Standardized field sobriety tests (SFSTs) are the foundation of most DUI arrests in the United States. The National Highway Traffic Safety Administration (NHTSA) standardized three tests in the 1970s and 80s: Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn, and the One-Leg-Stand. Each has documented accuracy issues, and in most states FSTs are voluntary — but officers rarely tell you that.
Horizontal Gaze Nystagmus (HGN)
The officer holds a pen or finger 12–15 inches from your face and moves it side to side while watching your eyes for involuntary jerking. NHTSA claims 77% accuracy at predicting BAC at or above 0.10.
Nystagmus has dozens of medical causes unrelated to alcohol: head injury, inner-ear disorders, certain medications (including SSRIs and some blood-pressure drugs), eye-muscle defects, and even fatigue. Officer technique is critical — improper angle, distance, or pace invalidates the test, and most patrol officers are not trained well enough to administer it reliably.
Walk-and-Turn
The officer instructs you to walk nine heel-to-toe steps along an imaginary line, turn on one foot, and walk nine steps back, while counting aloud and keeping your arms at your sides. NHTSA claims 68% accuracy.
The test is difficult on uneven pavement, in bad weather, while wearing heels or boots, with knee or back injuries, or for anyone over age 65 or more than 50 pounds overweight. The test also requires the officer to give and demonstrate the instructions in a specific way — failure to do so invalidates the test.
One-Leg-Stand
Stand on one leg with the other foot raised six inches off the ground, and count out loud ('one-thousand-one, one-thousand-two…') for 30 seconds. NHTSA claims 65% accuracy.
Strongly affected by age (60+), weight, balance disorders, leg or back injuries, footwear, and surface conditions. Even sober, well-conditioned individuals routinely fail this test, particularly at night beside a busy roadway.
Can You Refuse Field Sobriety Tests?
In nearly every state, FSTs are voluntary and refusal alone cannot be used as evidence of guilt at trial. Officers will not tell you this — they will phrase the request as a command. You may politely decline.
This is different from chemical tests (breath, blood, urine), which are governed by implied-consent laws and trigger automatic license suspension if refused after arrest.
Non-Standardized Tests
Officers sometimes administer additional tests not validated by NHTSA: the alphabet (recite from D to P), counting backwards, finger-to-nose, finger-count, or the 'Romberg' balance test (eyes closed, head back, estimate 30 seconds).
Because these tests are not validated, defense attorneys frequently move to exclude them from trial — and many courts grant the motion.
How Attorneys Challenge FSTs
Strategies include: cross-examining the officer on training currency and proper administration; introducing medical records establishing the driver's pre-existing condition; presenting weather and road-surface evidence; showing dash-cam or body-cam video that contradicts the officer's narrative; and calling defense experts on SFST limitations.
A well-prepared FST cross-examination is one of the highest-leverage moments in any DUI trial.
Frequently Asked Questions
Are field sobriety tests mandatory?
No — in nearly every state, field sobriety tests are voluntary, and refusal alone cannot be used as evidence of guilt at trial. Officers rarely volunteer this information.
How accurate are FSTs?
NHTSA's own validation studies put accuracy at 65–77% per test under ideal conditions. Real-world accuracy is lower because of medical issues, age, weather, and footwear — meaning roughly 1 in 4 sober drivers can fail.
Can I refuse the breathalyzer too?
Pre-arrest portable breath tests (PBTs) are usually optional. Post-arrest evidentiary breath, blood, or urine tests are governed by implied consent — refusal triggers automatic license suspension and additional penalties.
What if I have a medical condition that affects FSTs?
Tell the officer at the scene and document it. Bring medical records to your attorney — pre-existing balance, vision, or neurological conditions are powerful defenses against SFST failure.
Will the dash-cam video help my defense?
Often yes. Dash-cam and body-cam video frequently contradicts the officer's written report — drivers who 'failed badly' on paper often look fine on tape. Always demand all video evidence in discovery.
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Safety notice and legal disclaimer
Never drive after drinking or using impairing substances. If you have been arrested or charged with a DUI/DWI, contact a licensed attorney in your state immediately — administrative license deadlines often run within days of arrest.
This page is general legal information published by the DUIGuide.us editorial team, not legal advice, and it does not create an attorney-client relationship. Laws change frequently; verify statutes and court rules with official state sources or licensed counsel. See our editorial policy and full disclaimer.