What percentage of the time can the Horizontal Gaze Nystagmus test determine if a subject's BAC is above 0.08?

The Horizontal Gaze Nystagmus (HGN) test is a key component of the Standardized Field Sobriety Tests (SFST) used to assess whether a driver is impaired due to alcohol. Research has shown that the HGN test can reliably indicate the presence of alcohol in a subject's system, specifically when a person's Blood Alcohol Concentration (BAC) is at or above the legal limit of 0.08%.

When evaluating the effectiveness of the HGN test to determine a BAC of 0.08 or greater, studies indicate an accuracy rate of approximately 88%. This figure arises from analyzing the physiological responses of intoxicated individuals, particularly the involuntary jerking of the eyes (nystagmus) that becomes more pronounced with higher levels of intoxication.

This reliability makes the HGN test an important tool for law enforcement officers when assessing potential DUI situations, as it provides a scientific basis for indicating impairment based on observable eye movements. Understanding this accuracy helps reinforce the significance of the HGN test in DUI investigations, supporting its use in making informed decisions during roadside assessments.