U.S. EPA Proposes Strictest Vehicle Emissions Standards to Date

In April, the United States Environmental Protection Agency ("EPA") proposed the strictest pollution standards for cars and trucks to date. In particular, EPA has proposed new greenhouse gas ("GHG") emissions standards for light-duty and medium-duty vehicles— including passenger cars, light trucks, and large pickups and vans with a gross vehicle weight rating of between 8,501 and 14,000 pounds—to be phased in over model years 2027 through 2032. The proposed standards are intended to accelerate the transition to hybrid and electric vehicles in the United States.

Light-Duty Vehicles 

For light-duty vehicles, the proposed GHG emissions standards would increase in stringency each year over a six-year period. The light-duty GHG standards are footprint-based, meaning they are based on a vehicle's wheelbase multiplied by its track width. Under the footprint-based standards, each manufacturer has a unique fleet carbon dioxide performance target, with fleet average emissions calculated at the end of the model year based on the product-weighted average emissions of each vehicle in the fleet. 

EPA proposes to adjust the relative slope and offset between the car and truck footprint standards curves. One primary reason for this change is to address increasing vehicle sizes, which have offset gains in fuel economy emissions reductions. EPA posits that a slope too steep would foster upsizing, while a slope too flat would incentivize overall fleet downsizing. Still, the proposed slopes are flatter than those in previous rulemakings, in part, to reflect EPA's projection that future fleets will be characterized by greater numbers of battery-electric vehicles. 

The cutpoints, the low and high footprint boundaries within which the sloped portion of the footprint curve resides, are flat. EPA's proposal increases the lower cutpoint for the car and truck curves by one square foot per year from model years 2027 through 2030, from 41 to 45 square feet. This is intended to provide less stringent standards for the smallest vehicles, which EPA describes as being among the "cleanest" vehicles and often the most affordable for consumers. In turn, the proposal's gradual reduction of the upper cutpoint for trucks by one square foot per year from model years 2027 through 2030 is intended to address consumer trends of upsizing to larger full-size pickup trucks.

The proposed carbon dioxide minimum and maximum footprint targets and the corresponding cutpoints for cars and light trucks, as well as the slope and intercept defining the linear function for footprints falling between the minimum and maximum footprint values, are represented in the tables below. For footprints falling between the minimum and maximum, EPA calculated the targets with the formula: Slope x Footprint + Intercept = Target. 

Medium-Duty Vehicles

For medium-duty vehicles, EPA is proposing to revise the existing standard for model year 2027. As with light-duty vehicles, the proposed standards would increase in stringency each year between model years 2027 through 2032. The medium-duty vehicle standards are based on a work-factor metric designed for commercially-oriented vehicles and account for payload, towing, and 4-wheel drive equipment. The projected targets for medium-duty vans and pickups and the combined medium-duty fleet are represented in the table below. 

Other Changes

This proposal also includes revisions to existing GHG credit programs. EPA is proposing to limit the eligibility for air conditioning ("AC") system efficiency credits for tailpipe carbon dioxide emissions control to internal combustion engine vehicles starting in model year 2027, and to remove refrigerant-based AC provisions for both light- and medium-duty vehicles. EPA is further proposing to sunset the off-cycle credits program for both light- and medium-duty vehicles. The off-cycle credits program provides three pathways in which manufacturers can accrue off-cycle carbon dioxide credits for use of technologies that achieve real-world carbon dioxide reductions that are not adequately captured by emissions compliance tests. 

Heavy-Duty Vehicles

In a separate notice of proposed rulemaking, EPA is also proposing to promulgate new GHG standards for heavy-duty highway vehicles starting in model year 2028, and to revise certain GHG standards for model year 2027, with decreasing emissions proposed for each year through model year 2032. EPA is not proposing to mandate the use of a specific technology but rather anticipates that a compliant fleet will include a diverse range of zero-emission vehicles and internal combustion engine vehicle technologies. The proposed carbon dioxide emissions standards are broken down by (i) vocational vehicles (urban, multipurpose, and regional), with different standards based on weight class and whether the vehicle has a diesel-fueled, compression-ignition or gasoline-fueled, spark ignition (with the lowest proposed carbon dioxide emissions being 97 grams/ton-mile for regional, heavy compression-ignition vehicles by 2032); (ii) optional custom chassis vocational vehicles (e.g., school buses, concrete mixers, motor homes, etc., with the lowest proposed carbon dioxide emissions being 149 grams/ton-mile for school buses by 2032); (iii) tractors, with different standards based on roof height (low, mid, and high), class, and cab (with the lowest proposed carbon dioxide emissions being 48.1 grams/ton-mile for low roof, Class 8 sleeper cab tractors by 2032); and (iv) heavy-haul tractors (with carbon dioxide emission standards of 41.1 grams/ton-mile by 2032). 

Impact 

The impact on vehicle manufacturers—and, by extension, consumers—is expected to be significant. If the proposed standards are enacted, EPA projects that approximately 67% of new light-duty vehicle sales and 46% of new medium-duty vehicles sales in model year 2032 may be composed of electric vehicles, depending on the compliance pathways chosen by manufacturers. EPA projects that this will result in a cumulative carbon dioxide emissions reduction of 8,000 million metric tons through 2055. EPA estimates that the proposed heavy-duty vehicle emissions standards will result in an additional net carbon dioxide cumulative emissions reduction of 1.8 billion metric tons from 2027 through 2055. 

The last iteration of GHG emissions standards for light-duty vehicles, for model years 2023 through 2026, was challenged in court by a number of states; litigation regarding those standards remains ongoing. And, on April 26, 2023, the U.S. Senate voted 50-49 to overturn heavy-duty vehicle emissions standards for nitrogen oxide, particulate matter, hydrocarbon, and carbon monoxide, questioning the feasibility of implementation and expressing concern over potential economic impacts. As EPA's proposed standards for model years 2027 and beyond are more stringent, and the feasibility of implementing them is already being hotly debated, additional litigation in the future is expected.

EPA held a three-day virtual public hearing on the proposed emissions standards for light-duty and medium-duty vehicles and changes to GHG credit programs on May 9-11, 2023. Comments on the proposed rule must be received on or before July 5, 2023. 

EPA held a two-day virtual public hearing on the proposed emissions standards for heavy-duty vehicles on May 2-3, 2023. Comments on that proposed rulemaking must be received on or before June 16, 2023.

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