The federal fuel-economy requirement for new cars and light trucks will reach an estimated 34.9 miles per gallon in model year 2031 under a final rule announced Monday, well below the 49.3 mpg fleetwide level projected under the standards it replaces.

The National Highway Traffic Safety Administration said the change will reduce the technology manufacturers must add to comply with federal law, while its own analysis projects that vehicles will use more gasoline than they would have under the previous rule. The result is a policy tradeoff: lower near-term manufacturing costs against higher fuel use and household spending over a vehicle's life.

The rule, signed Sept. 25 and announced Sept. 28, covers model years 2022 through 2031. It is scheduled to take effect 60 days after publication in the Federal Register, according to the agency's final rule.

What the final rule changes

For model year 2031, NHTSA set projected fleetwide requirements of 40.2 mpg for passenger cars and 26.4 mpg for light trucks, producing the combined 34.9 mpg estimate. The standards are corporate averages, not a requirement that every vehicle achieve the headline number. Each automaker's obligation depends on the size and mix of vehicles it sells, and the laboratory-based compliance figures are not the same as the fuel-economy number motorists see on a window sticker.

The agency's rule summary also ends trading of compliance credits between manufacturers beginning with model year 2028. Automakers may still earn and use credits within their own fleets under statutory limits. Other revisions change how some vehicles are classified and how manufacturers calculate their fleets beginning in model year 2030.

Those technical changes matter because credit trading had allowed companies exceeding their targets, including electric-vehicle makers, to sell credits to manufacturers that fell short. Removing that market shifts the compliance calculation even as the overall targets become less demanding.

Lower compliance costs do not guarantee lower prices

NHTSA estimates the rule will reduce regulatory technology costs for a model year 2031 vehicle by $1,289, assuming manufacturers pass the savings to buyers. The Transportation Department said in its announcement that the change could save consumers about $138 billion over five years and lower the average price of a new vehicle by roughly $1,300.

Those are modeled estimates, not guaranteed discounts. Automakers set prices according to competition, demand, product mix and financing conditions as well as production costs. The final rule therefore supports a narrower conclusion: manufacturers are expected to spend less on fuel-saving technology than under the prior standards. Whether, when and how much of that difference reaches buyers will be determined in the market.

Agency calculations reviewed by Reuters put the industrywide technology-cost reduction at $60.6 billion through model year 2031. The analysis attributed $20.4 billion to General Motors, $6.6 billion to Stellantis and $5.8 billion to Ford, with smaller but still multibillion-dollar reductions for Toyota and Honda.

Drivers are expected to buy more gasoline

The same federal modeling projects that gasoline consumption through 2050 will be 4.6% higher than under the standards being replaced. NHTSA also estimates that a vehicle subject to the new rule will cost its owner more than $1,600 in additional fuel over its useful life, according to a separate Reuters report.

That comparison is relative to the previous policy baseline. It does not mean national fuel use must rise every year in absolute terms: fleet turnover, vehicle choices, travel patterns, gasoline prices and electric-vehicle adoption will all affect actual consumption. It does mean the agency expects the rule itself to produce more fuel use than keeping the earlier standards in place.

The distribution of costs will also differ. A lower purchase price, if realized, arrives when a buyer acquires a vehicle. Fuel costs accumulate over years and depend on how far the vehicle is driven and future gasoline prices. High-mileage drivers would be more exposed to the latter, while people who drive relatively little could place greater weight on the upfront cost.

Automakers gain flexibility as the market shifts

The Alliance for Automotive Innovation, which represents most large manufacturers, said the rule better aligns the federal program with the law and current market conditions. Automakers have argued that consumer adoption of electric vehicles and other highly efficient models has not matched assumptions embedded in earlier federal targets.

Environmental organizations counter that the rollback transfers costs from manufacturers to drivers and increases oil consumption and pollution. The Associated Press reported those competing reactions while noting that the administration presented the rule as an affordability measure in a market where new-vehicle prices remain a central concern. The administration's price claims and the agency's fuel-cost projections can both be true if vehicles cost less to build but more to operate.

The final rule is likely to face court challenges, and the administrative record shows that NHTSA is relying on a revised interpretation of its authority and the economic practicability of stronger standards. Litigation could focus on whether the agency adequately explained its reversal, assessed statutory factors and accounted for environmental and consumer costs.

For manufacturers, the immediate task is product planning. Model-year decisions are made years ahead, so companies must weigh the looser federal requirements against state rules, global efficiency standards, battery investments and consumers' demand for both larger vehicles and lower operating costs. A federal rollback reduces one source of pressure, but it does not erase those other forces.

For buyers, the central point is similarly practical. The rule may lower the cost embedded in a new vehicle, but federal analysts also expect it to increase gasoline spending. The eventual balance will depend less on the 34.9 mpg headline than on actual sticker prices, the vehicles people choose, how much they drive and what they pay at the pump.