The Trump administration moved to further relax federal fuel-efficiency requirements this week, but California clean car rules continue to serve as the most consequential backstop for vehicle emissions in the United States. The administration’s new plan is largely symbolic since Congress had already removed the fines for violating federal standards, and broader cuts to climate authority have left Washington with little leverage over carbon pollution from cars, which account for about 16 percent of U.S. greenhouse gas emissions, according to federal data.
Even so, California retains enough authority to keep nudging automakers toward higher efficiency. State rules remain in force and effectively set a minimum level of performance that carmakers risk penalties if they dip below. The administration has been working to curtail California’s ability to craft its own standards, but has not fully succeeded. For now, the state’s constrained but active program is the most significant emissions policy in the country.
California’s unique role stems from a decades-old waiver allowing it to go beyond federal tailpipe limits. Severe smog in Southern California in the mid-20th century led the state to adopt its own standards before Congress enacted the Clean Air Act. Recognizing those air-quality challenges, Congress allowed California to continue setting its own vehicle rules.
While the state cannot directly set fuel economy, reducing gasoline consumption is the primary way to cut greenhouse gas emissions from conventional cars, so carbon limits can produce similar outcomes to federal mileage rules.
California’s influence extends nationwide. Other states may opt into its program, and 19 jurisdictions, including the District of Columbia, currently do.
To avoid building multiple versions of the same models, many manufacturers design fleets to comply with California’s benchmarks. States following California’s standards accounted for about 40 percent of U.S. new car sales in 2022, magnifying the state’s sway over the market.
The administration and its allies in Congress have advanced efforts to roll back California’s authority. Last year, lawmakers voted to block the state’s plan to phase out sales of new gasoline-powered cars by 2035 after the EPA urged Congress to act, prompting California to sue.
“What we’re seeing is a thinly veiled attempt by the president to retaliate against California for choosing progress over regression,” California Attorney General Rob Bonta said after filing the case.
With the phaseout paused, California plans to enforce its prior emissions standards, which otherwise would have expired in 2026. These rules will not require further year-over-year reductions but could prevent backsliding.
The administration asked Congress to overturn these standards as well, but a federal judge blocked that attempt in early September.
Automakers have not said whether they will stay on track for California’s rescinded requirements should courts revive them. The industry has weathered repeated policy reversals across administrations and is cautious about committing in the face of uncertainty.
President Donald Trump announces the rollback of the 2009 Endangerment Finding in February 2026. The scientific finding allowed the EPA to regulate climate-warming emissions.
Anna Moneymaker / Getty Images
The market is also shifting. Automakers argued the now-revoked Biden fuel-efficiency rules clashed with buyer preferences.
Companies increased electric vehicle production in part to meet those standards, but demand lagged, a trend that deepened after federal incentives were rolled back. At the same time, higher gasoline prices have boosted interest in fuel-sipping models, with hybrids reaching a record 16 percent of passenger vehicle sales by summer 2026.
Some manufacturers remain committed to EV development given global trends. “We’re in for the long haul, and we’re maybe a little slower on EVs, for instance,” General Motors President Mark Reuss said at a conference this week.
“That’s OK, but the whole world is moving that way, and so we invested in the platforms that are EV platforms.”
Analysts say market forces alone are unlikely to deliver emissions cuts at the pace needed for climate goals. California’s remaining rules set a baseline, but the blocked phaseout would drive deeper reductions across automakers’ lineups.
The future of the stricter California program will likely be decided in court. Legal experts note the state has a strong case to restore its authority because Congress used an unusual maneuver to revoke it, one that the Government Accountability Office and the Senate parliamentarian previously said was unlawful.
“There are multiple levels of shenanigans, depending on your viewpoint, that are being litigated,” said Rebecca Higgins, vice president of Policy at the Eno Center for Transportation. “That creates tremendous uncertainty.”
A court could find the congressional and administrative actions invalid, and the phaseout plan could return if Democrats retake the White House in 2028. Another lawsuit could have even broader ramifications.
The administration is seeking to nullify California’s underlying authority to regulate greenhouse gas emissions on the grounds that it effectively dictates fuel economy. Federal courts have sided with California on this point before, but the Supreme Court has not ruled on the question, and the current conservative majority has often favored the administration’s positions.
“That one feels like it could have the potential to sort of reset the authorities going forward,” Higgins said.
What California clean car rules mean for Hawaiʻi
Hawaiʻi residents track these developments closely. Vehicle standards that California sets can shape what models are available nationwide, influencing prices and fuel savings for island drivers who pay some of the country’s highest gasoline and electricity rates.
Any weakening of the program could slow the arrival of more efficient cars to local dealerships, while a court-backed restoration could accelerate access to hybrids and EVs that reduce fuel costs and emissions across the islands.
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