According to the new rule, the EPA will require automakers to increase the average fuel economy of their new vehicles by 1.5 percent between model years 2021 and 2026. Eventually, that standard will lead to cars that average about 40 miles per gallon. By contrast, the previous 2012 Obama-era standard pushed manufacturers to increase the average fuel economy of their cars and trucks by five percent annually. Had the EPA continued to enforce that standard, automakers would have had to build vehicles that averaged 54 miles per gallon eventually.

The Trump administration estimates lowering the fuel economy standard will save most consumers about $1,000 on their next car purchase, thereby allowing a greater number of Americans to buy newer, safer and ultimately cleaner cars. It also argues the new standard will help make the US automotive industry more competitive by reducing regulatory costs by as much as $100 billion through model year 2029.

However, most experts disagree on those points. According to a recent estimate by Consumer Reports, rolling back the fuel economy standard to 1.5 percent will increase the average net cost of a new vehicle by $2,100, eliminating any upfront savings.

On the climate front, an estimate by the Environmental Defense Fund suggests the rollback will add 1.5 billion metric tons of greenhouse gas emissions into the air by 2040. What's more, the agency estimates the new rule will lead to 18,500 more premature deaths, 250,000 more asthma attacks and 350,000 other respiratory issues by the middle of the century. All this at a time when a worldwide pandemic is inflicting thousands of Americans with a potentially lethal respiratory disease.

The one silver lining in all this is that the rollback isn't as drastic as the EPA's original proposal. When the agency first proposed modifying the rule in 2018, it recommended freezing the standard at 2020 levels. Had the agency put that rule in place, the average fuel economy would have stayed at 37 miles per gallon.

States like California are likely to legally challenge the rollback, particularly as the EPA attempts to use the rule to enforce a national fuel economy standard. Last year, the state and four automakers -- Ford, BMW, Volkswagen and Honda -- agreed to a voluntary pledge to make their engines more efficient by about 3.7 miles per gallon every year until 2026.