For purposes of this article, a person is under the influence of an alcoholic beverage or any drug, or the combined influence of an alcoholic beverage and any drug, when as a result of drinking an alcoholic beverage or using a drug, or both, his or her physical or mental abilities are impaired to a degree that he or she no longer has the ability to operate a motor vehicle, boat or vessel, or aircraft with the caution characteristic of a sober person of ordinary prudence under the same or similar circumstances. For purposes of this article, the presumptions described in Sections 23152 and 23155 of the Vehicle Code shall apply.
Ca. Gov. Code § 53153