Field Sobriety Test Defense — Florida DUI

Field sobriety tests in Florida are voluntary — you are not legally required to perform them — and even the three standardized NHTSA tests are only as reliable as the officer who administers them. The National Highway Traffic Safety Administration validated only three standardized field sobriety tests, and only when administered exactly according to NHTSA protocol. When officers deviate from that protocol — as they frequently do — the tests lose their scientific validity, and the evidence they produce should not be used to convict you of DUI under Florida Statute § 316.193.

Legally reviewed by Tonmiel Rodriguez, Board Certified Criminal Trial Lawyer — last reviewed June 2026.

Are Field Sobriety Tests Required in Florida?

No. Field sobriety tests are entirely voluntary in Florida — you have no legal obligation to perform them, and there is no administrative penalty for refusing them (unlike the breath test refusal under § 316.1932). The officer is not required to tell you they are voluntary. Most people perform field sobriety tests because they don’t know they can decline, or because they believe that cooperating will help them. Field sobriety test performance is almost always used against the driver — officers are trained to document every observable indicator of impairment, and even sober people can fail standardized tests under stress, in poor conditions, or with certain physical limitations.

What Are the Three NHTSA Standardized Field Sobriety Tests?

The National Highway Traffic Safety Administration (NHTSA) has validated exactly three standardized field sobriety tests (SFSTs) for use in DUI investigations: the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg Stand (OLS). These are the only tests with peer-reviewed scientific validation — and that validation is conditional on strict protocol compliance. NHTSA’s own research found that when officers deviate from standardized administration, the test’s correlation to impairment drops significantly or disappears.

Test	What It Measures	Validated Accuracy (per NHTSA)	Common Administration Failures
Horizontal Gaze Nystagmus (HGN)	Involuntary eye jerking as gaze moves to side	88% — when properly administered	Wrong stimulus distance (12–15 inches), too-fast stimulus movement, improper clues count
Walk-and-Turn (WAT)	Divided attention — follow instructions + walk heel-to-toe	79% — when properly administered	No designated line, improper demonstration, sloped/uneven surface, inadequate lighting
One-Leg Stand (OLS)	Balance and divided attention — stand on one leg for 30 seconds	83% — when properly administered	Uneven surface, wind, improper timing, failure to demonstrate correctly

Even at their validated accuracy rates — with perfect administration — the NHTSA tests produce false positives. An 88% accuracy rate on HGN means 12 out of every 100 people the officer calls “impaired” are not impaired. That is not beyond a reasonable doubt. And those accuracy rates assume perfect administration — something that happens far less often in the field than in controlled research conditions.

What Are Non-Standardized Field Sobriety Tests and Are They Valid?

Non-standardized field sobriety tests — finger-to-nose, alphabet recitation, counting backward, hand-pat test, Romberg balance — have no peer-reviewed scientific validation as indicators of impairment and no NHTSA-approved protocol. NHTSA’s own literature does not endorse them for evidentiary purposes. Officers sometimes administer these tests in addition to (or instead of) the standardized battery, but the results carry no established scientific correlation to alcohol or drug impairment. I challenge the use of non-standardized test results at trial and seek jury instructions on their lack of scientific foundation.

What Physical and Environmental Factors Affect Field Sobriety Test Performance?

NHTSA’s own research identifies multiple non-alcohol factors that can cause field sobriety test failure in sober individuals. I review all of these in every case and document the conditions at the scene:

• Age: Persons over 65 have documented difficulty with balance tasks independent of alcohol. NHTSA notes this in the standardized battery training manual.
• Weight: Individuals more than 50 pounds overweight have difficulty with One-Leg Stand due to physiological balance demands.
• Footwear: High heels, flip-flops, or shoes with elevated soles affect Walk-and-Turn and One-Leg Stand performance. The NHTSA manual allows the officer to let the subject remove footwear — failure to offer this is an administration error.
• Road surface: Uneven pavement, gravel, graded shoulders, grass, or wet surfaces all affect balance test performance. NHTSA requires a “hard, dry, level, non-slippery surface.”
• Lighting: Inadequate lighting affects the officer’s ability to observe clues and the subject’s ability to perform the tasks. Flashing police lights behind the subject create vestibular interference with HGN.
• Wind: Wind gusts affect balance during One-Leg Stand.
• Anxiety and stress: Being stopped by police produces elevated stress and anxiety that can mimic impairment indicators independently of alcohol.
• Medical conditions: Inner ear disorders, vertigo, BPPV (benign paroxysmal positional vertigo), nystagmus conditions, orthopedic issues (knee, hip, ankle injuries), and neurological conditions all affect test performance independently of alcohol.
• Medications: Certain prescription and OTC medications cause nystagmus (anticonvulsants, certain antibiotics, some sedatives) or affect balance and coordination independently of alcohol.

How Do I Challenge Field Sobriety Test Evidence in a Florida DUI Case?

