Revision of Tier 4 Criteria Pollutant Standards, Part 1: Amendments to Phase-In Schedule for Light-Duty and Medium-Duty Vehicles
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Rule Summary
On May 14, 2026, the U.S. Environmental Protection Agency proposed the first phase of a two-part rulemaking, this Part 1 action proposes to adjust the implementation timeline from model year 2027 to MY 2029 for the Tier 4 criteria pollutant standards for light- and medium-duty vehicles.
This proposal focuses on providing manufacturers and suppliers additional lead time to adapt to evolving market conditions, regulatory requirements, and feasibility challenges, while maintaining strong environmental protections. This proposal also reinforces the Agency’s commitment to protecting American workers, lowering costs for consumers, and restoring regulatory balance while continuing to deliver meaningful emissions reductions under the existing Tier 3 program.
This Part 1 action will provide the time needed for EPA to reconsider the longer-term Tier 4 standards in a future Part 2 rulemaking where EPA will address potential updates to Tier 4 standards and related program elements.
Documents Related to this Proposal
- Fact Sheet: EPA Delays Unattainable Biden-era Tier 4 Criteria Pollutant Standards for Light-Duty and Medium-Duty Vehicles (pdf)
- Notice of Proposed Rulemaking (pdf)
- Regulatory Impact Analysis (pdf)
Comment and Public Hearing Information
Public hearing details and public comment opportunity will be added here when they're available.