One's blood alcohol content (BAC) level is how police determine whether or not someone is driving while under the influence, as defined by law. The BAC that is required for such a finding can vary by state. In Pennsylvania, for instance, a BAC of 0.08 or above indicates that the a person is legally drunk and can be charged with driving while intoxicated or while under the influence if operating a motor vehicle and apprehended by police. Even though individuals who are at this level and driving may not consider themselves to be drunk, the law clearly states that this is the magic number that will warrant a drunk driving arrest.
A good observation to make with respect to one's BAC level and the level at which a person feels impaired is that personal feelings on the matter of impairment while consuming alcohol and driving don't matter. It is true that each person's tolerance level is different and a lot of this has to do with the size and weight of a person. However, the equalizer is the BAC level and that is not subjective but an objective measurement of alcohol intake. It is important to note that although the BAC limit in Pennsylvania is 0.08, alcohol impairment can begin much earlier.
There is some evidence that impairment can begin at a BAC as low as .02 percent. So, while for criminal purposes, such a BAC level might not lead to an arrest as a drunk driver, it might be used as evidence in a civil trial with regard to determining the fault apportionment in an injury accident. Anyone injured in an accident in which the other driver may have been drinking should explore all legal options open to him or her as far as getting compensation for medical expenses, lost wages, and pain and suffering.
Source: Pocono Record, "Be wary of risks of drinking and driving in Pennsylvania," Debbie Kulick, May 23, 2014