Section 177 of the Clean Air Act (42 U.S.C. § 7507) lets a qualifying state adopt California’s vehicle emission standards in place of the federal baseline for new cars and trucks sold within its borders. It is the only lawful route for a state other than California to require stricter tailpipe rules than the EPA sets nationally. As of early 2025, roughly 17 states plus the District of Columbia had used it to adopt some version of California’s standards, together making up more than a third of the national new-vehicle market.
What Section 177 Actually Does
The Clean Air Act preempts states from writing their own vehicle emission standards. The statute is blunt: no state can adopt or enforce any standard controlling emissions from new motor vehicles, and no state can require its own certification or inspection as a condition of selling or registering a new car.1Office of the Law Revision Counsel. 42 U.S.C. 7543 – State Standards
California is the sole exception. Because it regulated vehicle emissions before the federal government did, it can obtain EPA waivers to set its own standards, and the California Air Resources Board (CARB) has used that authority to push rules well beyond the federal floor.
Section 177 is the bridge. Under 42 U.S.C. § 7507, any state with an approved State Implementation Plan under Part D of the Act can adopt and enforce California’s vehicle emission standards for any model year, provided the state’s standards are identical to California’s waiver-approved standards and both California and the adopting state finalize them at least two years before the model year begins.2Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas
The Part D hook ties the provision to nonattainment planning, but nearly every state has some area out of attainment for ozone or another criteria pollutant, so the threshold is easy to meet in practice. The result is a binary system. A state either follows the federal EPA standards or adopts California’s package. No state can invent its own emission requirements, cherry-pick individual CARB rules, or blend elements of both.
The Identicality Requirement
The word “identical” in the statute does serious work. A Section 177 state cannot tweak, strengthen, or weaken the California standards it adopts. The law bars creation of a “third vehicle” built to specifications that differ from both the federal and California certifications.2Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas The point is manufacturing logistics: a vehicle certified to California standards automatically meets the requirements in every Section 177 state. When CARB updates its rules, a Section 177 state that wants to stay current must run its own rulemaking, but the substance it adopts cannot deviate from what CARB finalized.
The Two-Year Lead Time
Both California and the adopting state must finalize the standards at least two full years before the start of the affected model year.2Office 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 Most manufacturers start producing a new model year in the fall of the prior calendar year, so the clock effectively runs from about two years before that fall start.
A worked example: if a state finishes rulemaking in early 2024, the earliest the new standards can apply is the 2027 model year, which manufacturers begin producing around fall 2026. Miss the deadline for a given model year and the adoption is unenforceable for that year, because the statutory conditions for the preemption exception have not been met. State administrative procedure laws add their own notice-and-comment timelines on top of the federal clock.
Which States Have Adopted California Standards
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, along with the District of Columbia.4U.S. Department of Energy. Adoption of California’s Clean Vehicle Standards by State
Participation is not uniform. Pennsylvania adopted the LEV criteria pollutant standards but not the zero-emission vehicle sales requirements. Virginia’s situation has been politically contested: the state adopted California standards through legislation in 2021, and Governor Glenn Youngkin later announced the state would not follow California’s more aggressive Advanced Clean Cars II provisions. The District of Columbia, though not a state, has adopted both the LEV and ZEV programs.
The Programs States Adopt Under Section 177
Three CARB programs drive most of the current activity.
Advanced Clean Cars II (ACC II), finalized by CARB in 2022, requires an increasing share of each manufacturer’s new light-duty vehicle sales to be zero-emission or plug-in hybrid, starting at 35% for the 2026 model year and rising to 100% by 2035. Around a dozen states plus DC had adopted ACC II before its legal footing was challenged in 2025, with enforcement beginning in the 2026 or 2027 model year depending on the state.
Advanced Clean Trucks (ACT) 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 this rule, with implementation dates from 2024 to 2027.
The underlying LEV criteria pollutant standards remain the baseline that every Section 177 state adopts. All three programs depend on California holding valid EPA waivers for the standards involved.
What Section 177 Means for Buying or Registering a Vehicle
Section 177 standards apply to new vehicles. If you buy a car in a federal-only state and move to a Section 177 state, whether you can register it turns on whether it still counts as new. The general industry threshold is 7,500 miles. A vehicle with fewer than 7,500 miles at the time it was acquired is treated as new and must carry the destination state’s emission certification. A vehicle with more than 7,500 miles is treated as used and can generally be registered as long as it meets federal EPA standards.
This matters most if you move between states or buy across state lines to get a model your local dealer does not stock. Dealers in Section 177 states are responsible for ensuring the new vehicles on their lots carry the correct California emission certification. Buying a new federal-only certified vehicle from an out-of-state dealer and trying to register it in a Section 177 state can produce registration delays or outright denials.
Penalties for Non-Compliance
The Clean Air Act imposes civil penalties for violations of its vehicle emission provisions. Under 42 U.S.C. § 7524, a manufacturer or dealer who violates the Act’s prohibited-acts provisions faces penalties of up to $25,000, with each non-compliant vehicle counting as a separate offense, and ongoing 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 compliance through their own laws, which can include registration blocks for vehicles that lack proper emission certification and state-level fines for dealers who sell non-compliant vehicles.
Why the Framework Is Now Uncertain
Section 177 only works if California holds valid EPA waivers for the standards being adopted. The statute permits adoption of “California standards for which a waiver has been granted.”2Office of the Law Revision Counsel. 42 U.S.C. 7507 – New Motor Vehicle Emission Standards in Nonattainment Areas A Congressional Research Service analysis confirmed that when a California waiver is withdrawn, Section 177 states have no authority to enforce the associated standards.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 had never before been used to overturn adjudicatory orders like waiver decisions, and they point to determinations by the Government Accountability Office and the Senate Parliamentarian that the waivers were not subject to the CRA.
The outcome 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 versions of the LEV program were not targeted and remain in place for now. If you are a regulator, manufacturer, dealer, or buyer whose plans depend on these rules, track that litigation. The answer could reshape the vehicle emission landscape across more than a dozen states.