Challenging the “Horizontal Gaze Nystagmus” (HGN) Test in Atlanta’s Humid Climate

The “Horizontal Gaze Nystagmus” (HGN) test is ineffective in Atlanta’s humid climate.In the humid climate of Atlanta, the “ Horizontal Gaze Nystagmus” (HGN) test is ineffective.

The roadside stop often progresses to the standardized field sobriety tests in the Atlanta metro area when a driver is suspected of driving while intoxicated. One of the most commonly used tests for this is the Horizontal Gaze Nystagmus test (also referred to as the HGN test), which is one of the various physical and mental tests taken on the pavement. In this test, the officer will place a stimulus (penlight or fingertip) in front of the driver’s face and ask the driver to follow it with their eyes only, keeping their head as still as possible. There are specific involuntary eye tracking clues that officers will look for to establish probable cause for an arrest including no smooth pursuits, distinct jerking at a forty-five degree angle and when jerking begins before the forty-five degree angle. The HGN test is presented to judges and juries as a foolproof scientific test with strict guidelines, but closer look shows that the test is far from reliable, especially in the unique environmental and physiological stress conditions in Georgia.

The only way to comprehend why the HGN test often gives a false result is to examine the variables that impact on human eye mechanics during a traffic stop. The physical context in which the Atlanta roadway corridor exists creates extreme visual and atmospheric distortions that are only briefly mentioned in police training manuals. Georgia’s notorious weather results in extreme humidity, pollen, and moisture in the night which can lead to eye irritation, dryness and squinting. In addition, drivers who are stopped on the main roads, such as the Downtown Connector, Interstate 85 or on a surface street in midtown and the Buckhead area are greeted by the bright headlamps of oncoming traffic and flashing lights from several stopped police cruisers. When an individual tries to follow a moving stimulus while emergency lights blink and the lights from traffic are flashing, it is natural for his or her eyes to go through the same optokinetic stress and involuntary eye fatigue that the officer is taught to identify as chemical changes.

In addition to environmental distractions, the mechanics of administering the HGN test are extremely precise and roadside officers rarely achieve this level of precision. The NHTSA recommends that the stimulus be positioned at a very specific distance from the person to be tested’s face, moved at exact temporal intervals, and at a specific distance from flashing lights. At an Atlanta traffic stop, officers may have to rush through the process, and may move the stimulus too rapidly or not consider the uneven, sloping roadside shoulder. Any officer who moves the object too quickly or attempts to hold the object at an improper angle will negate the time that is necessary to accurately observe the onset of the nystagmus and will give false positives. Furthermore, and significantly, many physiological events, not related to alcohol, can cause the same involuntary eye movements as drinking alcohol, and thus, a medical or environmental reaction can be confused with a criminal charge.

The risk that is associated with the improperly administered or environmentally influenced HGN test is that juries often view the test as scientific evidence and give disproportionate weight to what they believe it is. The test is cloaked in medical jargon making fact-finders think that there is no room for error. But an experienced defense attorney is well-versed in how to deflate that sense of certainty when looking at dashcam and body-worn camera data. Asking the officer who made the arrest about environmental factors, positioning mistakes, speeding on the test, and not trying to eliminate flashing light interference can completely invalidate the validity of the state’s observations.

An aggressive defense of a technical field sobriety test means challenging the subjective observations of the roadside. A skilled defense team can establish that the officer’s observations were based on a faulty set of circumstances, including local weather conditions, visual glare and procedural shortcuts, all of which rendered the evidence obtained by the officer suspect. James Yeargan is well versed in the laws of the state of Georgia and has a good understanding of the mechanics of the field testing used by police to determine impairment, so that when the charges are complicated and you are charged with a DUI due to bad science in their procedures, you will have a strong legal representative on your side who will fight to demystify the science and protect your constitutional rights in the process.