What measurement do states use for determining Driving While Intoxicated or Driving Under the Influence?

States typically use blood alcohol concentration (BAC) as the primary measurement for determining Driving While Intoxicated (DWI) or Driving Under the Influence (DUI). A BAC of 0.08% or higher is commonly considered legally impaired for drivers aged 21 and over. For commercial drivers and those under 21, the legal limits may be lower. BAC is usually measured through breath, blood, or urine tests.