Last updated: September 9, 2026
Quick Answer: Standardized field sobriety tests (SFSTs) are three roadside assessments, the Horizontal Gaze Nystagmus, Walk and Turn, and One Leg Stand, validated by the National Highway Traffic Safety Administration (NHTSA) to detect alcohol impairment. Officers score each test by counting specific observable clues. The more clues present, the stronger the evidence of impairment.
Key Takeaways
- The three NHTSA-standardized tests are the Horizontal Gaze Nystagmus (HGN), Walk and Turn (WAT), and One Leg Stand (OLS).
- Each test has a fixed number of scored clues, officers are trained to count them, not make a general impression.
- HGN is considered the most reliable of the three, with NHTSA research citing roughly 88% accuracy when administered correctly.
- Medical conditions, fatigue, footwear, and road surface can all affect performance and produce false clues.
- Refusing a field sobriety test carries different legal consequences than refusing a breathalyzer, knowing the difference matters.
- A driver can show zero clues on all three tests and still be arrested if other evidence supports impairment.
- Conversely, a driver can pass all three tests and still face a DUI charge if a breathalyzer or blood test shows illegal BAC.
- Officers must complete NHTSA-approved training to administer these tests; improper administration can be challenged in court.
- Field sobriety test results are one piece of evidence, not a conviction, they can be contested by a defense attorney.
What Are the Three Standardized Field Sobriety Tests
The three NHTSA-standardized field sobriety tests are the Horizontal Gaze Nystagmus (HGN), the Walk and Turn (WAT), and the One Leg Stand (OLS). These are the only tests with validated research behind them; non-standardized tests such as the Romberg balance test or finger-to-nose test carry no NHTSA backing.
For a broader overview of how these assessments work in practice, see this guide to field sobriety tests.
Brief breakdown of each test:
- Horizontal Gaze Nystagmus: The officer moves a stimulus (pen or light) horizontally across the driver’s field of vision and watches for involuntary eye jerking.
- Walk and Turn: The driver walks heel-to-toe along a line for nine steps, turns, and walks back. The officer watches for eight specific clues.
- One Leg Stand: The driver raises one foot six inches off the ground and counts aloud for 30 seconds. The officer watches for four clues.
How Do Police Use Field Sobriety Tests to Detect Drunk Driving
Officers use standardized field sobriety test clues officers look for as a structured scoring system, not a pass/fail impression. Each observed clue is counted, and a threshold number of clues creates probable cause to arrest.
NHTSA research established these thresholds:
| Test | Total Possible Clues | Clues Needed for Impairment Indicator |
|---|---|---|
| Horizontal Gaze Nystagmus | 6 | 4 or more |
| Walk and Turn | 8 | 2 or more |
| One Leg Stand | 4 | 2 or more |
When used together, NHTSA data suggests the three-test battery correctly identifies a BAC of 0.08% or higher approximately 91% of the time under controlled conditions. Real-world accuracy is lower due to environmental variables and officer error.
What Clues Do Officers Look for in the Horizontal Gaze Nystagmus Test
The HGN test checks for nystagmus, an involuntary jerking of the eye, which alcohol amplifies. Officers score three clues per eye, for a maximum of six total clues.
The six HGN clues (three per eye):
- Lack of smooth pursuit, the eye jerks rather than tracking smoothly as the stimulus moves side to side.
- Distinct nystagmus at maximum deviation, the eye jerks clearly when held at the far edge of the visual field for at least four seconds.
- Onset of nystagmus prior to 45 degrees, the eye begins jerking before the stimulus reaches a 45-degree angle from center.
The third clue (onset before 45 degrees) is considered the strongest indicator of significant impairment. For a detailed breakdown of this test, see Horizontal Gaze Nystagmus.
What Clues Do Officers Look for in the Walk and Turn and One Leg Stand Tests
These two “divided attention” tests measure both physical coordination and the ability to follow instructions simultaneously, a combination alcohol disrupts.
Walk and Turn clues (8 total):
- Cannot keep balance during instructions
- Starts before instructions are finished
- Stops while walking
- Misses heel-to-toe contact
- Steps off the line
- Uses arms for balance (raised more than six inches)
- Makes an improper turn
- Takes the wrong number of steps
Two or more clues indicate likely impairment. Learn more about the Walk and Turn test and the One Leg Stand test.
One Leg Stand clues (4 total):
- Sways while balancing
- Uses arms for balance
- Hopping
- Puts foot down before 30 seconds
Can You Fail a Field Sobriety Test While Sober
Yes. A completely sober person can display multiple clues on all three tests. This is one of the most important facts about standardized field sobriety test clues officers look for, the tests measure balance, coordination, and attention, all of which are affected by factors other than alcohol.
