• Transportation Secretary Sean Duffy says sharply reduced vehicle fuel economy standards will be announced soon, signaling a major rollback of US efficiency policy.
  • NHTSA's August 28 interpretive rule on truck engines lays the legal groundwork for weaker standards, while a final light-duty CAFE rule is imminent.
  • The moves could ease compliance pressure on automakers and truck makers but may increase fuel costs for consumers and fleets over time.

A Shift in Regulatory Course

The Trump administration is preparing to finalize a significant easing of federal vehicle fuel economy standards, a move that would represent one of the most consequential reversals of US climate and energy policy in years. Transportation Secretary Sean Duffy indicated that the new rules, which would sharply reduce requirements for passenger cars and trucks, are imminent.

The most concrete step so far came on August 28, when the National Highway Traffic Safety Administration (NHTSA) issued an interpretive rule targeting medium- and heavy-duty truck engines. While the action does not itself lower existing standards, it establishes a legal basis for a future rulemaking that could substantially weaken them. The agency said it will no longer interpret the Energy Independence and Security Act of 2007 as authorizing separate fuel-efficiency standards for standalone truck engines, arguing that Congress authorized standards for complete vehicles, not individual components.

"The government should not be dictating engine-by-engine efficiency mandates," NHTSA Administrator Jonathan Morrison said in a statement. "Manufacturers need the flexibility to design trucks that meet the needs of their customers."

Current truck standards technically remain in place while NHTSA conducts a separate rulemaking to "reset" the program. The agency said it will exercise enforcement discretion consistent with its new interpretation in the interim.

A Broader Rollback

The truck action is distinct from, but politically connected to, the administration's proposed overhaul of light-duty CAFE standards. In December, NHTSA proposed setting an all-light-duty fleet average of about 34.5 miles per gallon by model year 2031, compared with approximately 50.4 mpg under the 2024 standards. That proposal had completed White House review by mid-August, signaling a final rule could come any day.

Automakers have largely welcomed the prospect of relaxed targets, which would reduce the pressure to invest in expensive efficiency technologies. "This is a common-sense approach that recognizes the real-world challenges of transitioning our fleet," said a spokesperson for the Alliance for Automotive Innovation. However, environmental groups have vowed to challenge the rollback in court. "These standards are the single biggest step the US has taken to combat climate change," said Dan Becker, director of the Safe Climate Transport Campaign. "Rolling them back is a gift to the oil industry."

Implications for Trucking and Consumers

For the trucking industry, the interpretive rule could shift compliance from efficiency mandates on individual engines to whole-vehicle performance, giving manufacturers more design flexibility. But critics warn that without a separate engine standard, real-world fuel consumption could rise.

"Diesel is our biggest cost after labor," said Tom Jensen, a fleet manager at a regional carrier. "If fuel economy slips, it hits our bottom line immediately."

The rule does not require drivers to alter existing vehicles or change operations immediately, but its effects would come gradually through future truck designs. The administration frames the rollback as an affordability measure, arguing that prior rules raised vehicle prices and limited consumer choice. Opponents counter that a cheaper vehicle at purchase may cost more to operate over its lifetime.

NHTSA's legal reasoning hinges on a narrow reading of the 2007 energy law, citing the Supreme Court's Loper Bright decision to argue that agencies lack broad authority. This strategy is likely to be central in expected litigation.

What Happens Next

NHTSA is expected to issue a proposed rule to revise the heavy-duty fuel-efficiency program shortly, which will clarify whether only the separate engine requirement will be removed or if complete-vehicle targets will also be lowered. Legal challenges are all but certain, focusing on the agency's statutory authority and economic analysis.

Meanwhile, the final light-duty CAFE rule is pending, and any announcement will trigger immediate market reactions. In the long term, weaker federal standards could widen the policy gap with stricter jurisdictions like California and the EU, complicating global product planning for automakers.

For now, the industry is watching closely. "This is a significant departure from decades of regulatory policy," said former NHTSA chief counsel Paul Hemmersbaugh. "But the legal details will determine how much actually changes."

As of press time, NHTSA had not responded to requests for comment on the timing of the final rules.