale in the state, purchasing ZEV credits from another manufacturer, or earning credits from ZEV deliveries in other states with ZEV mandates. Manufacturers may receive partial credit toward the ZEV requirements by producing transitional ZEVs, which includes plug-in hybrid vehicles.
Washington Vehicle Emissions Standards. In 2005, the Legislature directed the Department of Ecology (Ecology) to implement California's LEV standards, and in 2020, to implement California's ZEV standards. Ecology implemented LEV and ZEV standards through adopting, by reference, the following California regulations in Washington: (1) Advanced Clean Cars, (2) ACC II, (3) Omnibus, and (4) ACT. Ecology is currently undergoing rulemaking to amend the ACT and Omnibus rules.
Vehicles and vessels in Washington must be registered with the Department of Licensing. The Clean Car Law requires vehicles across Washington State to be certified to California emission standards. All new passenger cars, SUVs, vans, and pickup trucks, model year 2009 and newer, must be certified to California emission standards. New vehicles that do not meet these standards cannot be registered, leased, rented, licensed, or sold for use in Washington. Used vehicles must be certified to California emission standards if:
Ecology must adopt rules to implement motor vehicle emission standards that maintain consistency with the CAA, and is prohibited from adopting California's motor vehicle emission standards.
References to California's emission standards and associated certification label are removed from provisions in current law relating to vehicle registration and sales, and state patrol enforcement of air conditioning safety requirements.
Statutory authority adopting California's motor vehicle emission standards, and directing Ecology to implement those standards, including the ZEV requirements, is repealed.