Alcohol does not affect everyone in the same way. A lightweight woman will have a higher BAC than an overweight man even if all the other circumstances (such as type and quantity of drinks) are the same. Physical traits, from food intake to age to overall health, influence how fast and how much each person metabolizes alcohol.

With so many factors involved that make everyone have varying BAC levels, why is the legal limit 0.08 percent? What is so special about that number?

The history behind the law

Before 0.08 percent became standard, every state had a different limit. Some chose a higher number, some chose lower and some did not have a maximum percentage at all. Both the National Highway Traffic Safety Administration and President Clinton were influential in pushing for a consistent legal limit of 0.08 percent across the nation in the 1990s.

The government used grants as an incentive for states to comply, and now all use that standard. Illinois adopted the law in 1997. Utah’s limit recently decreased to 0.05 percent, and every state has stricter guidelines for underage drunk drivers.

Why 0.08 percent?

There are many reasons for choosing 0.08 percent:

  • It is high enough to be fair to the average person who has only one drink.
  • Research shows that virtually everyone experiences significant impairment by this level. (However, the law also says that even if intoxication does not show, having a BAC of 0.08 percent is enough to warrant criminal charges.)
  • It is effective at reducing the number of deaths from drunk driving accidents.
  • The risk of getting in a crash is highest when drivers are at 0.08 percent or above.
  • Other comparable countries use this percentage or a lower one.
  • The public supports this number.

Despite using this number as the standard, impairment often happens sooner, even as low as 0.02 percent. Therefore, a driver may still face a DUI if he or she is under the legal limit but shows signs of being unable to drive safely.