Impairment Begins Long Before You Are Legally Drunk

It's not a question of whether you are legally intoxicated, it's a question of whether or not it is safe to drive when you have consumed any amount of alcohol. Research shows that impairment begins long before a person reaches the blood alcohol concentration level necessary to be guilty of drunken driving.

Legal Limit for Drunk Driving

In all 50 states, the legal limit for drunk driving is a blood alcohol concentration (BAC) level of .08.

A 120-pound woman can reach a .08 BAC level after only two drinks and an 180-pound man can be at .08 after only four drinks.

A "drink" is either one shot of liquor, a five-ounce glass of wine or one beer, all of which contain the same amount of alcohol.

At a .08 BAC level, drivers are so impaired that they are 11 times more likely to have a single-vehicle crash than drivers with no alcohol in their system. But 25 years of research has shown that some impairment begins for both males and females even after one drink.

At .02 BAC Level

At the .02 blood alcohol concentration level, experiments have demonstrated that people exhibit some loss of judgment, begin to relax and feel good. But tests have also shown that drivers at the .02 level experience a decline in visual functions, affecting their ability to track a moving object and experience a decline in the ability to perform two tasks at the same time.

These changes may be very subtle and barely noticeable to the person who has had only one drink, but in an emergency situation while behind the wheel of a vehicle, they could cause the driver to react (or not react) as they would without having had a drink.

At .05 BAC Level

At the .05 BAC level, people begin to exhibit exaggerated behavior, experience loss of small-muscle control -- such as being able to focus their eyes quickly -- have impaired judgment, lowered alertness and a release of inhibition.

If someone with a BAC level of .05 gets behind the wheel, they would be operating the vehicle with reduced coordination, a further diminished ability to track moving objects, more difficulty in steering and a markedly reduced response in emergency situations.

At .08 BAC Level

When someone drinking is approaching the borderline of legal intoxication, studies show that he or she has poor muscle coordination -- affecting their balance, speech, vision, reaction time and hearing -- find it more difficult to detect danger, and exhibit impaired judgment, self-control, reasoning ability and memory.

A driver with a BAC of .08 will find it more difficult to concentrate, judge the speed of the vehicle, experience reduced information processing capability and exhibit impaired perception.

Slower Reaction Time

For the person who is drinking, the above impairments may be hardly noticeable at the time, but the slow reaction times that they can produce could prove fatal in an emergency driving situation. That's why it is not a good idea to drive no matter how much or how little that you have had to drink.

There is another consideration: Alcohol affects people differently. Some people have a higher response to drinking alcohol than others.

In other words, people with a high response to alcohol can experience signs of impairment at the .02 BAC level that others do not experience until the .05 level.

Is There a Safe BAC Limit?

For this reason, in some states, drivers can be arrested for driving while impaired even if their blood alcohol concentration is lower than the legal limit if the law enforcement officer believes he has probable cause based on the behavior and reactions of the driver.

It's simply not a wise choice to get behind the wheel no matter how much you have had to drink. The only safe driving limit is .00 percent.

Sources:
National Highway Traffic Safety Administration
American Medical Association
National Commission Against Drunk Driving
National Institute on Alcohol Abuse and Alcoholism