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A Nip or Two Nips Driving Skills

Drinking small amounts impairs reaction to unusual situations

WEDNESDAY, Oct. 23, 2002 (HealthDayNews) -- No one will try to take away your car keys after you've had just a beer or two.

Yet drinking even significantly less than the legal limit can seriously impair your ability to respond well in unusual driving situations, experts say. Impairment in judgment can begin at much lower levels than the 0.08 percent blood alcohol concentration (BAC) level that makes it illegal to drive in many states, says Maurice Dennis, director of the Center for Alcohol and Drug Education Studies at Texas A&M University.

Yet people still think that's the magic bullet, and any amount consumed below that means it's safe to drive, he says. "People think if the legal limit is .08 it's OK if I'm at .07999." Dennis recently completed an as-yet unpublished study that suggests differently.

Dennis took 19 people of varying ethnicity and age and trained them in driving behavior. "Not everyone can drive equally well to start with," he explains.

Six of them didn't drink any alcohol. The rest were offered any type and amount of alcohol they wanted. When it was thought that their BAC was about 0.04 percent, the volunteers had their blood and breath analyzed for alcohol levels, and they were then asked to drive through a closed course.

The course included six different exercises of varying difficulty. In three of the simpler tasks, they were asked to perform exercises such as driving between cones. In the more difficult driving tests, they had to do things like maintain control of the car as they came out of a skid. "That's where they had greater losses," Dennis says.

Evaluators watched the drivers and rated them, but did not know who had consumed alcohol. When the subjects completed the first driving test, they drank more until their BAC was about 0.07 and then were re-tested. The last driving test was done when their BAC was 0.10.

"We saw losses [in skill] even at .04," Dennis says. "These increased at higher levels."

On average, a small woman will have a BAC of 0.04 after just one or one and a half beers, he says. For a 150-pound man, it's closer to two beers.

Usually, imbibing a bit and driving are not a problem, Dennis notes. It's when "something out of the ordinary happens," he says. "You've taken away the edge."

Dennis cites the example of driving sober but occasionally running a red light. Usually there may be little traffic, and your indiscretion is not a problem. However, as you continue to run red lights, your chances of being involved in an accident increase dramatically, he notes.

The same holds true with driving after drinking a bit. Under normal circumstances, all is fine. But one day, you may have had a few, get behind the wheel, and be behind someone who suddenly slams on the brakes, leaving you to decide to brake or swerve into another lane where there may be a pedestrian or other car.

In Dennis' experiment, when a driving emergency arose, those who had just a beer or two tended to make poor decisions, he says.

Dennis believes the blood alcohol level at which one is legally not allowed to drive should be 0.05.

Some impairment in judgment definitely exists by a BAC of 0.04, agrees James Fell, who is on the national board of directors of Mothers Against Drunk Driving. "Plenty of people are involved in crashes at lower levels. The probability of being involved in a crash increases at every level [of alcohol consumption]," he says.

"We're not prohibitionists," Fell asserts. But "if you're going to drink, make sure someone else drives for you."

What To Do

Find out more about blood alcohol concentration from Indiana University. What's your limit? The University of Oklahoma Police Department has an online BAC calculator.

SOURCES: Maurice Dennis, Ph.D., director, Center for Alcohol and Drug Education Studies, Texas A&M University, College Station; James Fell, member, board of directors, Mothers Against Drunk Driving, Calverton, Md., and director, Traffic Safety and Enforcement Programs, Pacific Institute for Research and Evaluation
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