Revision of Tier 4 Criteria Pollutant Standards, Part 1: Amendments to Phase-In Schedule for Light-Duty and Medium-Duty Vehicles

What it does

The U.S. Environmental Protection Agency (EPA) is reconsidering the Tier 4 criteria pollutant standards for new motor vehicles promulgated within the final rule entitled "Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty Vehicles." This reconsideration will occur in two separate, but coordinated, rulemakings. In this Part 1 rulemaking, the EPA is proposing to amend the phase-in schedule for the Tier 4 criteria pollutant standards for certain vehicles to address changing circumstances and feasibility concerns. These amendments, if finalized, would extend the Tier 3 standards for certain vehicles to model years (MYs) 2027 and 2028 such that the Tier 4 standards for these vehicles would phase in starting with MY 2029. The EPA is also proposing other changes to the test protocols used to evaluate emissions performance for certification and related regulatory issues. Potential amendments to the Tier 4 standards and other program elements will be proposed separately in a future Part 2 rulemaking.

The Environmental Protection Agency's summary, as published in the Federal Register.

What it would change

3 parts of Title 40 of the Code of Federal Regulations:

40 CFR 85, 40 CFR 86, 40 CFR 1066

Before this

No earlier Federal Register document under regulation identifier 2060-AW96 since Jan. 1, 2025.

What happens next and when

Comments. Comments must be received on or before July 6, 2026, at 11:59 p.m. Eastern Time. Comments on the information collection provisions submitted to the Office of Management and Budget (OMB) under the Paperwork Reduction Act (PRA) are best assured of consideration by OMB if OMB receives a copy of your comments on or before July 6, 2026.

The agency's dates, word for word.

Check it yourself

• The document in the Federal Register
• Docket EPA-HQ-OAR-2025-3297 on Regulations.gov
• Title 40 on eCFR

The record as published

Source: the Federal Register (public domain). The document in the Federal Register