Being arrested for Driving While Intoxicated (DWI) in North Texas can be horrifying. Most of the time you are pulled over for some small technical reason, and the police officer asks you how much you have had to drink before conducting a DWI investigation. After the police officer asks you for your license and registration, they typically ask you to perform a series of tests which quite frankly, are set up for you to fail.
The first test is the eye test. Technically, it is called the Horizontal Gaze Nystagmus (HGN) test. What the police officer doesn't tell you or state on your video is that Nystagmus is a naturally occurring phenomenon in all of us. Alcohol does not create nystagmus (the jumping of your eyes when a stimuli is moved in front of it) it only magnifies the presence of nystagmus.
As such, the police officer really doesn't gain anything he didn't already know when he does the HGN test on you. He is just trying to stack the cards in a subsequent prosecution. He knew you were drinking and then drove. Well, that is not against the law in Texas. It is only against the law to be intoxicated while driving.
Secondly, the police officer has you to perform a walk and turn test in the investigation prior to ask you to stand on one leg. These "road side olympics" are obviously set up for you to fail.
Similarly, even if you fail a blood or breath test does not mean that you will be convicted. Your blood continues to absorb alcohol long after you have had your first drink. The state's expert witness will have to submit to cross examination on the subject of retrograde extrapolation. Often times, the state's own expert witness will have to testify that it is possible that your blood alcohol concentration level was below the legal limit when you were driving although you later failed the breath test. All the jury needs is one reasonable doubt to find you not guilty.