The Agenda and Staff Presentation are now available - Public Workgroup to Discuss In-Use Testing Concepts for the Off-Road New Diesel Engine Tier 5 Rulemaking: May 2, 2022

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April 25, 2022

The Agenda and Staff Presentation are now available - Public Workgroup to Discuss In-Use Testing Concepts for the Off-Road New Diesel Engine Tier 5 Rulemaking: May 2, 2022

The California Air Resources Board (CARB) staff has posted the agenda and the staff presentation for the public workgroup meeting scheduled for May 2, 2022.

The California Air Resources Board (CARB) staff invites you to participate remotely in a public workgroup meeting 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 workgroup meeting, CARB staff will discuss concepts for an off-road in-use testing program. An in-use testing program is an important element to ensure an engine family’s emissions compliance throughout useful life through real-world emissions data collection and testing with portable emission measurements systems (PEMS). In-use testing programs conducted by engine manufacturers currently exist for heavy duty on-road compression ignition engines and large off-road spark ignition engines. An in-use program for off-road compression ignition engines currently does not exist for Tier 4 engines. A manufacturer-run in-use program for the Tier 5 standards would help ensure the emission benefits are maintained throughout affected engines’ useful lives.

CARB staff is developing a concept for an in-use testing program for the Tier 5 rulemaking. Staff would like to share their initial concept of a multiphase in-use program. The concept includes NOx sensor data collection, analysis, and submission of engine family data from manufacturers on an annual basis. Manufacturers would fulfill their in-use requirements if the reported engine families fall within the emission standards based on the sensor data. However, if an engine family’s screening results showed excess emissions based on the sensor data, then CARB would require real-world testing with PEMS to investigate in-use emissions for a compliance determination.

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

Date:                 May 2, 2022
Time:                 9:00 a.m. – 2:00 p.m.
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 workgroup. 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, 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. The “Q&A” feature on Zoom will also be available to provide comments and ask questions. This workgroup will be recorded for future viewing.

Notice to all stakeholders: Tier 5 rulemaking document/communication retention is now in effect retroactive to June 1, 2021. Communications with CARB are a part of the Tier 5 rulemaking administrative record.

Staff’s presentation, and any additional webinar related documents, will be made available prior to the workgroup meeting on CARB’s website.


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 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 technologies at that time: diesel particulate filters (DPF) and selective catalytic reduction. 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 are 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 staff will update the test procedures and consider first-time off-road on-board diagnostics. CARB staff’s proposal is tentatively scheduled for Board consideration in 2024-2025 timeframe, 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 workgroup is the second 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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