By Linda Carroll

(Reuters Health) – The blood-alcohol threshold for being considered legally impaired in the U.S. may be too high, according to a study that finds a meaningful percentage of crashes happen when drivers are below that limit.

Among the crashes involving drinking drivers with blood-alcohol levels under the legal limit, more than half of fatalities were individuals other than the driver, researchers found.

Moreover, crashes involving a drinking driver with blood alcohol under the legal limit of 0.08 grams per deciliter of blood, or 8%, were more likely to result in youth fatalities, compared to accidents with drivers above the legal limit, according to the report in the American Journal of Preventive Medicine.

“Basically, you could say that the risk for a fatal crash increases with increasing blood alcohol concentrations, starting with 0.02,” said study coauthor Dr. Tim Naimi, a physician and professor at Boston University. “What I think most people don’t understand is that the limit of 0.08 is simply a political compromise. In Scandinavian countries the limit is 0.02 and in the rest of the developed world it’s 0.05.”

Some U.S. states impose a lower cutoff, and the researchers found that lower limits were associated with a reduced number of fatal crashes compared to states with the 8% threshold.

In 2017, more than 12,000 vehicle crash fatalities involved a driver with a measurable blood alcohol concentration (BAC), the researchers note.

To look at trends in crashes involving blood alcohol concentrations below the legal limit, the researchers analyzed data from the National Highway Traffic Administration’s Fatality Analysis Reporting System (FARS), which includes accidents resulting in at least one fatality within 30 days of the crash.

Based on 16 years (2000 to 2015) of fatal crash data, Naimi and colleagues found that among the more than 600,000 motor vehicle deaths, 223,471, or 37%, were due to crashes involving at least one driver with a positive BAC test.

Among those fatalities, 33,965, or 15%, were in accidents involving a driver who tested positive but below the legal limit.

“We’re not saying that crashes involving blood-alcohol concentrations below the legal limit are as big of a problem as those with blood-alcohol concentrations above the limit,” Naimi said. “But blood-alcohol concentrations between 0.05 and 0.08 are a strong risk factor. There’s a policy debate currently going on as to whether we should reduce the legal limit in this country.”

One thing the researchers can’t say is whether the accidents among those with BACs below the legal limit would have happened even without alcohol being involved.

“What we can say is that any amount of alcohol in the body is impairing,” said Johnathan Ehsani, an assistant professor in the department of health policy and management at the Johns Hopkins Bloomberg School of Public Health.

“Impairment begins with the first drink,” said Ehsani, who was not involved in the new study. “The risk of an accident is doubled at 0.05, and at 0.08 the crash risk is four times that of someone with zero alcohol in their body.”

There’s nothing special about 0.08, Ehsani said. The risk of a crash steadily trends upward with increasing blood-alcohol concentrations, he added.

Where the limit is set depends on the American public’s tolerance for risk, Ehsani said. “If we set the limit at 0.05, it’s clear that it will save lives.”

SOURCE: American Journal of Preventive Medicine, online March 15, 2020.