February 27, 2026, at 8:30 a.m. – 3:30 p.m.
California Air Resources Board (CARB) staff invite you to participate remotely in a public workshop on February 27, 2026, from 8:30 a.m. – 3:30 p.m. to discuss potential standards for off-road new diesel engines in California, referred to as Tier 5 standards. The Tier 5 rulemaking aims to reduce oxides of nitrogen (NOx) and particulate matter (PM) emissions from new off-road compression-ignition engines sold in California. During the workshop, CARB staff will discuss draft amendments to the off-road new diesel engine emissions standards, including changes to the On-Board Diagnostics (OBD), Off-Road In-Use Testing (ORIUT), and Tier 5 elements since the last workshop on October 8, 2024. The ORIUT and OBD portions of the workshop are technical in nature.
CARB staff will also discuss the applicability of the Large Spark-Ignition engine standards regulation to hydrogen internal combustion engines. Staff will discuss potential amendments to the In-Use Off-Road Fleet regulation. Finally, we will discuss potential changes to the Tier 4 In-Use Test Procedures.
Staff has uploaded the Off-Road Low NOx Demonstration Program – Stage 3 Addendum Field Cycle Performance report for stakeholder reference.
Before adopting any regulations, CARB will conduct public hearings and other administrative proceedings according to the provisions of the California Administrative Procedure Act, Chapter 3.5 (commencing with section 11340), part 1, division 3, title 2, of the Government Code.
The workshop meeting will be held via Zoom webinar:
Workshop Date: February 27, 2025
Time: 8:30 a.m. – 3:30 p.m.
Location: Zoom Webinar
After registering, you will receive a confirmation email with details on how to join the workshop. Please use the link and password to join the workshop on the morning of the meeting. If you are using a tablet or smartphone, 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 potential regulatory concepts, please use Zoom’s “raise hand” feature. The “raise hand” button is in the Zoom webinar window. For those joining via conference call, press #2 to raise your hand. The “Q&A” feature on Zoom will also be available, allowing participants to provide comments and ask questions. This workshop meeting will be recorded for future viewing.
Background
Currently, CARB’s regulations for new off-road diesel engines are largely harmonized with the United States Environmental Protection Agency’s regulations for nonroad diesel engines. Off-road and nonroad refer to the same type of engine or equipment. 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 and selective catalytic reduction. As of model year 2020, more than half of all new off-road compression-ignition engine families continue to be certified in California to the Tier 4 final emission standards without the use of diesel particulate filters. Exhaust aftertreatment technology has matured significantly in the last 20 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 considering cleaner exhaust emission standards for NOx (up to 90% cleaner than today’s Tier 4 standards) and PM (up to 75% cleaner than today’s Tier 4 standards). Other elements include enhanced in-use compliance testing, more representative useful life periods, OBD requirements (applicable for the first time to this category), and a new low-load test cycle.
This workshop is the tenth public event in CARB’s development of potential Tier 5 regulations. CARB staff invites industry, fleet owners, trade associations, representatives of non-governmental organizations, environmental groups, air districts, members of the community, and other interested stakeholders to participate and provide feedback.
Contact
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.
Stay Connected
If you are interested in receiving automatic email updates on Tier 5 rulemaking development activities, please subscribe to our email list.
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