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Does DWI Require Proof Of Your Exact BAC At The Time Of Arrest?

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Does DWI Require Proof Of Your Exact BAC At The Time Of Arrest?


Under Texas law, a person is legally too drunk to drive if their blood-alcohol content (BAC) is at least 0.08 percent. Police and prosecutors often rely on breath or blood analysis to establish a defendant’s BAC. Of course, such tests typically measure a defendant’s BAC sometime after they are actually placed under arrest. Does that mean the prosecution has to “extrapolate” the defendant’s actual BAC at the time they were first pulled over by the police?

The short answer to that question is “no.” Texas courts have long held that “retrograde extrapolation” of a defendant’s BAC is unnecessary to consider the result of a Breathalyzer or similar test as evidence in a criminal DWI trial. Keep in mind, a BAC test is not the only evidence that a jury may rely upon in finding a defendant guilty of drunk driving. The arresting officer’s observations of the defendant’s state is often just as crucial in establishing legal intoxication.

Man Sentenced to 4 Years Following Third DWI Conviction

Take this recent Texas appeals court decision, Ortiz v. State. The defendant in this case had a prior criminal history. Specifically, he was convicted twice of DWI in Texas, once in 2000 and again in 2004. In July 2014, he was arrested for a third time on suspicion of DWI. The defendant subsequently skipped bail and evaded capture for three years, when he was apprehended and finally faced trial for the third DWI charge.

At trial, the jury heard testimony from the arresting officer. It also considered the results of the defendant’s Breathalyzer tests from when he was initially arrested before skipping bail. There were actually two tests performed, each of which indicated a BAC at least three times the legal limit.

The jury convicted the defendant of his third DWI offense. The trial judge imposed a prison sentence of four years. On appeal, the defendant challenged the sufficiency of the evidence against him. More specifically, he pointed to the lack of any retrograde extrapolation of his BAC.

The appellate court rejected that argument as without merit. The judges cited prior case law from the Texas Court of Criminal Appeals, which has held, “Breath or blood test results can be relied upon, even without retrograde extrapolation testimony, along with other evidence of intoxication to determine whether a particular defendant was intoxicated, as the term is defined, at the time of driving.”

Here, the appellate court reasoned there was no reason to believe that the defendant’s BAC would have been any higher than it was when he was arrested–he did not consume any additional alcohol while in police custody. More to the point, the court said the arresting officer’s testimony provided sufficient testimony to support a finding of drunk driving. For example, the officer said she observed the defendant “driving across a yellow line into the lane of oncoming traffic.” She also smelled alcohol on his breath after initiating the subsequent traffic stop.

Speak with a Brazoria County, Texas DWI Attorney Today

If you are detained on suspicion of drunk driving, the best thing you can do is refuse to answer any questions–especially with respect to where you have been that evening–and contact an experienced Pearland DWI/DUI lawyer. Call Keith B. French Law, PLLC, today to schedule a case evaluation.


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