Believe it or not, authorities can arrest you for DUI even when your blood alcohol concentration is under the legal limit of 0.08%. The legal limit is the point at which the law presumes that you are too drunk to drive. However, alcohol can have an effect on you and your driving ability well before you reach the legal limit.
If law enforcement can demonstrate that you were impaired while driving, that may be more significant to the court than your actual BAC. The following are predictable effects on driving at different BAC levels.
0.15% (approximately twice the legal limit)
Unsurprisingly, functions necessary for driving, such as your auditory and visual processing and your ability to focus, become substantially impaired at this level. You also typically experience major loss of balance and have significantly less muscle control than normal.
0.08% (legal limit in Pennsylvania)
At this level, your perception becomes impaired and your capability to process information becomes reduced. Controlling your speed and concentrating on the driving task become more difficult, and you may experience loss of short-term memory.
Your ability to divide your attention, i.e., perform two tasks at the same time, declines at this level. This can be bad news when you are driving as it may become more difficult to think about working the pedals with your feet while steering with your hands. Tracking a moving target with your eyes also becomes more difficult due to decline in visual functions. At this level of intoxication, you may experience an alteration of your mood, as well as some loss of judgment.
At this level, you may experience reduction of both your alertness and your coordination. Focusing your eyes can become more difficult due to loss of control over your small muscles, which can result in further reduced tracking ability. You may experience difficulty steering and impaired judgment.
By this point, your thinking has slowed down, and as a result, your reaction time has deteriorated. Your ability to brake appropriately and maintain lane position is reduced thanks to your lack of coordination.
The National Highway Traffic Safety Administration recommends that you refrain from driving if you have been drinking any alcohol at all.