Understanding the HGN Test in California DUI Cases

The horizontal gaze nystagmus test (HGN) is often the first field sobriety test administered in a California DUI investigation. Customarily, the police officer does not need probable cause to arrest before requesting a driver to perform a field sobriety test such as an HGN. The biggest source of error on the HGN is the failure of the officer to properly administer the test. Indeed, there are at least 25 different steps that need to be performed to properly conduct the HGN test. The National Highway Traffic Safety Administration training manual says that the procedures must be followed with precision and that failure to do so renders the results unreliable. In a DUI trial the jury should be made aware that the tests are standardized field sobriety tests—not randomized field sobriety excursions. It must be explained to the jury that an agency of the federal government (NHTSA) has established that the tests must be given in a particular manner or they are not reliable. No freelancing is permitted. Even if the officer administered the HGN test flawlessly, the test is still subject to attack. In fact, HGN can be caused by a number of reasons other than alcohol intoxication. HGN occurs naturally in some people who are not under the influence. Also, fatigue, illness, hypertension, and common drugs like caffeine or aspirin may contribute to HGN.

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