Can You Really Drive with a Blood Alcohol Level of .4?

For many drivers, especially moderate or non-drinkers, the blood alcohol concentration (BAC) numbers on warning signs are a bit mysterious. What is .08 anyway? And how many drinks is that?  And what about those news reports of people driving with BACs as high as .4?  How can they do that?

Simply put, alcohol dissolves pretty evenly in one’s blood. Very quickly after you take a drink, alcohol enters your bloodstream. One bottle of beer will raise one’s BAC to about .02 in under an hour. Obviously other factors are involved: your weight, age, sex, and individual metabolism. But generally speaking, five or more drinks in about two hours (four or more drinks for adult females) brings the BAC to 0.08% or above, the legal limit for driving in all 50 states, according to the NIAAA.

There is a phenomenon called tolerance that occurs with people who are long term, chronic heavy drinkers.    Chronic tolerance is a bodily adaptation that makes a person need to drink more and more alcohol to get the same effect, or inversely, an adaptation that causes less and less response to a recurring dose.   To read more about what this is and is not, read this article.   It does not mean that the person is any less unable to drive if they are alcohol “tolerant”.  The per se BAC of .08 means that they are considered to be driving under the influence, even if the effects of that dose of alcohol do not cause the same effects as a person who is non tolerant.

How Blood Alcohol Level Affects Driving Ability

  • .02: Relaxation, loss of inhibition.
  • .05: Mild euphoria, more intense emotion, and decreased caution (drivers take note!)
  • .08: Vision, reaction time, hearing, coordination, and judgment are all weakened. You are legally drunk and not allowed by law to drive
  • .15: Drunkenness obvious to anyone. Words are slurred, walking is difficult.
  • .2: Confusion, nausea, and considerable difficulty walking or standing.
  • .3: or over:   the person is at high risk of alcohol poising and potentially fatal symptoms.  Seek medical attention right away.

While a personal breath test device is one way to make sure you haven’t had too much, it is very important to understand that you can be too impaired to drive at a BAC of less than .08.   In Utah, for example, the per se BAC limit is .05.   Per se means that the BAC reading alone is a enough proof that you were too impaired to drive.  That doesn’t mean, however, that you can be a .07 and still be “legal to drive.”   If the arresting officer has probable cause to pull you over for suspected impaired driving, and your driving behavior is risky,  you can still be charged under other statutes, such as California’s “wet reckless” or New York’s “Driving While Ability Is Impaired by Alcohol” statute.   Several states have these designations, including Colorado.

Best idea — figure out a sober ride home before you drink — there’s an app (or two!) for that!