When Alcohol Takes The Wheel: What's Your Limit?

This week, the National Transportation Safety Board recommended lowering the legal limit of blood alcohol content for drivers to .05 or even lower. Currently, it's illegal to drive in all states with a BAC of .08 or higher. Host Scott Simon speaks with Dr. Anthony Liguori of Wake Forest School of Medicine about alcohol's impact on driving ability.

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SCOTT SIMON, HOST:

You can legally drink and drive in the United States, but there's a limit. In every state, drivers can't get behind the wheel if their blood alcohol content is .08 or higher, but the National Transportation Safety Board wants the states to lower the legal limit to .05 or even lower. Now, that would bring the United States into agreement with much of the rest of the world.

The NTSB is convinced that lowering the limit would reduce the number of fatal accidents. Right now, about 10,000 people die every year in drunk driving accidents. Dr. Anthony Liguori is an associate professor at the Wake Forest School of Medicine. He joins us from the campus there, in North Carolina. Thanks very much for being with us.

DR. ANTHONY LIGUORI: My pleasure. Thanks for having me.

SIMON: How much are we talking about an average man or women would drink, to get to that .08 limit?

LIGUORI: Well, first we have to define what a drink is. A standard drink is a 12-ounce bottle of beer, 5 ounces of wine, an ounce and a half of hard liquor. All of those are equivalent to one standard drink. You get the same amount of alcohol from each of them. And for a man, it would take about four to five of those drinks in a two-hour period, to get to .08. For a woman, it would take fewer. It would take three to four drinks.

SIMON: What happens to someone's driving ability when they've had that much to drink?

LIGUORI: Well, over 90 percent of studies show impairment at the .08 level. And if you take a moment to consider all the elements of driving - reaction time, control of the vehicle, divided attention, vigilance if you're on an hour-long trip - all of those are impaired at .08 as is decision-making, and your ability to control your speed.

SIMON: What difference would the .05 limit conceivably make?

LIGUORI: Well, I gave that list of elements of driving. If you consider those, at .08, all of them are impaired. At .05, most of them are impaired. My laboratory, we have a driving simulator and in the simulation, we have folks go along a highway at about 55, 60 miles per hour. At random time points, a fence will appear in front of them suddenly, and they have to hit the brake.

If you consider a car goes 84 feet per second at that speed, at .08, before you can even react, the car's going to move an extra 10, 11 feet - before you even have the power to stop it. At .05, it'll move maybe 5 feet. So if you imagine you're on a highway, and there are other vehicles in front of you and there's a, you know, a collision in front of you and you need to suddenly brake quickly, that's an important difference.

SIMON: The legal limit in much of the United States, I gather, used to be nearly twice what it is now. Was that reckless?

LIGUORI: Well, I think people were not as well-informed. I think people still are not sufficiently informed of what alcohol can do to behavior. Point 08 is not a switch. It's not that you get to .08 and all of a sudden, things are dangerous. Dangers start at .01, .02. You see impairments at levels even that low.

SIMON: Dr. Anthony Liguori is an associate professor of medicine at the Wake Forest School of Medicine. Thanks very much for being with us, Doctor.

LIGUORI: Oh, it's my pleasure.

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SIMON: And you're listening to NPR News.

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