The Three Standardized Field Sobriety Tests used in Montgomery County, Texas as explained by board certified criminal defense attorney Brian Foley. 

Horizontal Gaze Nystagmus (HGN):
The HGN test is designed to detect involuntary jerking of the eyes, known as nystagmus, which can be exacerbated by alcohol or certain drugs. During the test, the officer will observe the driver's eyes as they follow a moving object, such as a pen or flashlight, from side to side. The officer looks for specific indicators of impairment, such as the inability to smoothly track the object or the onset of nystagmus at certain angles.

Walk-and-Turn (WAT):
The WAT test assesses a person's balance, coordination, and ability to follow instructions. The driver is instructed to take nine heel-to-toe steps along a straight line, turn around, and take nine steps back. The officer observes for signs of impairment, such as stepping off the line, using arms for balance, or failing to turn properly.

One-Leg Stand (OLS):
In the OLS test, the driver is asked to stand on one leg while keeping the other foot approximately six inches off the ground. They must count aloud by thousands (e.g., "one thousand one, one thousand two," etc.) until told to stop. The officer looks for indicators of impairment, such as swaying, hopping, or putting the foot down.

Developed by the National Highway Traffic Safety Administration (NHTSA), the 9-Step Walk and Turn test aims to evaluate a suspect's divided attention and balance. It operates on the premise that alcohol impairment impairs cognitive abilities and motor skills. Law enforcement officers undergo training to administer this test as part of the standard protocol for DWI investigations.

Administering the 9-Step Walk and Turn Test

During the 9-Step Walk and Turn test, the suspect is instructed to take nine heel-to-toe steps along a straight line, turn, and take nine heel-to-toe steps back. Specific instructions include keeping arms at the sides, maintaining balance, and counting each step aloud. The officer scrutinizes for indicators of impairment, such as:

- Inability to maintain balance during instructions.
- Initiating the test prematurely.
- Pausing while walking.
- Failure to touch heel-to-toe.
- Stepping off the line.
- Using arms for balance.
- Incorrect number of steps.
- Improper execution of the turn.

Interpreting the Test Results

The first field sobriety test is called the HGN, which stands for the Horizontal Gaze Nystagmus. This is an eye test that is conducted by police officers when they think that somebody's intoxicated. Typically, they'll have already pulled over your vehicle or responded to a crash or something like that, and then they'll say, "Hey, I want to just do some tests with you to make sure you're okay to drive. Will you come over here and do that?" And people will just automatically do it. 

The first thing you should know is that you can refuse to give these tests. It doesn't mean that you're not going to get arrested; a lot of times just refusing to do all the tests alone can get you arrested. But if they don't do any of the tests, then it's hard for them to collect evidence that you've lost the normal use of your mental and physical faculties, and therefore it's harder for the state to prosecute the case. 

So, the HGN test looks for nystagmus; it is the involuntary jerking of the eye muscles, and this happens when alcohol effects or other central nervous system depressants affect your very tiny muscles that control your eye movement. So if you move your eyes left to right, and you're following a stimulus that's what the officer is gonna try to do; they're gonna try to hold their finger or a pen about 12 to 15 inches away from your eyes and slightly above, and then move it back and forth like this. 

If they see this involuntary jerking of the eyes as they move it, they'll call that lack of smooth pursuit. If they see it in each of your eyes, that's two out of six Clues; they will look and they will hold it all the way to the side, making you look as far over to the side as you can, and they'll call that if they see your eye kind of twitching, bouncing like that, then they'll call that the second two Clues, one in each eye, and that is nystagmus at maximum deviation. 

Then they approximate a 45-degree angle between your shoulder and your chest basically, and if they see the nystagmus prior to reaching the 45 degrees, then they call that the third clue. You know, it's pretty similar to the other ones. I don't know that every officer really understands what they're doing, but they do get a significant amount of training in the academy on it, and most of the time, I find that jurors don't find this test particularly reliable because either they can't see the jerking of the eyes themselves or it's just too complex to explain. 

So the next test is the nine-step walk and turn. They're looking for eight different clues in this test: an inability to maintain balance during the instruction phase, initiating the test prematurely or starting too soon, stopping while walking, failure to touch heel to toe on each step, stepping off of the line, using arms for balance, incorrect number of steps, and an improper execution of the turn, which is probably the strangest part of the test. They ask you to leave your lead foot planted and make a series of small steps pivoting around that lead foot. It's nine steps forward, nine steps back. I've seen people go as far as like 34 steps because the officer had not given the proper instruction to them on how many steps to go. Sometimes officers will give an instruction to take three steps instead of nine, and they'll do this because they're trying to demonstrate only three steps instead of taking the full nine themselves. Sometimes it's because the officer is not particularly good at doing this while they're sober, and sometimes it's because of Officer safety; they're trying to not turn their back to a suspect that they're detaining for DWI investigation. 

But the horizontal gaze and nystagmus and the walk and turn combined, officers in their field sobriety training manual say that if you have the minimum number of Clues which is two out of eight on this test and you have four out of six on the HGN, that that's like an 80% likelihood that someone has an alcohol concentration above 0.10. And this is all due to some studies that were done back in the '70s; they've been doing these same field sobriety tests on the roadside since then. Certainly, there's probably been some better ways to look at these things since then, but there's not a great incentive for law enforcement to do that; they're already trained. Many generations of law enforcement now have already been trained on these field sobriety tests, and they continue to do them. 

What most people do when they're on a jury when they look at somebody in the DWI, they're looking at this test right here and the one leg stand as the main evidence: did they think that you're doing this in a way that a sober person would do it, even if you make a few mistakes, or are you doing it in a way that somebody who's intoxicated might do it? There's a difference between stepping a little bit off the line and almost falling down, and that's kind of what we're looking for when we're watching a video to see if we have a good case for our client to take the trial. The last test for the standardized field sobriety test is the one-leg stand test, and this is where you lift one foot approximately six inches off the ground, you point your toe, look at your toe, and count: 1001, 1002, 1003, and so on, until the officer tells you to stop. He actually doesn't tell you; he's going to go for about 30 seconds, but he just tells you to keep doing it. He's looking to see if you hop on one foot, if you use your arms for balance, meaning lift them more than six inches away from your side, see if you sway back and forth, and see if you put your foot down before the 30 seconds goes up. So if you get two out of four clues on this test, then the officer is going to say that you are intoxicated based on this test. And so, it can be a very good test for our clients if they're able to do well on it, and if you have particularly bad balance, you have bad knees, a bad ankle, you have an old sports injury, this test can be almost impossible for you. So it's important to have a look at the prior medical history of anybody who's taking this test so that you don't end up getting judged as intoxicated for something that's really out of your control.