California: Heavy-duty: ZEV


California has set ambitious goals to transition medium- and heavy-duty vehicle (MHDV) sales and operations to zero-emission vehicles. The California Air Resources Board (CARB) has adopted and is developing further regulations to encourage this transition to zero-emission MHDVs. On the supply side, the Advanced Clean Trucks rule sets minimum zero-emission sales share requirements for manufacturers through 2035. Demand-side rules include the Innovative Clean Transit rule, Zero-Emission Airport Shuttle regulation, and expected rules on Advanced Clean Fleets.


In 2020, Governor Gavin Newsom signed Executive Order N79-20 which enumerated multiple goals to reduce emissions from the transportation sector by accelerating the adoption of zero-emission vehicles (ZEVs). These goals included 100% of medium- and heavy-duty vehicles (MHDVs) in California being zero-emission (ZE) by 2045 and 100% of drayage trucks being ZE by 2035 for all operations where feasible. CARB endorsed these targets in Resolution 20-19 and added the following targets: 100% ZE drayage truck, last mile delivery, and government fleet operations by 2035; 100% ZE refuse truck and local bus fleet operations by 2040; and 100% ZE capable utility fleet operations by 2040. Governor Newsom also signed, along with fourteen other states and the District of Columbia, the Multi-State MHDV ZEV Memorandum of Understanding in 2020. This memorandum of understanding set ZE MHDV sales targets as 30% by 2030 and 100% by 2050. CARB’s draft 2020 Mobile Source Strategy from April 2021 aims for 100% ZE MHDV sales by 2035.

Both existing and new regulations will support these goals. The Innovative Clean Transit rule and ZE Airport Shuttle regulation were proposed in 2018 and adopted in 2019. The Advanced Clean Trucks rule was proposed in 2019 and adopted in 2020. As of August 2021, CARB is developing the Advanced Clean Fleets rule, and a final staff proposal and Board consideration are expected by the end of 2021.

California is using various mechanisms to ensure a smooth and timely MHDV ZE transition. Policies like the Innovative Clean Transit rule set demand-side requirements, compelling fleets to acquire and operate ZEVs to decrease emissions. Other policies like the Advanced Clean Trucks rule set supply-side requirements, ensuring manufacturers will produce and sell enough ZEVs to make a ZEV transition possible. Other statewide measures include fiscal incentives to lower the cost of acquiring ZEVs and to fund charging stations; the Low Carbon Fuel Standard (LCFS) that gives credits to fuel providers to build infrastructure supporting ZEVs; and the Cap-and-Trade Program, which requires large emitters like fuel providers to decrease emissions.

Technical standards

Innovative Clean Transit

The Innovative Clean Transit (ICT) regulation sets zero-emission (ZE) bus fleet purchasing requirements for California transit agencies. This rule does not apply to the following transit agencies: school districts, Amtrak, Caltrain, and Caltrans. It also does not apply to the following vehicles: school buses, trolleybuses, and vehicles on rails.

Separate requirements exist for large and small transit agencies. A large transit agency is defined as a transit agency that operates in either the South Coast or San Joaquin Valley Air Basin and operates > 65 buses annually or a transit agency that operates outside of the South Coast and San Joaquin Valley Air Basins and operates ≥ 100 buses in areas with a population ≥ 200,000 people.

The ICT regulation requires that the number of ZE buses that need to be purchased every year by an agency needs to be equal to at least the number of new bus purchases multiplied by the percent requirement, rounded to the nearest whole number. To encourage early acquisition of ZE buses, Bonus Credits are awarded for ZE buses already in the fleet or placed into service before 2022. One Bonus Credit can replace one ZE bus purchase. The minimum required number of ZE buses can be met with any combination of new ZE bus purchases and Bonus Credits. Bonus Credits can only count once towards meeting the ICT requirements. Because Bonus Credits expire in 2028, from 2029, all new buses purchased by transit agencies must be ZEVs.

ZE bus purchasing timelines
  Large transit agency Small transit agency
Compliance start date % of new bus purchases that must be ZEa % of new bus purchases that must be ZEa
January 1, 2023 25
January 1, 2026 50 25
January 1, 2029 100 100
a The percent of new bus purchases sets a minimum benchmark that can be fulfilled with any combination of new ZE bus purchases and existing ZE buses that have not already been used in accounting for the required number of minimum ZE bus purchases
Bonus Credits for early acquisition of ZE buses
Type of ZE bus Requirement Number of Bonus Credits Expiration of Bonus Credits
Fuel cell electric In fleet before 2018 2 End of 2028
Fuel cell electric Placed in service 2018–2022 1 End of 2028
Battery electric In fleet before 2018 1 End of 2028
Electric trolleybusa Placed in service 2018–2019 0.1 End of 2024
a Although trolleybuses are not subject to the purchasing requirements in the ICT rule, electric trolleybuses can still generate Bonus Credits toward compliance.

In addition to credits, CARB will allow transit agencies to implement and operate a ZE Mobility Program instead of purchasing a ZE bus. A ZE Mobility Program is a program that provides other ZE mobility services (bikes, scooters, other ZEVs with GVWR ≤ 14,000 lbs., or a combination of these). A large transit agency’s program must achieve 320,000 passenger miles per year, and a small transit agency’s program must achieve 180,000 passenger miles per year in order to replace one ZE bus purchase.

