USDOT Plans Major Fuel Economy Rollback for Heavy-Duty Truck Engines

USDOT to reverse fuel economy standards for heavy-duty commercial vehicle engine makers

The U.S. Department of Transportation’s National Highway Traffic Safety Administration is moving to narrow its authority over fuel economy requirements for standalone medium- and heavy-duty truck engines.

On Aug. 28, 2026, NHTSA announced a new interpretive rule that would reverse an Obama-era policy involving fuel efficiency standards for commercial vehicle engines. The agency said the earlier approach went beyond the authority granted by Congress by allowing regulators to address engines separately from the vehicles in which they are installed.

Under the new interpretation, NHTSA would continue regulating fuel economy for complete vehicles, including medium- and heavy-duty trucks and work vehicles. However, the agency would no longer claim authority to set fuel economy requirements for standalone engines or dictate specific engine and powertrain designs.

For truck manufacturers, the change would leave more of the engineering decisions tied to meeting vehicle-level standards in their hands. Manufacturers could choose how to combine engines, transmissions and other powertrain technologies to meet applicable fuel economy requirements for a complete truck.

NHTSA said the revised interpretation is intended to align the agency’s regulations with federal law and court decisions. The agency’s position is that its statutory authority covers the fuel efficiency of vehicles, rather than individual components such as engines.

“The rule—which went far beyond Congress’ intent—restricted manufacturers’ ability to design innovative approaches to meet commercial truck fuel efficiency standards,” NHTSA said in a news release. “Under the Trump Administration, NHTSA is returning that authority to vehicle manufacturers who can best decide how to improve fuel efficiency.”

NHTSA Administrator Jonathan Morrison said manufacturers, rather than federal regulators, are best positioned to determine how engines should be designed for different commercial applications.

“American innovators—not Big Government—know how best to design vehicle engines,” Morrison said. “The Trump Administration is getting out of the way so manufacturers can decide how they want to meet fuel efficiency requirements.”

He also said bringing the commercial truck fuel efficiency program into what NHTSA considers its proper legal limits could lower truck prices and support U.S. manufacturers and their employees.

What would change for truck manufacturers

The proposed interpretation would not eliminate fuel economy requirements for complete commercial vehicles. Instead, it would change where NHTSA draws the regulatory line.

Manufacturers would still need to meet applicable fuel efficiency standards for finished trucks and work vehicles. The difference is that NHTSA would not separately regulate the fuel economy performance of an engine before it is installed in a particular vehicle.

That distinction matters because commercial trucks are built for a wide range of operating conditions. A powertrain selected for regional delivery, for example, may have different requirements from one designed for long-haul freight, vocational work or heavy-duty applications. The agency said giving manufacturers greater control over engine and powertrain choices would allow them to tailor equipment to the needs of commercial buyers while still meeting vehicle-level requirements.

For professional drivers and fleets, the immediate effect would be tied primarily to future equipment development and purchasing decisions rather than to current trucks already in service. The announcement does not cancel existing vehicle fuel economy requirements, and it does not change the basic need for manufacturers to certify complete vehicles under applicable federal standards.

Industry concerns over standalone engine rules

Industry groups had previously objected to standalone engine regulations during public comment periods. Their position was that NHTSA was exceeding its statutory authority by regulating engine components instead of limiting its oversight to complete vehicles.

NHTSA ultimately agreed with that interpretation. In the interpretive rule scheduled for publication in the Federal Register, the agency said it lacks legal authority to establish fuel efficiency rules for heavy-duty truck engines independently of the vehicles those engines power.

Because the action is an interpretive rule, it addresses how NHTSA understands the scope of its existing authority. The announcement describes the move as a reversal of the agency’s Obama-era policy on engine-only fuel economy regulation, rather than a repeal of all commercial vehicle fuel efficiency requirements.

The distinction between engine-level and vehicle-level regulation will be important as manufacturers continue developing new powertrains. Under NHTSA’s interpretation, the agency would set requirements for the finished truck while allowing manufacturers to determine which engine technologies, transmissions and other design choices are used to meet those requirements.

The announcement did not provide specific changes to fuel economy targets for individual truck classes or identify particular engine technologies that would be affected. It also did not state that existing trucks would need to be modified.

For drivers, the practical significance will depend on how manufacturers apply the additional design flexibility to future trucks. The federal government’s stated policy is to preserve fuel efficiency requirements for complete vehicles while reducing regulation of standalone engines. The next steps will involve the rule’s publication and the implementation of NHTSA’s revised interpretation within the commercial vehicle fuel economy program.