In California, An Expert Witness, Alone, Will Not Provide a BAC-Lowering Defense

DUI defendants often obtain expert witnesses at the request of their attorneys. In cases where multiple tests are performed and your BAC appears to keep rising with each additional test, experts are sometimes used to argue that when you were actually driving your vehicle, your alcohol was still under the legal limit — and that it reached the legal limit only after you were arrested, escorted to wherever your chemical test was performed, and administered the test.

That matters because per se DUI laws require the Government prove your BAC was above a threshold limit while you were driving. If your BAC is very high, or your BAC is relatively constant for multiple tests, this isn’t usually an issue. But when you’re just barely above the threshold, this might be your primary defense. After you consume alcohol, it takes a certain amount of time for the alcohol be absorbed into your bloodstream (and alter your BAC). The rate of absorption changes based on your body chemistry, how much you ate, what you drank, genetics, and various other things a good expert witness will consider.

In the California case, Coffey v. Shiomoto, Ashley Coffey’s BAC started at 0.08 the first time she was tested, and made its way up to 0.096 by her last test. Here’s what happened in Ashley’s case:

On November 13, 2011, at almost 2 a.m. (a time, by the way, officers are trained that most people on the road are intoxicated), Ashley was traveling on State Route 55 in Orange County when the police officer reported observing her swerving between lanes on three occasions. When he turned on his emergency lights, the Sergeant reported that Ashley began drifting left until she was in the carpool lane. Finally, when he turned on his sirens, Ashley pulled to the right and stopped her vehicle.

The Sergeant observed red eyes and a strong odor of alcohol coming from the car. Ashley denied drinking any alcohol that night despite the fact, the court observed, that she had just turned 21 and admitted being in a bar.

Ashely was administered Standardized Field Sobriety Tests (SFSTs) and performed poorly on two of the three SFSTs. Based on everything they observed, the officers placed Ashley under arrest about a half-hour after they stopped her vehicle.

About an hour after her vehicle was stopped, Ashley submitted to a breath test that registered a 0.08 BAC. Three minutes later, a second breath test registered a BAC of 0.09. Ashely was then transported to the Orange County jail where her blood was drawn one-and-a-half hours after she was driving — this time her blood result yielded a 0.96 BAC.

At this point, the police officer took Ashley’s license and issued her an administrative suspension order and a temporary driver’s license. She was later charged with DUI and accepted a plea to a misdemeanor reckless driving charge. Nonetheless, her license remained suspended as the criminal and civil components are considered separately, so she opposed the suspension with the Department of Motor Vehicles (DMV).

Ashley hired an expert witness who testified that because her BAC was consistently rising during the tests, and was only a 0.08 for the first test half-an-hour after she last drove, logically her BAC would have been under 0.08 when she was driving. The Hearing Officer was not persuaded by the expert’s testimony for four reasons:

  1. The expert himself did not examine the testing devices;
  2. He offered no opinion regarding whether the devices were in working order;
  3. He conducted no scientific tests himself; and
  4. He did not show that any other experts within the scientific community had reached similar conclusions.

The California Supreme Court in reviewing appeals like these can only substitute its opinion in lieu of a hearing officer’s finding when it finds the hearing officer “acted in arbitrary, capricious or patently absurd manner.” In this case, they did not think the DMV’s decision met any of these requirements, and so they affirmed the suspension.

Bottom Line: If you fight a DUI charge based on a "rising BAC" defense, you (or your lawyer) must provide evidence as to the reliability and working order of the testing devices as well as demonstrate scientifically that your conclusions are supported by the evidence and by the scientific community.

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