The public event marks CARB’s next step to promulgate new, lower NOx standards for heavy-duty engines and vehicles.

By: Arthur Foerster and Reed McCalib


On Wednesday, January 23, 2019, the California Air Resources Board (CARB) will hold a public workshop in Sacramento focusing on potential regulatory changes that would lower oxides of nitrogen (NOx) emissions for new, on-highway heavy-duty vehicles and engines. Members of the public may attend the workshop in person or via webcast. (Event details are included at the end of this article.)

According to the agency’s public notice, CARB staff will discuss potential regulatory updates, challenges, and implementation strategies as the agency pushes for ever-lower emission standards. In particular, staff will discuss durability demonstration requirements, a supplemental certification test cycle for low-load operations, zero emission credits, in-use testing protocols, longer useful life and warranty periods, warranty claim reporting, lower particulate matter (PM) emissions, and NOx emissions tracking. Staff will also provide updates on ongoing low-NOx demonstration projects and will explain next steps in the rulemaking process.

CARB’s Vision and Related Efforts

The upcoming workshop marks the next step in CARB’s ongoing effort to promulgate new, lower NOx standards for heavy-duty engines and vehicles, based on the agency’s position that doing so is necessary to attain federal air quality standards. NOx emission standards for on-highway, heavy-duty engines have already significantly decreased from the 6.0 grams per brake horsepower hour (g/bhp-hr) standard in effect in 1990, to the 0.20 g/bhp-hr standard in effect today. In 2013, CARB established voluntary NOx standards as low as 0.02 g/bhp-hr to encourage the development and purchase of cleaner engines. Now, CARB is again considering lowering the mandatory standard this year in response to air quality concerns across the state.

CARB first introduced its current plan for reducing on-highway, heavy-duty NOx emissions at a public workshop in November 2016. The workshop featured presentations on a number of topics, including reduction goals, warranty, low-load testing, and other related issues. In later workshops, CARB proposed a multi-step process that would first address warranty periods, followed by other low-NOx control measures. Rulemaking on increases in warranty periods and other related changes for model year 2022, as well as subsequent model years, is currently in progress.

CARB’s current regulatory review is part of a broader national effort to decrease NOx emissions from heavy-duty vehicles and engines. In November 2018, the United States Environmental Protection Agency (US EPA) announced the “Cleaner Truck Initiative” to develop regulations to reduce heavy-duty NOx emissions nationwide. CARB has signaled its intent to coordinate its regulatory efforts with US EPA.

Workshop Information

Date:               Wednesday, January 23, 2019

Time:               9:00 a.m. to 1:00 p.m. PT

Location:         Byron Sher Auditorium, Second Floor
                        Cal/EPA Headquarters Building
                        1001 “I” Street
                        Sacramento, California 95814


The public is invited to submit comments and questions during the workshop via email to CARB staff’s presentation and related documents will be made available online prior to the workshop at

Latham & Watkins will continue to monitor and report back on state- and federal-level regulatory developments in the heavy-duty space.