FAQ: Advanced Clean Fleets Regulation (updated March 2026) (PDF download)
The Advanced Clean Fleets (ACF) regulation is a component of the California Air Resources Board’s (CARB) overall strategy to accelerate the transition of California’s medium- and heavy-duty trucks to zero-emissions vehicles (ZEV) where feasible by 2045. This regulation was designed to work in conjunction with the Advanced Clean Trucks (ACT) regulation that CARB approved in March 2021. The ACF establishes zero‑emission vehicle (ZEV) purchase requirements for fleets, while the ACT imposes ZEV sales requirements on truck manufacturers. However, subsequent actions by the Trump Administration—most notably its refusal to support California’s Clean Air Act (CAA) waiver authority—has restricted CARB’s ability to implement and enforce key elements of these regulations.
Although the ACF was approved by CARB in April 2023, it cannot be enforced on federal or private fleets because the U.S. Environmental Protection Agency did not grant a CAA waiver. The regulation continues to apply to state and local government (SLG) fleets, for which no federal waiver is required.
In early 2025, CARB withdrew its waiver and authorization request after it became clear that the incoming federal Administration was unlikely to grant approval. Subsequently, on September 25, 2025, CARB voted to repeal the ACF’s Drayage and High-Priority Fleets requirements[1] to avoid confusion and uncertainty for those entities. The repeal is expected to take effect on January 1, 2027. CARB is currently advancing additional amendments[2] to align the regulation with AB 1594 and provide greater flexibility through expanded exemptions and allowances for internal combustion vehicles where zero‑emission options are not feasible.
[1] California Air Resources Board. (2025, September 25). CARB adds flexibility to truck fleet requirements with amendments to help owners continue zero‑emission progress. https://ww2.arb.ca.gov/news/carb-adds-flexibility-truck-fleet-requirements-amendments-help-owners-continue-zero-emission
[2] Notice of Public Availability of Modified Text and Availability of Additional Documents. Proposed Amendments to Advanced Clean Fleets and Low Carbon Fuel Standard Regulations. Posted April 2, 2026. https://ww2.arb.ca.gov/rulemaking/2025/acfab1594
The ACF regulation applies only to SLG fleets operating medium‑ and heavy‑duty on‑road vehicles with a GVWR over 8,500 pounds in California. The amendments approved on September 25, 2025 extended the ZEV purchase requirement timeline for these fleets.
- The SLG 50% ZEV purchasing requirement was moved back three years from January 1, 2024 to January 1, 2027. The 100% ZEV purchasing requirement was also delayed the 2030.
- The exemption for small fleets and designated low population counties was extended until 2030.
FAQ: Availability and Use of Compressed Natural Gas (CNG) Trucks under the ACF*
(PDF download)
*Disclaimer: Please note that the descriptions below are for informational purposes only. It is the responsibility of every fleet to conduct your own research to determine whether your operations are in compliance with the various provisions of the ACF regulation.
Yes. Those with CNG trucks in their California fleet prior to January 1, 2024 can continue to operate those trucks.
There are several pathways under which a state and local government (SLG) fleet can continue to purchase new CNG trucks to add to their California fleet. Purchasing CNG trucks powered by renewable natural gas (RNG) can provide a readily available alternative to “legacy” diesel trucks that can help fleets meet their sustainability goals immediately using a low carbon, cost-effective, CARB-certified option with a built-out fueling network.
State and Local Government Agency Fleets:
- Existing CNG Trucks. You can continue to operate your existing CNG truck as long as you want because public fleets are not subject to the SB 1 Useful Life requirement.
- Truck Purchases[1]. CNG trucks can be purchased without exemption through 2030 as long as they are no more than 50% of the fleet additions in a given year. State or local government agencies with 10 or fewer trucks and fleets operating in a designated low-population county are exempt from the ZEV purchase requirement through 2030 and may continue purchasing CNG vehicles during that period.
- No Retirement Mandate. There is no mandated retirement of your SLG CNG trucks under the ACF.
Near-Zero Emission Vehicles (NZEV):
- Through 2035, NZEVs, defined as hybrid plug-ins, are counted the same as zero-emission vehicles (ZEV) for purposes of the ACF. Combustion technology is agnostic and can include RNG. NZEVs are not subject to the Useful Life requirements.
High Priority, Federal and Drayage Fleets:
- These fleets are no longer subject to the ACF per amendments approved by CARB on September 25, 2025[2]. These fleets can purchase whatever is legal in accordance with applicable federal, state, and local laws.
[1] California Air Resources Board. (2025, September 25). CARB adds flexibility to truck fleet requirements with amendments to help owners continue zero‑emission progress. https://ww2.arb.ca.gov/news/carb-adds-flexibility-truck-fleet-requirements-amendments-help-owners-continue-zero-emission
[2] Id.
Fleets who qualify for and are granted an exemption under the following provisions may purchase CNG trucks according to the terms and conditions of the relevant provisions:
- Daily Usage Exemption
- ZEV Purchase Exemption
- Declared Emergency Event: Mutual Aid Assistance
- Non-Repairable Vehicle provision