The US Environmental Protection Agency (EPA) is proposing new, stronger standards to promote clean air and reduce pollution from heavy-duty vehicles and engines starting in model year (MY) 2027.

The proposed multi-pollutant rule would further reduce air pollution from heavy-duty engines and vehicles across the United States, including ozone and particulate matter (PM). In addition, as part of this rulemaking, EPA is proposing targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program (HD GHG Phase 2). This proposed rulemaking builds on and improves the existing emission control program for on-highway heavy-duty engines and vehicles.

EPA is co-proposing two regulatory options for new NO_x standards: proposed Option 1 and proposed Option 2. The proposed rulemaking would change key provisions of the heavy-duty emission control program, including the standards, test procedures, regulatory useful life, emission-related warranty, and other requirements. The two regulatory options (proposed Options 1 and 2) would result in different numeric levels of the standards and lengths of useful life and warranty periods.

The requirements in the proposed Option 1 and the proposed Option 2 would lower emissions of NO_x and other air pollutants (PM, hydrocarbons (HC), air toxics, and carbon monoxide (CO)) beginning as early as model year (MY) 2027.

EPA estimates that if finalized as proposed:

• Proposed Option 1 would reduce NO_x emissions from heavy-duty vehicles in 2040 by more than 50%; by 2045, a year by which most of the regulated fleet would have turned over, heavy-duty NO_x emissions would be more than 60% lower than they would have been without this action.

• Proposed Option 2 would reduce heavy-duty NO_x emissions in 2045 by 47%.

• In 2045, the proposed Option 1 would result in total annual monetized ozone- and PM_2.5-related benefits of $12 and $33 billion at a 3% discount rate, and $10 and $30 billion at a 7% discount rate.

• In the same calendar year, proposed Option 2 would result in total annual monetized ozone- and PM_2.5-related benefits of $9 and $26 billion at a 3% discount rate, and $8 and $23 billion at a 7% discount rate.

Given the analysis we present in this proposal, we currently believe that Option 1 may be a more appropriate level of stringency as it would result in a greater level of achievable emission reduction for the model years proposed.

—“Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards”

The proposed revisions to existing GHG standards for MY2027 and beyond would set updated GHG emissions standards for subsectors where electrification is advancing at a more rapid pace. These sectors include school buses, transit buses, commercial delivery trucks, and short-haul tractors.

In a separate action, EPA will be setting new GHG emissions standards for heavy-duty vehicles as soon as model year 2030. This action will more comprehensively address the long-term trend towards zero emissions vehicles across the heavy-duty sector.