California’s Advanced Clean Fleets regulation

The Advanced Clean Fleets (ACF) rule is a demand-side requirement for fleets to phase in zero-emission vehicles. It is part of a comprehensive strategy to reduce heavy-duty transportation greenhouse gas (GHG) emissions and provide cleaner air. This policy update summarizes the timeline, projected benefits, and other key elements of the ACF rule if it were to be applied to all vehicles in the state. It also puts the rule in the context of other zero-emission heavy-duty vehicle (HDV) policies in California and compares the rule with fleet purchase requirements in other major vehicle markets.

On January 13, 2025, the California Air and Resources Board (CARB) withdrew its request for a waiver from the U.S. Environmental Protection Agency (EPA) needed to implement stricter emission standards on all vehicles in California under the Clean Air Act. However, California currently plans to apply the rule to state and local fleets, which it can do without a waiver. If the ACF rule were to be applied to all vehicles in the state as drafted, CARB estimates that it would reduce 327 million tons of carbon dioxide-equivalent GHG emissions and deliver $106.6 billion statewide net benefits between 2024 and 2050.

If applied to the full scope of vehicles instead of only state and local fleets, the ACF rule would reduce pollution and GHG missions from medium- and heavy-duty vehicles in California and provide long-term cost savings for fleets. A full list of estimated benefits is provided in the table below.

Table. Estimated statewide cumulative benefits of the Advanced Clean Fleets regulation through 2050