U.S. heavy-duty vehicle NOx standards: Updates to emission limits, testing requirements, and compliance procedures
This policy update summarizes key elements of the rule “Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards,” published by the U.S. Environmental Protection Agency in December 2022. The rule applies to heavy-duty vehicles starting in model year 2027. The EPA estimated the rule will reduce NOX emissions from U.S. on-road heavy-duty vehicles by 14% in 2030, 44% in 2040, and 48% in 2045 compared to today’s standards.
The regulation, part of the EPA’s Clean Trucks Plan, tightens emission limits from 200 mg/bhp-hr for all diesel engines covered under the rule to 35 mg/bhp-hr for Otto-cycle and Class 4–5 diesel trucks and 50 mg/bhp-hr for Class 6–8 diesel trucks. The new regulation also replaces the not-to-exceed (NTE) testing approach for diesel engines with a two-bin moving average window (MAW) methodology to allow the collection of emissions data across a wider range of operating conditions to be used in determining compliance.
The new rule extends the useful life and warranty requirements starting in model year 2027 and includes mechanisms to generate compliance credits up to model year 2026 to reward the early introduction of engines and vehicles that meet future standards.