NHTSA Admits: No Power to Regulate Truck Engines Alone—Program Reset!
Published Date: 8/31/2026
Rule
Summary
The National Highway Traffic Safety Administration is issuing this interpretive rule regarding the scope of its authority to set fuel economy standards for commercial medium- and heavy-duty on-highway vehicles and work trucks. This rule describes NHTSA's authority to set vehicle standards, which 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 in a separate rulemaking. 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.
Analyzed Economic Effects
3 provisions identified: 2 benefits, 0 costs, 1 mixed.
No Separate Engine Standards
NHTSA says it does not have authority under the Energy Independence and Security Act (EISA) to set fuel economy standards for engines on their own for commercial medium- and heavy‑duty on‑highway vehicles and work trucks. The agency says EISA requires standards for whole vehicles (including work trucks and vehicles with GVWR 10,000 pounds or more) but did not authorize separate engine-only standards.
MDHD Program Will Be Reset by Rulemaking
NHTSA will review and reset the medium- and heavy‑duty on‑highway vehicle and work truck (MDHD) program in a separate notice-and-comment rulemaking to bring regulations into alignment with this interpretation. The agency says it will consider whether any adjustments to the vehicle standards are warranted and will review relationships with EPA rules including EPA's 2023 NOX standards noted as taking effect in model year 2027.
Enforcement Follows New Interpretation
Effective August 31, 2026, NHTSA will exercise enforcement of affected MDHD standards in line with this interpretation (i.e., not treating engines as separately regulated). The agency also says this interpretive rule does not itself change existing standards or any rights or obligations under the MDHD program.
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Key Dates
Department and Agencies
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