Retrograde extrapolation is a technique used by police departments and prosecutors to determine and prove a person’s blood-alcohol level at the time they were operating a vehicle, as opposed to when the sample was actually collected. Crime lab chemists will apply a formula that approximate the average rate of decline and a person’s blood-alcohol level and use that to estimate a person’s blood-alcohol level at a time prior to the sample being taken. Although Arizona courts accept retrograde extrapolation as a method of proving intoxication, it is far from a perfect science.

The results of a retrograde extrapolation can be inaccurate for several reasons. First, each person metabolizes alcohol at a different rate, and simply applying the average rate of metabolization to every sample guarantees some inaccurate results. Furthermore, if a defendant consumed alcohol shortly before their arrest, their blood alcohol level may increase rather than decrease in the time before their sample is taken. If standard retrograde extrapolation is applied, the result would be inflated and inaccurate.

In the recently decided case, the defendant was charged with an aggravated DUI after he was involved in a single-car accident and police were called. He was arrested, booked in jail, and given a breath test over 2 hours after he was stopped. His test result was nearly three times the legal limit in Arizona, and he was subsequently charged with aggravated DUI. According to the case history discussed in the appellate opinion, prosecutors used retrograde extrapolation to estimate the defendant’s blood alcohol content at the time of his arrest. The defendant was convicted of the charges against him and sentenced to a significant prison term.

The defendant appealed his conviction. Among other issues, he challenged the propriety of using retrograde extrapolation to estimate his blood alcohol level. Because his blood-alcohol level was nearly three times the legal limit when the test was administered, the high court was not convinced that the use of retrograde extrapolation to estimate an even higher BAC when he was operating a motor vehicle was prejudicial to his defense. Essentially, the court found that with or without retrograde extrapolation, the state could have easily proven that he was over the limit while he was driving the vehicle. The court also rejected the defendant’s other contentions, and his conviction was affirmed.

Are You Preparing a Defense to Arizona DUI Charges?

If you or someone you know has been arrested or charged with a DUI or other crime in Arizona, retaining an experienced criminal defense attorney can make the difference between a conviction and a dismissal or acquittal. The Law Office of James E. Novak is staffed by qualified attorneys who know how to fight against Arizona DUI charges. James Novak is an experienced Maricopa County criminal defense attorney who can skillfully handle a variety of Arizona criminal cases, including DUIs. We can help you develop the best defense to the charges brought against you. To schedule a free consultation and discuss your case today, call 480-413-1499.

An important component of drunk driving cases is blood alcohol concentration. Let’s go over the basics and legal limits of BAC right now.

Understanding Blood Alcohol Concentration (BAC)

Blood alcohol concentration (BAC) refers to the percentage of alcohol present in a person’s blood. It’s a standard way for law enforcement to assess the intoxication level of a motorist.

Basic Blood Alcohol Concentration (BAC) in the State of Arizona

The BAC legal limit in Arizona is 0.08. This is the federal legal limit as well. A BAC in excess of 0.08 means that a motorist is legally intoxicated.

Keep in mind that a BAC under 0.08 may also be grounds for a drunk driving arrest if a motorist is driving recklessly or erratically regardless.

What is the BAC for aggravated DUI charges?

Some states issue more serious penalties when a motorist is operating a vehicle while severely intoxicated. Arizona is such a state, issuing aggravated DUI charges for severe levels of intoxication.

The legal limit for an aggravated DUI charge is 0.15.

Commercial Drivers Have a Different BAC Legal Limit

Given their duties and amount of time on the road, commercial drivers are held to a different standard when it comes to BAC. The legal limit for commercial drivers is 0.04, just half the legal limit of non-commercial motorists.

Zero Tolerance for Minors Drinking and Driving

If you are a minor, there is a zero tolerance policy when it comes to drinking and driving. This means that your BAC should be 0.00 or around that percentage. If a minor is caught intoxicated while operating a vehicle, he or she will be charged with a DUI, even if the BAC measured is well within the legal limit.

Are measures of BAC always accurate?

Not always.

Field sobriety tests only measure coordination and certain kinds of cognitive tasks, not the actual amount of alcohol in someone’s bloodstream.

To measure BAC, law enforcement often uses breathalyzer tests, blood tests, or urine tests. Each of these methods presents their own potential drawbacks links to poorly calibrated equipment, human error, or a mixture of both. False positives are not unheard of, and they are ultimately unacceptable.

How a Drunk Driving Defense Attorney Can Help You

If you are charged with drunk driving, partnering with a skilled defense attorney will help ensure that you receive a fair hearing an that all of your legal options are properly explored. An attorney well versed in drunk driving defense strategies can note irregularities or inaccuracies in testing, and may even point to violations of a motorist’s Constitutional protections during a traffic stop. It pays to have that kind of expertise on your side, and additional guidance moving forward.

Learn More About Drunk Driving Laws in Arizona

For more information about your legal rights, be sure to contact a skilled defense attorney about your drunk driving charge. At The Law Office of James Novak, we will fight diligently on your behalf to ensure your receive a fair shake from the law.