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The blood-alcohol limit in the U.S. is 0.08% — a cutoff that implies that any blood-alcohol content (BAC) south of 0.08% is safe, or at least not illegal.

But a new study published in the journal Addiction suggests that there is no such thing as a safe BAC, and that driving after consuming even a small amount of alcohol — just one beer, for instance — is associated with incapacitating injury and death.

The safety of "buzzed" driving has been on the minds of the public recently, in light of the death of MTV's Jackass star Ryan Dunn, 34, who crashed his car on a highway in Chester County, Pa., at high speed, also killing his passenger, Zachary Hartwell, 30. Hours before the crash, Dunn posted a photo on his Twitter account showing him drinking. The manager of a local bar, Barnaby's of America, told the Philadelphia Inquirer that Dunn had been in late that night with friends, but didn't seem drunk when he left.

It's unknown whether or how much alcohol played a role in Dunn's crash. But the new study by two demographers at the University of California, San Diego, found that drivers who consumed even a single drink before getting behind the wheel were more likely than sober drivers to get into car crashes; those accidents were also on average more severe than those involving sober drivers.

David Phillips and Kimberly M. Brewer of UCSD's sociology department looked at accident and injury data from the Fatality Analysis Reporting System (FARS) database, which tracks every car accident in the U.S. involving at least one fatality; between 1994 and 2008, those accidents involved 1,495,667 people. The researchers used FARS because it includes drivers' BAC (in 0.01% increments) and logs car crashes occurring in all U.S. counties, at all times of day, every day of the week.

The researchers focused on the association between drivers' BAC and the severity of car crashes. By definition, accidents included in FARS are severe and the researchers were not able to examine injuries that occurred in non non-fatal accidents. Instead, they calculated the ratio of severe to non-severe injuries in FARS crashes and compared that to drivers' BAC.

What the authors found was that the severity ratio increased significantly even when drivers were merely buzzed. A BAC of just 0.01% — about the equivalent of one light beer for a 180-lb. man over the course of two hours — was associated with accidents that were 37% more severe than those involving completely sober drivers.

Car crashes involving a driver with a BAC of 0.01% resulted in 4.33 severe injuries for every minor injury; in crashes involving sober drivers, there were an average 3.17 severe injuries for every minor injury.

Why do buzzed drivers have more dangerous accidents? In large part because they are more likely to speed, less likely to wear a seat belt and more likely to be driving the "striking vehicle," compared with sober drivers, the study found. (The police reported that Dunn's Porsche may have been traveling at more than 100 miles per hour when it careened off the road and flipped before crashing into a tree.)

The researchers found a dose-response between BAC and accident severity. For every 0.01% that the driver's BAC increased, so too did the average speed of the driver's vehicle and severity of crash injuries.

The researchers controlled for other variables that are known to contribute to accident risk and fatality, such as time of day, day of week, time of year, age of the driver, and drivers' fatigue and inattention. The association between BAC and crash severity persisted.

For instance, more accidents happen on weekends, during summer, between the hours of 8 p.m. and 4 a.m., and when drivers are tired, but the effect of BAC on dangerous accidents remained after researchers accounted for these factors.

In the last year of their study period, the authors noted, there were 50,430 vehicles and 84,026 people involved in fatal automotive accidents; among these, there were 37,261 deaths and 10,048 incapacitating injuries. A high BAC was the leading risk factor for these crashes.

That's why many nations have set legal limits for BAC, though they tend to vary widely: Germany, home to the autobahn, allows a BAC of 0.05%, while Japan's legal limit is 0.03% and Sweden's is just 0.02%.

"We hope that our study might influence not only U.S. legislators, but also foreign legislators, in providing empirical evidence for lowering the legal BAC even more," Phillips said in a statement. "Doing so is very likely to reduce incapacitating injuries and to save lives."

• Meredith Melnick
• The blood-alcohol limit in the U.S. is 0.08% — a cutoff that implies that any blood-alcohol content (BAC) south of 0.08% is safe, or at least not illegal.