NHTSA Clarifies Fuel Economy Standards Apply to Vehicles, Not Engines

Fuel economy standards for commercial trucks will now focus only on complete vehicles. NHTSA issued an interpretive rule stating it lacks the legal authority to set separate standards for engines. The agency will only regulate the fuel economy of the whole truck.

This interpretation takes effect on August 31, 2026. Until a new rulemaking is finished, NHTSA will enforce fuel economy requirements based on this vehicle-only approach.

NHTSA will review its existing fuel economy standards in a separate rulemaking. The agency will update those rules to match this new interpretation of the law.

The rule covers commercial medium- and heavy-duty on-highway vehicles and work trucks. Fleet managers and drivers should note that future compliance requirements will focus on the whole truck rather than the engine alone.

Source: Federal Register — https://www.federalregister.gov/documents/2026/08/31/2026-17756/resetting-nhtsas-fuel-economy-program-commercial-medium--and-heavy-duty-on-highway-vehicles-and-work