2025 CARB Regulations for Trucks Operating in California

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What is the California Air Resource Board?

CARB is the California Air Resources Board, and they are charged with protecting the public from the harmful effects of air pollution and developing programs and actions to fight climate change in the state of California. From requirements for clean cars and fuels to adopting innovative solutions to reduce greenhouse gas emissions, California has pioneered a range of effective approaches that have set the standard for effective air and climate programs for the nation, and the world.

What are CARB Regulations?

The California Air Resources Board (CARB) regulations are intended to reduce emissions from vehicles, fuels, and other sources operating in California to improve air quality and public health. The state of California is working to adopt and implement regulations around commercial vehicles driven in California. CARB regulations are complicated, not always clear, and subject to change. The Board continually updates and revises its regulations to address emerging challenges and advance its goals of improving air quality and reducing emissions; so, be sure to review multiple sources and note the dates the information was published.

Below are highlights of the new CARB regulations that affect any vehicle that operates or drives in or through California. Most of what you see below is taken directly from the CARB website to make this document as accurate as possible.

Who is Affected?

High Priority Fleet - High priority fleets are entities that own, operate, or direct the operation of at least one vehicle in California, and that have either $50 million or more in gross annual revenue, or that own, operate, or direct the operation of a total of 50 or more vehicles.

New CARB Regulations

CARB regulations have changed. In order to comply with CARB’s new regulations (as of January 2025), affected fleet owners have two options: following the Model Year Schedule or choosing the ZEV (Zero Emission Vehicle) Milestone Option.

1. Heavy-Duty Vehicles (Trucks and Buses)

• Regulation: Heavy-Duty Omnibus Regulation
  • January 1, 2025: Stricter NOx standards for 2025 model year heavy-duty engines go into effect. This includes:
    • Reduced NOx emissions limits.
    • Fleets must remove internal combustion engine vehicles at the end of their useful life, as specified in the regulation.
• Regulation: Advanced Clean Fleets (ACF)
  • January 1, 2025: Large fleet owners (public and private) must start reporting fleet data and developing plans for zero-emission vehicle (ZEV) transition.
  • Starting in 2025, CARB will provide a ZEV Purchase Exemption List for vehicle configurations unavailable as ZEVs or NZEVs. If a fleet owner needs a configuration not on the market, they may purchase a new ICE vehicle with a California-certified engine.

2. Advanced Clean Cars II (Passenger Vehicles)

• 2025 Model Year Vehicles: ZEV credit requirements for manufacturers increase.
• Automakers will be required to meet increasing sales quotas for battery electric, plug-in hybrid, and hydrogen fuel cell vehicles.

3. Advanced Clean Trucks (ACT) Rule

• January 1, 2025: ZEV sales requirements for medium- and heavy-duty truck manufacturers escalate.
• Manufacturers that sell Class 2b-8 trucks with combustion engines in California must also sell a growing percentage of zero-emission trucks each year from 2024 to 2035. By 2035, at least 55% of Class 2b-3 truck sales, 75% of Class 4-8 straight truck sales, and 40% of truck tractor sales must be zero-emission.

4. At-Berth Regulation – Coming January 1, 2025

• To reduce pollution from ships docked at California ports, CARB will require tanker and roll-on-roll-off vessels to use a CARB Approved Emission Control Strategy (CAECS) starting January 2025. This rule targets emissions while vessels are berthed, helping improve air quality around ports.

5. Heavy-Duty Vehicle Engine Requirements

• For years, CARB has enforced stricter standards for diesel engines. To legally operate a heavy-duty vehicle in California, the engine must be a 2010 model year or newer. This upgrade ensures vehicles meet current emissions standards and reduce harmful pollutants like nitrogen oxides and particulate matter.

6. Low-Use Exemption for Older Engines

• Trucks with engines older than model year 2010 might still qualify for a low-use exemption (1,000 miles per year). This exemption allows limited operation for vehicles that aren’t used frequently, giving some flexibility to operators with older equipment.

When Do the New CARB Regulations Go Into Effect?

The new CARB regulations affect engines built on or after January 1, 2025. Note that the engine model year is the guide, not the truck model year.

Common Acronyms & Terms Glossary

ACF – The Advanced Clean Fleets Regulation requires fleets that are well suited for electrification to transition to zero-emission vehicles (ZEV) through requirements to both phase-in the use of ZEVs for targeted fleets and requirements that manufacturers only manufacture ZEV trucks starting in the 2036 model year.  

ACT – The Advanced Clean Trucks regulation is a manufacturers ZEV sales requirement and a one-time reporting requirement for large entities and fleets.  

CARB – The California Air Resources Board (CARB) is responsible for regulating air quality and implementing measures to reduce air pollution in California. 

g/bhp-hr – Grams per brake horsepower – hour.  A standard of measure commonly used by the EPA and CARB to measure emissions from an engine

High Priority Fleet - High priority fleets are entities that own, operate, or direct the operation of at least one vehicle in California, and that have either $50 million or more in gross annual revenue, or that own, operate, or direct the operation of a total of 50 or more vehicles (currently interpreted as the total US fleet, not just CA). 

NOx - Nitrogen Oxides are a family of poisonous, highly reactive gases which form when fuel is burned at high temperatures. Ground-level ozone (the main ingredient in smog) is formed by a chemical reaction between VOCs and NOx in the presence of sunlight. Ozone concentrations can reach unhealthful levels when the weather is hot and sunny with little or no wind. 

Omnibus NOx – California’s Nitrogen Oxide (NOx) emissions standard set by the Heavy-duty Omnibus regulations for new California-certified 2024 through 2026 model year engines which is 0.050 g/bhp-hr.  

ZEV - Zero Emission Vehicle (electric)

Again, as these regulations are ever changing, be sure to stay up to date on CARB regulation updates, as well as which laws in California apply to the new CARB regulations.

Where can I learn more and stay up to date?

CARB Heavy Duty Omnibus Regulation Page

CARB Low-Nox Page 

CARB Low Nox Fact Sheet

Register for e-mail updates directly from CARB