After finalizing in April fuel efficiency standards for cars manufactured in model years 2012 through 2016, the U.S. Environmental Protection Agency and the Department of Transportation are back to work, laying out options for model years 2017 through 2025.

On Friday, the agencies published a notice of intent asking for comment on four different miles-per-gallon requirements of increasing stringency. The proposals would require average mpg levels in 2025 of 47, 51, 56, and 62, leading to carbon dioxide outputs of 190, 173, 158, and 143 grams per mile, respectively. The agencies did not state a preference among the four options.

Any of the standards would prevent hundreds of millions of metric tons of climate-altering CO2 emissions and save hundreds of millions of barrels of oil. In each case, fuel savings would eventually offset the higher price tags for new cars.

Environmentalists are calling for the Obama administration to adopt the strictest standard – 62 mpg by 2025. Ann Mesnikoff at the Sierra Club said:

With higher gas prices always on the horizon, making cars go further on a gallon of gas is a no-brainer. The oil disasters this past summer in the Gulf and the Kalamazoo River add urgency to setting strong standards to help break our dirty and dangerous addiction to oil. […] Consumers will save far more at the pump than the technologies cost. There is no reason to aim lower. 

There are still a variety of issues for the agencies to work out. The New York Times’ Green Blog has a good description of some of the thorny questions regulators will need to answer, including how to treat plug-in hybrids”

Obviously there is no emission from the car, but if coal or natural gas were burned to make the electricity, how should those emissions be counted? […]

For cars like the Volt, which are supposed to run up to 40 miles on electricity before switching to gasoline, the regulators would have to make some kind of projection about how many miles were driven under each fuel. 

The notice is not an official notice of proposed rulemaking, which will come later, after the agencies publish at least one more preliminary notice, according to the EPA press release. In May, President Obama called for EPA and DOT to begin the standard-setting process.

The administration deserves credit for getting an early start on the next round of standards. Also, given the hostility with which business leaders and conservatives are treating regulation these days (especially greenhouse gas regulation), it is not insignificant that EPA and DOT announced their plans just a month before the midterm elections: It would have been easy to sweep the notice under the rug until afterwards, but the agencies didn’t.