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Home / News / Newsfeed / CARB’s Advanced Clean Fleets Regulation

CARB’s Advanced Clean Fleets Regulation

September 26, 2023
Image of a semi truck driving down a highway surrounded by grassy fields and a blue sky
For more information, please visit CARB’s website at: https://ww2.arb.ca.gov/our-work/programs/advanced-clean-fleets.

The California Air Resources Board (CARB) approved the Advanced Clean Fleets (ACF) regulation on April 28, 2023, which requires the transition to zero-emission vehicles (ZEVs). The regulation is anticipated to become law in 2023, and requirements begin as early as January 1, 2024. The ACF regulation applies to vehicles of all fuel types with gross vehicle weight ratings (GVWRs) over 8,500 pounds.

High-Priority and Federal (HPF) Fleets

HPF requirements apply to all federal fleets with at least one applicable vehicle and to private fleets that meet the “high priority” threshold in one of the following two ways, when considering all companies under common ownership:

  1. Annual gross revenue of $50 million or more with at least one vehicle; or
  2. own or direct 50 or more vehicles in California, regardless of revenue.

The default compliance schedule requires that vehicle acquisitions starting January 1, 2024, must be ZEVs. Beginning January 1, 2025, existing vehicles have a compliance phase-out when they reach their minimum useful life (MUL).

As an alternative to the MUL phase-out, the fleet can choose the Zero-Emission Milestone (ZEM) Compliance Option, which allows fuel-based vehicle purchases at any time, so long as the fleet meets the milestones shown in Table 1. There are three milestone groups (MGs). MG1 includes box trucks, vans, two-axle buses, yard tractors, and light-duty package delivery vehicles. MG2 includes work trucks, day cab tractors, and three-axle buses. MG3 includes sleeper cap tractors and specialty vehicles.

Table 1: Zero-Emission MG and ZEV Purchase Schedules

MG Percent Fleet Purchased
10% 25% 50% 75% 100%
1 2025 2028 2031 2033 2035+
2 2027 2030 2033 2036 2039+
3 2030 2033 2036 2039 2042+


State and Local Government Agency (SLGA) Fleets

Under the ACF regulation, public fleets have two compliance options:

  1. The SLGA purchase compliance schedule of 50% ZEV purchases from January 1, 2024, through December 31, 2026, and 100% ZEV purchases starting January 1, 2027; or
  2. The ZEM Compliance Option defined in the ACF regulation for HPF fleets, as described above.


Starting January 1, 2024, any newly registered drayage vehicle must be a ZEV. Legacy trucks registered by December 31, 2023, will phase out when they reach the MUL or January 1, 2035, whichever occurs first. Legacy trucks must visit a port or intermodal railyard at least once annually and must report annual odometer readings to track MUL status. There are exemptions and extensions that vary for each type of fleet. Some exemption categories include backup vehicles (1,000 miles per year), annual 5-day pass, mutual aid assistance, and fuel-based vehicle purchases for ZEV unavailability or when ZEVs do not meet daily operational needs, ZEV infrastructure delay, and ZEV delivery delay.


Manufacturers must meet a 100% zero emission sales requirement starting January 1, 2036.


Yorke Engineering specializes in air quality consulting and environmental consulting for stationary and mobile sources, including dispersion modeling, health risk assessments, permitting, emission inventories, air quality compliance systems, etc. Yorke Engineering has assisted over 1,800 customers, including a wide variety of industrial facilities and government organizations throughout California. Learn more about how we can help you here: Air Quality | Yorke Engineering, LLC (yorkeengr.com).

Air Quality Tip

Amendments to the In-Use Off-Road Diesel-Fueled Fleets regulation were finalized on August 18th and have an implementation date of January 1, 2024. For more information, visit: https://ww2.arb.ca.gov/our-work/programs/use-road-diesel-fueled-fleets-regulation

Main Office:

31726 Rancho Viejo Rd. Suite 218
San Juan Capistrano, CA 92675

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