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The draft potential Tier 5 Regulation Order, draft potential Tier 5 Test Procedures, and draft potential Tier 4 In-Use Compliance Test Procedures are now available.
California Air Resources Board (CARB) staff has posted the draft potential Tier 5 Test Procedures, the draft potential Tier 4 In-Use Compliance Test Procedures, and the draft potential Tier 5 Regulation Order, which will be discussed at the February 27, 2026, public workshop. Staff has made substantial updates to the previous draft of the potential Tier 5 Regulation Order (released October 8, 2024). These updates include changes to the potential Tier 5 standards for criteria pollutants and greenhouse gases, implementation timelines, the Off-Road In-Use Testing program, zero-emission credits, durability demonstrations, and potential requirements for hydrogen-fueled internal combustion engines. We are seeking feedback from stakeholders by May 4, 2026. The documents are drafts for discussion purposes and may be revised and/or reorganized in the future.
The workshop meeting will be held via Zoom webinar:
Workshop Date: February 27, 2026
Time: 8:30 a.m. – 3:30 p.m.
Location: Zoom Webinar
Before adopting any regulations, CARB will conduct public hearings and other administrative proceedings in accordance with 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.
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 on the draft Regulation Order and draft Test Procedures for the Tier 5 rulemaking.
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.
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