Is A Rising Blood Alcohol Concentration A Defense To DUI In California?


If you are arrested for driving under the influence of alcohol and your blood alcohol level is only slightly above the legal threshold of 0.08%, your attorney might consider what is called the “rising blood alcohol” defense. Without getting into the scientific details, this defense asserts that at the time you were driving, your blood alcohol level was lower than the level you registered at the time of your arrest.

Depending on a number of circumstances including your weight, whether you were drinking on an empty or full stomach, and other factors, the alcohol you imbibe can take 30 minutes to an hour or more to rise to its peak blood alcohol level in your body.

Using a hypothetical example: A 180-pound man has 3 drinks over the course of a two-hour meal. Immediately after his last drink, he gets in his car and after driving for five minutes is stopped by the police. About 20 minutes after the stop, the police arrest the driver and he blows a .09% on the breathalyzer test. Yes, he is slightly over the legal limit but was he over the legal limit 20 minutes before when he was actually driving? It is quite possible that his body had not completely absorbed the alcohol at the time of the traffic stop and therefore, he was below the legal limit. In other words, his blood alcohol level was still rising at the time of the stop and by time the chemical test (breathalyzer) was performed, it had risen to .09%.

As this example suggests, it is not always easy to prove the driver’s blood alcohol content was rising but was below the legal limit at the time he or she was actually behind the wheel. Establishing this defense always requires the testimony of a DUI defense expert. These experts are scientists who will review the timeline of the stop to arrest, the forensic test results, and all relevant factors personal to the driver, such as the driver’s weight.

It is a rare occurrence that a misdemeanor DUI charge actually goes to trial, but the expert evidence will be presented to the district attorney during the pre-trial phase, which usually involves negotiating a plea bargain. Ultimately, it is impossible to prove what the driver’s blood alcohol content was at the time he or she was driving because there was no chemical test taken at precisely that point. But if the DUI defense expert’s evidence is convincing, it is often enough to persuade the district attorney to dismiss the charge or to negotiate with the defense attorney to charge the driver on a lesser charge.

For obvious reasons, the rising BAC defense is only a viable defense when the driver’s BAC is only slightly above the legal limit. It may also be effective when the driver tests just over the “aggravated DUI” limit of .15%, which carries stiffer penalties. In such a case, the rising BAC defense can result in a conviction on just a straight DUI (between .08% and .15%) and save the driver from the harsh penalties that are invoked upon conviction of an aggravated DUI.