Understanding CARB’s Advanced Clean Trucks Regulation

The Advanced Clean Trucks (ACT) regulation is a California Air Resources Board (CARB) rule that requires truck manufacturers to sell a growing percentage of zero-emission trucks in California. Adopted in 2020 and effective starting with the 2024 model year, it was the first rule of its kind in the world and became the model for several other states.

In 2025, Congress revoked the federal waiver California needs to enforce ACT, and the rule is now tied up in court. This guide explains what ACT requires, how its credit system works, which states adopted it, where it stands in October 2026 and what it means for fleets.

This article is for general education, not legal advice. For official requirements, consult CARB at ww2.arb.ca.gov.

What ACT Requires

ACT applies to manufacturers that sell Class 2b through Class 8 trucks (8,501 pounds GVWR and up) in California, including chassis and complete vehicles. Starting with model year 2024, each manufacturer must sell zero-emission vehicles (ZEVs) as a rising percentage of its annual California sales.

The rule groups vehicles into three categories with different targets:

ACT supports California’s broader goal, set by a 2020 executive order, for all medium- and heavy-duty vehicles operating in the state to be zero-emission by 2045 where feasible.

How Compliance Works: Deficits and Credits

ACT doesn’t simply count trucks. It uses a credit system:

• Deficits. Every on-road truck a manufacturer sells in California creates a compliance obligation (a deficit) equal to its sales multiplied by the required percentage for that category.
• Credits. Selling zero-emission trucks earns credits. Near-zero-emission vehicles, such as plug-in hybrids with a minimum electric range, earn partial credits.
• Weight class modifiers. Heavier vehicles count more, reflecting their greater emissions impact. A Class 8 tractor is worth more credit than a Class 2b van.
• Trading and banking. Manufacturers can bank surplus credits for future years and trade credits with other manufacturers, with limits on how credits can be used across categories.

This gives manufacturers flexibility in how they meet the requirement while still driving overall zero-emission sales.

Reporting Requirements

When adopted, ACT also included a one-time Large Entity Reporting requirement. Large employers, including retailers, manufacturers and brokers, and fleet owners with 50 or more trucks had to report information about their shipments, shuttle services and existing fleet operations. CARB used this data to shape later fleet rules.

Which States Adopted ACT?

Under Section 177 of the Clean Air Act, other states can adopt California’s vehicle standards. States that adopted ACT include Oregon, Washington, New York, New Jersey, Massachusetts and Vermont, with several others adopting or considering it at various times. Because these states depend on California’s federal waiver, the 2025 congressional action affects them too. Several have delayed or paused enforcement, and some are reconsidering their timelines.

2026 Status: The Federal Waiver Fight

Here is how ACT ended up in legal limbo:

1. 2023: EPA granted California the Clean Air Act waiver needed to enforce ACT.
2. 2023: CARB and major truck manufacturers signed the Clean Truck Partnership, in which manufacturers agreed to follow California standards, including ACT, in exchange for more lead time and flexibility.
3. January 2025: CARB withdrew its waiver request for the separate Advanced Clean Fleets (ACF) rule.
4. June 2025: Congress passed, and the President signed, resolutions under the Congressional Review Act (CRA) nullifying EPA’s waivers for ACT, the Omnibus Low NOx rule and Advanced Clean Cars II.
5. June 2025: California sued, arguing that waivers are not “rules” subject to the CRA.
6. After the revocation: Manufacturers and CARB went to court over whether the Clean Truck Partnership still binds manufacturers.

As of October 2026, manufacturers are not treating ACT sales requirements as enforceable while the courts decide. Depending on the outcome, the requirements could be restored, modified or permanently blocked. Follow developments on our 2026 Regulation Tracker.

ACT vs. Advanced Clean Fleets

ACT is often confused with its companion rule, Advanced Clean Fleets.

What ACT Means for Fleets

ACT never required fleets to buy zero-emission trucks. Its effects were indirect:

• Availability. The rule pushed manufacturers to develop and stock zero-emission models for California.
• Pricing and deals. To earn credits, manufacturers had incentives to price zero-emission trucks competitively or offer deals.
• Diesel supply. Some feared manufacturers might limit diesel sales in California to stay in compliance. With enforcement on hold, that pressure has eased.

Common Misconceptions About ACT

“ACT bans diesel trucks.” It doesn’t. Even at its 2035 targets, ACT would allow 25% to 60% of new truck sales in California to be diesel or other combustion vehicles, depending on category. The 2036 all-zero-emission sales requirement was part of the separate ACF rule, and CARB has said it isn’t enforcing the parts of ACF that need a federal waiver.

“ACT applies to trucks registered outside California.” ACT counts sales by manufacturers into California (and into states that adopted it). It doesn’t restrict out-of-state trucks from driving in California.

“Used trucks are affected.” ACT applies to new vehicle sales. It doesn’t require fleets to retire or replace existing trucks.

“The rule is gone for good.” Not necessarily. California’s lawsuit challenging the 2025 revocation is pending, and a future change in federal policy could revive waiver-based rules. Fleets making long-term purchase plans should account for that possibility.

The Bottom Line

CARB’s Advanced Clean Trucks regulation requires manufacturers, not fleets, to sell a growing share of zero-emission trucks, reaching 40% to 75% of sales by 2035 depending on vehicle category. Congress revoked the federal waiver in 2025, and California’s legal challenge is pending, so manufacturers aren’t treating the rule as enforceable for now. Fleets should watch the litigation because it affects truck availability and pricing, but ACT itself doesn’t require any fleet to buy an electric truck.

Frequently Asked Questions

Does ACT require me to buy electric trucks?

No. ACT applies to manufacturers. The fleet-purchase rule was Advanced Clean Fleets, most of which isn’t being enforced for private fleets.

Is the Advanced Clean Trucks rule still in effect?

It remains on California’s books, but Congress revoked the federal waiver in June 2025. California is challenging that in court, and manufacturers aren’t treating the sales requirements as enforceable until it’s resolved.

What states follow California’s ACT rule?

Oregon, Washington, New York, New Jersey, Massachusetts and Vermont adopted ACT. Several have delayed or paused enforcement since 2025.

What is a near-zero-emission vehicle under ACT?

A vehicle, such as a plug-in hybrid, that meets minimum all-electric range requirements. It earns partial credit toward a manufacturer’s ACT obligation.