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The HGN Trap: How Police SOPs Often Force Arrests in Gwinnett County DUI Cases — Even When Common Sense and the Other Field Sobriety Tests Say “Not Impaired”

As a Gwinnett County DUI lawyer who has handled hundreds of DUI cases across Gwinnett, Lawrenceville, Suwanee, Duluth, and Loganville, I see the same troubling pattern over and over again. A driver is pulled over. The officer runs the three standardized field sobriety tests (SFSTs) approved by the National Highway Traffic Safety Administration (NHTSA). The driver nails the Walk-and-Turn and One-Leg-Stand tests — zero clues of impairment, steady balance, flawless coordination under stress. Yet the officer still makes the arrest based almost entirely on the Horizontal Gaze Nystagmus (HGN) test.

Why? Because many police departments’ Standard Operating Procedures (SOPs) and NHTSA-based training essentially compel officers to treat four or more HGN clues as automatic probable cause for arrest — even when the other two tests, the driver’s normal speech and demeanor, and basic common sense scream the opposite.

This is backwards. And in my experience, it leads to unnecessary arrests that can be successfully challenged in Gwinnett County State Court.

The Three Standardized Field Sobriety Tests — What They Actually Measure

Georgia law enforcement officers are trained to use the same three NHTSA-validated tests in almost every DUI investigation:

  • Horizontal Gaze Nystagmus (HGN or “eye test”): The officer moves a pen or finger side-to-side in front of your eyes and looks for involuntary jerking (nystagmus). Six possible clues (three per eye). Four or more clues supposedly indicate a blood-alcohol concentration (BAC) at or above 0.08.
  • Walk-and-Turn (WAT or “heel-to-toe”): Nine steps heel-to-toe down an imaginary line, turn, and nine steps back. Eight possible clues.
  • One-Leg Stand (OLS): Stand on one leg while counting out loud for 30 seconds. Four possible clues.

NHTSA’s own studies have always shown that HGN is the single most “accurate” test in their battery — around 77–88% depending on the study. But here’s what the training manuals and SOPs rarely emphasize to the officer on the side of the road: HGN is also the most subjective and prone to false positives. Medical conditions, fatigue, certain medications, inner-ear problems, even anxiety or the flashing lights of the patrol car can produce the exact same eye movements.

Meanwhile, the Walk-and-Turn and One-Leg-Stand are true divided-attention tests. They require you to process instructions, maintain balance, and coordinate movement under stress — exactly the skills alcohol and drugs impair in real-world driving. If a driver performs these tests perfectly (or near-perfectly), that is powerful evidence of sobriety.

The SOP Problem: “HGN Positive = Arrest” Becomes the Default

Video thumbnail: headline about police SOPs and DUI arrests; center image shows a hand holding a baton with a red X, flanked by two white stick figures with green checkmarks. In practice, many departments train officers that four or more HGN clues create probable cause for arrest. The other tests are treated as “corroboration” rather than independent indicators. Departmental SOPs and field training often tell officers: if HGN shows impairment, proceed to arrest — even if the driver aced the physical tests, showed no slurred speech, no odor of alcohol, walked steadily back to the patrol car, and exhibited zero signs of intoxication to the naked eye.

Officers are human. They follow their training and their department’s procedures to protect themselves from liability and to avoid “letting a drunk go.” The result? A driver who is stone-cold sober (or well below the legal limit) gets arrested because one subjective test overrode two objective performance tests and plain old common sense.

I’ve had clients tell me the officer literally said on bodycam: “Your eyes are jerking, so I’m placing you under arrest — even though you did great on the other tests.” That statement alone becomes gold in cross-examination.

Why It Should Be the Opposite: Common Sense and Science Agree — Especially When You Consider the 40+ Other Causes of Nystagmus

If someone can:

  • Walk a straight line heel-to-toe without stumbling,
  • Stand on one leg for the full 30 seconds without swaying or putting a foot down, and
  • Show no other outward signs of impairment…

…then the most likely explanation is that they are not appreciably impaired. HGN should raise a question — not dictate an arrest. Yet current SOPs and training often force the opposite priority.

The science backs this up. Medical authorities, including NHTSA’s own training materials, acknowledge that there are well over 40 named types of nystagmus (many of which produce the exact same involuntary jerking observed during the HGN test) that have nothing whatsoever to do with alcohol or impairing drugs (https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/horizontal_gaze_nystagmus-the_science_and_the_law.pdf). These include:

This is not defense-attorney speculation. It is straight from leading medical school textbooks on Ophthalmology, and I quote:

“Unfortunately, the fact that alcohol can produce horizontal gaze-evoked nystagmus has led to a ‘roadside sobriety’ test conducted by law enforcement officers. Nystagmus as an indicator of alcohol intoxication is fraught with extraordinary pitfalls: many normal individuals have physiologic end-point nystagmus; small doses of tranquilizers that wouldn’t interfere with driving ability can produce nystagmus; nystagmus may be congenital or consequent to structural neurologic disease; and often a sophisticated neuro-ophthalmologist or oculographer is required to determine whether nystagmus is pathologic. It seems unreasonable that such judgments should be the domain of cursorily trained law enforcement officers, no matter how intelligent, perceptive, and well-meaning they might be.”

— Duane’s Clinical Ophthalmology, Volume 2, Chapter 11, p. 20 (Tasman & Jaeger, eds., 1994)

This mismatch between one subjective test and everything else creates exactly the kind of reasonable doubt that wins DUI cases in Gwinnett County State Court.

How We Fight It in Court

When I take a Gwinnett DUI case, my team systematically attacks over-reliance on HGN:

  • We review the bodycam or dashcam to show the officer’s own words and observations.
  • We highlight perfect or near-perfect performance on Walk-and-Turn and One-Leg-Stand.
  • We bring out medical records, prescription medications, or other non-alcohol explanations for any HGN clues — often supported by the 40+ alternative causes listed above.
  • We cross-examine the officer on NHTSA’s own limitations, the textbook warnings, and the department’s SOPs that discouraged him or her from using common sense.
  • We demand that the jury (or judge in a bench trial) look at the totality of the evidence — not just one test.

Time and again, this approach results in reduced charges, dismissals, or not-guilty verdicts.

If You’ve Been Arrested After “Passing” the Walk-and-Turn and One-Leg-Stand

Don’t assume the HGN test sealed your fate. It didn’t. Georgia law still requires the State to prove impairment beyond a reasonable doubt, and a flawed arrest decision based on SOP-driven over-reliance on HGN — especially when 40+ other medical explanations exist — is fertile ground for a strong defense.

If you or a loved one was arrested for DUI in Gwinnett County after performing well on the physical field sobriety tests, contact my office immediately. The first 30 days after arrest are critical for preserving evidence, subpoenaing training records, and building a winning strategy.

Call George Creal, Jr. at (404) 333-0706 or visit www.georgecreal.com today for a free, confidential consultation.

Your future shouldn’t be decided by one test that ignores everything else that points to innocence. Let’s fight it together.

Gwinnett County

 

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