This means that, even for critics who are not interested in reducing greenhouse gases from cars, there’s still an argument to be made for keeping vehicle fuel standards, said Antonio Bento, an environmental economics expert at the University of Southern California and one of the study’s co-authors.

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“What the paper shows is that even if those environmental benefits are very, very low, if nothing else, from a safety reason, you have a reason to move forward with the standards,” he said.

The federal Corporate Average Fuel Economy, or “CAFE” standards, were first introduced in the United States in 1975. In 2012, the Obama administration approved a more stringent set of standards, which would steadily increase the efficiency of certain vehicles through 2025. The standards also changed some of the ways efficiency requirements are applied to cars of different sizes.

Facing opposition from the automobile manufacturing industry, the administration later conducted a review of the standards but concluded at the end of 2016 that they would remain in place. However, the Trump administration decided in March to reopen this review — meaning it could decide to weaken or remove the Obama administration’s update.

Pushback against the CAFE standards is hardly new. Over the decades, industry members and other critics have levied a variety of arguments against them, and one of the most common from the beginning has been the idea that fuel standards sacrifice safety. Many critics have suggested that lighter-weight cars — which are typically more fuel efficient — are more likely to produce fatalities in an crash.

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This may indeed be the case if you’re looking at a weight change in only one car. Say you observe a crash between two SUVs, both around the same size. If you downsize one of those vehicles to a Smart car, the chance of its passengers being injured or killed may increase. On the other hand, if you downsize both vehicles, the overall risk of fatality might actually become smaller than it was to begin with.

The researchers argue that, in the past, critics have only examined the effects of reducing an individual vehicle’s weight and not the standards’ overall effects on all vehicles in circulation — an important distinction.

“What CAFE actually does is it doesn’t just lower the weight of one vehicle,” said Kevin Roth, an environmental economist at the University of California at Irvine and another co-author of the study. “It changes the entire composition of the fleet.”

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The researchers (who included Bento, Roth and co-author Kenneth Gillingham of Yale University) focused their study on two effects of the original CAFE standards: a reduction in the average weight of all vehicles on the road and a change in the dispersion of their weight — that is, how much variation there is in the weight of individual cars.

Dispersion is what really causes safety problems, the researchers note. If you think about the scenario with the SUV and the Smart car, the problem wasn’t just that the Smart car, by itself, is a lightweight vehicle — it’s that it was pitted against a much heavier one.

Automakers’ responses to fuel economy standards tend to produce a reduction in the average weight of vehicles on the road, as well as an increase in their weight dispersion. The relevant safety question, then, is whether an increase in weight dispersion, or a decrease in mean weight, is the more dominant outcome.

To investigate, the researchers analyzed data on vehicles sold in the United States between 1954 and 2005 to see how their weight changed after the original CAFE standards were introduced in 1975. Next, they collected police reports on 17 million car crashes across 13 states between 1989 and 2005, noting which ones produced fatalities and the weights of the vehicles involved.

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Finally, the researchers conducted a series of simulations to see how these crashes might have turned out if the original CAFE standards had not been introduced and the vehicles’ weights had not been adjusted. The simulations suggested that 171 to 439 fewer fatalities occurred each year with the standards in place than without them, depending on factors such as the year and the location of the crashes.

“I think one of the findings of this study is that these [safety] concerns have been drummed up as the reason to get rid of this standard,” Roth said. “We’re essentially showing that these concerns are probably overblown.”

In fact, some of the changes the Obama administration made to the CAFE standards were designed to address safety concerns, according to Joshua Linn, a senior fellow at environmental research nonprofit Resources for the Future. (Linn was not involved with the new study but has provided comments on the working paper to the authors.) The study suggests that, in reality, this was probably never actually a problem, he said.

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However, the new study addresses only the effects of the original CAFE standards — not the Obama administration’s update, which may take years to produce noticeable changes in the composition of vehicles on the road, Roth noted. This means that the researchers can’t say for certain that their findings apply to the Obama standards under review.

But they may suggest that “there’s no reason to think that removing the standards is going to improve safety on the road,” Roth said.

It remains to be seen whether the safety argument will become a major point in the talks about the CAFE standards’ future under the Trump administration. So far, many of these discussions have revolved around the costs and logistics manufacturers face in complying with the current rules. Last week, automakers reportedly met with the heads of the Transportation Department and Environmental Protection Agency to discuss some of these issues.