If you’ve ever been pulled over on suspicion of DUI in Arizona, there’s a good chance the officer asked you to perform field sobriety tests. These tests — often the walk-and-turn, the one-leg stand, and the horizontal gaze nystagmus (HGN) — are presented as routine, even scientific. But the reality? These tests are highly flawed, deeply subjective, and based on outdated validation studies that haven’t been meaningfully updated since the 1990s.
At Grand Canyon Law Group, we’ve seen too many good people arrested — and later prosecuted — based on shaky evidence collected during these flawed roadside tests. So let’s take a deeper dive into what these tests really are, why they’re unreliable, and why your best option is to politely decline to perform them if stopped.
What Are Field Sobriety Tests?
Field sobriety tests (FSTs) are a set of physical and cognitive tasks used by law enforcement during DUI investigations to evaluate whether a driver is impaired. The three most commonly used and so-called “validated” tests are:
- Horizontal Gaze Nystagmus (HGN) Test
- Walk-and-Turn (WAT) Test
- One-Leg Stand (OLS) Test
These were standardized by the National Highway Traffic Safety Administration (NHTSA) decades ago. But “standardized” doesn’t mean scientific — and it certainly doesn’t mean fair.
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The Outdated Science Behind FSTs
Let’s start with the elephant in the room: the studies used to validate these tests were conducted in 1977, 1981, and 1998 — over 25 years ago. There has not been a comprehensive national review or update since then. Think about how much science, medicine, and technology have changed in that time. We’ve gone from flip phones to smartphones — yet we’re still using the same DUI tests from the 1990s?
Worse, the original studies had major limitations, including:
- Small sample sizes
- Uncontrolled conditions
- Highly subjective interpretation by officers
- No peer-reviewed data
Even NHTSA admits these tests are not 100% accurate, and when you look closely at the data, the error rates are significant — especially when administered outside of lab conditions (i.e., on the side of the road at night, in stressful, chaotic situations).
Breaking Down the Tests — and Their Flaws
1. Horizontal Gaze Nystagmus (HGN)
What it is: The officer asks you to follow a pen or small object with your eyes while they look for involuntary jerking movements in the eyes — a phenomenon called “nystagmus.”
Why it’s flawed:
- Many medical conditions and even fatigue can cause nystagmus.
- Officers are not medical professionals. Their subjective interpretation of eye movement can be wildly inaccurate.
- Environmental conditions (wind, flashing lights, darkness) make accurate observation difficult.
- Nystagmus can be caused by medications, illness, or even caffeine.
Key flaw: There is no video or audio record of what the officer sees. The only evidence is their own written observation, which is almost impossible to challenge unless they mishandled the test.
2. Walk-and-Turn Test (WAT)
What it is: You’re told to take nine heel-to-toe steps on a straight line, turn on one foot, and walk back.
Why it’s flawed:
- Balance and coordination can be affected by anxiety, footwear, terrain, and even weather conditions.
- There is no standard “line” on the road — you may be asked to walk on gravel, sloped pavement, or in the dark.
- Age, weight, and physical condition heavily impact performance.
- The test includes complex instructions, and “failing” often has more to do with confusion or nervousness than actual impairment.
Key flaw: Officers often score people as “failing” for incredibly minor things — like lifting arms for balance or miscounting steps — none of which actually proves intoxication.
3. One-Leg Stand Test (OLS)
What it is: You’re asked to stand on one leg and count out loud for about 30 seconds while the officer observes for balance and swaying.
Why it’s flawed:
- Statistically unreliable for anyone over 65 or more than 50 pounds overweight.
- Anxiety, poor footwear, and uneven ground dramatically affect results.
- Even completely sober people can fail this test — especially at night, in stressful situations.
- Fatigue, inner ear issues, or minor injuries can skew performance.
Key flaw: There is no baseline for what your balance should be. The officer compares your performance to their own idea of “normal.”
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Why Declining FSTs Is Often the Smartest Move
In Arizona, you are NOT legally required to take field sobriety tests. Politely declining won’t get you into more legal trouble — and it could prevent the state from collecting weak, misleading evidence that will later be used against you in court.
Remember: these tests are designed to gather evidence, not to help you prove your innocence.
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What Should You Do Instead?
If you’re pulled over and asked to perform field sobriety tests:
- Stay calm and polite.
- Ask to speak with an attorney.
- Respectfully decline the tests.
- Do not volunteer information.
- Do not argue — let your lawyer fight for you later.
How Grand Canyon Law Group Fights DUI Charges in Arizona
At Grand Canyon Law Group, we’ve helped countless clients challenge DUI charges based on unreliable FST results. As former prosecutors, we know exactly how the state builds these cases — and more importantly, where their weaknesses are.
- We challenge the officer’s training and test procedures
- We file motions to suppress flawed evidence.
- We bring in expert witnesses to expose the tests’ unreliability.
- We fight to get your charges reduced — or dismissed entirely.
Our team has successfully defended DUI cases throughout Maricopa County and beyond, including Phoenix, Mesa, Scottsdale, Tempe, and Chandler.
A DUI charge can have lifelong consequences — from losing your license and skyrocketing insurance to damaging your career and personal life. But just because you were arrested doesn’t mean you’ll be convicted.
We can help you fight back.
Call Grand Canyon Law Group at (480) 573-6441 for a confidential case review — or contact us online today.
Let us help you take control of your case and protect your future
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