While the study focused primarily on midsize vehicles, it concluded that existing technology like 8-speed transmissions, advanced turbochargers and lighter materials were most likely enough, on their own, to allow automakers to meet the 2025 standards. Electric or fuel-cell vehicles might still be bonuses for automakers, but they were unlikely to be necessary to reach the goal. The study was conducted by the National Research Council of the National Academy of Sciences, which brought together experts from the auto industry, academia and environmental groups. It evaluated more than 100 combinations of fuel-saving technologies to measure both fuel savings and economic cost.

The cost of carrying out the new rules, the study found, would be significantly less than expected — roughly half of what a previous 2011 report by the same group had estimated. “This is a good early indication that things are on track to meet the fuel efficiency goals on time and at a reasonable cost,” said Roland Hwang, director of the Natural Resources Defense Council’s energy and transportation program. “There were lots of claims flying back and forth early on about how much this would cost, and now we know it’s going to be very affordable by comparison.”

In calculating the cost to automakers of getting a typical midsize car to meet the 2025 target, the study offered two estimates: $1,200 or $1,700, depending on certain assumptions. By comparison, the 2011 study had estimated those costs could be higher than $3,000. “This is great news,” said Dan Becker, a director at the Center for Auto Safety, an advocacy group. “It shows that you can achieve these fuel economy targets with a conventional vehicle, using normal engines, and to do so cost effectively.”