On August 31, 2026, NHTSA published an Interpretive Rule in the Federal Register (F.R. Vol. 91 No. 167; Docket No. NHTSA-2026-1948) affecting 49 CFR Parts 523, 534, and 535. These Rules deal with the scope of NHTSA’s authority to set fuel economy standards for medium and heavy duty on-highway vehicles and work trucks. These Rules describe NHTSA's authority to set vehicle standards, but does not include the authority to set separate standards for engines. NHTSA will review its existing Standards applicable to commercial medium and heavy-duty on-highway vehicles and work trucks for consistency with this Interpretation Rule in a separate rulemaking action. Pending the rulemaking process, NHTSA will exercise its enforcement authority with regard to affected Standards in accordance with the interpretation set forth in this Rule.
This Interpretative Rule will help ensure the efficient functioning of the market for these commercial vehicles by limiting regulation to its legally authorized scope. It will also help ensure that manufacturers have flexibility in how best to meet the Standards and needs of their sophisticated commercial customers, who make business decisions that account for their own fuel economy needs. The NHTSA will review its regulations for consistency with this interpretation in a separate rulemaking. This Interpretive Rule was applicable as of August 31, 2026.