Every field sobriety test challenge starts with the dashcam and bodycam video. The video is objective — it shows the road surface, the lighting, the weather, the officer’s demonstration, and the subject’s actual performance. I request all video in every DUI case immediately, because video retention policies vary and footage can be purged. The video often shows things the officer’s report does not mention: uneven pavement, the absence of a real heel-to-toe line, an abbreviated demonstration, a 23-second OLS count called as 30 seconds, or a subject asking for instruction clarification that was refused.

I also request the officer’s training records, SFST certification, and the date of their last NHTSA refresher. An officer trained in 2010 who has not had a refresher is administering a 2010 version of the protocol — the NHTSA manual has been updated, and a dated certification is a cross-examination point. I obtain the arresting officer’s SFST certification date and the version of the NHTSA manual used in their training in every case.

• Video review — dashcam, bodycam, DUI investigation room video
• NHTSA protocol deviation — improper demonstration, clue miscounting, wrong stimulus distance
• Surface and environmental conditions at the time of the test
• Officer’s training records, SFST certification, NHTSA manual version
• Medical conditions affecting balance, coordination, or nystagmus
• Footwear and footwear accommodation offer (or lack thereof)
• Non-standardized test challenge — no scientific validity, jury instruction
• Physical characteristics — age, weight, prior injuries affecting balance
• Medications with known effects on nystagmus or balance

How Is the HGN Test Different From the Walk-and-Turn and One-Leg Stand?

The HGN (Horizontal Gaze Nystagmus) test is fundamentally different from the two walk/balance tests. HGN measures an involuntary physiological response — the jerking of the eyes at the extremes of gaze — that the subject cannot control or mask, regardless of effort. The Walk-and-Turn and One-Leg Stand are divided attention tests that measure the ability to follow instructions and maintain balance simultaneously, which a person can attempt to perform perfectly while impaired, or can fail while perfectly sober. HGN is therefore considered the most scientifically reliable of the three, but it is also subject to the most distinct vulnerabilities: many medications cause nystagmus (including anticonvulsants, certain antibiotics, and muscle relaxants), certain neurological conditions produce nystagmus, and flashing lights behind the subject can introduce vestibular-induced nystagmus that the officer may interpret as an impairment clue. The stimulus must be held 12–15 inches from the face, at eye level, and moved at a precise speed — deviations in any of these parameters change the scientific validity of the result.

Related DUI Defense Pages

• DUI Defense in Florida — Complete Overview
• First DUI in Florida — Penalties and Defense
• DUI Breath Test — Intoxilyzer 8000 Defense
• DUI Blood Test Defense — Florida
• DUI Refusal — Refusing the Breath Test (Trenton’s Law)
• Second DUI in Florida — Enhanced Penalties
• Criminal Defense — Polk County

Frequently Asked Questions — Field Sobriety Tests in Florida DUI Cases

Do I have to take field sobriety tests in Florida?

No. Field sobriety tests are completely voluntary in Florida. Unlike the breath test under § 316.1932’s implied consent law, there is no statutory requirement to perform field sobriety tests and no administrative penalty for declining. The officer is not required to tell you they are optional. If you are stopped for DUI, you may politely decline the tests. Declining does not prevent an arrest if the officer has probable cause from other observations, but it does eliminate the field sobriety test evidence from the case.

What are the standardized field sobriety tests in Florida DUI cases?

The three NHTSA-standardized field sobriety tests used in Florida DUI investigations are the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg Stand (OLS). These are the only tests validated by peer-reviewed research as correlating to alcohol impairment, and only when administered exactly per NHTSA protocol. No other field sobriety test has NHTSA validation, and results from non-standardized tests carry no established scientific reliability.

Can medical conditions cause a false field sobriety test failure?

Yes. Multiple medical conditions cause performance issues on field sobriety tests independent of alcohol: inner ear disorders and vertigo affect balance and produce nystagmus; orthopedic injuries to the knee, hip, or ankle affect Walk-and-Turn and One-Leg Stand; neurological conditions cause nystagmus; and certain medications cause nystagmus as a side effect. Age over 65 and weight more than 50 pounds above ideal are NHTSA-recognized factors that independently affect performance. I document all relevant medical history in every field sobriety test case.

What happens if the officer made mistakes during the field sobriety tests?

Officer deviations from NHTSA protocol during administration directly undermine the scientific validity of the test results. These deviations are documented through video review and cross-examination on the officer’s training records and NHTSA manual version. If the deviation is significant — wrong stimulus distance on HGN, inadequate demonstration on Walk-and-Turn, timed OLS incorrectly — the results can be challenged in a motion in limine to exclude or through cross-examination that diminishes their weight with the jury.

Can a sober person fail field sobriety tests?

Yes. NHTSA’s own validated accuracy rates mean a percentage of sober individuals fail each test even under ideal conditions — 12% false positive rate for HGN, 21% for Walk-and-Turn, and 17% for One-Leg Stand, under research conditions. Under real-world roadside conditions — uneven pavement, flashing police lights, stress, traffic noise, improper administration — false positive rates are higher. This is a core argument in every field sobriety test defense: failing a roadside test at midnight on an uneven shoulder in traffic is not the same as failing a test in a controlled laboratory setting.

