Federal regulators are quietly gathering data, running simulations and publishing report after report. This summer, a two-year, $35 million investigation by the EPA and National Highway Traffic Safety Administration (NHTSA) will spark a long-simmering debate about the future of green cars in the U.S.

Automotive News reported that automakers and environmental groups are watching closely as the agencies assemble an argument for maintaining or adjusting federal fuel economy targets. This midterm review is part of the deal finalized in 2012 to double the U.S. fleet’s average fuel economy from that of 2008.

The 2025 model year goal calls for a 54.5 mpg fleetwide average — or an adjusted real-world average of about 40 mpg on Monroney stickers. The review promises to be tense as gasoline prices remain low, consumers turn away from green cars and costs of new technology stack up. The feds’ analysis will affect automakers’ product strategies for a decade.

“This is not by any means a ‘check-the-box’ exercise,” said Christopher Grundler, director of the EPA’s Office of Transportation and Air Quality. “There’s a lot at stake.”

In June, the EPA, NHTSA and the California Air Resources Board will publish a report outlining key factors for the midterm review. This will be followed by discussions, a proposed rule in 2017 and a final decision by April 1, 2018.

Automakers have a cornucopia of green options that include lightweighting, downsizing engines and electrification to boost fuel economy, so the question isn’t if they can rise to the challenge, but how? And crucially for consumers, how much will it cost?

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