EPA Delays Tier 4 Vehicle Emission Rules by Two Years
Published Date: 5/18/2026
Proposed Rule
Summary
The EPA is changing the timeline for new pollution rules on light and medium vehicles. Instead of starting tougher Tier 4 standards in 2027, some vehicles will keep the easier Tier 3 rules through 2028, with Tier 4 kicking in from 2029. This gives manufacturers more time to meet the new rules without rushing, helping keep costs and challenges in check.
Analyzed Economic Effects
4 provisions identified: 3 benefits, 1 costs, 0 mixed.
Two-Year Delay of Tier 4 Start
The EPA proposes to keep the existing Tier 3 pollution rules in place for model years (MYs) 2027 and 2028 and delay the Tier 4 criteria pollutant standards so Tier 4 would phase in starting with MY 2029. You (vehicle manufacturers and related businesses) would have two extra model years of the familiar Tier 3 requirements to adjust product plans and compliance strategies.
Change to Tier 4 Phase-In By Weight
The EPA proposes to replace the mandatory Tier 4 requirements for light- and medium-duty vehicles up to 6,000 pounds GVWR and to remove the optional Tier 4 schedule for vehicles over 6,000 pounds GVWR. This change specifically targets how vehicles are phased into Tier 4 based on the vehicle weight threshold of 6,000 pounds GVWR.
EPA Lowers BEV Sales Projections
The EPA projects battery electric vehicle (BEV) market share of 8 percent in MY 2027 and 12 percent in MY 2028, down from prior projections of 26 percent (MY 2027) and 31 percent (MY 2028). The proposal cites changes such as the June 2025 CRA resolution blocking California's ACC II waiver and the July 2025 OBBB changes to BEV tax incentives as factors behind the lower BEV projections.
Delay of New Emissions Test Protocols
The EPA proposes to delay changes to the emissions test protocols used for certification until model year 2029. Certification testing procedures that were to change with Tier 4 would remain aligned with Tier 3 through MYs 2027 and 2028.
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Key Dates
Department and Agencies
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