Both the U.S. Environmental Protection Agency and National Highway Traffic Safety Admin. are expected to propose auto makers achieve a fleet-fuel economy of up to 60 mpg (3.9 L/100 km) when the two agencies release their first estimates on potential mandates for 2025 next month.

The federal offices, along with the California Air Resources Board, recently concluded a round of information gathering from auto makers, suppliers, state governments and other stakeholders.

The EPA and NHTSA are expected to use the feedback this month to draft a Notice of Intent to Issue a Proposed Rule for 2017-2025 fuel-economy and emissions standards.

Last year, the EPA and NHTSA issued a breakthrough set of rules, driving auto makers toward a U.S. a corporate average fuel economy of 34.1 mpg (6.9 L/100 km) by 2016. Each year, CAFE will average an increase of 4%, beginning in 2011 with ’12 vehicles.

Together with tailpipe emissions targets, which offer auto makers credits for improving vehicle functions such as air conditioners, the U.S. fleet will reach 35.5 mpg (6.6 L/100 km) by 2016.

The notice due from the agencies by Sept. 30 represents the first step in the next round of CAFE rulemaking. The EPA and NHTSA then will seek comments on proposals within the notice before going back behind closed doors to craft a final rule, due as early as 12 months from now.

While the notice will not set a firm target for 2025, experts say 60 mpg likely will be among the proposed bogies.

“We’ve called on them to set 60 mpg by 2025,” says Brendan Bell, a Washington representative for the Union of Concerned Scientists’ clean-vehicle program. The UCS played a key role in helping the government draft the 2016 rules, suggesting the 35.5 mpg mark ultimately decided upon.

“We think that is where the technology can take us,” Bell tells Ward’s. “I don’t think 60 mpg will be out of the realm of possibilities. Certainly it is at the high end, but not out of the realm.”

The 2025 rule will cap upwards of three product cycles, allowing auto makers to leverage a host of coming technologies, such as downsized and turbocharged engines; lightweight materials; and hybrid, plug-in hybrid and full-electric propulsion systems.

Bell expects the industry to witness a major shift in vehicle mix between 2017 and 2025. “We’ll see if EVs are working their way into the market as planned,” he says.

Last week, Hyundai Motor America announced a goal of achieving 50 mpg (4.7 L/100 km) for its fleet by 2025. HMA President and CEO John Krafcik told journalists in Traverse City, MI, for the annual CAR Management Briefing Seminars the auto maker shared its goal with the EPA and NHTSA during meetings earlier this year.

“Our approach with them has been to be transparent, share information and not hold any cards to the chest,” Krafcik said. “They’ve seen numbers from us consistent with our (50 mpg) commitment.”

John DeCicco, a senior lecturer in the University of Michigan’s School of Natural Resources and Environment, and a CAFE debate veteran, senses the Obama Admin. would like to act ambitiously.

“The current administration wants to deliver on the environment and move forward while they have the authority,” he says.

In the last 25 years, CAFE rules have pushed combined fleet-fuel economy for light-vehicles up by less than 2%, according to Ward’s data. But new regulations are expected to ratchet up CAFE nearly 30% in the next six years and by a potential 118% in the next 15 years.

“Politically, we’ve crossed the threshold, and it is OK to regulate vehicle efficiency again,” DeCicco says.

The federal agencies also continue to work on the first-ever, medium- and heavy-duty truck rules that would run from 2014 to 2018, with a goal to implement the first batch in 2012.

jamend@wardsauto.com