The Science Behind DUI Per Se

The Science Behind DUI Per SeDriving under the influence (DUI) per se makes it illegal to operate a motor vehicle when your blood alcohol content (BAC) is over the legal limit. A DUI per se is usually determined by a breath or a blood test. In Maryland, the required BAC for DUI per se is .08% or higher. But why have these legal limits been set and what do they mean?


Blood alcohol content or BAC is the concentration of alcohol in the blood measured by volume, as a percentage. For example, a BAC of .20 means that 1 part per 500 in an individual’s blood is alcohol. The law uses this number as an indication of how intoxicated a person might be. The liver processes about one serving of alcohol per hour. When someone is drinking more than the liver can eliminate, the BAC will rise.


According to the Centers for Disease Control and Prevention (CDC), as your BAC increases, so do the side effects. When your BAC is:

  • .02%–this will have the lowest impact on your brain. You’ll feel more relaxed, experience an altered mood and may make poor judgments
  • .05%–at this level you make speak louder, and your behavior may become more exaggerated. Your vision may start to become blurry, your judgment impaired, and your coordination reduced. It may be unsafe for you to drive at this point.
  • .08%–this is the legal limit for DUI per se in most states. At this level, you lose more coordination and your balance, speech, reaction times, and even hearing get worse. Standing still, focusing on objects, and avoiding obstacles become much harder. It is now considered unsafe for you to drive.
  • .10%–you will most likely be visibly intoxicated at this point. You will have much less control over your balance and muscles, and it will be harder to walk and talk.
  • .15%–this BAC is very high, and you may have increased difficulty in your ability to walk and talk. Balance and coordination are very impaired.

DUI per se stands at .08% because scientists have determined that the skills needed to drive safely are significantly impaired at this point. The ability to correctly get signals from the brain has been affected.


If you’ve been arrested for DUI per se, you need the help of an experienced DUI attorney. The attorneys at Alpert Schreyer, will work hard to get you the best possible outcome. Contact us online or call us at (301) 494-9620 for a free consultation.

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