Under the California Advanced Clean Fleets settlement announced in May 2025, the California Air Resources Board agreed to repeal the core private-fleet provisions of its Advanced Clean Fleets regulation, ending the mandates that would have forced large trucking companies and port drayage operators to phase out diesel trucks. The deal resolved a lawsuit brought by a Nebraska-led coalition of 17 states and locked in CARB’s concession that it cannot enforce the rule’s 2036 zero-emission truck sales requirement without a federal waiver it no longer holds.
What CARB Agreed To Do
Chief District Judge Troy L. Nunley signed the stipulation and order on May 2, 2025 in the U.S. District Court for the Eastern District of California, holding the case in abeyance while CARB moves to repeal the rule. Nebraska Attorney General Mike Hilgers announced the settlement publicly on May 6, 2025.
The agreement sets firm deadlines. CARB had to present a repeal proposal at a public hearing no later than October 31, 2025, and must submit the completed rulemaking to California’s Office of Administrative Law by August 31, 2026. If the Office of Administrative Law has not approved the repeal by October 15, 2026, the parties are required to file a joint statement outlining next steps.
CARB also agreed not to enforce any of the high-priority or drayage fleet requirements for conduct occurring between November 1, 2023 and the date the repeal becomes final. That non-enforcement window matters because CARB had previously reserved the right to enforce the rules retroactively once it obtained a federal waiver, warning operators that diesel trucks added in the interim could later be forced off the road.
On the manufacturer-side provision, CARB conceded it cannot enforce the requirement that all medium- and heavy-duty vehicles sold in California be zero-emission starting with model year 2036 unless it first obtains an EPA preemption waiver for that specific provision.
Which Requirements Are Gone
The repeal covers the two categories of private fleets that had drawn most of the industry opposition.
High-priority fleets, defined as companies with more than 50 trucks or over $50 million in annual revenue, would have had to begin purchasing only zero-emission trucks for new additions starting in January 2024, or meet percentage targets under an alternative milestone schedule. Internal combustion vehicles would have been retired after reaching 13 years, 800,000 miles, or 18 years of age. Those obligations are being rescinded.
Drayage fleets, meaning trucks serving California’s ports and intermodal rail yards, would have had to register only zero-emission trucks starting January 1, 2024, with all drayage trucks required to be zero-emission by 2035. Those obligations are also being rescinded.
CARB moved faster than the settlement required. On September 25, 2025, the Board voted to repeal the drayage, high-priority, and federal fleet requirements from the California Code of Regulations. A 15-day notice of modified text was issued on April 2, 2026, with a public comment period closing April 17, 2026. A second round of proposed revisions was published on June 1, 2026, with comments due June 16, 2026.
What Still Applies to Government Fleets
The state and local government fleet requirements were not part of the settlement and remain in effect, though CARB modified them through the same rulemaking. The amended rules extend the 50% zero-emission purchasing requirement for government fleets by three years, pushing it from a 2024–2026 window to 2024–2029, and delay the 100% zero-emission purchasing mandate from 2027 to January 1, 2030. Small agencies with 10 or fewer vehicles in certain counties receive additional extensions.
CARB has maintained that private companies operating under contract for government entities still count as part of those entities’ fleets, a position that drew over 200 opposition comments during the rulemaking.
How the Rule Collapsed
CARB adopted the Advanced Clean Fleets regulation in April 2023, with an effective date of October 1, 2023. Because the rule regulated private fleets under standards stricter than federal law, CARB needed an EPA preemption waiver under the Clean Air Act before it could enforce the private-fleet provisions. CARB submitted its waiver request on November 15, 2023 and, while waiting, said it would not take enforcement action against drayage or high-priority fleets.
The EPA never ruled. On January 13, 2025, one week before President Trump took office for his second term, CARB voluntarily withdrew the waiver application, citing “impending uncertainty” from the incoming administration. With no waiver, the private-fleet requirements were unenforceable as a practical matter.
The Nebraska-led coalition had filed suit in May 2024, arguing the rule violated the U.S. Constitution’s dormant Commerce Clause, the Clean Air Act, and the Federal Aviation Administration Authorization Act. Their practical argument was that California’s role as a national supply chain hub meant the rule would reshape trucking fleets nationwide regardless of where companies were based. The settlement followed several months later.
The coalition included Nebraska, Alabama, Arkansas, Georgia, Idaho, Indiana, Iowa, Kansas, Louisiana, Missouri, Montana, Oklahoma, South Carolina, Utah, West Virginia, Wyoming, the Nebraska Trucking Association, and the Arizona State Legislature.
What Replaces the Mandate
CARB has signaled it is “retooling” its approach to heavy-duty vehicle emissions through a new initiative called Drive Forward, which combines incentive funding, market outreach, and infrastructure planning rather than purchase mandates. New regulatory proposals under the Drive Forward framework are not expected for several years.
Governor Newsom also responded to the broader federal pushback by signing Executive Order N-27-25 on June 12, 2025, directing CARB to continue pursuing zero-emission vehicle standards and to develop new Advanced Clean Cars III regulations as a backup.
What the Settlement Did Not Resolve
The settlement addressed the Advanced Clean Fleets rule specifically. It did not touch the parallel federal fight over California’s authority to set stricter vehicle emission standards in general.
On June 12, 2025, President Trump signed three congressional joint resolutions under the Congressional Review Act revoking EPA waivers the Biden administration had granted for California’s Advanced Clean Trucks rule, its Advanced Clean Cars II program, and its heavy-duty low-NOx omnibus rule. EPA Administrator Lee Zeldin stated that the Congressional Review Act bars the EPA from approving future waivers for California that are “substantially the same” as those revoked.
California, joined by ten other states, sued the federal government in the U.S. District Court for the Northern District of California, arguing that the Congressional Review Act does not apply to EPA waiver decisions and that the revocations violate the separation of powers and principles of federalism. That case remains pending, with briefing expected into 2026. Its outcome could determine whether California retains the legal foundation to impose any vehicle emission standards stricter than federal rules.
The Advanced Clean Trucks rule, which required manufacturers to sell increasing percentages of zero-emission trucks, was designed to work alongside the ACF rule; ACT was to create the supply and ACF the demand. With the ACF private-fleet mandates being repealed and the ACT waiver revoked at the federal level, both halves of that structure are, for now, off the table for private fleets in California.
Where Things Stand
CARB is finalizing the formal repeal, with the August 31, 2026 submission deadline to the Office of Administrative Law approaching. Until the repeal becomes final, the non-enforcement commitment in the settlement covers the intervening period back to November 1, 2023, so fleet operators that added diesel trucks during the waiver-review years are not exposed to retroactive enforcement on the high-priority or drayage provisions.
Government fleets should plan around the amended schedule, with the 50% purchasing requirement running through 2029 and the 100% requirement starting January 1, 2030. Private high-priority and drayage fleets no longer face the ACF purchase, registration, or retirement obligations, though the broader question of California’s waiver authority is still being litigated and could reshape the regulatory picture again.