EPA Tier 4 Criteria Pollutant Standards Phase-In Delay (Light- and Medium-Duty Vehicles)

Current understanding

EPA has issued a proposed rule to delay the phase-in of Tier 4 criteria pollutant emissions standards for certain light-duty and medium-duty vehicles, extending Tier 3 standards through model years 2027–2028 and pushing full Tier 4 compliance to MY 2029. The agency cites changed circumstances and feasibility concerns as justification. The action is a proposed rule and not yet final; comment and interagency review remain pending.

Evidence log

• 2025-06-12 — Providing congressional disapproval under chapter 8 of title 5, United States Code, of the rule submitted by the Environmental Protection Agency relating to “California State Motor Vehicle and Engine Pollution Control Standards; Advanced Clean Cars II; Waiver of Preemption; Notice of Decision”.: cross-connection with emissions-standards: Both reflect federal actions relaxing or nullifying near-term vehicle emissions requirements — CRA disapproval of California’s ACC II waiver alongside delayed phase-in of EPA Tier 4 light- and medium-duty criteria pollutant standards. (novelty: 3)

Open questions

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