Orland Park DUI Attorney for Retrograde Extrapolation

DuPage County Criminal Defense Lawyer Helping Address Blood Alcohol Tests in DUI Cases

When a person is arrested on suspicion of drunk driving and charged with DUI, they will need to understand the potential options for defense. There are many factors that can affect DUI cases, and an experienced attorney can provide guidance on the defense strategies that may be used. At Issa Law, LLC, our lawyer has a strong understanding of the legal issues and types of evidence that may play a role in DUI cases. We can provide strong, effective representation to help resolve these cases successfully.

Issues Affecting Blood Alcohol Concentration and DUI Charges

The timing between a stop and subsequent arrest for DUI and the breath or blood analysis that may be used to determine the presence and amount of alcohol in a driver's system can play a crucial role in a case. These issues may determine whether or not prosecutors can meet the burden of proof to obtain a conviction for DUI. Due to numerous circumstances that may arise, a breath analysis at the police station may come hours after a person was driving while they were allegedly under the influence. However, this delay in testing will not necessarily bode well for the driver. For instance, if someone was stopped and arrested for DUI, and two hours later, a breath analysis revealed they had a blood alcohol concentration (BAC) of .16, it may be fair to presume that at the time the person was driving, they were over the legal limit of .08. This argument assumes that the person had not consumed any other alcohol in the two-hour time span, among many other assumptions.

However, some situations are not as clear-cut as the example above. Let us assume the same fact pattern above, but this time, the driver's blood alcohol concentration is .06 at the time of testing. How will this affect the case? Will the DUI charge that would apply if a test shows a BAC of .08 or above be dismissed? 625 ILCS 5/11-501(a)(1) states that no person shall drive or be in actual physical control of a motor vehicle when that person's blood alcohol concentration is .08 or more. In this situation, prosecutors could still file charges and secure a conviction, even if the person's blood alcohol concentration at the time of testing is under the legal limit. What the prosecutors would use to prove their case is called "retrograde extrapolation."

Retrograde extrapolation is based on the theory that when a person's blood alcohol concentration is measured through an analysis of their blood or breath at a particular time, they may have allegedly had a higher blood alcohol concentration at the time that they were operating a vehicle. In order to use retrograde extrapolation, the prosecutors would need a forensic toxicologist to testify. The forensic toxicologist would calculate what the driver's blood alcohol concentration was at the time the driver was operating the vehicle based on the results of a blood, breath, or urine test and how much time had passed.

Nonetheless, there are many evidentiary rules that prosecutors and forensic toxicologists will need to meet in order for the toxicologist to testify at trial and explain what they believed the driver's BAC was at a certain point. In order for the toxicologist to testify, the prosecution must show that the information used in the toxicologist's calculation was reliable and that he or she performed the calculations using a method that is generally accepted within the field of forensic toxicology.

If the toxicologist takes into account factors such as a driver's age, weight, height, the amount and types of alcohol consumed, typical alcohol absorption rates, and the types and amounts of food consumed before, during, and after drinking, a court may find the toxicologist's calculations to be more reliable. If however, these key variables are not used in the toxicologist's calculations, a court may find the toxicologist's opinions to be less reliable, and their calculations may not be allowed to be used as evidence against the driver. This was the case in the appellate court decision in People v. Floyd.

As you can see, when it comes to retrograde extrapolation, the formulas and information used by the expert witnesses prosecutors hire to testify against a driver can be complex, and they involve intricate rules of evidence. In a situation where a person is faced with a DUI charge, it is advisable for that person to hire an attorney who is experienced in DUI laws, the rules of evidence, and issues related to expert witnesses. An experienced lawyer may even be able to argue a "reverse retrograde extrapolation" theory; that is, if a person was stopped and tested with a BAC of .08 or slightly above within a short time afterward, and it can be shown that the driver had consumed alcohol in a very brief time before driving, it may be possible to argue that at the time the driver was stopped, his or her BAC was under the legal limit. To date, no case law has addressed the issue of reverse retrograde extrapolation, and it is unknown how that argument would be addressed in a court of law.

Contact Our Will County DUI Defense Lawyer

To learn how we can help you determine the best approach to take during your DUI case, contact our office at 708-966-2408 and arrange a consultation today.