Clean Air Act Section 177 is the federal provision that lets any qualifying state adopt California’s vehicle emission standards in place of the federal ones, giving the country a two-tier system for new cars and trucks. Codified at 42 U.S.C. § 7507, the section applies to states with an approved State Implementation Plan under Part D of the Act, and it requires those states to copy California’s standards exactly rather than write their own.1Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas As of early 2025, roughly 17 states and the District of Columbia had adopted some version of California’s standards through this route, together making up more than a third of the national new-vehicle market.
Why the Section Exists
The Clean Air Act generally preempts states from setting their own vehicle emission standards. The statute is direct about it: no state may adopt or enforce its own standards for emissions from new motor vehicles, and no state may impose its own certification or inspection as a condition of sale or registration.2Office of the Law Revision Counsel. 42 U.S.C. 7543 – State Standards That rule keeps automakers from having to build fifty different versions of the same car.
California is the one exception. Because California was regulating vehicle emissions before the federal government stepped in, before March 30, 1966, the Act gives it a waiver process to set its own standards. The EPA Administrator must grant the waiver unless the agency finds California’s protectiveness determination arbitrary, finds the state doesn’t need separate standards to meet “compelling and extraordinary conditions,” or finds a conflict with federal requirements under Section 202(a).2Office of the Law Revision Counsel. 42 U.S.C. 7543 – State Standards The California Air Resources Board (CARB) has used this authority for decades to push standards well above the federal floor.
Section 177 is the door that lets other states join California’s tier. Without it, every state outside California would be locked into the federal baseline.
The Two Conditions a State Must Meet
A state adopting under Section 177 has to satisfy two statutory conditions.
The Standards Must Be Identical to California’s
Section 177 states cannot strengthen, weaken, or otherwise modify the California standards they adopt. The statute explicitly forbids creating a “third vehicle,” meaning a vehicle built to specifications that match neither the federal nor the California certification.1Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas A vehicle certified to California standards therefore satisfies the rules in every Section 177 state automatically. When CARB updates its standards, a Section 177 state that wants to stay current must run its own rulemaking to adopt the update, but the substance of what it adopts has to track CARB.
The choice is binary. A state either follows the federal EPA standards or takes California’s package wholesale. Cherry-picking is not allowed.
Both Sets of Rules Must Be Final at Least Two Years Before the Model Year
Section 177 requires California and the adopting state to finalize their standards at least two full years before the start of the affected model year.1Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas Federal regulations define a model year as the manufacturer’s annual production period that includes January 1 of the named calendar year.3eCFR. 40 CFR 85.2302 – Definition of Model Year Because most manufacturers begin producing a new model year in the fall of the prior calendar year, the two-year clock runs roughly from two years before that fall start.
A concrete example: rulemaking that finishes in early 2024 can apply no earlier than the 2027 model year, which manufacturers would begin producing around fall 2026. Miss the two-year mark and the adoption is unenforceable for that model year, because the statutory condition for the preemption exception hasn’t been met. States also have to run their own administrative procedure requirements, which typically add public notice and comment periods on top of the federal timeline.
The States That Have Adopted, and Which Programs
According to the Department of Energy, the following states had adopted California’s Low Emission Vehicle (LEV) standards as of 2025: Colorado, Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, and Washington, plus the District of Columbia.4U.S. Department of Energy. Adoption of California’s Clean Vehicle Standards by State
Not every state on that list has adopted every California program. Pennsylvania adopted the LEV criteria pollutant standards but not the zero-emission vehicle sales requirements. Virginia’s participation has been politically contested: the state adopted California standards through legislation in 2021, and Governor Glenn Youngkin later announced Virginia would not follow California’s more aggressive Advanced Clean Cars II provisions.
Beyond the LEV baseline, Section 177 has become the main pathway for states to adopt California’s zero-emission vehicle sales mandates. Advanced Clean Cars II (ACC II), which CARB finalized in 2022, requires an increasing share of each manufacturer’s new light-duty sales to be zero-emission or plug-in hybrid, starting at 35% for the 2026 model year and rising to 100% by 2035. About a dozen states plus DC had adopted ACC II before its legal footing was challenged in 2025. The Advanced Clean Trucks (ACT) rule extends similar requirements to medium- and heavy-duty vehicles, reaching 55% of lighter commercial vehicles and 75% of heavier trucks by the 2035 model year. Eleven states including California had adopted ACT, with implementation dates ranging from 2024 to 2027.
What It Means If You’re Buying or Registering a Vehicle
Section 177 standards apply to new vehicles. If you buy a car in a federal-only state and try to register it in a Section 177 state, the treatment turns on whether the vehicle is “new” or “used.” The industry threshold is 7,500 miles. A vehicle with fewer than 7,500 miles when acquired is treated as new and must carry the destination state’s emission certification. A vehicle above that mileage is treated as used and can typically be registered if it complies with federal EPA standards.
This matters most if you move between states or shop across state lines for a model your local dealers don’t carry. Dealers in Section 177 states are responsible for ensuring the new vehicles on their lots have the correct California certification. Buying a new federal-only vehicle from an out-of-state dealer and bringing it home for registration in a Section 177 state can lead to delays or an outright denial.
Penalties for Non-Compliance
Under 42 U.S.C. § 7524, a manufacturer or dealer that violates the Clean Air Act’s prohibited-acts provisions faces civil penalties of up to $25,000, with each non-compliant vehicle counted as a separate offense. Continuing violations can reach $25,000 per day. Individual consumers who tamper with emission control equipment face a separate, lower penalty of up to $2,500 per violation.5Office of the Law Revision Counsel. 42 U.S.C. 7524 – Civil Penalties Section 177 states also enforce through their own laws, which can include registration blocks and additional fines on dealers who sell non-compliant vehicles.
The Framework’s Current Legal Uncertainty
Section 177 rests entirely on California holding valid EPA waivers. The statute only permits adoption of “California standards for which a waiver has been granted.”1Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas If a waiver goes away, Section 177 states lose the authority to enforce the associated standards. A Congressional Research Service analysis confirmed exactly that outcome: when a California waiver is withdrawn, Section 177 states have no authority to enforce the related rules.6Congressional Research Service. California and the Clean Air Act Waiver
In 2025, Congress passed Congressional Review Act resolutions disapproving three California waivers granted by the prior administration: the Advanced Clean Cars II waiver, the Advanced Clean Trucks waiver, and the Omnibus Low NOx waiver. In June 2025, California and ten other states filed a federal lawsuit challenging those resolutions. The states argue that the CRA was designed to apply only to federal rules of general applicability and has never before been used to overturn adjudicatory orders like waiver decisions. They say both the Government Accountability Office and the Senate Parliamentarian had determined the waivers were not subject to the CRA.
The result of that litigation will decide whether Section 177 states can enforce their adopted versions of ACC II, ACT, and the Low NOx standards. Older California waivers covering earlier LEV standards were not targeted by the CRA resolutions and remain in place for now. If you’re tracking these rules as a buyer, dealer, or manufacturer, the pending case is the thing to watch, because it will reshape what Section 177 actually means across more than a dozen states.