Laws that declare it illegal to drive a vehicle above a certain alcohol level, as measured by a blood or breath test. In most states, the per se limit is .08% or greater. Violating the per se law has nothing to do with one's ability to drive a car safely; it is based solely on body chemistry. The only question is whether the driver was above the legal limit at the time of driving. NOTE: since breath or blood testing always takes place after the time of driving, it does not directly answer the question of BAL at the time of driving. The alcohol level at the time of testing may be higher, lower, or the same, when compared to the time of driving.