STANDARD FIELD TESTS

In Harris County or Houston, Texas, an officer investigating you for DWI is likely to ask you to perform three field tests: The One Leg Stand, the Walk and Turn, and the Horizontal Gaze Nystagmus test. (The Pen test). There are other tests that can be given to a suspected drunk driver, and although they will be given evidentiary value, they are not considered "standardized". In Counties the size of Harris, Fort Bend, Montgomery and Brazoria County, these tests must be video taped.

PHYSICAL AND MENTAL ARE TESTED

Police officers trained in the administration of these DWI tests, are instructed to judge the suspects performance on both physical dexterity AND mental ability. As a result, an officer may give a "failing" grade to an accused based only on the police officer's opinion that a suspect didn't follow his instructions. Although standardized field tests are touted to be an objective way to judge intoxication, the interpretation of the officer comes into play, turning the entire exercise into a subjective evaluation.

HORIZONTAL GAZE NYSTAGMUS (HGN)

Medical research has shown that when a central nervous system depressant is introduced into a person's body, the eyes will jerk involuntarily. This involuntary jerking is called nystagmus. Alcohol is a central nervous system depressant. Some officers are trained to identify nystagmus. When an officer gives a Horizontal Gaze Nystagmus (HGN) test he places a stylus - usually a penlight - 15 inches from the eyes of the suspect, and moves it back and forth in front of the suspect's eyes in three stages. The officer interprets any perceptive movement of the eyes to determine whether a nervous system depressant is present.
Nystagmus is a medical condition, irrespective of whether it is caused by alcohol. Many individuals have perceptive jerking of the eyes for other reasons than the ingestion of a nervous system depressant. In the great majority of instances, the officer performing this test has no medical training and so cannot distinguish a natural nystagmus from an alcohol induced one. Because the eyes are not usually video taped during this test, medical experts cannot independently review the officer's interpretation.

"STANDARDIZED" NOT SCIENTIFIC

The "standardized" field tests were developed thirty years ago and adopted by the National Highway Traffic Safety Administration (NHTSA). Prosecutors often claim these "standardized" field tests are scientific, since they have been given NHTSA's seal of approval. However, they are anything but scientific, and were chosen by NHTSA simply because they were considered the most reliable indicators of intoxication after considering the variety of tests that law enforcement had been using on the street. However, as NHTSA admits, whether the tests are "reliable" depends on the physical ability of the suspect being tested and whether the officer correctly implements the test. NHTSA's research shows the one leg stand test to be a correct indicator of intoxication only 65% of the time. The walk and turn achieves a 68% grade in making the same determination.

LAWYER MUST CHALLENGE FIELD SOBRETY TESTS

An attorney well versed in these field sobriety tests understands their limitations and should explain these weaknesses to the jury. Without a proper presentation, the jury may be left with the impression that the officer's results are scientifically based. In particular, the prosecution presents the HGN test as medical proof of intoxication. The defense lawyer's mission should be to pull back the curtain on this fallacy and reduce the HGN to what it actually is; an uninformed medical opinion by an untrained officer made after waiving a pen in front of a terrified suspect on the side of the road.

For more information visit our DWI web site.