Advanced Clean Trucks

The Advanced Clean Trucks (ACT) rule establishes ZE sales requirements for all manufacturers that certify on-road vehicles with GVWR > 8,500 pounds for sale in California. This regulation does not apply to school districts with school bus-only fleets, transit agencies subject to the ICT rule, or emergency vehicles. Additionally, manufacturers selling 500 or fewer heavy-duty trucks (HDT) in California are exempt but can generate credits to be banked, traded, or sold (see below).
Starting with model year (MY) 2024, truck manufacturers must meet the following ZEV sales requirements:

Required ZEV sales as a percent of total sales based on model year and group
MY Class 2b–3 pickup trucks and vans Class 4–8 rigid trucks Class 7–8 rigid trucks
2024 5% 9% 5%
2025 7% 11% 7%
2026 10% 13% 10%
2027 15% 20% 15%
2028 20% 30% 20%
2029 25% 40% 25%
2030 30% 50% 30%
2031 35% 55% 35%
2032 40% 60% 40%
2033 45% 65% 40%
2034 50% 70% 40%
2035 and beyond 55% 75% 40%

Compliance with the ACT regulation is based on a credit and deficit accounting system. Deficits are accrued based on a manufacturers’ total HDT sales each year; this includes sales of internal combustion, ZEV, and ‘near zero-emission vehicles’ (NZEV), which are defined as hybrid electric vehicles with externally rechargeable energy storage systems that allow for an all-electric range (i.e., PHEVs). Both credits and deficits are calculated. Deficits are calculated per sales group by multiplying the number of vehicles sold by the percent sales requirement and a weight class multiplier (WCM). Credits are calculated per sales group by multiplying the sales of ZEV by the appropriate WCM. The WCM serves to account for larger trucks emitting more; manufacturers with larger trucks that emit more will accrue more deficits that need to be offset with more ZEV and NZEV credits. NZEV multipliers are calculated by multiplying the respective ZEV credit value by 0.01 and the all-electric range of the NZEV in miles; this multiplier is capped at 0.75 and will always be 0.75 starting in 2030 when eligible NZEVs must have a minimum all-electric range of 75 miles.

Weight class multipliers
Group/subgroup Weight class multiplier
Class 2b–3 pickup trucks and vans 0.8
Class 4–5 subgroup in Class 4–8 rigid trucks 1
Class 6–7 subgroup in Class 4–8 rigid trucks 1.5
Class 7–8 subgroup in Class 4–8 rigid trucks 2
Class 7–8 tractor trucks 2.5

To reward early sales of ZEVs, credits can be accrued with ZEV and NZEV sales starting with MY 2021. These early credits can be banked until MY 2030. Once the MY 2024 sales requirements begin, excess credits can be banked for five subsequent model years. Each model year, manufacturers must generate or yield banked credits equal to the number of deficits, with NZEV credits meeting up to at most half of deficits. Additionally, although any credits generated can be used to cover any deficits generated by Class 2b–3 and Class 4–8 vehicles, deficits generated by Class 7–8 tractors can only be met with credits generated by Class 7–8 tractors. However, manufacturers that accrue 25 or fewer deficits from Class 7–8 tractors can offset these deficits with credits from any group. Manufacturers have one model year to make up outstanding deficits, which can only be covered with ZEV credits. Credits can also be traded and sold between manufacturers.

Aside from manufacturer sales requirements, the ACT includes a requirement for large entities, large fleet owners and brokers, and government agencies that operated HDVs in 2019 to report business practices and emissions reductions goals. CARB will use this information to develop future ZEV purchasing requirements.

The following states have also adopted ACT – Massachusetts, New Jersey, New York, Oregon, and Washington.

Advanced Clean Fleets

As of August 2021, CARB is developing the Advanced Clean Fleets rule, and a final staff proposal and Board consideration are expected by the end of 2021. Preliminary materials on the forthcoming rule have been released by CARB staff. According to these materials, the rulemaking will attempt to achieve ZE truck and bus fleet operations in California by 2045 (and earlier where possible) and will include fleet purchasing and operating rules for both public and private fleets. It is expected to prioritize benefits in disadvantaged communities and apply to vehicles with a GVWR > 8,500 pounds—excluding transit vehicles covered by ICT, school buses, and emergency vehicles.

Zero-Emission Airport Shuttle

The Zero-Emission Airport Shuttle regulation requires ZEV purchases for shuttles that operate at or near regulated airports in California. The rule applies to fleet owners of Class 2b–8 commercial vehicles with GVWR > 8,500 pounds that transport passengers to and from regulated airports. There is a purchasing requirement starting in 2023, when all new shuttle purchases must be ZEVs. The ZE fleet composition requirement compliance schedule is shown in the table below:

ZE airport fleet compliance schedule
Compliance deadline Fleet ZEV requirement
December 31, 2027 33%
December 31, 2031 66%
December 31, 2035 100%

This regulation does not apply to vehicles subject to the ICT regulation.

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