Comments close: Amendments and Nonconformance Penalties for Model Year 2027 and Later Heavy-Duty Highway Engines and Amendments to Inducement Provisions for SCR-Equipped Diesel Engines

The U.S. Environmental Protection Agency (EPA) has released a draft regulatory impact analysis and proposed rule amendments concerning heavy-duty highway engines for model year (MY) 2027 and beyond. The proposal introduces nonconformance penalties (NCPs) and refines inducement provisions for Selective Catalytic Reduction (SCR) systems, which are designed to ensure operators maintain high-quality Diesel Exhaust Fluid (DEF) and prevent tampering with emission control systems. The document clarifies that the EPA is not reopening the underlying standards or program requirements established in the 2023 Final Rule, but is instead focusing on targeted technical amendments. These include adjustments to emission-related warranty periods, useful life provisions, and test procedures. The EPA has extended its inventory analysis period to 2055 to better account for fleet turnover, utilizing the updated MOVES5.R2 modeling version. Key technical considerations include the use of ISO 22241-1:2019 standards for DEF, which requires a 32.5 percent urea concentration. The proposal also addresses potential exemptions for Arctic conditions in Alaska, similar to existing provisions for American Samoa and the Northern Mariana Islands. The EPA estimates that these revisions will have a negligible impact on CO2 emissions and a minor impact on NOX inventory levels.