How does HGN testing fit into the overall DUI investigation process?

The HGN (Horizontal Gaze Nystagmus) test is classified as one of the primary field sobriety tests utilized during a DUI investigation. Its purpose is to observe the involuntary eye movements that can indicate impairment due to alcohol consumption. When an officer suspects a driver may be under the influence, they typically conduct several field sobriety tests, and HGN is a crucial component because it provides objective indicators of impairment.

HGN testing involves assessing the eyes for nystagmus while the driver follows a stimulus, such as a pen or a finger. Specific criteria, such as the angle of onset of nystagmus and the degree of nystagmus at maximum deviation, help establish a correlation between alcohol impairment and eye response. This evidence can be compelling in determining a driver’s level of impairment, thereby fitting into the overall DUI investigation process as an essential assessment tool at the roadside.

In this context, HGN serves as a legitimate part of the investigative protocol, rather than a secondary test or one used solely after arrest or just for drug detection. By understanding the role of HGN testing, law enforcement can better evaluate driving impairment directly at the scene.