Staff’s presentations for the June 27, 2023, workgroup meeting is now available

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June 20, 2023

Public Workgroup Meeting on June 27, 2023, to Discuss the Off-Road New Diesel Engine Tier 5 Rulemaking:

Concepts for Useful Life, Warranty, and Selective Catalytic Reduction (SCR) Inducement

Agenda and Staff’s Presentations Now Available

The California Air Resources Board (CARB) staff has posted the agenda and the staff’s presentations for the public workgroup meeting scheduled for June 27, 2023.

CARB staff invites you to participate remotely in this public workgroup meeting to discuss concepts for the off-road new diesel engine Tier 5 rulemaking including a useful life, warranty, and selective catalytic reduction (SCR) inducement strategies.

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

Date:                 June 27, 2023
Time:                 9:00 a.m. – 12:00 p.m.
Location:           Zoom Webinar / Teleconference


After registering, you will receive a confirmation email containing information about joining the workgroup meeting. Please use the link and password to join the workgroup 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 workgroup meeting, if you wish to provide comments or ask questions on the potential 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. The “Q&A” feature on Zoom will also be available to provide comments and ask questions. This workgroup meeting will be recorded for future viewing.

The agenda and staff’s presentations are available.


Currently, CARB’s regulations for new off-road diesel engines are largely harmonized with the U.S. 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 kiloWatt (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 technologies at that time: diesel particulate filters (DPF) 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 18 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 potential amendments to the current Tier 4 off-road diesel engine standards for the Tier 5 rulemaking. Staff will likely propose 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 tailpipe carbon dioxide (CO2) emission standards for off-road engines will also likely be proposed by CARB. CARB staff is considering proposing possible elements such as enhancing in-use compliance testing, proposing more representative useful-life periods, and developing a low-load test cycle. CARB staff will also propose to update the test procedures and consider first-time off-road OBD requirements. CARB staff’s proposal is tentatively scheduled for Board consideration in the 2025 timeframe, with implementation beginning as early as the 2029 model years.

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

This workgroup meeting is the fifth 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 stakeholders. CARB staff invites participants to provide feedback on the potential concepts presented at the workgroup meeting.



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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