CHICAGO – When do you know you have had too much to drink to safely drive?

That is difficult to say because a person who has consumed too much alcohol lacks the ability to make that call.

Someone who is dizzy or lightheaded from drinking may ignore such warning signs because they cannot recognize the risks, says Brad Fralick, adviser to Illinois Secretary of State Jesse White on drunken driving issues.

“In your impaired mind, you’re OK, but you’re really not a good judge of whether you’re OK,” Fralick said. “When your judgment is gone, so is your ability to count. That’s why it is so important to designate a driver before you start drinking. Then you don’t have to worry about how many you had.”

On average, a 170-pound male has to consume four drinks within an hour to reach a blood-alcohol content (BAC) of .08 percent, the national legal standard to be considered driving while intoxicated. A 137-pound female would have to consume three drinks in an hour to reach .08.

But a study conducted in 2000 for the National Highway Traffic Safety Administration concluded driving skills start to erode for most drivers at .02 percent, or one drink, and can decline significantly by .04.

The study measured reaction times, the ability to stay in lanes, avoid collisions, maintain vehicle speed and other driving skills.

Susan Ferguson, vice president of the Insurance Institute for Highway Safety, a research and lobbying group financed by major insurers, says the use of “drunk” instead of “impaired” encourages drinkers to ignore common sense about driving.

Fralick says the average person needs one hour to metabolize, or break down, one drink so it has negligible or no effect on his or her driving ability.

Does that mean two drinks per hour are too many?

“There is no way that a human being can metabolize that much alcohol in an hour,” he said.

Fralick says the effects of two drinks vary based on a person’s gender, weight, ability to absorb alcohol and how much they have eaten. Men, on average, can absorb 9 percent more alcohol than women because of their greater muscle mass.

Having two more drinks in the next hour will compound any effects, because after two hours they will have consumed four drinks, but their body may have metabolized only two.

“It’s not just how many drinks you have consumed in a certain period, it’s that you’ve consumed beyond what the body can metabolize in that time,” he said.

One way to address that is to alternate between alcohol and soft drinks or water.

Drinking on an empty stomach speeds alcohol to the bloodstream, where it starts affecting the brain and other organs sooner, said Fralick, formerly the executive director of the Illinois chapter of Mothers Against Drunk Driving.

On a full stomach, it can take up to six hours for all alcohol to reach the bloodstream, where it starts to affect the brain and other organs, according to Fralick. On an empty stomach it takes 30 minutes to two hours, he said.

The National Institute on Alcohol Abuse and Alcoholism adds alcohol’s effects are heightened by medicines that depress the central nervous system, such as sleeping pills, antihistamines, antidepressants, anti-anxiety drugs and some painkillers.

Medicines for diabetes, high blood pressure and heart disease also can have harmful interactions with alcohol.

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(c) 2004, Chicago Tribune.

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AP-NY-11-26-04 0613EST