Horizontal Gaze Nystagmus Test Admissibility

Field Sobriety TestingIn an effort to keep you up to date with the latest developments in the law, we wish to advise you that on December 1, 2014, the Pennsylvania Supreme Court decided the case of Commonwealth v. Weaver, which upheld a police officer’s use of the “horizontal gaze nystagmus” (HGN) test in establishing probable cause to make a DUI arrest.

The HGN test is a common component of “field sobriety tests,” which are the roadside checks that police do before bringing someone in for a blood draw or breathalyzer. In an HGN test, the police officer holds his pen in front of the driver’s face and tells the driver to “follow it with your eyes, not your head.” The officer then moves the pen slowly side to side, to the edges of the driver’s field of vision, in an effort to force the driver to look as far to the left and the right as possible. The test rests on the presumption that an intoxicated person’s eyes will twitch when held in this strained position.

The results of an HGN test are not admissible at trial to prove that the driver was intoxicated. This is because Pennsylvania courts have recognized that the test is unreliable. Police officers are not doctors, and cannot be expected to make medical determinations about the degree of involuntary eye movement caused by intoxication. Additionally, alcohol is not the only cause of nystagmus, and some underlying medical conditions can lead to false indicators of intoxication.

Although the result of an HGN test is not admissible at trial, police officers are nevertheless permitted to administer the test and use the results in making a determination of whether there is probable cause to arrest a driver for DUI.

This seems paradoxical, but police routinely use inadmissible evidence in their investigations. The Pennsylvania courts take the position that simply because a test is not sufficiently reliable to be admitted in a courtroom does not mean that it cannot be used by police to further their investigation. Tests and evidence which will never be admitted at trial may be relied on by police in determining whether a crime has been committed and whether the accused is the perpetrator, especially when taken in conjunction with other admissible evidence and information. For this reason, the PA Supreme Court concluded that the police may continue to use the HGN test during traffic stops to help to determine whether a driver is impaired, but cannot use the results of the HGN test to prove the driver’s guilt at trial.

It is critical to understand changes such as these and it can be difficult to navigate alone. If you or anyone you know has any questions concerning a DUI arrest or prosecution, please feel free to contact us. We guarantee that you will speak with an attorney well versed in the recent changes to the DUI laws.

Posted on December 1, 2014, in Alcohol, Criminal Law, DUI, Family Law, Underage Drinking and tagged , , , . Bookmark the permalink. Comments Off on Horizontal Gaze Nystagmus Test Admissibility.

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