In the United States, a BAC level of what value is legally considered impairment?

• A. 0.05
• B. 0.10
• C. 0.08
• D. 0.12

Answer: (C)

Understanding how blood alcohol concentration relates to driving impairment is essential. A BAC of 0.08% is the level at which many states consider an adult driver legally impaired. At this threshold, essential driving skills—reaction time, coordination, attention, and judgment—are noticeably reduced, which significantly increases crash risk. The law adopts a per se limit: if your BAC is at or above 0.08, you’re legally impaired to drive, regardless of other signs.

It's useful to know impairment can begin at lower levels and progresses with more alcohol. Some contexts use different limits; for example, commercial drivers are often held to a 0.04 limit, and underage or zero-tolerance laws can be stricter. Still, 0.08% remains the widely used standard for adult drivers in many states.