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What is BAC and how does it impact a DWI?

BAC Defined

BAC stands for Blood Alcohol Content and it measures the amount of alcohol in the bloodstream. It is typically measured after a DWI stop with a sample from a breathalyzer or a blood draw. The two digit number that is returned from the analysis of the sample can have a big impact on your DWI case.

There are many factors that are going to affect your BAC. Obviously the amount of alcohol consumed is a major factor. But also, when were the drinks consumed and over how long a time period? How much did you eat? How much do you weigh? At the end of the day, it’s not even a great measure of intoxication because tolerance can vary widely between individuals. Even though it is a very rough estimation of intoxication, laws and courts rely heavily on it because it is seemingly such an objective measure.

.08 – DWI presumed

If the reading is over .08, a DWI is presumed under the law. This means that the prosecutor does not even need to show evidence that driving was impaired. As long as they can show that your BAC was over .08, that is sufficient evidence for a DWI. Importantly, the State must show that your BAC level was .08 at the time of driving.

Since BAC fluctuates up and down, a reading over .08 not taken at the time of driving might not be sufficient evidence that it was over .08 when the car was being operated. For example, a drink consumed right before getting behind the wheel might propel the BAC over .08 after the driving has concluded. For these reasons, a reading over .08 is not an automatic “guilty”. A reading that is slightly over .08 can often be reduced to a lesser charge.

.15 – Enhancement to a Class A DWI

A BAC over .15 can result in the charge being enhanced from a class B misdemeanor to a Class A misdemeanor. A class A carries higher maximum jail time and fine (from 180 days and $2,000 to 1 year and $4,000) Importantly, there is a minimum jail sentence of 30 days with a class A misdemeanor. However, just because a DWI is charged as a class A does not mean that’s where it will end up. Depending on the facts of the case, it can often be dropped to a class B, dropping the minimum jail time all the way down to 3 days.

DWI when below .08

Some people are surprised that a prosecutor may continue with a DWI prosecution even when the BAC is lower than .08. This can happen for two reasons. First, .08 is the level where DWI is presumed. It’s not a necessary element for proving the DWI, it just makes the prosecdutoer’s job easier. They can also simply show that the driver did not having “the normal use of mental or physical faculties by reason of the introduction of alcohol”. Note that they do not have to show that the driver was over .08 to prove intoxication.

A second factor that people forget about is that alcohol is not the only way someone can become intoxicated. It can also be by way of “a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body.”

When a blood test comes back below .08 in Travis County and the officer believes the person was intoxicated, their policy is to immediately send the sample to DPS for drug testing. For a number of reasons, a DWI based on drugs rather that alcohol is going to be a more complicated case. For example, the timing of the effect of the drug vs. it remaining in the blood stream can create significant issues for the prosecution. However, prosecutions for drug DWIs against drivers who are below .08 BAC can and do happen all the time.

Rob Chesnutt is an attorney at ATX Legal. He handles criminal defense in Travis, Hays and Williamson counties, and personal injury cases across Texas. This blog post is for educational purposes only and is not legal advice. If you would like legal advice for your specific issue, you can call us at 512-677-5003, or visit atx.legal to set up a free case evaluation.

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