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Field Sobriety Tests

What Are Field Sobriety Tests?

Field Sobriety Tests (FSTs) are a battery of mental and physical tests developed by the National Highway Traffic Safety Administration (NHTSA). These tests are used to assess a person’s overall impairment to determine whether the subject has lost the normal use of their mental or physical faculties due to the introduction of a chemical substance (most commonly alcohol).

Divided Attention Tests

FSTs are considered “divided attention” tasks which require a subject to concentrate on more than one task at the same time. Driving a motor vehicle requires use of both mental and physical faculties. Introduction of alcohol affects the driver’s ability to adequately divide attention, often forcing drivers to concentrate on one area of operating a motor vehicle while ignoring other ones (i.e. ignore a traffic signal while concentrating on one’s speed). While impaired, most people can successfully concentrate on a single task fairly well but impaired most drivers cannot divide their attention between multiple tasks.

Right to Refuse

What most people don’t know, and are not told by the officer, is that these tests are not mandatory. However, the officer who stopped your car won’t tell you this and will use the results of the tests to justify your arrest and to accumulate evidence to be used against you in court. Although the tests are supposed to test your ability to perform divided attention tasks, they are actually designed for failure and to make you appear impaired. Remember, it is your right to respectfully refuse to submit to any FSTs, whether on the street or at the station.

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Types of Field Sobriety Tests

There are three standardized FSTs most commonly used by the police:

These are the only three tests that have been scientifically validated by the NHTSA as reliable indicators of intoxication. Keep in mind that they are not 100% accurate even when administered and interpreted perfectly. With regard to the three standardized FSTs, the government has admitted, and it is documented in the law enforcement DWI training manual, that it is necessary to emphasize this validation when:

If any one of the standardized field sobriety test elements is changed, the validity is compromised.

Non-Standard Tests

Other commonly used but non-standardized tests include:

Remember, you are very likely being video taped any time you are speaking with a police officer or performing any tests. Act accordingly, be polite, respectful and never forget that this tape will be shown to your jury at trial. This is an opprtunity to testify to the jury without taking the stand at trial, so take the opportunity to tell the officer that you are not intoxicated.

Learn More About FSTs and the NHTSA

Horizotal Gaze Nystagmus (HGN)

This test refers to the involuntary and pronounced jerking of the eye as it moves laterally inside the eyesocket. When this occurs, the person is unaware of the jerking and cannot control it. This involuntary jerking becomes more pronounced and visible as persons’ blood alcohol increases. Theoretically, this is the most reliable of the FST’s. However, nystagmus is a natural, normal phenomenon which is present to some degree in all people.

When the HGN test is administered, the officer holds a stimulus (usually a pen) 12-15 inches in front of your eyes. The officer will ask you to follow the stimulus with your eyes, without moving your head. The officer will start with the left eye and look for 3 specific clues:

1. Lack of Smooth Pursuit

As the eye moves from side to side, does it move smoothly or does it noticeably jerk (bounce)? The jerking is similar to how a windshield wiper jerks across a dry windshield. There is a standardized pace the officer is to utilize when conducting this phase of the test. From the center of the face, they are to move the pen all the way out to the side (45 degrees) at pace taking approximately 2 seconds, then 2 seconds back to center, then repeating with the right eye. They are to repeat the procedure. If they have the eyes move too fast, not only are they performing the test improperly, this can cause, and the government has admitted, that such quick movement of the eyes in itself may cause nystagmus.

2. Distinct Nystagmus at Maximum Deviation

The Officer will move the pen as far to one side as possible and have you follow with your eyes. The Officer will then hold that position for a minimum 4 seconds. The Officer is looking for a distinct jerking (bouncing) of the eye. The test is then repeated with the other eye. However, it is important to note that some people exhibit slight jerking of the eye at maximum deviation even without the presence of alcohol. Additionally, if the eye is moved to the side too quickly, this also may cause the nystagmus.

3. Onset of Nystagmus Prior To 45 Degrees

As the eye tracks the pen towards one side, the Officer will observe whether the eye begins to jerk (bounce) prior to reaching a 45-degree angle (about halfway from the nose out to the shoulder). The Officer should move the pen at a pace that should take approximately 4 seconds to reach 45-degrees. It is important to take the full 4 seconds when checking for onset. If the stimulus is moved too fast, the officer could take your eye beyond 45 degrees, or if the eye is moved to 45-degrees too quickly, this may cause the nystagmus.

The maximum number of clues in each eye is 3, for a total of 6 clues. The original research has shown that if the test is administered properly and 4 or more clues are present, then there is 77% probability that the person’s BAC is .1 or above. However, Texas law will not allow an officer to speculate on the Defendant’s BAC based on the results of SFTs.

Walk & Turn Test

This is the first of only two divided attention tests that have been validated by the National Highway Transportation and Safety Administration (NHTSA) and consists of the instruction phase and the walking phase. During the instruction phase, the subject must stand with the right foot directly in front of the left foot with the heel and toes touching, while keeping their arms at their side. The subject must listen to the officer as he explains how to do the test while maintaining the very awkward stance. Any deviation from the instruction stance (arms at side, heel toe touching) will be taken as a sign of intoxication.

During the walking phase, the person takes 9 heel-to-toe steps (heel and toe must touch after each step), then turns while pivoting on one foot and takes 9 heel-to-toe steps back, all while counting the steps out loud. The steps are taken down a straight line and if an actual line is not present the person is instructed to walk down an imaginary line. The officer is looking for 8 specific clues:

The original NHTSA studies have shown that if 2 or more clues are present, the test is 68% accurate at predicting intoxication.

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Law Office of Brett A. Podolsky
917 Franklin St. Ste 510
Houston, TX 77002