NHTSA Validation Studies: What They Actually Show — and What They Don’t

The studies the government relies on to validate these tests are far more limited than prosecutors want the jury to believe. The National Highway Traffic Safety Administration (NHTSA) funded three original studies in the 1970s and 1980s — by Tharp, Burns, and Moskowitz — that established the Standardized Field Sobriety Test (SFST) battery. Those studies were conducted under controlled conditions with trained researchers observing subjects walking on a designated line, not on the shoulder of I-4 at 2 AM with headlights and traffic behind them.

The NHTSA studies found that when all three tests (HGN, WAT, OLS) are administered exactly as trained and evaluated together, an officer can classify subjects as above or below 0.10 BAC with 83–91% accuracy. That number does not mean what it sounds like. The validation threshold was 0.10, not 0.08 (Florida’s legal limit). An accuracy rate of 83% means roughly 1 in 6 classifications is wrong. The figures also assume perfect, standardized administration on a sample of laboratory volunteers, not people with back injuries, inner ear problems, or anxiety disorders. And subsequent independent research has repeatedly failed to replicate the original NHTSA accuracy figures in real-world conditions.

I attack the NHTSA studies in every FST-dependent case. The studies themselves say these tests are not validated for the roadside. They are not validated for surfaces other than a dry, flat, level roadway. They are not validated for people over 65, people more than 50 pounds overweight, or people with any musculoskeletal or neurological condition. If you fit any of those categories, the test result means almost nothing.

Medical Conditions That Defeat FST Reliability

Field sobriety tests measure physical and cognitive function. Any medical condition affecting balance, coordination, vision, or attention will produce “clues” on these tests — even with zero alcohol in the system. I raise this in virtually every FST case because most people have at least one relevant condition and never think to mention it.

Inner ear conditions: Benign paroxysmal positional vertigo (BPPV), Ménière’s disease, labyrinthitis, and even prior ear infections can cause balance impairment that mimics alcohol intoxication on the OLS and WAT tests. These conditions are common and often undiagnosed.

Neurological conditions: Multiple sclerosis, peripheral neuropathy, and prior traumatic brain injury affect both balance and eye movement. HGN can appear at angles below 45 degrees in people with nystagmus from non-alcohol causes including naturally occurring nystagmus (present in 3–7% of the population) and nystagmus from prescription medications including antihistamines, antidepressants, and anti-seizure drugs.

Musculoskeletal conditions: Prior knee surgery, ankle instability, hip replacement, degenerative disc disease, and sciatica directly affect the ability to perform the OLS and WAT without the clues the officer is looking for. NHTSA’s own manual excludes people with back, leg, and inner ear problems from reliable FST assessment.

Anxiety and stress: Standing on the side of a road at night with police lights flashing, being told you are under investigation, and performing physical tests while being scrutinized — that scenario produces physiological stress responses that impair performance in sober individuals. Elevated cortisol, heart rate elevation, and attention splitting are real and measurable.

Officer Training Requirements and Scoring Criteria

Officers who administer SFSTs in Florida are required to complete NHTSA-standardized training — typically a 24-hour SFST practitioner course. Advanced DUI enforcement officers may hold an ARIDE (Advanced Roadside Impaired Driving Enforcement) or DRE (Drug Recognition Expert) certification. I request the officer’s training records in discovery for every field sobriety case, because an officer who has not been properly trained, or who was trained but administered the test outside of NHTSA standards, has produced unreliable results.

HGN scoring: The officer is checking for three clues in each eye — lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. Maximum possible clues: 6. Four or more clues indicates possible impairment. But HGN must be administered with the stimulus held 12–15 inches from the face, at eye level, and moved at the proper speed. Too fast, too slow, too close, or at the wrong angle invalidates the result. The officer must also properly check for equal tracking (both eyes moving together) before beginning.

WAT scoring: The officer watches for 8 clues across the instructional and walking phases. Clues include: cannot keep balance during instructions, starts too soon, stops walking, misses heel-to-toe (gap greater than ½ inch), steps off the line, uses arms for balance (more than 6 inches from body), loses balance on turn, takes wrong number of steps. The test requires a real or imaginary line, and the NHTSA manual specifies the surface must be dry, hard, level, and non-slippery. A gravel shoulder, grass, or sloped roadway is not a valid testing surface.

OLS scoring: The officer watches for 4 clues: sways while balancing, uses arms for balance, hops, or puts foot down. The subject must hold the raised foot 6 inches from the ground, toes pointed forward, for 30 seconds. Most people — sober or not — struggle to complete 30 seconds of one-leg standing in stressful conditions. Two or more clues indicates possible impairment, but studies show a high false positive rate for this test independent of alcohol.

When I cross-examine an officer on FST administration, I use the NHTSA manual against them — because that manual is their training document, and any deviation from it is admissible proof that the test was not conducted according to the very standards the State relies on to establish its reliability.