BAC is a term of art in DUI law which refers to “blood alcohol concentration”. The BAC is a seemingly objective measurement of the number of grams of alcohol present in the bloodstream of the alleged drunk driver. For most drivers, in most states throughout the United States, the presumptive level of per se impairment in DUI cases is reached at a concentration of 0.08 parts per ml.
For those with commercial driver licenses and/or operators of commercial vehicles, the BAC for presumptive impairment drops down to 0.04 parts per ml. Finally, for those under legal drinking age, the operative BAC threshold becomes 0.02 parts per ml.