Trump administration moves to unwind Obama-era truck engine efficiency rules 

NHTSA announced Friday that it has adopted a new interpretation of federal law limiting the agency’s authority to regulating the fuel efficiency of complete medium- and heavy-duty vehicles — rather than separately regulating engines, transmissions, tires and other vehicle components.

The action does not eliminate federal fuel-efficiency requirements for commercial trucks. Instead, NHTSA says manufacturers should have greater freedom to determine how an entire vehicle meets federal efficiency requirements, including through improvements to engines, transmissions, aerodynamics, cab designs or tires.

“The Trump Administration is getting out of the way so manufacturers can decide how they want to meet fuel efficiency requirements,” NHTSA Administrator Jonathan Morrison said in a statement.

Morrison said aligning the program with the administration’s interpretation of federal law will lower commercial truck prices and benefit U.S. manufacturers. NHTSA did not provide an estimate of how much the regulatory change could reduce the cost of new trucks.

The interpretive rule takes aim at regulations developed under the Obama administration as part of a sweeping effort to reduce fuel consumption and greenhouse gas emissions from commercial trucks.

Regulatory battle dates to Bush administration

The origins of the federal program predate the Obama administration.

The Energy Independence and Security Act of 2007, signed into law by President George W. Bush, directed NHTSA to establish a fuel-efficiency improvement program for commercial medium- and heavy-duty vehicles. 

The Obama administration implemented that mandate beginning in 2011 and expanded it through the Phase 2 greenhouse gas and fuel-efficiency standards finalized jointly by NHTSA and the Environmental Protection Agency in 2016.

The Phase 2 regulations established standards for combination tractors, trailers, heavy-duty pickups and vans, vocational vehicles and certain engines powering tractors and vocational trucks. The standards were designed to reduce fuel consumption and greenhouse gas emissions through model year 2027.

At the time, federal regulators estimated the program would save truck owners approximately $170 billion in fuel costs over the life of the regulations. They also projected that buyers of new long-haul trucks in 2027 could recover the additional investment in fuel-saving technology in less than two years through lower fuel costs.

The rules were also intended to accelerate adoption of technologies ranging from more efficient engines and powertrains to aerodynamic equipment and lighter-weight components.

When fully phased in, regulators projected tractors could achieve up to 25% lower fuel consumption and carbon dioxide emissions compared with equivalent 2018 tractors.

Trump administration challenges NHTSA’s authority over engines

The Trump administration actions on Friday are drawing a legal distinction between vehicles and their individual components.

NHTSA said EISA authorizes the agency to establish a fuel-efficiency program for commercial vehicles, but unlike the Clean Air Act — which gives EPA authority over engine emissions — EISA does not give NHTSA explicit authority to regulate engines or components such as transmissions and tires.

The agency also cited the Supreme Court’s 2024 Loper Bright Enterprises v. Raimondo decision, which overturned the Chevron doctrine governing judicial deference to federal agencies’ interpretations of ambiguous statutes.

NHTSA pointed as well to a recent U.S. Court of Appeals for the D.C. Circuit decision that the agency says found it lacks authority to regulate the fuel efficiency of nonvehicle components.

Under NHTSA’s new interpretation, regulators could continue setting fuel-efficiency requirements for a completed commercial vehicle while giving manufacturers more latitude over which technologies they use to achieve those targets.

Trucking industry had sought flexibility under Phase 2

The emphasis on manufacturer flexibility echoes some of the concerns raised by the trucking and manufacturing industries when the Phase 2 standards were adopted a decade ago.

Industry reaction to the final 2016 rule was generally positive, although fleets and manufacturers emphasized the importance of keeping compliance costs manageable and allowing enough time to develop and deploy new technologies.

American Trucking Associations officials were “cautiously optimistic” when the standards were finalized, according to a news release. ATA said it was pleased regulators had addressed concerns over technology-development lead times and flexibility, while warning that the program’s ultimate success would depend on fleets’ willingness to purchase the new technologies.

Daimler Trucks North America similarly supported the Phase 2 goals but said the rules needed to establish long-term targets for the entire vehicle rather than focusing solely on the engine, while providing manufacturers and customers enough flexibility to determine economically feasible ways of reaching the targets, according to Heavy Duty Trucking.

Other manufacturers also supported the overall efficiency objectives. Paccar said it would meet the standards while delivering fuel-efficient Kenworth and Peterbilt trucks, while Volvo Group North America called improved fuel economy a goal stakeholders could unite around but described the targets as a significant challenge for the industry.

The shift could also carry trade-offs. Engine-specific standards were designed to accelerate deployment of technologies that reduce diesel consumption and greenhouse-gas emissions. 

EPA and NHTSA estimated the broader Phase 2 program would save truck owners about $170 billion in fuel costs and reduce CO₂ emissions by roughly 1.1 billion metric tons over the lifetime of covered vehicles. 

Removing NHTSA’s engine-level requirements could give manufacturers greater flexibility and potentially lower upfront equipment costs, but the effect on long-term fuel consumption and emissions will depend on how the agency structures its vehicle-level standards.

Existing standards don’t disappear yet

Friday’s action does not immediately repeal the existing medium- and heavy-duty standards.

NHTSA said the interpretive rule establishes the legal foundation for a forthcoming notice-and-comment rulemaking that would formally reset its medium- and heavy-duty vehicle program.

Until that process is completed, the agency said it will exercise its enforcement authority consistent with its new interpretation.

The move also concerns NHTSA’s fuel-efficiency authority and does not, by itself, eliminate EPA’s separate authority under the Clean Air Act to regulate emissions from heavy-duty engines.