When is a person legally impaired while drunk?

A person is legally considered impaired while drunk when their blood alcohol concentration (BAC) reaches 0.08% or higher in most states in the U.S. This level indicates that their ability to operate a vehicle safely is significantly compromised due to alcohol's effects on coordination, judgment, and reaction time. However, impairment can occur at lower BAC levels, and individuals can be charged with DUI if their driving ability is affected regardless of their BAC.