Every state has a legal limit for blood alcohol concentration. In most states, including Illinois, the legal limit is 0.08%. If your BAC is above that limit, the law presumes that you are too drunk to drive.
However, it is possible to face charges for driving under the influence even if your BAC is under the legal limit. Research shows that alcohol starts impairing your ability to drive even with a BAC less than 0.08%.
How does alcohol affect driving ability at lower blood alcohol concentrations?
According to AAA, alcohol can start impairing driving ability at a blood alcohol concentration of 0.02%. A 150-pound person can reach this level after drinking a 12-ounce beer over the course of an hour. At this point, you may notice an effect on your coordination, and the alcohol could also affect your judgment and decision-making capability.
With two drinks, your BAC may be between 0.04% and 0.05%. At this point, your reaction time begins to slow down, making it more difficult to avoid obstacles in the road by braking or steering. After three drinks, your BAC may be between 0.06% and 0.07%. Your reaction time becomes even slower, and your reasoning is not reliable.
How can you face charges if your BAC is below the legal limit?
If law enforcement officers have probable cause to believe that you may be under the influence, they have the authority to arrest you. Any evidence of your impairment is admissible in court. Your BAC is only one piece of evidence, but if authorities can demonstrate impairment in other ways, you may not only face charges but the court may convict you.
There are many factors that influence how alcohol affects you. BAC is a convenient benchmark, but you should not assume that there is no impairment and you are safe from prosecution as long as it remains under the legal limit.