EPA Proposes To Delay Tier 4 Light- And Medium-Duty Vehicle Emissions Standards By Two Model Years

What Happened: The U.S. Environmental Protection Agency (EPA) recently proposed to delay Biden-era Tier 4 emissions standards for light- and medium-duty vehicles by two years, extending Tier 3 standards through model years (MYs) 2027 and 2028.

Who is Impacted: Manufacturers of light- and medium-duty vehicles in the U.S.

What Companies Should Consider Doing: Regulated entities should carefully review the proposed rule, evaluate its potential impact on production plans, and consider submitting comments to inform EPA’s decision by July 6, 2026.

Background

Section 202(a) of the Clean Air Act (CAA) authorizes EPA to promulgate air pollutant emission standards for new motor vehicles. Using this authority, EPA enacted “Tier 3” vehicle criteria pollutant emissions standards in 2014, which took effect in MY 2017. In 2024, EPA promulgated a final rule establishing the phase-in of more stringent “Tier 4” emissions standards, effective MY 2027 and continuing through MY 2032. The final rule