Sam Ori, executive director of the Energy Policy Institute at the University of Chicago, explained that the fuel economy standard was designed to adapt to consumer behavior. It’s measured based on the vehicle’s footprint, so larger cars and trucks have to meet less stringent targets.

So if people buy more SUVs, a car company is allowed to have a lower average fuel economy. On the other hand, this can push carmakers to build larger and larger vehicles (witness the growth of crossover SUVs^[22]).

“Footprint-based standards incentivize automakers to make bigger vehicles,” he said.

A car company can also reduce its greenhouse gas emissions with tactics like limiting coolant leaks and by buying credits. Based on current trends and projections, the EPA estimates that the current rules will require a real-world average fuel economy^[23] of 36 miles per gallon by 2025, up from 24.7 miles per gallon in 2016.

To make sure the rules are working, the EPA is required to conduct a midterm evaluation^[24] to make sure manufacturers are doing their best and to see whether the rules are too strict.

The Obama administration reported in January 2017, shortly before Trump took office, that everything was hunky-dory. Then-EPA Administrator Scott Pruitt^[25] said it wasn’t.

“The Obama Administration’s determination was wrong,” Pruitt said^[26] in a press release. “Obama’s EPA cut the Midterm Evaluation process short with politically charged expediency, made assumptions about the standards that didn’t comport with reality, and set the standards too high.”

But the document the EPA links to as background for the rollback announcement reports that the ruling from former EPA Administrator Gina McCarthy was “based on an extensive technical record, created over 8 years of research, review of several hundred published reports, hundreds of stakeholder meetings, and multiple opportunities for the public to provide input.”

Ori said the new proposal is thin on its technical justifications. “It does not rise to the level of what the Obama administration did to put these rules into place,” he said.