EPA Proposes to Pause Biden-Era Tier 4 Vehicle Emission Standards

In April 2023, the Biden EPA proposed — and in 2024 finalized — what it called “multi-pollutant emission standards” for model year 2027 and later light-duty and medium-duty vehicles. The rules were designed to be so stringent that the only practical path to compliance was mass electrification of the vehicle fleet. EPA’s own projections assumed electric vehicles would represent between 54 and 67% of new car sales by 2030-2032. That projection has not materialized. As of 2025, EVs account for less than 10% of new U.S. vehicle sales — well short of the trajectory the agency assumed when setting these standards.

The market verdict has been unambiguous. Major automakers have responded to weak consumer demand by pulling back from EV commitments at scale:

• General Motors announced a $4 billion investment to boost internal combustion engine vehicle production and a $6 billion restructuring to unwind earlier EV commitments.
• Ford canceled plans for a three-row electric SUV, delayed additional EV launches until 2028, and recorded a $19 billion write-down on its electric vehicle investments.
• Stellantis is scrapping its plug-in electric vehicle lineup, citing weak customer demand, and has taken a $26.5 billion charge against EV investments.
• Honda reduced EV spending by 30%.
• Hyundai halted electric vehicle production at its Alabama facility to shift focus toward vehicles consumers are actually purchasing.

These are not signs of an industry dragging its feet on innovation. They are signs of an industry responding honestly to what consumers want to buy. The Tier 4 standards — premised on a market that does not exist — would have forced manufacturers to comply with rules calibrated to a fantasy, raising vehicle prices and constraining consumer choice in the process.

What EPA Is Proposing

EPA’s proposal is structured in two parts:

• Part 1: provides a two-year delay. Manufacturers would continue complying with the current Tier 3 standards in model years 2027 and 2028, with Tier 4 standards — if retained — beginning no earlier than model year 2029. This initial step is subject to a 45-day public comment period.
• Part 2: will undertake a comprehensive reconsideration of the Tier 4 program for model year 2029 and beyond, including potential revisions to the standards themselves, implementation timelines, phase-in structures, and other program elements. EPA has indicated it intends to propose Part 2 this year.

It is worth noting that the Tier 3 standards currently in force are not lax. According to EPA, they deliver emission reductions of up to 80% compared to earlier standards. The argument for retaining the Biden-era Tier 4 standards was never about protecting air quality — Tier 3 already does that. It was about engineering consumer choice out of the equation.

IER’s Position

IER has consistently opposed the use of vehicle emission regulations as a backdoor EV mandate. In comments filed with EPA on the underlying 2023 proposed rule, IER argued that standards calibrated to force electrification — rather than to achieve attainable emission reductions — exceed the agency’s statutory authority and impose economic costs on consumers without commensurate environmental benefit.

The Congressional Review Act disapproval of California’s vehicle emission waivers and the vehicle provisions of the One Big Beautiful Bill Act have already begun dismantling the federal EV mandate architecture. EPA’s Tier 4 pause continues that correction.

IER urges all interested parties — including manufacturers, dealers, fleet operators, and individual consumers — to submit comments during the 45-day comment period on Part 1. IER further urges EPA to use the Part 2 rulemaking to replace the Biden Tier 4 framework with standards that are technology-neutral, achievable without mandating electrification, and respectful of the choices Americans make in the vehicle market.