The California Air Resources Board (CARB) announced it will formally repeal the High Priority Fleet and Drayage Fleet provisions under the Advanced Clean Fleets (ACF) regulation by October 31, 2025, with final action required by August 31, 2026. This decision follows a legal settlement with a coalition of 17 states led by Nebraska, along with various trucking industry groups, and an earlier agreement with the California Trucking Association (CTA).

As part of the settlement, CARB also agreed not to enforce the ACF’s 2036 mandate requiring 100% zero-emission sales of new medium- and heavy-duty trucks unless it first secures a waiver from the U.S. Environmental Protection Agency (US EPA). This mandate would have required all new trucks sold in California to be zero-emission vehicles (ZEVs) beginning in 2036.

With the removal of these provisions, CARB would likely have to adopt a new regulation to reimpose similar zero-emission truck purchasing requirements in the future. Currently, CARB is barred from enforcing ACF on private sector fleets following the withdrawal of their waiver request to the US EPA in January 2025.

At the same time, several states that follow California’s clean truck rules—commonly referred to as Section 177 or “adopting states”—are reevaluating their implementation timelines and pausing enforcement of zero-emission truck mandates. These delays are largely driven by concerns over charging infrastructure, legal uncertainty, and market readiness. As of now, at least six of the eleven “adopting states” have taken such action, including the most recent declarations by Oregon, Vermont, and Pennsylvania:

• Pennsylvania: On May 10, 2025, the Pennsylvania Department of Environmental Protection announced extending its suspension of the state’s version of the Heavy-Duty Low NOx Omnibus regulation (Heavy-Duty Diesel Emissions Control Program) until January 2, 2028, due to ongoing legal and political uncertainty.

• Vermont: On May 13, Governor Phil Scott issued Executive Order 04-25, directing the Agency of Natural Resources to pause enforcement of electric vehicle sales mandates related to the Advanced Clean Trucks (ACT), Omnibus, and Advanced Clean Cars II (ACC II) programs through December 31, 2026. The order cited concerns over charging infrastructure limitations and the technological readiness of heavy-duty ZEVs.

• Oregon: On May 15, the Oregon Department of Environmental Quality (DEQ) issued a memo to exercise enforcement discretion for the ACT rule for all model year 2025 and 2026 Class 2b-8 vehicles. DEQ had previously proposed issuing credits to manufacturers during this period to ensure continued availability of internal combustion trucks in the state’s market.

These actions signal a growing concern among states about the practical challenges of implementing zero-emission truck regulations—particularly around infrastructure readiness, technological feasibility, and regulatory uncertainty—highlighting the need for more flexible timelines and coordinated support to ensure successful adoption.