Blood Alcohol Concentration (BAC)

Blood alcohol concentration or BAC refers to the percentage of alcohol in a driver's blood stream. It is measured as weight per unit of volume. Typically this measurement is converted to a percentage such as 0.10%, which indicates that one-tenth of a percent of a person's blood is alcohol. Because alcohol affects the cognitive and motor functions of a driver, including information processing, decision making, and hand-eye coordination, it is currently illegal to drive with a BAC of 0.08% or higher in every state.

A driver's BAC can be affected by several factors: age, body weight, gender, food consumed, amount of drinks consumed in a specific time period, and the number of drinks consumed. Most drivers who reach the illegal BAC limit will begin to experience a lack of balance, slurred speech, impairment of motor skills, and diminishing vision and judgment. Consider, however, it is not necessary to have a BAC above the illegal limit to be arrested and convicted of DUI. Many drivers are convicted with a lower BAC if the state can prove they were operating their vehicle while they were impaired.