Definition of "Under the Influence" in DUI cases.

California Vehicle Code section 23152(a) makes it a criminal offense to drive under the influence of alcohol. The question then arises, what is the definition of "under the influence" in DUI cases in California?

Under the influence does not require proof of being "drunk". There is no such thing as "drunk driving". The word "drunk" implies an elevated level of intoxication greater than merely being under the influence of alcohol.

People can be impaired to drive at different blood alcohol levels depending on their tolerance for alcohol. The law presumes that a person is under the influence legally if a blood or breath test gives a reading over a .08%. This is a rebuttable presumption however, and not everyone is impaired at this level. The law also says that a person may be legally impaired to drive with a blood or breath alcohol level over .05%, depending on the evidence. Under a .05%, and a person is considered legally sober to drive.

However, in DUI refusal cases in California, there is no blood or breath test evidence, and the Prosecution must attempt to prove impairment without a chemical test reading. The driving pattern, field sobriety tests, objective symptoms and the circumstances of the refusal are then relevant.

California jury instructions indicate that a person is "under the influence" if, as a result of taking alcohol or drugs, his or her mental or physical abilities are so impaired that he or she is no longer able to drive a vehicle with the caution of a sober person using ordinary care, under similar circumstances.