DUI Field Sobriety Test Challenged by Illinois Court

Eye test (HGN) used to determine intoxication called not scientifically valid by Illinois Supreme Court.

When a motorist is stopped for suspicion of drunk driving one of the field sobriety tests used by law enforcement is called the horizontal gaze nystagmus test. Excluding breath or blood tests, it has been considered the most reliable way of determining intoxication. The Illinois Supreme Court, however, has handed down a decision that impacts the admissibility of such test results during trial.

The horizontal gaze nystagmus test, or HGN, calls for an officer to take a pen and place it approximately six inches from a suspected drunk driver’s face. The person must track the movement of the pen as the officer moves it side to side. The clues to possible intoxication are an inability to follow the pen smoothly without noticeable jerking; an increased jerking of the eye when made to look as far as possible to the side and hold for five seconds; and a jerking of the eye before reaching 45 degrees to the side. The National Highway Traffic Safety Administration says HGN tests have a 77 percent accuracy rate in identifying motorists with a blood alcohol content above the legal limit.

The HGN test can be inconclusive though, and some people are naturally nystagmus, meaning their eye twitches. Other field tests can be used during a suspected DUI traffic stop, such as a one-leg stand, walk and turn and having the motorist touch a finger to tip of nose. Additionally some officers ask suspects to count or recite the alphabet, though those are not standardized tests.

DUI defense attorneys say there are many factors that can cause the eyes to jerk, including stress, fear and viral infections. There are many types of nystagmus too, not all of which are taught to those administering field sobriety tests. In courtroom cross-examination, officers often fail to accurately determine a 45 degree angle, critical to the outcome of a HGN test.

The Illinois Supreme Court decision stems from to a case involving suspected driving under the influence. The suspect had broken her toe and could not perform certain field sobriety tests and the blood sample taken 6.5 hours after her arrest revealed no alcohol in her system. The most influencing factor in the outcome of her DUI trial was the result of an HGN test.

The Supreme Court returned the case to a lower court with the finding that horizontal gaze nystagmus tests are not scientifically valid, thus adding Illinois to a small list of states where the admissibility of HGN tests during trial has not been decided. In three states, HGN tests are not admissible. The majority of courts allow juries in DUI cases to hear HGN results.

Prosecuting attorneys say that the HGN is part of an overall body of evidence they and the police use to try cases, though they admit the high court ruling will make a big difference on weaker suspected drunk driving cases that rely mainly on HGN test results.

Tags: Field Sobriety Test |  Horizontal Gaze Nystagmus