Common reasons a sober person may fail:
- Nervousness or anxiety
- Age (individuals over 65 show reduced balance performance)
- Weight (NHTSA notes the OLS is less reliable for people more than 50 pounds overweight)
- Footwear (heels, boots, or sandals affect the WAT and OLS)
- Uneven or sloped road surface
- Bright headlights or flashing patrol lights
- Fatigue after a long drive or work shift
For a deeper look at reliability concerns, see are field sobriety tests reliable.
What Medical Conditions Affect Field Sobriety Test Results
Several medical conditions directly mimic or produce the same clues officers score as signs of impairment. Officers are trained to ask about medical conditions before administering tests, but they do not always do so.
Conditions that affect HGN:
- Inner ear disorders (labyrinthitis, Meniere’s disease)
- Multiple sclerosis
- Brain injury or stroke
- Certain prescription medications (anticonvulsants, sedatives)
- Caffeine and nicotine can cause minor nystagmus
Conditions that affect WAT and OLS:
- Knee, hip, ankle, or back injuries
- Neurological conditions affecting balance
- Vertigo
- Diabetes (hypoglycemia can cause confusion and unsteady movement)
Any of these conditions can become the basis of a legal challenge to the test results.
How Accurate Are Standardized Field Sobriety Tests Really
NHTSA’s own validation studies reported accuracy rates of 77% for OLS, 68% for WAT, and 88% for HGN when administered under controlled conditions by trained officers. Combined, the battery reached 91% accuracy in those studies. However, independent researchers have found lower real-world accuracy, particularly when tests are given on uneven surfaces, in poor lighting, or by officers who deviate from the standardized protocol.
For a focused analysis of this question, see are field sobriety tests accurate.
The key caveat: these accuracy figures apply only when the officer follows the NHTSA protocol exactly. Any deviation, wrong stimulus speed, wrong instructions, wrong surface, invalidates the standardized basis of the test.
What Happens If You Refuse a Field Sobriety Test
In most U.S. states, field sobriety tests are voluntary. A driver can legally refuse without triggering automatic license suspension (unlike refusing a chemical breathalyzer or blood test, which falls under implied consent laws).
What refusal means in practice:
- The officer may still arrest based on other observations (odor of alcohol, slurred speech, erratic driving).
- Refusal cannot be used as direct evidence of guilt in most jurisdictions, but prosecutors may argue it as consciousness of guilt.
- Refusing a breathalyzer after arrest carries mandatory penalties in nearly every state.
Before deciding whether to take these tests, read should I take a field sobriety test for a practical breakdown of the tradeoffs.
Can You Challenge Field Sobriety Test Results in Court
Yes. Field sobriety test results are not automatically conclusive evidence. Defense attorneys regularly challenge them on several grounds.
Common legal challenges:
- Officer failed to follow NHTSA standardized protocol
- Test was administered on an uneven or sloped surface
- Driver had a documented medical condition affecting performance
- Officer lacked proper NHTSA training or certification
- Dashcam or bodycam footage contradicts the officer’s clue count
- Environmental conditions (rain, poor lighting, traffic noise) compromised the test
For context on how breath test evidence is challenged in parallel, see challenging the breath test.
What Are Common Mistakes People Make During Sobriety Tests
Many drivers unintentionally generate clues through behavior that has nothing to do with alcohol. Understanding these mistakes helps illustrate why the standardized field sobriety test clues officers look for are easy to trigger under stress.
- Starting too early: Beginning the walk before the officer finishes instructions counts as a clue, even for a sober person eager to comply.
- Talking during the test: Asking questions mid-test or explaining yourself divides attention and disrupts balance.
- Wearing inappropriate footwear: High heels or thick-soled boots should be removed if offered the option, most officers will allow it.
- Looking down: On the OLS, looking down at your foot rather than at a fixed point ahead increases sway.
- Counting too fast or too slow: On the OLS, counting “one-one-thousand, two-one-thousand” at an inconsistent pace can cause early foot placement.
How Do Fatigue and Stress Affect Field Sobriety Test Performance
Fatigue and acute stress both degrade the divided attention skills these tests measure. A driver who has been awake for 20+ hours may show balance and coordination deficits comparable to mild alcohol impairment, according to sleep research from the American Academy of Sleep Medicine (2000). Stress triggers the sympathetic nervous system, which can cause trembling, rapid eye movement, and difficulty following multi-step instructions, all of which overlap with scored clues.
Officers are not required to account for fatigue or stress when scoring clues, which is one reason these results are frequently contested.
