I. DUI Under Subsection (a)

Subsection (a) is the first of the two ways in which the State can prove a defendant violated the law prohibiting driving while under the influence of alcohol or drugs.

1. Elements Under Subsection (a)

   1. Driving a motor vehicle

      The first element of DUI requires the State to show that the defendant drove a motor vehicle. To satisfy this first element, the State must show some movement of the vehicle. This element requires that the State show “volitional movement” of the vehicle in question. California courts have found that a “slight movement” of the vehicle is sufficient to satisfy this element. Further, movement of the vehicle in question may be proved by circumstantial evidence, which by inference, indirectly proves the defendant was driving.

   2. Driving While Under the Influence

      The second element of DUI requires the State to prove that at the time driving, the defendant was under the influence of alcohol or drugs. A person is under the influence alcohol, a drug, or combination of both, when as a result of drinking and/or using a drug (illegal or legal) the person’s physical or mental abilities are impaired to such a degree that the person no longer has the ability to drive a vehicle with the caution a sober and ordinary person would use under the same or similar circumstances.

      To show that alcohol or drugs impaired a defendant’s physical or mental abilities at the time of driving, the State often relies on the subjective, personal observations of the investigating officer. An officer may testify regarding his observation of erratic driving maneuvers, the defendant’s physical appearance, slurred speech, failed field sobriety tests, or other factors tending to show the defendant’s physical or mental state.

   Hence, under subsection (a), a person with an unknown BAC level or a BAC below 0.08 may still be found to be under the influence, if based on the subjective factors listed above, a judge or jury finds the person’s mental or physical abilities were impaired due to alcohol and/or drugs.

II. DUI Under Subsection (b)

1. Elements Under Subsection (b)

   1. Driving a motor vehicle

      As above, this element is satisfied by evidence that defendant caused a volitional movement of the vehicle. As under subsection (a), the State cannot obtain a conviction for DUI under subsection (b) unless the driving element is satisfied.

   2. At the time of driving, defendant had a BAC% of 0.08 or higher

      Subsection (b) provides the State with an objective test by which to prove the offense of DUI. To obtain a conviction, the State must prove that at the time of driving a motor vehicle, a defendant’s blood alcohol content was 0.08 or higher.

      Under subsection (b), the law presumes that if a person’s BAC is 0.08% or greater at the time of a blood or breath test, the person is guilty of DUI, regardless of whether she was actually experiencing the physical or mental effects of alcohol and/or drugs.

      It is possible for a person to be intoxicated with a BAC level below 0.08. On the other hand, it is also possible for a person to be above that level while maintaining normal mental or physical faculties. However, once a level of 0.08 is proved, a judge or jury may (but is not required) to infer that the person’s physical or mental abilities were impaired as required for a DUI conviction.

      A toxicology report is frequently used as evidence showing that the defendant’s BAC% was 0.08 or higher at the time of driving—not the time at which the test was administered. An expert may testify as to calculation methods that may establish the defendant’s BAC% at the time of driving regardless of the levels present at the time of the test.

2. Blood, Breath, or Urine Testing and Consent

   A defendant’s BAC% is established by executing a blood or breath test. By driving within the state of California, a driver is deemed to have given his or her consent to chemical testing of his or her blood or breath for the purpose of determining the alcoholic content of his or her blood.

   Prior to arrest, submission to taking such a test is voluntary but upon arrest, refusal to complete the required test subjects the defendant to fines, license suspension, and even imprisonment upon conviction. Upon being arrested, an arrestee has the right to choose between a blood or breath test and the arresting officer must inform the arrestee of her right to choose. If a blood or breath test cannot be administered, the driver is also deemed to have consented to taking a urine test and must take the urine test. These additional punishments are further discussed under the punishment section below.