EPA Proposes Two-Year Delay to Stricter Vehicle Pollution Standards

The Environmental Protection Agency has formally proposed delaying tougher federal vehicle pollution standards by two model years, a move that would give automakers until model year 2029 to begin complying with the stricter “Tier 4” requirements.

In a notice published in the Federal Register on May 18, the EPA proposed keeping current Tier 3 criteria-pollutant standards in place for model years 2027 and 2028 for light- and medium-duty vehicles. The proposal, announced May 14, is titled “Revision of Tier 4 Criteria Pollutant Standards, Part 1: Amendments to Phase-In Schedule for Light-Duty and Medium-Duty Vehicles.” The agency describes it as Part 1 of a broader reconsideration of the Biden-era rule.

The practical effect would vary by vehicle class, but the overall shift is straightforward: Tier 4 would no longer begin in model year 2027. For vehicles up to 6,000 pounds gross vehicle weight rating, or GVWR, mandatory Tier 4 requirements for model years 2027 and 2028 would be replaced by Tier 3 requirements. For heavier covered vehicles, EPA would remove optional Tier 4 standards for those years and delay related testing changes until model year 2029.

EPA says the two-year delay is needed because the 2024 rule assumed a much larger battery-electric vehicle market share than current conditions support. In the proposal, the agency says slower-than-expected electric vehicle uptake, along with other regulatory and policy changes, has altered the compliance landscape and raised concerns about whether manufacturers have enough lead time and technical feasibility to meet Tier 4 in model years 2027 and 2028. EPA says it is acting under Section 202(a) of the Clean Air Act, which requires the agency to consider feasibility, cost and lead time when setting motor-vehicle emission standards. The agency also projects the delay would save more than $1.7 billion, or “hundreds of dollars saved per vehicle.”

EPA says current Tier 3 standards already produce substantial emissions cuts, which the agency describes as up to 80%. The standards at issue here govern criteria pollutants from vehicles — including smog-forming pollutants and particulate matter — rather than directly rewriting greenhouse-gas limits in this specific action.

The rule now under review was finalized by the Biden administration on April 18, 2024. It set stricter emissions standards for light- and medium-duty vehicles for model years 2027 through 2032. This new action does not finalize any change; it starts a rulemaking process that could revise the phase-in schedule while EPA considers broader changes later.

The agency has opened that public process now. Public hearings are scheduled for June 3 and 4, and written comments are due by July 6. EPA says a separate Part 2 rulemaking may revisit the Tier 4 standards themselves, as well as the phase-in schedule and testing procedures.

The proposal matters beyond Washington because vehicle development programs are planned years in advance. Changing the compliance start date can affect engineering schedules, certification testing and supply-chain planning for automakers and suppliers.

EPA also pointed to a broader shift in federal policy since the 2024 rule was issued. In the proposal, the agency cites the administration’s Feb. 18, 2026, rescission of the 2009 greenhouse-gas Endangerment Finding and repeal of federal vehicle greenhouse-gas standards as part of the changed regulatory environment. EPA Administrator Lee Zeldin said in a May 14 news release that the proposal is meant to “return EPA regulations to reality” while the agency works through its reconsideration of Tier 4.