Laws and lawyers frequently refer to the offense of driving with a .08% blood alcohol concentration (BAC) or higher as DUI "per se." At a BAC of .08% or higher, a crime occurs regardless of whether the alcohol had (or could have had) any effect on the motorist’s driving. (Lower limits apply to drivers who are under the age of 21.) Some states also have per se Drug DUI laws that make it illegal to drive with a certain concentration of select drugs in your system. Simply driving with that particular blood alcohol or drug concentration is enough for a conviction.
Conversely, some drivers are surprised to learn that they can be convicted of driving under the influence even if they didn’t have a BAC of .08% while driving. In most states, a DUI conviction can also be based on driving while impaired—whether or not your BAC was above .08%. (Learn more about the differences between per se and impairment offenses.)
Why the DUI Per Se Rule is So Strict
To some, the DUI per se rule seems unfair—after all, .08% BAC is highly arbitrary given not only the tolerance that people can develop over a lifetime of drinking, but also the variability in rates of absorption and metabolism. And for some people, it may take only a few drinks to reach a BAC of .08%. But whatever the fairness of the per se limit may be, all states have DUI per se laws.
Lobbying groups have encouraged legislatures to create per se DUI laws. These efforts involved scientific opinions stating that anybody with a BAC of .10% or more could reasonably be considered under the influence. Ultimately, the National Highway Traffic Safety Administration (NHTSA) reduced the figure to .08%. All states adopted that figure when the federal government made its implementation a condition of receiving federal transportation aid. And with it, prosecutors were given a shortcut that allowed them to prove a DUI without proving actual impairment.
The per se idea was later adapted to apply to drug DUIs in some states.
Fighting DUI Per Se
We surveyed readers who were charged with driving under the influence and asked them about their alleged BAC levels. Almost 60% percent of our respondents reported that the indicated BAC was .10% or higher. Only 40% reported having a BAC lower than .10% or that they refused a chemical test.
These results are particularly relevant when considering those who tend to fight DUI charges. As a general trend, people charged with a DUI are more inclined to contest the charge if the breath or blood test shows a BAC of .10% or less. (Read about the costs and case outcomes reported by drivers with various BAC levels.) For those who fight, the battle is often over issues like the accuracy of the sampling process and the testing of the sample.
To that end, our survey also covered those who took breathalyzers and challenged the test results. Of those who contended a breathalyzer was inaccurate:
- 37.5% pleaded guilty to a lesser charge
- 25% pleaded guilty to a DUI
- 25% were convicted of a DUI after trial, and
- 12.5% had the charges dismissed.
Of course, whether you fight your DUI case should depend on much more than general trends. For a realistic picture of your chances, consult an experienced DUI attorney.