Designated drivers don't always abstain, UF study finds

June 10, 2013

GAINESVILLE, Fla. — Maybe better call that cab, after all: A new University of Florida study found that 35 percent of designated drivers had quaffed alcohol and most had blood-alcohol levels high enough to impair their driving.

Adam Barry, an assistant professor of health education and behavior at UF, and his team interviewed and breath-tested more than 1,000 bar patrons in the downtown restaurant and bar district of a major university town in the Southeast. Of the designated drivers who had consumed alcohol, half recorded a blood-alcohol level higher than .05 percent — a recently recommended new threshold for drunken driving.

“If you look at how people choose their designated drivers, oftentimes they’re chosen by who is least drunk or who has successfully driven intoxicated in the past — successful meaning got home in one piece … that’s disconcerting,” Barry said.

The results are published in the July issue of the Journal of Studies on Alcohol and Drugs.

The researchers recruited patrons as they left bars between 10 p.m. and 2:30 a.m. across six Friday nights before home football games in fall 2011. The mean age of the 1,071 people who agreed to be tested was 28. Most were white male college students, while 10 percent were Hispanic, 6 percent were Asian and 4 percent were African-American.

After completing a 3-5 minute interview about demographic data and alcohol-related behaviors, participants then had their blood-alcohol content tested with a hand-held breath-testing instrument.

The non-driving participants had significantly higher levels than the designated drivers, but 35 percent of the 165 self-identified designated drivers had been drinking. Seventeen percent of all those drivers tested had blood-alcohol levels between .02 and .049 percent, while 18 percent were at .05 percent or higher.

The National Transportation Safety Board last month recommended all 50 states adopt a blood-alcohol content cutoff of 0.05 compared with the 0.08 standard used today to prosecute drunken driving. The American Medical Association made the same recommendation in the 1980s, Barry said.

Barry said he doesn’t know why a designated driver would consume alcohol, but factors could include group dynamics or the driver’s belief that one or two drinks won’t impair his skills if he is an experienced drinker.

Some field-based research suggests designated drivers might drink because the group did not consider who would drive before drinking commenced. Barry also suggested that it’s tricky for anyone to accurately evaluate their own sobriety.

“That’s the insidious nature of alcohol — when you feel buzzed, you’re drunk,” he said.

There is no universally accepted definition of a designated driver, according to the research. Although most U.S. researchers say drivers should completely abstain, international researchers believe they can drink as long as his or her blood-alcohol level remains below the legal limit. However, the U.S. limit is much higher than in most other countries.

At .08 percent, the U.S. has one of the highest allowable legal limits of any developed country. Countries such as Denmark, Finland and Greece use the .05 level; Russia and Sweden are at .02; and Japan has a zero percent tolerance.

Co-researchers were Beth H. Chaney and Michael L. Stellefson, also assistant professors in health education and behavior, College of Health and Human Performance.