California Air Resources Board

The Heavy-Duty Engine and Vehicle Omnibus Regulation (Omnibus Regulation) was adopted on September 9, 2021, and became effective on December 22, 2021, to drastically cut smog-forming nitrogen oxides (NOx) from conventional heavy-duty engines. The Omnibus Regulation will significantly increase the stringency of NOx emissions standards and will also lengthen the useful life and emissions warranty of heavy-duty diesel engines for use in vehicles with a gross vehicle weight rating (GVWR) greater than 10,000 pounds. The more stringent NOx emission standards begin with the 2024 model year engines and become more stringent with 2027 and subsequent model year engines.

In 2020, the only manufacturer of diesel-fueled heavy-duty urban bus engines announced that it will no longer produce these types of engines to be certified in California, beginning with the 2024 model year, and plans to increase the price of the diesel-fueled urban bus engines starting with the 2022 model year. This creates a potential obstacle for transit agencies that are currently working diligently to comply with the Innovative Clean Transit (ICT) regulation. The ICT regulation requires all public transit agencies to gradually phase into clean fleets by reducing 100% of tailpipe emissions. The Transit Agency Diesel‑Fueled Bus and Engine Exemption Request (Exemption Request), was then added to the Omnibus Regulation (title 13, CCR, section 1956.8(a)(2)(F)) to support transit agencies with clean fleet purchase requirements. If an Exemption Request is granted, the transit agency can purchase or re-power buses with engines that are certified to both the federal emission standards for 2010 and later model year diesel-fueled medium heavy‑duty or heavy heavy-duty engines and vehicles.

CARB prepared the Transit Agency Diesel-Fueled Bus & Engine Exemption Request Guidance Document, which summarizes the conditions, requirements, and procedures of requesting an exemption. CARB also hosted a webinar for transit agencies on the requirements and process of requesting an exemption under the Omnibus Regulation. The webinar was held virtually on February 4, 2022, from 10:00 a.m. to 12:00 p.m. Pacific Time. The recording of the webinar is posted on the ICT - Meetings and Workshops webpage along with the other related materials.

To learn more about the Omnibus Regulation, please visit its rulemaking webpage at the Heavy-Duty Low NOx website. Please subscribe to the Heavy-Duty Low NOx email list to receive the latest updates and notices of upcoming events related to this program.