Measuring BAC Impairment, When Are You In Violation

The amount of alcohol in a person’s body is measured by the weight of the alcohol in a certain volume of blood. This is the blood alcohol concentration, or “BAC.” The measurement is based on grams per deciliter (g/dl), and in most states a person is considered legally intoxicated if his or her BAC is .10g/dl (.10) or greater; that is, alcohol makes up one-tenth of one percent of the person’s blood.

With each drink consumed, a person’s BAC increases. Although outward appearances vary, virtually all drivers and motorcycle operators are substantially impaired at .08 BAC. Laboratory and on-road research shows that the vast majority of drivers, even experienced drinkers, are significantly impaired at .08 with regard to critical driving tasks such as braking, steering, changing lanes, divided attention tasks, and judgement. The risk of being in a crash rises gradually with each BAC level, but then rises very rapidly after a driver reaches or exceeds .08 BAC, compared to drivers with no alcohol in their system.

While there is no “safe” amount of alcohol for drivers, most people can drink moderately and drive legally when the illegal per se limit is set at .08 BAC. A 170-pound male typically would have to consume more than four drinks in one hour on an empty stomach to reach a BAC of .08. A 135-pound female typically would have to consume three drinks in the same time frame