“Per se” laws in DUI or DWI cases generally establish that once an individual is shown to have a blood-alcohol concentration (BAC) at or above .08 percent, that person will be considered intoxicated by law. In such circumstances, no further evidence of intoxication or impairment need be demonstrated for purposes of a DUI case. These days, all states have per se DUI laws that find any driver with a blood-alcohol concentration (BAC) at or above .08 percent to be intoxicated.
The existence of these laws throughout the United States means that it is important for individuals who are drinking to realize that, regardless of how sober they themselves feel and behave, it is their BAC that matters in the eyes of the law once they get behind the wheel
Should it exceed the per se legal limit, they will legally be presumed to be impaired. These laws make it easier for the prosecution to establish that an individual was impaired, without requiring much on-scene evaluation such as sobriety testing and the like.