The Agenda and Staff Presentations are Now Available - Public Workshop to Discuss the Off-Road Diesel New Engine Emissions Standards (Tier 5 Rulemaking) on November 3, 2021

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November 1, 2021

The Agenda and Staff Presentations are Now Available - Public Workshop to Discuss the Off-Road Diesel New Engine Emissions Standards (Tier 5 Rulemaking)

November 3, 2021

The California Air Resources Board (CARB) staff has posted the agenda and staff presentations for the Tier 5 Rulemaking webinar scheduled on November 3, 2021.

CARB staff invites you to participate remotely in this workshop to discuss possible concepts and strategies to reduce oxides of nitrogen (NOx) and particulate matter (PM) emissions from new, off‑road compression-ignition (CI) engines.

During the workshop, CARB staff will discuss possible elements for more stringent exhaust standards for all off-road engine power categories, including those that do not currently utilize exhaust aftertreatment, such as diesel particulate filters (DPFs) and selective catalytic reduction (SCR).

The workshop will be held via Zoom webinar at the following date and time:

Date:             November 3, 2021 

Time:             9:00 am - 2:00 pm (Pacific Time)

Location:       Zoom Webinar/Teleconference

Please register for the webinar using the link below.


After registering, you will receive a confirmation email containing information about joining the workshop. Please use the link and password to join the workshop the morning of the meeting. If you are using a tablet or smart phone, please download the Zoom app. Ensure the latest version of Zoom is installed on your device.

During the workshop, if you wish to provide comments or ask questions on the regulatory concepts, please use Zoom’s “raise hand” feature. The “raise hand” button can be found on the Zoom webinar window. For those who are joining via a conference call, press #2 to raise your hand and *6 to unmute/mute. The “Q&A” feature on Zoom will also be available to provide comments and ask questions. This workshop will be recorded for future viewing.

The workshop materials are now available on CARB’s website.


Currently, CARB’s regulations for new off-road diesel engines are largely harmonized with the United States Environmental Protection Agency’s for nonroad diesel engines. Off-road and nonroad refer to the same type of engine or equipment with off-road being used exclusively in California. The engines in this sector are land-based and range from less than 19 kilowatts (kW) to well over 560 kW in rated power. The existing Tier 4 emission standards were adopted in 2004 and were based on the capabilities of the best available control technologies at that time: DPFs and SCR. As of model year 2020, more than half of all new off-road CI engine families continue to be certified in California to the Tier 4 final emission standards without DPFs. Exhaust aftertreatment technology has matured significantly in the last 17 years. Significant reductions in PM and NOx are now feasible beyond the current Tier 4 standards of 0.02 grams per kilowatt-hour (g/kW‑hr) and 0.40 g/kW-hr for 56 – 560 kW engines, respectively.

CARB staff is working on amendments to the current Tier 4 off-road diesel engine standards for the Tier 5 rulemaking. It will likely include more stringent exhaust emission standards for NOx (up to 90 percent more stringent) and PM (up to 75 percent more stringent) than today’s Tier 4 standards. First-time carbon dioxide (CO2) emission standards for off-road engines may also be proposed by CARB. CARB staff is considering possible elements such as enhancing in-use compliance, proposing more representative useful life periods, and developing a low load test cycle. CARB may also consider incorporating a hybrid powertrain test cycle and test procedures, as well as first-time off-road on-board diagnostics. CARB staff’s proposal is tentatively scheduled for Board consideration in September 2024, with implementation in 2028.

CARB is currently contracting with the Southwest Research Institute (SwRI) to investigate the feasibility of standards lower than Tier 4 standards. SwRI is working on assessing the feasibility of lower NOx, PM, and CO2 emission standards.

This workshop is the first public event in CARB’s Tier 5 rulemaking. CARB staff invites participation from industry, fleet owners, trade associations, non-governmental organization representatives, environmental groups, air districts, and other interested and knowledgeable stakeholders. CARB staff hopes participants will provide feedback, identify any issues with the potential concepts, and evaluate potential technical and programmatic components of a future, comprehensive Tier 5 program.


If you have questions, please contact: Tier 5

If you require a special accommodation or need this document in another language or in an alternate format (i.e., Braille, large print), please contact Isabel Guerra as soon as possible, but no later than 15 business days before the scheduled webinar. TTY/TDD/Speech to Speech users may dial 711 for the California Relay Service.

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