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A study finds that many designated drivers drink alcoholic beverages before driving, and their blood alcohol levels can impair their ability to drive and put them and their passengers at risk of a car accident.

For the study, published in the July issue of the Journal of Studies on Alcohol and Drugs, researchers at the University of Florida tested the blood alcohol levels of 1,071 people leaving Gainesville, FL, bars between 10:00 P.M. and 2:30 A.M. on Friday evenings, the nights before scheduled Gators home football games on Saturdays. The breath test found that of the 165 people who said they were designated drivers, 41% had been drinking. Although 17% of those had blood alcohol levels of 0.02 or lower, 18% had levels of 0.05 or higher, Nancy Shute writes for the NPR Health blog Shots.

In an NBC News Health article, Melissa Dahl quotes Adam E. Barry, Ph.D., lead author of the study:

‘I recognize the levels we have in our article is not .08,’ the blood-alcohol content limit for legal driving in all 50 states, Barry says. But for most individuals, by the time they reach a .02 BAC, ‘driving tasks such as divided attention are impacted. Once you hit .05, that’s basically when the vast majority of the literature says you are significantly impaired.’

Designated drivers, Dahl notes, are those who volunteer to refrain from drinking alcohol on a given night, in order to be sober to give rides home to others who are drinking. She goes on to write: “Too often, sometime around last call in far too many bars across the country, a cringe-worthy survey of sorts is done among drinking buddies: Who here is ‘least drunk’? The winner (‘winner’) is awarded the keys, and named the night’s designated driver.”

Dahl quotes Barry: “There’s evidence that says designated drivers often times are chosen because they’re least intoxicated — or they’re chosen because they’ve successfully driven a car intoxicated previously.” But Barry pointed out that there is not an agreed-upon definition of ‘designated driver,’ even in the academic literature. “Is it a person who abstains from alcohol entirely, or who maybe has a drink or two but stays under the legal limit for driving?,” he asked.

In the study (in which the average age of the people tested was 28), 40% of those tested were not students. Researchers found that the older a driver was, the higher their blood alcohol level was, Dahl writes.

This blog reported on May 15 that the National Transportation Safety Board is asking states to lower the definition of drunk driving to a blood-alcohol reading of no more than .05%. Most countries in Europe already have the lower level as their standard; for example, Germany, France, and Italy have a limit of .05%, and Sweden, Norway, and the Netherlands, have a limit of .02%, Dahl writes.

In Colorado, a blood alcohol level of .08 is a DUI offense; and a blood alcohol level of .05 but less than .08 is a DWAI offense, according to And a June 11 article on this blog listed the 10 Colorado counties with the most DUIs.

The study concludes:

Considering the low BAC [breath alcohol concentrations] levels at which driving-related abilities are negatively affected, these findings identify the need for consensus across researcher, layperson, and communication campaigns that a DD [designated driver] must be someone who abstains from drinking entirely. […]

DDs who consume alcohol (regardless of level) or are selected because they are deemed ‘least intoxicated’ (Knight et al., 1993) place both themselves and their passengers at greater risk for injury. Should the current status quo continue, it is likely that the scientific literature will continue to indicate that DD campaigns fail to effectively prevent impaired driving (Calafat et al., 2009; DeJong and Wallack, 1992; Ditter et al., 2005; Grube, 2007).

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