Retrograde Extrapolation in Los Angeles DUI Cases

  • May 26, 2017

    In California, there are two different ways to be a drunk driver. One way is to operate a motor vehicle while you’re under the influence of alcohol. Another way to be a drunk driver is to drive with an unlawful bodily alcohol content.

    If you have an unlawful bodily alcohol content while you drive, it doesn’t matter if the alcohol influenced your ability to drive or not. Either way, you’ve broken the law. California Vehicle Code Section 23152(b) VC prohibits driving a vehicle when your bodily alcohol level is a .08 or higher.

    Although it’s illegal to drive a motor vehicle with an unlawful bodily alcohol content, it’s not illegal to have a bodily alcohol content that’s over a .08. That means that if you’re not driving a vehicle while your bodily alcohol level is over the legal limit, you haven’t broken a law. This poses a significant problem for law enforcement investigations into drunk driving.

    The problem is that law enforcement has to prove your bodily alcohol content at the time that you’re driving the vehicle. Minutes and even hours can pass from the time that you’re driving a vehicle to the time that you take a chemical test. That can make the chemical test woefully inaccurate for demonstrating your alcohol level at the time that you operated the vehicle.

    Police officers don’t have a way to test your alcohol at the time you’re driving. They have to rely on a process called retrograde extrapolation. That process estimates a person’s alcohol level at the time they drove a vehicle based on the chemical test that they took later. Basically, it’s a backwards projection to arrive at a person’s likely alcohol level at the time they drove the vehicle.

    The prosecutor might bring an expert to trial to talk about retrograde extrapolation. Your Los Angeles DUI lawyers should be prepared to argue aggressively against this expert. Ultimately, retrograde extrapolation is nothing more than a guess. It might not be enough to convince a jury that you should face the serious consequences that come with a drunk driving conviction.

    You can also hire your own expert. Your DUI attorneys can help you find an expert to review the state’s case. That expert can help you explain to the jury that the process of retrograde extrapolation is far from scientifically certain. The expert can explain to the jury that there’s reasonable doubt as to your true alcohol level at the time you operated the vehicle.

    In some cases, a person’s bodily alcohol content can rise after their arrest. When a person drinks shortly before driving a vehicle, their alcohol content might be lower at the time that they’re driving than it is by the time they take the breath or blood test hours later. This is another scenario where it’s helpful to have an expert witness.

    Your expert witness can explain to the jury how the body absorbs alcohol. Every person’s body absorbs alcohol differently. What you eat, the water in your system and the period of time you consume alcohol are just a few of the factors that can affect how your body absorbs and then eliminates alcohol.

    Your expert can explain how it’s possible and even likely for a person’s alcohol level to rise after they’re arrested for drunk driving. If this is what might have happened, this can create enough reasonable doubt for a jury to find you not guilty of the drunk driving charge. A DUI attorney can help you evaluate your case and arrange to bring a helpful expert with you to your day in court

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