Public Workgroup August 8, 2022, to discuss the off-road new diesel engine Tier 5 rulemaking: Low Load Cycle, hybrid credits, capping standards and small volume manufacturers

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July 8, 2022

Public Workgroup August 8, 2022, to Discuss the Off-Road New Diesel Engine Tier 5 Rulemaking: Development of a Low Load Cycle, Concepts for Hybrid Credits, Carbon Dioxide, Nitrous Oxide, and Methane Capping Standards, and Small Volume Manufacturer Provisions

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 it's potential methodology for developing a Low Load Cycle (LLC) proposal applicable to off-road diesel engines between 56 and 560 kilowatts (kW) that is indicative of engine operations under low load and low exhaust temperature conditions. Certification of off-road diesel engines is currently based on emissions tests performed over the Nonroad Transient Cycle (NRTC) and various modal cycles such as the C1, C2, D1, and D2, depending on power and speed type of the engine. These certification cycles are intended to represent the entire spectrum of off-road diesel equipment operation, and therefore provide a good basis for predicting the emissions performance in the real world. However, off-road engines frequently operate at low load in the real world, while the NRTC and steady-state cycles do not sufficiently account for low load operations. A study conducted by the Southwest Research Institute (SwRI) showed that today's off-road engines do not control NOx emissions effectively during low load operations. A representative LLC will help control off-road engine emissions during low load conditions, and thus help reduce adverse health impacts and improve air quality throughout the state.

CARB staff is developing an LLC from real-world activity data to represent off-road operations characterized by low loads. Staff will share their proposed method for developing an LLC. The proposed method is adapted from methodology used to develop the on-road LLC in the Stage 2 Heavy-Duty Low NOx program. Staff will describe data pre-processing and cleanup, moving microtrip window analysis and window selection, load distribution analysis, and clustering analysis and solicit feedback from stakeholders.

CARB staff is also proposing a concept for a NOx emissions credit mechanism for off-road hybrid systems. Under staff’s potential concept, the default NOx credit level would be set at 5 percent of the Tier 5 standard if certain conditions are met. The original equipment manufacturer (OEM) could request CARB staff’s consideration for a higher credit level if the OEM provides NOx emissions test data supporting the higher level of NOx credit for the hybrid system. CARB staff are considering whether to propose to monitor and take enforcement actions as necessary to ensure NOx emissions from hybrids are at or below the allowed credit levels.

Staff will introduce the potential concept of capping standards for carbon dioxide (CO2), nitrous oxide, and methane emission levels as part of the Tier 5 amendments. The purpose of these potential standards is to ensure that these greenhouse gases do not increase as a result of manufacturers recalibrating their engines to meet more stringent NOx and/or CO2 standards. Staff will present analyses of certification data and solicit feedback from stakeholders as to the appropriate capping standards for these pollutants.

To address concerns regarding the cost-effectiveness of requiring manufacturers with relatively small engine sales volumes in California to meet the entirety of Tier 5 requirements, staff will introduce a potential concept defining small volume manufacturers in California. Additionally, staff will discuss, and solicit feedback from stakeholders regarding the need and reasonableness of potentially allowing California small volume engine manufacturers to comply with less stringent Tier 5 certification requirements than non-small volume manufacturers.

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

Date:                 August 8, 2022
Time:                 9:00 am – 4:00 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 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.

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 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 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 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, 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 on-board diagnostics. CARB staff’s proposal is tentatively scheduled for Board consideration in the 2024-2025 timeframe, with implementation in 2028.

CARB is currently contracting with the 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 meeting is the third 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 will provide feedback on and, identify any issues with the potential concepts, and 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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