About 15% of alcohol-related road deaths in the United States involve drivers with blood alcohol concentrations below the legal limit, a new study finds.

Researchers analyzed 16 years (2000 to 2015) of U.S. motor vehicle crash data. They found that 37% of the more than 600,000 motor vehicle deaths during that time involved at least one driver with alcohol in their blood.

But of those cases, 15% involved drivers with below the legal blood alcohol concentration (BAC) limit of 0.08%, and 55% of the deaths in such cases involved people other than the drinking driver.

"Our study challenges the popular misconception that alcohol-involved crashes primarily affect drinking drivers, or that BACs below the legal limit don't matter," said study lead investigator Dr. Timothy Naimi, of Boston Medical Center. His team published the findings March 15 in the American Journal of Preventive Medicine.

There was another tragic finding: Crashes involving blood alcohol levels below the 0.08% legal limit were more likely to result in deaths to young people, compared to crashes involving blood alcohol levels above that cutoff.

The study also found that more restrictive alcohol policies were associated with a 9% decrease in the likelihood that a crash involved alcohol at levels below the legal limit. This relationship was consistent across a wide range of subgroups and at a blood alcohol cutoff of 0.05%.

The U.S. National Transportation Safety Board and the U.S. National Academies of Sciences, Engineering, and Medicine have already recommended reducing the legal BAC limit from 0.08% to 0.05%. In 2018, Utah became the first state to do so.

Other countries that have adopted the 0.05% limit have had declines in traffic crashes, Naimi's team pointed out.

"Lower-alcohol crashes have been underestimated as a public health problem," Naimi said in a journal news release. "Our research suggests that stringent alcohol policies reduce the likelihood of fatal accidents involving drivers with all levels of alcohol blood concentration."

Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in New York City, has seen the tragic consequences of drunk driving firsthand.

He wasn't involved in the new research, but said it "provides ample evidence that impairment occurs well below the legal limit, putting other drivers and pedestrians also at high risk for serious injury and death. It further argues for the need to lower the limit to .05 [percent] or even .03 to reduce injuries and death."

Drinking and driving remains one of the leading causes of injury-related death in the United States, the Boston researchers said. However, most research on the topic focuses on alcohol above the legal limit of 0.08%, but impairment can begin at a BAC as low as 0.03%, they said.

Glatter agreed.

"The bottom line is that if you drink any amount of alcohol, you should not be behind the wheel," he said.