California Air Resources Board and heavy-duty manufacturers announce New Clean Truck Partnership

A historic joint agreement, called the Clean Truck Partnership, was announced on July 6, 2023, between the California Air Resources Board (CARB) and a number of heavy-duty engine and vehicle manufacturers.  Under the Agreement, CARB has committed to modify its Heavy-Duty Omnibus (Low NOx) Regulation to provide manufacturers with additional flexibility and to more closely align with EPA’s heavy-duty criteria pollutant regulations, while the industry signatories have agreed to support the transition to heavy-duty zero-emission vehicles regardless of the outcome of pending litigation challenging CARB’s authority to implement such regulations.  Notably, CARB has also agreed that its staff will propose and recommend adoption by the Board of the minimum four-year lead time and three-year stability periods for future criteria emissions regulations affecting new heavy-duty on-highway engines and vehicles, consistent with provisions contained in the Clean Air Act.

See Clean Truck Partnership Agreement announced by CARB on July 6, 2023.


CARB had adopted its Omnibus Regulation on September 9, 2021, and it became effective on December 22, 2021.  CARB sought a waiver from the U.S. Environmental Protection Agency (EPA) in January 2022 before then requesting additional time before EPA acted on CARB’s waiver request.  The additional time presumably allowed CARB to negotiate with manufacturers to reach the announced Agreement and will allow CARB to make the planned modifications to the Omnibus Regulation before obtaining a waiver from EPA under the Clean Air Act.

CARB’s Executive Officer, Steven S. Cliff, Ph.D., signed the Clean Truck Partnership Agreement on behalf of CARB.  Industry signatories to the Agreement include the Truck and Engine Manufacturers Association (EMA) and EMA members Cummins Inc.; Daimler Truck North America; General Motors Company; Hino Motors Limited, Inc.; Isuzu Technical Center of America, Inc.; Navistar, Inc.; PACCAR Inc.; Stellantis N.V.; and Volvo Group North America. 

CARB: Key Commitments Under the Agreement

Under the Clean Truck Partnership Agreement, CARB is committing to revise the existing compliance flexibility provisions in the Omnibus Regulation by raising the existing caps on legacy engines and streamlining other provisions and to amend the Omnibus Regulation’s 2027 and later model year requirements to align with EPA’s Clean Trucks Plan 2027 Low NOx final rule.  CARB has also committed to preparing Manufacturers Advisory Correspondence guidance addressing compliance with the flexibility provisions.

CARB is also committing to provide implementation flexibility related to CARB’s Emission Warranty and Information Reporting program and Advanced Clean Trucks (ACT) regulations.  Specifically, CARB will use its discretion to not require automatic recalls at the regulatory trigger points for MY2024-2034 engines but will “take into consideration the newness of the technology and information submitted by manufacturers before making recall decisions,” as well as EPA’s recall decisions.  CARB has also agreed to introduce a credit pooling concept for credits and deficits generated in California and Section 177 states that have adopted CARB’s ACT Regulation via a public workshop in calendar year 2023.

While committing to harmonize its regulations with EPA’s Clean Trucks Plan criteria pollutant regulations, CARB has made clear that it will maintain its certification program, independently evaluating certification applications rather than issuing “deemed to comply” certifications based on EPA certificates of conformity, and that it will maintain its on-board diagnostic (OBD) program and its Clean Idle label requirement, though proposing to align with EPA’s 10 grams per hour idle standard.

EMA and Manufacturers: Key Commitments Under the Agreement

In exchange for the commitments from CARB, the manufacturers have agreed to meet certain specified CARB regulations regardless of the outcome of any litigation challenging the waivers or authorizations for those regulations or CARB’s overall authority to implement those regulations.  In addition, EMA and the manufacturers have agreed not to initiate or participate in litigation challenging CARB’s issuance of the specified CARB regulations, including by filing amicus briefs in support of such challenges.  The specified CARB regulations include the Omnibus Regulation, Advanced Clean Trucks Regulation, Zero Emission Airport Shuttle Regulation, Zero Emission Powertrain Certification Procedure, and the 2018 HD Warranty Amendments.  EPA granted waivers for these other regulations, except the Omnibus Regulation, on April 6, 2023.

EMA and the manufacturers have also agreed to limit their advocacy by remaining neutral with respect to other states’ adoption of CARB’s Omnibus and ACT Regulations.  The manufacturers are committing to comply with the MY2027 and later Omnibus provisions in any Section 177 state that has adopted them, regardless of the outcome of any related litigation, and to “put forth their best efforts to sell as many zero emission trucks as reasonably possible in every state that has or will adopt CARB’s ACT regulations, even potentially exceeding any future U.S. EPA Phase 3 Greenhouse Gas requirements,” regardless of the outcome of any related litigation. 

Additionally, CARB, EMA, and the manufacturers have agreed to work together to actively promote needed infrastructure development and to resolve any issues that may require further amendments to the Omnibus or ACT Regulations.

Next Steps

  • No later than August 29, 2023, CARB will release a Notice of Public Comment Period to Consider Proposed Amendments to the Heavy-Duty Engine and Vehicle Omnibus Regulation to amend the existing compliance flexibility provisions to raise the legacy engine caps and streamline other provisions. 
  • No later than sixty (60) days after signing of the Agreement (or early September 2023), CARB’s Executive Officer will advise the CARB Board of his direction to CARB staff regarding the lead time and stability provisions.
  • No later than ninety (90) days after signing of the Agreement (or early October 2023), CARB’s Executive Officer will inform the CARB Board of the remaining provisions set forth in the Agreement.
  • No later than the first quarter of 2024, CARB staff will hold a workshop regarding the contemplated 2027 and later model year amendments to CARB’s Omnibus Regulation.
  • No later than the third quarter of 2025, CARB staff will release a formal rulemaking notice regarding the contemplated 2027 and later model year amendments to CARB’s Omnibus Regulation.
  • In addition, CARB will send a follow-up letter to the Petition for Reconsideration it filed with EPA regarding EPA’s Clean Trucks Plan 2027 Low NOx rule informing EPA that CARB plans to harmonize with EPA’s regulations, and CARB will not seek additional changes to EPA’s 2027 Low NOx rule.



Authored by Katie Lannon.


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