Standardized Field Sobriety Evaluation Page

NHTSA or the National Highway Transportation Safety Administration developed three Standardized field sobriety tests to help officers determine whether a DUI suspect’s blood alcohol content exceeds .08 percent. The three Field Sobriety Tests are the Horizontal Gaze Nystagmus, the Nine Step Walk & Turn, and the One Leg Stand.

Horizontal Gaze Nystagmus Test (HGN)

What is the HGN and how is it performed?

Horizontal Gaze Nystagmus (more accurately lateral gaze nystagmus) is a medical term describing the involuntary jerking of the eyes. Officers perform this alleged “scientific” field sobriety test on your eyes. With your head still he instructs you to follow his pen with your eyes as he moves his pen (he will call it a “stimulus” to make the test sound more scientific) back-and-forth across your field of vision. As he moves his pen from side to side, he watches your eyes to see whether they jerk involuntarily; he is trained that central nervous system depressants (like alcohol or antidepressants) cause this involuntary jerking.

He is trained to perform three different tests to detect this involuntary jerking, and assess a “clue” for each time he sees the jerking The first test is called Lack of Smooth Pursuit. The officer holds the stimulus 12-14 inches from your face and moves it from right to left. He watches to see whether your eyes move smoothly or if they move like a windshield wiper moving across a dry windshield. Lack of smooth pursuit is present when the eyes move in a jagged motion like a dry windshield wiper moving over a dry windshield. The officer assesses two clues if he sees lack of smooth pursuit in each eye.

The second test to detect nystagmus is called Distinct Nystagmus at Maximum Deviation. Here, the officer moves the stimulus to the far end of your peripheral vision. Once your eyes reach the maximum deviation, the officer holds his pen in that position for four seconds (at least). He looks to see whether your eyes remain still or whether they exhibit a pronounced jerking motion. If your eyes exhibit this pronounced jerking motion, then distinct nystagmus at maximum deviation is present. The officer assesses two clues if he sees distinct nystagmus at maximum deviation in each eye.

The third and final test the officer performs to detect nystagmus is called Onset of Nystagmus Prior to Forty-Five Degrees. The officer moves his pen slowly from the center of your face to the side of your face. If your eyes begin to jerk prior the officer reaching a forty-five degree angle from the center, then the officer will say you have onset of nystagmus prior to forty-five degrees.

The HGN a progressive evaluation. As your level of intoxication increases you begin to exhibit lack of smooth pursuit first, then distinct nystagmus at maximum deviation, and finally onset of nystagmus prior to 45 °. Officers testify that your alcohol content exceeds .08% when your eyes exhibit four or more clues on the HGN evaluation. To support their position, they cite studies conducted by NHTSA. However, the NHTSA studies are flawed, and provide no scientific basis for this claim.

Why the HGN test is not a good test.

First the NHTSA studies concluded the HGN test is only 77% accurate; this assumes that the officers conducted the test correctly. We all have nystagmus, however most of the time it is not detectable by the human eye; alcohol and drugs merely exaggerate this natural nystagmus to make it observable. Additionally, many people have an observable natural nystagmus. These factors contribute to false positive results on the HGN test.

Many officers perform this test incorrectly. Since the HGN test is considered a scientific test, the officer must administer the test the same way that it was validated. The National Transportation Safety Administration (NHTSA) validated the HGN test by performing it on subjects in a controlled environment. NHTSA mandates that the officer must perform the test according to their strict guidelines or the results are invalid. I have had a great deal of success convincing judges to suppress HGN results when officer administered the test incorrectly. If the HGN test is excluded the jurors in your case will never know that the officer administered the HGN test on you.

Furthermore, NHTSA’s study validating the HGN test is flawed in two ways. First, NHTSA used a flawed scientific method in analyzing their data. Second their data are inconsistent. The scientific method is erroneous because they grouped four clues (lack of smooth pursuit and distinct nystagmus at maximum deviation in both eyes) together with six clues on the HGN (add onset prior to 45) in the validation study. NHTSA wanted to know how many clues indicates a BAC exceeding .08 percent. NHTSA should have studied DUI subjects with four HGN clues to determine whether their BACs exceeded .08 percent, then study DUI subjects with six HGN clues asking the same question. Instead, NHTSA studied DUI subjects with four HGN clues with those having six clues. Six HGN clues indicates .08 or greater while four HGN clues does not, however NHTSA’s study did not seek to address this issue. NHTSA’s study is also flawed due to inconsistent data. Some NHTSA studies conclude that four HGN clues indicates a BAC exceeding .08 percent while Drug Recognition Officer (DRE’s) are trained in advanced DUI courses that four HGN clues means that the DUI subject’s BAC is lower than .05%. Under Georgia law the DUI suspect is presumed not to be impaired if his BAC is .05% or lower.

Your lawyer must be well versed in the NHTSA studies in order to either exclude the test from your trial, or show the jurors that the HGN test is meaningless.

PHYSICAL AND DIVIDED ATTENTION TESTS

There are two additional field sobriety tests recommended by NHTSA. These are the 9-Step Walk and Turn and the One Leg Stand. These considered divided attention tests because they test your coordination while they test your ability to process and remember information.

