Blood Alcohol Levels and Driving

by Reid K. Hester, Ph.D.

A friend and I have a disagreement (and a bet on it) about drinking and driving. My friend, Dennis, says that as long as you keep your blood alcohol level under the legal limit that it's OK to drive. He has a chart that shows him how much he can drink over time and still stay under our legal limit of 0.8. I think he's nuts. I can feel the effects of 1-2 beers and wouldn't want to put myself and others at risk by driving after I've drunk anything. So who's right?

I have the pleasure of informing you that you are the winner of the bet with your friend. In a very narrow and legal sense, he is correct but that's about as far as it goes. Most states now have a 'per se' limit of 80mg% (also known as 0.8) blood alcohol concentration (BAC). This means that if a driver is caught with a BAC at or above 80mg%, he or she is considered to be intoxicated regardless of whether they can pass a field sobriety test or not. A BAC of 80mg% will result in an arrest for driving while intoxicated (DWI) arrest.

However, you can be arrested for DWI even if you have a BAC less than 80mg%. If you have any positive BAC and fail a field sobriety test you can be arrested for DWI. Some states also have very low BAC limits for underage drivers.

But far more important than getting arrested is the risk you put yourself and others at if you drink and drive. Your judgment and reaction times don't just go down the tubes all of a sudden when your BAC gets to 70-80mg%. Rather, they decline as your BAC increases from 0mg%. As your BAC increases so does your risk for getting in an accident. There is no safe BAC for driving. So if you drink, don't drive. And if you drive, don't drink. If you're going out with your friends, designate a driver who won't drink. Or walk. Or take a taxi. Do what you have to so that you and your friends can get back home safely.

About the Author:

Reid K. Hester, Ph.D., Director, Research Division, Behavior Therapy Associates, 3810 Osuna Rd NE Suite 1, Albuquerque, NM 87109. Phone: 505.345.6100.

Originally published 02/19/98
Revised 8/15/08 by Marlene M. Maheu, Ph.D.

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