The Supreme Court of the state of Illinois issued a new ruling in 2010 concerning the use of the horizontal gaze nystagmus test (HGN). During an arrest for DUI, the police officer will ask the driver to stand still and follow a pen with his eyes, and keep his head motionless.
The HGN test is looking for nystagmus, which is the involuntary jerking of the eyes that can sometimes be produced by alcohol or drugs.
The ruling handed down by the Supreme Court is found in the People v. McKown decision. McKown was a defendant in a DUI trial in which the defense requested a scientific hearing on the accuracy of the test (known as a Frye hearing).
The Supreme Court stated the following:
- The HGN test cannot be used by the prosecution to prove intoxication.
- Horizontal gaze nystagmus shows only that it is possible the defendant is intoxicated.
- Most importantly, the officer cannot testify as to the defendant’s performance on the test unless it is shown that he is adequately and competently trained to perform the test according to standards.
The Supreme Court adopted several points in its ruling, such as the fact that there may be over 125 known causes of nystagmus. This point makes it clear that nystagmus only makes it possible, not probable, that the defendant was under the influence of alcohol or intoxicated on drugs
The Court indicated that defense lawyers should be allowed to use the standards for field sobriety testing from the National Highway and Traffic Safety Administration (NHTSA) to question the officer on the accuracy of the test.The NHTSA manual is key in DUI defense because it commits the officer to the following proposition: If the tests were not performed according to NHTSA standards, then they are not accurate or reliable detectors of impairment.
Finally, the Court indicated that the test is performed properly only when the subject (driver) is standing, not sitting in vehicle. This is an important point for the high frequency in which police officers will conduct the test while the suspect is in the driver’s seat.
Attorneys in Cook County should note that the Alcohol Influence Report from the Chicago Police Department actually says: ‘Only trained officers can administer the HGN.’