EPA grants two of three preemption waivers for CARB heavy-duty vehicle and engine regulations

What is the significance of EPA’s March 30, 2023 Notice of Decision (pre-publication) granting two separate requests for waivers of Clean Air Act (“CAA”) preemption for California Air Resources Board (“CARB”) regulations governing heavy-duty on-highway engines and vehicles?  These two waivers cover four separate regulations: (1) the Heavy-Duty (“HD”) Vehicle and Engine Emission Warranty Regulations and Maintenance Provisions, known as the 2018 HD Warranty Amendments, and (2) the  Advanced Clean Trucks (“ACT”) Regulation, Zero Emission Airport Shuttle (“ZEAS”) Regulation, and Zero-Emission Powertrain (“ZEP”) Certification Regulation.  Notably, EPA decided not to take action on CARB’s third waiver request—for the Omnibus Low NOx regulation—at this time, but will announce its decision at a future time by separate Federal Register notice. 

Although CARB adopted the HD Warranty Amendments in 2018, CARB only notified EPA officially in October 2021 and requested that EPA consider them to be within the scope of a previous waiver, which EPA declined to do.  Similarly, CARB adopted both the ZEAS Regulation and ZEP Certification Regulation in June 2019, but only requested a waiver in December 2021, along with the ACT Regulation adopted by CARB in January 2021.  These CARB regulations have been in place for several years but have not been enforceable without a waiver from EPA. EPA previously held a public hearing on the waiver requests in June 2022.

In granting the waivers of preemption, EPA paved the way for enforcement of the following CARB regulations:

  • 2018 Heavy-Duty Warranty Amendments.  The 2018 HD Warranty Amendments, previously adopted by CARB in June 2018, extend the emissions warranty periods for on-road heavy-duty diesel engines and diesel vehicles with a gross vehicle weight rating exceeding 14,000 pounds for model year (“MY”) 2022 and beyond.  In granting the waiver request, EPA noted that the warranty amendments constitute “accompanying enforcement procedures” rather than new standards and are squarely relevant to a manufacturer’s ability to produce compliant vehicles and engines. 
  • Advanced Clean Trucks.  CARB adopted the ACT Regulation in January 2021 which requires manufacturers to produce and sell increasing percentages of medium- and heavy-duty zero emission vehicles (“ZEV”) in California.  Notably, this would require manufacturers to achieve ZEV sales of over 50% of new heavy-duty vehicle sales by 2035. 
  • Zero Emission Airport Shuttle (“ZEAS”).  ZEAS established ZEV airport shuttle requirements for shuttle fleet owners servicing 13 airports in California.  The regulation establishes compliance deadlines, including that 33% of the total fleet must be ZEAS by the end of 2027, 66% by 2031, and 100% by 2035.  See 17 C.C.R. § 95690.5(a).  Certain shuttles are exempt from this requirement, including reserve airport shuttles, transit agency vehicles, or vehicles operated during an emergency. Id. § 95690.6(a)-(c).
  • Zero Emission Powertrain (“ZEP”) Certification Program. The ZEP Certification program is optional, and provides California standards, test procedures, and associated warranty and reporting requirements for new MY2021+ heavy-duty zero-emission powertrains.  Beginning with MY2024, ZEP certification is mandatory for manufacturers to generate ZEV credits under the ACT Regulation. 

EPA has a strong history of granting waivers of preemption to California to enforce its emissions regulations.  EPA cannot deny a waiver unless it finds that one of the three criteria for denial listed in the Clean Air Act is met.  Specifically, EPA may decide not to grant a waiver if the agency finds that California’s standards are: (1) arbitrary and capricious; (2) not needed to meet compelling and extraordinary conditions; or (3) the standards and accompanying enforcement procedures are not consistent with federal emission standards.  42 U.S.C. 7543(b).  EPA’s Notice granting the two additional waivers acknowledges California’s “pivotal role as a laboratory for innovation in the control of emissions from new motor vehicles.”  Notice of Decision, at 6. 

CARB is also working on its rulemaking for the Advanced Clean Fleets (“ACF”) Regulation and  recently announced it will conduct a public hearing to consider the proposed ACF Regulation on April 27 and 28, 2023. 



Authored by Joanne Rotondi, Kathryn Lannon, Hannah Graae, and Allisa Newman.

Joanne Rotondi
Washington, D.C.
Katie Lannon
Washington, D.C.
Hannah Graae
Washington, D.C.
Allisa Newman
Washington, D.C.


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