What Is the Difference Between Field Sobriety Tests and Breathalyzers
Field sobriety tests measure observable behavior and coordination; breathalyzers measure blood alcohol concentration (BAC) directly from a breath sample. They serve different legal purposes.
| Factor | Field Sobriety Tests | Breathalyzer |
|---|---|---|
| What it measures | Behavioral clues of impairment | BAC percentage |
| Refusal consequences | Usually none (varies by state) | License suspension (implied consent) |
| Admissibility | Officer testimony + video | Chemical test result |
| Challengeable | Yes, on protocol grounds | Yes, on calibration/maintenance grounds |
| Detects drugs | Partially (behavioral signs) | No (alcohol only) |
Can You Pass a Field Sobriety Test and Still Get a DUI
Yes. Passing all three field sobriety tests does not prevent a DUI arrest or conviction if a chemical test shows BAC at or above the legal limit. Officers can also arrest based on drug impairment that field sobriety tests do not reliably detect. Conversely, failing field sobriety tests while blowing below 0.08% may still result in arrest if the officer believes drug impairment is present.
What Training Do Police Officers Get for Administering Sobriety Tests
NHTSA requires officers to complete a standardized training course before administering SFSTs. The standard course is 24 hours of classroom and practical instruction. Officers learn the exact protocol for each test, how to score clues, and how to document results for court.
Advanced certification as a Drug Recognition Expert (DRE) requires an additional 72-hour course plus field certification. DREs are trained to identify impairment from 7 drug categories beyond alcohol.
Officers who skip steps, use non-standard stimuli, or give incorrect instructions have not administered a “standardized” test, and that distinction is legally significant.
Conclusion
The standardized field sobriety test clues officers look for follow a precise, NHTSA-defined scoring system, but that precision only holds when the protocol is followed correctly. Every clue has a specific definition, every test has a validated threshold, and every deviation from procedure creates a potential challenge.
Actionable next steps if you or someone you know has been arrested after field sobriety testing:
- Request and preserve all dashcam and bodycam footage immediately, this is the most powerful tool for evaluating whether the tests were administered correctly.
- Document any medical conditions, medications, footwear, road surface, or environmental factors present at the time of testing.
- Do not discuss test performance with anyone other than a defense attorney.
- Consult a DUI defense attorney who understands NHTSA protocol, improper administration is one of the most common and successful grounds for challenging test results.
Understanding what officers are actually scoring, and why those scores can be wrong, is the first step toward a meaningful defense.
Frequently Asked Questions
Q: How many clues does it take to fail a field sobriety test? A: For the Walk and Turn, 2 or more clues out of 8 indicate likely impairment. For the One Leg Stand, 2 or more out of 4. For HGN, 4 or more out of 6. These thresholds are set by NHTSA’s validation research.
Q: Can prescription medication cause you to fail a field sobriety test? A: Yes. Anticonvulsants, sedatives, antihistamines, and some blood pressure medications can produce nystagmus or impair balance and coordination, generating clues on all three tests.
Q: Are field sobriety tests required by law? A: In most U.S. states, field sobriety tests are voluntary for drivers. Refusing them typically does not carry automatic legal penalties, unlike refusing a post-arrest chemical test.
Q: Does wearing glasses affect the HGN test? A: Officers are trained to have drivers remove contact lenses if possible and to note glasses use. Certain lens prescriptions can affect eye tracking, though this is rarely a decisive factor.
Q: Can a video recording help challenge field sobriety test clues? A: Yes. Dashcam and bodycam footage often contradicts an officer’s written clue count. Courts have dismissed or reduced DUI charges when video showed the driver performed better than the officer reported.
Q: What happens if the officer skips part of the standardized instructions? A: Incomplete instructions mean the test was not administered in a standardized manner. Defense attorneys can argue that any clues observed are unreliable because the driver was not given the full protocol.
Q: Is the HGN test admissible in all states? A: Most states admit HGN evidence, but a few have restricted or excluded it. Admissibility rules vary by jurisdiction and can depend on whether the officer followed the exact NHTSA protocol.
Q: Can you request a different type of sobriety test? A: No. Drivers do not have the right to choose which tests are administered. Officers select from the standardized battery based on their training and circumstances.
Q: Does age affect field sobriety test accuracy? A: Yes. NHTSA acknowledges that individuals over 65 show naturally reduced balance performance, which can inflate clue counts on the Walk and Turn and One Leg Stand tests.
Q: Can a DUI charge be dropped if the field sobriety test was improperly administered? A: Improper administration does not automatically result in dismissal, but it weakens the evidence significantly. Combined with other favorable factors, it can lead to reduced charges or acquittal.
References
- National Highway Traffic Safety Administration (NHTSA). Standardized Field Sobriety Testing: Student Manual. U.S. Department of Transportation, 2018.
- Stuster, J., & Burns, M. Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent. NHTSA, 1998.
- American Academy of Sleep Medicine. Excessive Sleepiness and Driving Performance. 2000.
- Burns, M. Field Sobriety Tests: Development and Scientific Status. In D. Faigman et al. (Eds.), Modern Scientific Evidence, 2004.
