If you are ever pulled over by a California law enforcement officer while you are operating a motor vehicle and the officer suspects that you are under the influence of drugs or alcohol the officer will likely administer a number of “field sobriety tests”. These tests are intended to provide the officer with the probable cause necessary to actually arrest you for driving under the influence, or DUI. One of the tests that a law enforcement officer may conduct is a horizontal gaze nystagmus, or HGN. A better understanding of what the HGN test is, how it is conducted, and what the results mean is important if you ever find yourself the subject of the test.
In a typical DUI stop the law enforcement officer will ask you to exit the vehicle and stand off to the side on a sidewalk or other safe area. The officer will then explain that he or she is going to conduct a few field sobriety tests, or FSTs. You may be asked to walk in a straight line toe to toe, stand on one leg, or touch your finger to your nose. At some point you will probably also be asked to participate in the HGN test. Prosecutors and law enforcement officers argue that the HGN test is the most objective and scientifically accurate of all FSTs; however, the accuracy of the test has been debated and it’s admissibility in court has been challenged in many jurisdictions. Since it is used, however, you should understand the test.
An officer will ask you to look at an object—usually a pen or similar object—and then follow its movement as the officer moves the object directly in front of your face to one side and then back again with the process being repeated on the other side. The officer is looking for “nystagmus” which appears as a twitching or bouncing movement in your eye. The earlier that nystagmus begins to appear the higher the likelihood that you are under the influence of alcohol. At less than 45 degrees it is taken as an indication of driving under the influence.
While a properly administered HGN test may indeed indicate that a motorist has been driving under the influence, even the National Highway Transportation Safety Administration, or NHTSA, only admits that the test is accurate three out of every four times. Moreover, many officers do not administer the test properly and/or read the results properly. As a result, a motorist can end up charged with DUI when he or she was not actually drunk.
If you have been arrested for DUI in California and the HGN test was used during your stop be sure to have an experienced California drunk driving attorney review the test and overall stop.