Designated drivers are drinking, too.
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Designated drivers are drinking, too.

You're onto your third or fourth cocktail of the night, but it's okay because you're buddy's the designated driver. So you're in safe hands, right? Don't be so sure.

If he's truly taking one for the team and sipping on soda all evening, then yes, you're probably in good shape. But is he really skipping booze altogether? Or is he having just a couple of beers while the rest of you party? According to a new University of Florida study, more than one-third of designated drivers actually drink themselves. Some are even drunk.

To get the pulse on designated drivers' actual alcohol consumption, the researchers headed to an area with a bumping nightlife and gave blood alcohol tests to bar patrons – mostly men, average age 28 – who were on driving duty that night. A majority of these people did not drink at all, but of those who did, 18 percent had blood alcohol concentrations of 0.05 percent or higher. That BAC might not sound too crazy, but it could be the legal limit of the future. In May, the National Transportation Safety Board recommended that all states lower a driver's allowed BAC from 0.08 to 0.05.

Interestingly, the DDs who drank tended to be older, while the college-age drivers were more likely to refrain. And, according to lead study author Adam Barry, the highest BACs also belonged to the older participants.

DUI risk aside, even if your DD has just a bit of booze, your "safe" ride home suddenly becomes a whole lot riskier. "Driving skills are negatively impacted with very minimal alcohol," Barry says. "With a BAC of only 0.02 percent, there is substantial research to show impairment on some driving tasks, specifically divided attention. Once 0.05 percent is reached, the vast majority of people have significantly compromised psychomotor functions, such as paying attention to the road and keeping the car within the painted lines."

The other factor to consider, says Barry, is that carting around a carload of sloshed people presents its own problems. "Think about everything outside of the car that competes for a driver's attention: other cars, bikes, pedestrians, traffic signs, and signals," he says. "If a driver has been drinking, other issues like reduced peripheral vision and delayed eye focus further limit his abilities. On top of that, when you add all the things competing for his attention inside the car – rowdy passengers, cellphones, music, and climate controls – driving can become really dangerous."

Bottom line: "The only safe and responsible behavior of a designated driver is to abstain from drinking completely," Barry says.