Driving Under the Influence

“Driving Under the Influence” is defined as operating a motor vehicle while impaired by alcohol, other drugs or intoxicating compounds. In Illinois, a driver is legally considered to be under the influence if he/she has a blood-alcohol concentration (BAC) of .08 percent or greater, has used any illegal substance, or is impaired by medication. A driver's BAC is based on the ratio of alcohol to blood or breath. However, an individual showing alcohol levels between .05 and .08 percent may be convicted of DUI if additional evidence determines that the driver was impaired.

When the Illinois General Assembly passed legislation in 1997 to lower the illegal BAC limit to .08 percent from .10 percent, Illinois became the 15th state to impose such a change.

The effect of alcohol on an individual is determined primarily by two factors: the amount of alcohol consumed and the rate at which it is absorbed by the body. Other contributing factors include gender, body weight, alcohol tolerance, mood, environment and the amount of food consumed.

From the first drink, alcohol affects coordination and judgment. Even with a BAC well below .08 percent, a person's reaction time slows. The risk of being in a crash begins to increase between a BAC of .04 and .05 percent and increases rapidly thereafter. By the time a driver reaches a BAC of .06 percent, he/she is twice as likely to be involved in a fatal crash as a non-drinking driver. By the time a driver reaches a BAC of .08 percent, he/she is 11 times more likely to be killed in a single-vehicle crash than a non-drinking driver.

The only way to rid the body of alcohol is time. Fresh air, coffee, a shower and food cannot help a person sober up. It takes about one hour for the body to metabolize one drink. Each of the following has a comparable amount of alcohol and counts as one drink: one 12-oz. mug of beer, one 5-oz. glass of wine or one 1.5-oz. shot of hard liquor. (The amount of alcohol in a poured/mixed drink is dependent on the type of drink and the person who pours it.)

This edition of the DUI Fact Book is as accurate as possible at the time of publication. This manual does not cover every aspect of Illinois' DUI laws and should not be cited as a legal authority in court.