Understanding California’s Advanced Clean Fleet Regulation

The Advanced Clean Fleets (ACF) regulation, passed by California legislators on April 28th, aims to phase out medium- and heavy-duty (MDHD) internal combustion engine trucks to transition the state's transport system to zero-emissions vehicles (ZEVs) by 2045. The regulation establishes specific compliance pathways for high-priority fleets, drayage truck fleets, and public fleets, while providing extensions for infrastructure, electrical, and delivery delays.

• The Advanced Clean Fleets (ACF) regulation targets the phase-out of medium- and heavy-duty (MDHD) internal combustion engine trucks in California to support a state-wide transition to zero-emissions vehicles by 2045. The California Air Resources Board (CARB) estimates that the ACF could reduce emissions by nearly 25 million metric tons of CO2 from 2024 to 2041.
• High-priority fleets—defined as those with over 50 trucks or private companies with annual revenues exceeding $50 million—can comply via two options: a ZEV model year schedule, where all new purchases must be ZEVs starting January 2024 and ICE vehicles are retired based on age (13 or 18 years) or mileage (800,000 miles), or ZEV milestones, which use percentage targets based on vehicle size and model year.
• Drayage truck fleets operating at California ports or intermodal rail yards must purchase only ZEV trucks starting in 2024 and ensure all fleet trucks are ZEVs by 2035. They are required to report mileage for trucks over 12 years old by 2025 and remove trucks that reach 800,000 miles or 18 years (or 13 years if they exceed 800,000 miles).
• Public fleets owned by state and local government agencies must ensure 50 percent of new truck purchases are ZEVs between 2024 and 2026, with 100 percent of purchases being ZEVs from 2027 onward. Exemptions apply to specific agencies and counties with fewer than 10 vehicles.
• The California Air Resources Board (CARB) allows for flexibility through extensions and exemptions in four categories: infrastructure delays (one-year extension), electrical delays (subject to utility contracts and sunsetting in 2030), vehicle delivery delays (allowing temporary ICE use), and daily usage exemptions for ZEV models that do not meet duty-cycle requirements.

APA

RMI (2023). Understanding California’s Advanced Clean Fleet Regulation. https://rmi.org/resources/understanding-californias-advanced-clean-fleet-regulation/

Chicago

RMI. Understanding California’s Advanced Clean Fleet Regulation. 2023. https://rmi.org/resources/understanding-californias-advanced-clean-fleet-regulation/.

Wikipedia

{{cite report |author=RMI |title=Understanding California’s Advanced Clean Fleet Regulation |date=3 July 2023 |url=https://rmi.org/resources/understanding-californias-advanced-clean-fleet-regulation/ |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{rmi2023understanding, author = {{RMI}}, title = {{Understanding California’s Advanced Clean Fleet Regulation}}, institution = {RMI}, year = {2023}, month = jul, url = {https://rmi.org/resources/understanding-californias-advanced-clean-fleet-regulation/}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }