FAQs: Advanced Clean Fleets Regulation

FAQ: Advanced Clean Fleets Regulation (PDF download)

The Advanced Clean Fleets (ACF) regulation is a component of the California Air Resources Board’s (CARB) overall strategy to accelerate the transition of California’s medium- and heavy-duty trucks to zero-emissions vehicles where feasible by 2045. This regulation works in conjunction with Advanced Clean Trucks (ACT) that was approved by CARB in March 2021 to ensure that zero-emission vehicles (ZEV) are brought to market. The ACF is the purchase mandate on fleets and the ACT is the sales mandate on truck manufacturers.

The ACF regulation applies to fleets operating in California that are performing drayage operations, those owned by State and local government agencies, high priority fleets defined as an entity with 50 trucks or $50 million in annual revenue, and Federal fleets. It applies to fleets with medium- and heavy-duty on-road vehicles with a gross vehicle weight rating (GVWR) greater than 8,500 pounds, off-road yard tractors, light-duty mail and package delivery vehicles.

The ACF regulation is made up of four independent sections:

  • High Priority and Federal Fleets. Requires specified entities to phase zero-emission vehicles (ZEV) into their fleets beginning in 2024 according to one of two available compliance pathways—the “Model Year Schedule” (which is the default compliance pathway) or the “ZEV Milestones Option” (which is the alternate, opt-in compliance pathway).
  • Drayage Fleets. Requires all new drayage truck registrations into the CARB Online System be ZEV beginning January 1, 2024. Non zero-emission drayage trucks are allowed to register in the CARB Online System through December 31, 2023 and can continue to operate through their “minimum useful life[1].”
  • State and Local Agencies. Requires 50 percent of vehicles purchased by state and local government fleets (including city, county, special district, and State agency fleets) between 2024 and 2027 to be ZEV and 100 percent thereafter. Small government fleets (those with 10 or fewer vehicles) and government fleets in designated low-population areas are delayed until the 2027 purchase mandate.
  • Manufacturer Sales Mandate.  Tightens the manufacturers’ sales mandate under the Advanced Clean Trucks regulation to 100 percent ZEV medium- and heavy-duty vehicle sales starting on January 1, 2036.

[1] “Minimum useful life” is the minimum time period a vehicle may remain in the California fleet.  It is defined as the earlier of 18 years or 800,000 miles or a minimum of 13 years if the truck has over 800,000 miles.

The ACF was recently approved by CARB in April 2023 and is undergoing final adoption for implementation by January 1, 2024.

FAQ: High Priority and Federal Fleets (HPFF) Requirements under ACF (PDF download)

High Priority and Federal Fleets

Entities which operate medium- and heavy-duty vehicles in CA that meet the following thresholds:

  • Fleets that own, operate, or direct the operation of 50 or more vehicles in the total fleet, excluding light-duty package delivery vehicles, or
  • An entity that has $50 million or more in total gross annual revenues reported to the United States Internal Revenue Service, or
  • Fleet owners or a controlling party whose fleet in combination with other fleets operated under common ownership and control totals 50 or more vehicles in the total fleet, excluding light-duty package delivery vehicles, or
  • Any federal government agency fleet, or
  • Any state or local government agency fleet that elects to comply with the “ZEV Milestones Option.”
  • Hiring Entities that include any motor carrier, broker, governmental agency, person, or entity that hires and operates or hires and directs the operation of vehicles in California.[1]

Transit vehicles subject to the Innovative Clean Transit regulation commencing with title 13, CCR section 2023 are exempt from the regulation.

[1] Hiring entities that are subject to this regulation must follow the requirements found in Section 2015(g) of the “High Priority and Federal Fleet” requirements.

Vehicles operated in California that have a gross vehicle weight rating (GVWR) greater than 8,500 lbs., are light-duty package delivery vehicles, or are yard tractors.  There are limited exemptions:

  • School buses
  • Military tactical vehicles
  • Vehicles awaiting sale
  • Emergency vehicles
  • Historical vehicles
  • Dedicated snow removal vehicles
  • Two-engine vehicles
  • Heavy cranes
  • Vehicles in a test fleet
  • Vehicles subject to the regulation for Mobile Cargo Handling Equipment at Ports and Intermodal Rail Yards.

There are two compliance pathways under the High Priority and Federal Fleets provision:

  • Model Year Schedule (default compliance path)
    • Beginning January 1, 2024, any vehicle added to your California fleet must be a ZEV or NZEV.
    • For existing Internal Combustion Engine (ICE) vehicles, beginning January 1, 2025, ICE vehicles must be removed from your California fleet by January 1 of the calendar year after the minimum useful life mileage threshold is exceeded, or January 1 of the calendar year the engine model year is 18 years old or older, whichever occurs first.
  • ZEV Milestone Option (opt-in compliance path)
    • Beginning January 1, 2025, fleet owners must continuously meet or exceed the ZEV Fleet Milestone percentage requirements set forth below in Table A below.
    • The compliance requirement can be met with any mix of trucks within the Milestone Group.
    • Any fleet utilizing this option must waive their Useful Life protections provided under state law, known as “SB 1 protections.”

Table A: ZEV Fleet Milestones by Milestone Group and Year

Percentage of vehicles that must be ZEVs10%25%50%75%100%
Milestone Group 1: Box trucks, vans, buses with two axles, yard tractors, light-duty package delivery vehicles20252028203120332035 and beyond
Milestone Group 2: Work trucks, day cab tractors, pickup trucks, buses with three axles20272030203320362039 and beyond
Milestone Group 3: Sleeper cab tractors and specialty vehicles20302033203620392042 and beyond
Source: California Air Resources Board

Waste[1] and wastewater[2] fleet owners that meet the following criteria will be categorized into Group 3 of the “ZEV Milestones Option” for those vehicles in their California fleets as of January 1, 2024[3].  This provides fleets who do not fall under the “specialty vehicle” definition in Section 2015(b) additional time to comply with the ZEV purchase requirement.

  • Must be fueled exclusively with biomethane.
  • Eligible garbage vehicle configurations are rear-, side-, and front-loader compactor trucks, tractors exclusively used as transfer trucks, and roll-off trucks.
  • Eligible wastewater vehicle configurations are all vehicles that directly support the operation of facilities that collect and process diverted in-state organic waste to produce biomethane.

[1] A “Waste fleet” is defined as the vehicles owned and operated by a fleet owner that is contracted with a municipality that is mandated to support the hauling, transfer, and processing of diverted in-state organic waste to produce biomethane via franchise agreement or long-term contract, with either a minimum length of ten years or more, or with a minimum length of three years but includes a renewal provision when satisfying the contract terms.

[2] A “Wastewater fleet” is defined as the vehicles owned and operated by a government agency or subdivision that owns and operates a wastewater treatment facility, and the agency’s primary purpose is the collection, treatment, and recycling of wastewater and biosolids.

[3] HPFF Section 2015.2(e)(6)

There are several vehicle purchase exemptions and infrastructure delay extensions offered under the High Priority and Federal Fleets provision. They include:


  • Backup Vehicle Exemption. You may designate one vehicle as a backup vehicle during the January reporting period annually if the following criteria are satisfied:
    • The vehicle is operated less than 1,000 miles a year, excluding miles driven under contract during a declared emergency event, and
    • The fleet must report the vehicle as a backup vehicle and must submit odometer readings.
  • Daily Usage Exemption.  You may request an exemption to purchase a new internal combustion engine (ICE) of the same configuration as an ICE vehicle being replaced if no battery electric vehicle (BEV) is available for purchase that can meet the demonstrated daily usage needs of any existing vehicles of the same configuration within the fleet. If approved, you must place the order for the new ICE vehicle within 180 calendar days from the date in which the exemption was granted. You may use this exemption only if at least 10% of your California fleet is comprised of ZEVs or near-zero emissions vehicles (NZEVs[1]).
  • ZEV Purchase Exemption.  You may request exemptions to purchase a new ICE vehicle if a needed configuration is not available to purchase in ZEV or NZEV under either the ZEV Purchase Exemption List or the ZEV Purchase Exemption Application.
    • ZEV Purchase Exemption List
      • The Executive Officer will establish and maintain a list of vehicle configurations no later than January 1, 2025 at the following link:  CARB Advanced Clean Fleets
    • ZEV Purchase Exemption Application
      • If approved, you must place the new ICE vehicle orders within 180 days from the date the exemption is granted.
  • Exemptions Pursuant to Declared Emergency Event: 
    • Declared Emergency Response. Any vehicle dispatched by a local, state, federal or other responsible emergency management agency or its contractors to support a declared emergency event shall be exempt from the ZEV purchase requirement for the duration of the emergency event.
    • Mutual Aid Assistance. Fleet owners may obtain an exemption from the ZEV purchase requirement to purchase a new ICE vehicle if the fleet owners have a mutual aid agreement to send vehicles to assist other entities during a declared emergency event and the California fleet is comprised of a specified number of ZEVs at the time of the requested exemption. ICE vehicles purchased under the exemption are not restricted solely to mutual aid functions.  This exemption excludes pickup trucks, buses, box trucks, vans, tractors, or any vehicle configurations that can be purchased as NZEV.


  • ZEV Infrastructure Delay Extensions. You must request the following extensions at least 45 days prior to the next applicable compliance date for CARB to consider the request.
    • ZEV Infrastructure Construction Delays
      • May request an extension of up to 2 years if you experience construction delays beyond your control.
    • ZEV Infrastructure Site Electrification Delays
      • Until January 1, 2030, you may request an extension if the electric utility provider determines it cannot provide the requested power to the site where ZEVs will be charged or refueled before the fleet’s next ZEV compliance deadline.
      • You may request an initial extension of up to 3 years from the applicable compliance date, based on the amount of time the utility determines it needs to supply the needed power to the site.
      • You may request an additional 2 years if the utility still cannot supply the needed power by the end of any granted initial extension period.
  • Vehicle Delivery Delay Extension.  You may request an extension to delay removing your ICE vehicle from the fleet if you placed an order for a ZEV prior to the next applicable compliance date and the ZEV cannot be delivered to you by that date due to circumstances beyond your control. 

[1] NZEVs (near zero-emission vehicles) are plug-in hybrids with minimum all electric range.

  • Beginning January 1, 2024, fleet owners must meet the applicable reporting and recordkeeping requirements specified in sections 2015.4 and 2015.5, respectively, in the regulation.
  • Fleets are required to submit annual compliance reports beginning February 1, 2024 until February 1, 2045.  Reports must be submitted through the online CARB Advanced Clean Fleets in the TRUCRS reporting system unless otherwise specified. 
  • Fleets must keep the required reporting records and documentation for at least five years.  Fleet owners must make such records available in an electronic or paper format upon request or make them available to CARB staff within 72 hours of a written or verbal request for audit.

FAQ: Availability and Use of Compressed Natural Gas (CNG) Trucks under the ACF*
(PDF download) & (Infographic)

*Disclaimer:  Please note that the descriptions below are for informational purposes only. It is the responsibility of every fleet to conduct your own research to determine whether your operations are in compliance with the various provisions of the ACF regulation.  

Yes. Those with CNG trucks in their California fleet prior to January 1, 2024 can continue to operate those trucks.

There are several pathways under which a fleet owner can continue to purchase new CNG trucks to add to their California fleet.

Purchasing CNG trucks powered by renewable natural gas (RNG) can provide a readily available alternative to “legacy” diesel trucks and can help fleets meet their sustainability goals immediately using a low carbon, cost-effective, CARB-certified option with a built-out fueling network. 

High Priority and Federal Fleets: 

  • Model Year Schedule (default compliance path). You can continue to use your existing CNG-fueled truck up to and through the year it exceeds its statutory Useful Life. You will only be able to add new CNG trucks to your California fleet after January 1, 2024 with a CARB-issued exemption, unless you purchased it prior to the effective date of the ACF regulation.
  • ZEV Milestones Option (opt-in compliance path). Under this option, you can purchase new CNG trucks for your fleet if you have reached your Milestone Group requirement. You can achieve your milestone calculation with any mix of trucks in your specified Group[1].

Near-Zero Emission Vehicles (NZEV):

  • Through 2035, near-zero emission vehicles (NZEV), defined as a hybrid plug-in, are counted the same as zero-emission vehicles (ZEV) for purposes of the ACF. Combustion technology is agnostic and can include RNG. NZEVs are not subject to the Useful Life requirements. This provision does not apply to drayage.

State and Local Government Agency Fleets:

  • Existing CNG Trucks. You can continue to operate your existing CNG truck as long as you want because public fleets are not subject to the SB 1 Useful Life requirement.
  • Truck Purchases.  Beginning January 1, 2024, CNG trucks can be purchased without exemption through 2027 as long as they are no more than 50% of the fleet additions in a given year. State or local government agencies with ten or fewer trucks or those servicing a designated low population county can add CNG trucks to their fleet until 2027.
  • No Retirement Mandate. There is no mandated retirement of your CNG trucks under this section of the ACF.

[1] “Any ZEVs Count for Compliance. Any ZEV from any Milestone Group can be used to count toward the fleet’s ZEV Fleet Milestone requirement. For example, a fleet with box trucks and day cab tractors can meet the total ZEV Fleet Milestone requirement with ZEV day cab tractors instead of ZEV box trucks.” HPFF Section 2015.2(c).

Likely Yes. Fleets that have less than 50 trucks and less than $50 million in total gross annual revenues are generally not subject to the ACF and can continue to purchase CNG trucks.  However, small fleets under common ownership and control of that controlling entity could be subject to the ACF if the aggregate truck count of the controlling entity is 50 or greater.

CNG drayage trucks registered in the CARB Online System prior to January 1, 2024 can continue to operate until January 1, 2035 provided:

  • The truck visits a California seaport or intermodal railyard at least once annually, and
  • The truck does not exceed its Useful Life threshold.  

There are also several provisions that will allow you to continue using your CNG drayage trucks when certain conditions are met[1].

[1] Vehicle Delivery Delay Extension [Section 2014.2(a)] and the Infrastructure Delay Extensions [Section 2014.2(b)]

New CNG trucks cannot be registered and added into the CARB Online System beginning January 1, 2024.  Starting in 2035, only zero-emission drayage trucks will be allowed to provide drayage services in California.

Fleets who qualify for and are granted an exemption under the following provisions may purchase CNG trucks according to the terms and conditions of the relevant provisions:

  • Daily Usage Exemption
  • ZEV Purchase Exemption
  • Declared Emergency Event: Mutual Aid Assistance
  • Non-Repairable Vehicle provision

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