9-Step Walk and Turn

The walk and turn test tests your coordination in addition to your ability to recall and process information. There are two phases to this test. The first phase is the instructional phase, and the second phase is the performance phase.

During the instructional phase, the officer tells you to place your right foot in front of your left foot, touching heel to toe. He should tell you to remain in that position until he tells you to begin. The officer will tell you how perform the test during the instructional phase, and he will watch to see if you are able to keep your balance while he gives these instructions. He will count off if you:

1. Begin the test too soon (before she tells you to begin).
2. Break the heel to toe stance while she instructs you.
   During the performance phase of the Walk & Turn test he will watch to see whether you followed instructions and whether you were able to keep your balance while walking the straight line. She will count off during the performance phase if you:
3. Miss heel toe while walking a straight line.
4. Step off the imaginary straight line.
5. Use your arms for balance.
6. Stop while walking.
7. Take the incorrect number of steps.
8. Turn in a manner that deviates from the instructions.

One Leg Stand

The one leg stand also tests your coordination and your ability to comprehend instructions. During this test the officer tells you to raise the leg of your choice approximately six inches off the ground with your toe pointed straight. She then tells you to remain balancing in that position with your arms down by your sides, looking at your foot, and count by one thousands until she tells you to stop. Once you begin the test, she will look at her watch and stop the test once thirty actual seconds have elapsed. She will count off if you:

1. Hop
2. Sway
3. Use your arms for balance
4. Put your foot down

Field Sobriety Tests Do Not Accurately Determine Whether Driving Ability is Impaired.

Everybody is different. NHTSA developed these tests in a controlled environment. Their “test subjects” were dosed with alcohol and NHTSA studied the test subjects’ ability to perform these tasks at various blood alcohol levels. The conditions to which NHTSA’s test subjects were subjected are far different from the testing conditions to which a DUI suspect is subjected.

First, NHTSA’s initial test subjects were not under investigation for DUI. They were volunteers who agreed to drink alcohol and perform various tasks in a gymnasium. A typical DUI suspect has been pulled over by the police. He begins his experience with a sinking feeling as he sees the flashing blue lights behind him. He pulls his car to the side of the road and the officer tells him to step out of his car to perform field sobriety tests. NHTSA’s test subjects did not experience a DUI suspect’s level of anxiety. NHTSA’s volunteers did not begin their experience in by being ordered out of their car. Their heart did not quicken as they saw the blue lights behind them. Their hands did not begin to shake as the officer told them to get out of the car. They did not have an officer with a gun and a nightstick ready to take them to jail for failing to satisfactorily perform the tests. Most jurors understand that Field Sobriety tests are difficult under the best of circumstances. Jurors also understand that your performance on field sobriety may be the result of nervousness rather than alcohol impairment.

Second, FST’s do not test your driving ability. You are not guilty of DUI unless the State can prove that you were incapable of driving safely (or you were above the legal limit). Officers say that poor performance on FST’s is an indicator of impaired driving ability. This is simply not true. People practice driving everyday. DUI suspects only get one chance to perform FST’s. Officers do not let DUI subjects practice these tests. Even worse, the officers never tell the suspect what is required to pass the test so the suspect never knows what is expected of him. Again, everybody is different. Most people perform less well on FST’s under such stressful conditions. Therefore, there is no direct correlation between driving ability and performance on FST’s. One does not stand on one leg for thirty seconds while they drive a car. These are two completely unrelated skills.

NHTSA claims to have conducted “field” validation studies under arrest conditions; however their findings are unscientific as shown by their own data. Police officers often claim FST’s are 91-94% accurate in making the arrest decision at a .08 level. To support this claim, they cite the “California Study”. However, researchers used faulty science to “validate” FST’s. Most importantly they validated FST’s at a .08 level by using group of subjects with a sample mean (average) of .150 grams of alcohol. (see NHTSA’s table below). To validate FST’s at the .08 level, the researchers should have studied subjects closer to .08. Instead the researchers studied subjects who were obviously impaired.

To provide a real-world example of NHTSA’s flawed method, suppose that you want to know whether NASCAR fans can accurately predict whether cars exceed a 65-mile per hour limit. To scientifically answer that question, your NASCAR fans must see cars traveling near 65 miles per hour. The average speed of the cars tested should be close to 65 mph, the desired discrimination point, and the fans must guess whether each car exceeded 65 mph. A validation study is meaningless if the NASCAR fans watch cars traveling at 135 mph. 100% of the NASCAR fans will accurately predict the cars exceed 65 mph. The same is true when the slower cars travel at 20 mph. The fans will correctly predict those cars are slower than 65. Although the fans would accurately predict speed over and under 65 mph under those circumstances, the study does nothing to truly validate predictions at 65 mph.

Similarly, NHTSA studied DUI arrestees with mean BAC’s of .150 and non-arrest subjects with a mean BAC of .045 in the California study. In other words, those who were arrested, were obviously over a .08 since the average arrestee was .150 while the average non-arrestee was .045.

Click the charts below to get details about BAC’s.