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CARB workshop on heavy-duty engine and vehicle Omnibus regulation amendments

21 March 2024

The California Air Resources Board (CARB) hosted a public workshop on March 20, 2024 to discuss proposed amendments to the Heavy Duty Engine and Vehicle Omnibus Regulation. This follows from an agreement reached in July 2023, the Clean Truck Partnership (CTP), in which CARB committed to propose amendments to the Omnibus regulation that would generally align the emissions standards, associated test procedures, and accompanying enforcement provisions for 2027 and subsequent MY engines and vehicles with the corresponding provisions in the federal EPA-NOx rule.

The proposed amendments would align the certification standards, durability demonstration provisions, useful life period, warranty periods, off-cycle MAW methodology, interim compliance allowance and SCR inducement requirements with those of the EPA for 2027 and later model years. However, CARB is not committing to issue “deemed to comply certifications” based on US EPA certifications since they will maintain some different requirements, primarily for in-use testing.

While certification approaches will be up to engine and truck manufacturers, it appears that engines meeting CARB’s requirements would be certified for all 50-states while those only meeting EPA’s requirements would not.

While CARB is adopting the US EPA’s 2-Bin MAW methodology and off-cycle standards for 2027 and later MYs, CARB is proposing some different in-use requirements including:

With regards to the use of biodiesel, the EPA allows any commercially available biodiesel fuel blend that meets ASTM standards that is either expressly allowed or not otherwise indicated as an unacceptable fuel in the vehicle's owner or operator manual or in the engine manufacturer's published fuel recommendations. However, CARB wants to ensure manufacturers do not prohibit the use of CARB-approved commercial fuel via a statement in the manufacturer’s maintenance instructions in the owner’s manual nor deny warranty based on the use of such fuels. To meet this objective, CARB is proposing to allow any commercially available biodiesel fuel blend to be used for in-use testing.

While CARB is adopting the same 15 mg/bhp-hr interim NOx compliance allowance for MHDEs and HHDEs that is used by the EPA, CARB is proposing to allow it only for 2027 to 2034 MYs. The interim compliance margin is applicable to in-use engines.

Switching to the 2-Bin MAW methodology also requires changes to the “Real Emissions Assessment Logging” (REAL) NOx tracking.

Starting with the 2027 MY, CARB proposes to merge the California-ABT program with the federal-ABT program. This would allow the use of credits accrued under the federal-ABT program to certify 50-state engine families in California. However, there would be NOx Family Emission Limit (FEL) caps of 65 mg/bhp-hr for MY 2027 to 2030 and 50 mg/bhp-hr for MY 2031 and later. No credits from zero emission powertrains would be permitted for 2027 and later MY engines. There is no ABT program for HC, CO, or PM for 2027 and later MY engines.

Changes to the OBD requirements are still being developed. One of the issues is that aging for the purposes of demonstrating OBD compliance is not the same as EPA’s accelerated aging protocol for deterioration factor determination. CARB would like to explore opportunities to preserve representative OBD demonstrations while harmonizing between OBD aging and DF aging.

The next steps in the development of the proposed amendments include finalizing the rulemaking package by August 2025, posting it for the 45-day notice period in September 2025 presenting it at the Air Resources Board meeting in November 2025.

Source: CARB Heavy-Duty Low NOx program