NHTSA Clarifies Fuel Economy Authority for Medium- and Heavy-Duty Trucks

What Changed in NHTSA's Fuel Economy Authority

NHTSA issued an interpretive rule on August 31, 2026, clarifying that its authority to set fuel‑economy standards covers only vehicle standards for commercial medium‑ and heavy‑duty on‑highway vehicles and work trucks. The rule states that NHTSA does not have statutory power to set separate engine standards, a power reserved for EPA under the Clean Air Act.

Who Is Affected

The rule applies to carriers operating medium‑ and heavy‑duty on‑highway vehicles and work trucks. It does not apply to light‑duty vehicles, for which NHTSA has no authority to set standalone engine standards. Carriers with fleets in the affected classes should identify which vehicles fall under the new interpretation.

What Carriers Should Do

Carriers should review their current fleet classifications and confirm whether their vehicles are subject to the rule. They should also monitor the pending rulemaking that will examine existing standards for consistency with this interpretation. Until that rule is finalized, enforcement will follow the current interpretation, so carriers should stay alert to any enforcement actions.