Understanding California's 'Per Se' Law

"Per Se" laws assume that a person is guilty of driving under the influence of alcohol if the court can show that his or her blood alcohol concentration (BAC) is more than .08%. While a person could be "under the influence" with a lower BAC, a BAC that exceeds .08% does not always mean a driver is intoxicated.

“In 1990, California became the 28th state to implement an immediate driver license suspension law for alcohol impaired drivers, also referred to as an “Administrative Per Se (APS)” or “on-the-spot” license suspension law.

“Forty-two states currently have an APS law of some kind, and all 50 states and the District of Columbia have laws defining it as a crime to drive with a blood alcohol concentration (BAC) at or above .08%.

“The California APS law requires the Department of Motor Vehicles (DMV) to suspend or revoke the driving privilege of persons who are arrested for driving with a BAC of .08% or more, or who refuse a chemical test, upon arrest,” according to the California Department of Motor Vehicles.

The Per Se law seems reasonable at first glance: The court only needs evidence that the driver's BAC was above the legal limit to obtain a conviction. After all, a person is DUI if his or her BAC is more than .08%, right? Not always.

Some drivers may not actually be "under the influence" of alcohol, even though their BAC is .08%. Alcohol influences each person in different ways; while one driver might feel the effects of alcohol with a .05% BAC, another driver's alcohol tolerance might keep him or her from feeling under the influence with a much higher blood alcohol concentration.


During a DUI case, chemical testing is often considered conclusive evidence of DUI, but it’s incorrect to presume that such tests are foolproof. If a chemical test indicates that the driver's BAC exceeded the legal limit, prosecutors can use the Per Se law to obtain a conviction.

Generally speaking, blood evidence is the most accurate way to determine the amount of alcohol in a person's bloodstream. Even still, blood tests cannot measure how the alcohol affects your ability to operate a motor vehicle.

Suggested Reading: When is Someone Considered Too Intoxicated to Drive?

Breath and urine testing are somewhat less accurate than blood tests. Many factors can influence the outcome of a breathalyzer test. For example, you are more likely to produce a higher BAC test result if you used mouthwash or haven't eaten. In conclusion, just because someone’s BAC comes back at .08%, it doesn’t mean it can’t be effectively challenged by a skilled DUI defense lawyer.

Learn more about California’s Per Se law under Section 23152(b) of the Vehicle Code.

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