You can pass a field sobriety test, and sober people do it every day, but passing is not what most drivers picture. There is no score sheet and no letter grade. The officer counts specific behaviors called “clues,” and if your total stays below a set threshold on each test, you have effectively passed. The catch is that the thresholds are low, the clues are easier to trigger than they sound, and one peer-reviewed study cited in law enforcement training found that roughly one in four completely sober subjects showed enough indicators to be classified as impaired.
What “Passing” Actually Means
The National Highway Traffic Safety Administration built the field sobriety framework used across the country, and it does not work like a test you either finish or fail. During each exercise, the officer watches for a fixed list of predefined behaviors. Each behavior that appears is counted as a clue. If the total meets or exceeds the threshold for that test, the officer treats the result as evidence your blood alcohol concentration is likely at or above 0.08. Stay under the threshold and you have passed, though the officer will not use that word out loud.
Even administered correctly, the individual tests misclassify somewhere between 12 and 21 percent of people. The error runs in both directions: impaired drivers slip through, and sober drivers get arrested. Knowing the specific clues and thresholds tells you exactly what the officer is looking for, and what you have to avoid.
The Three Standardized Tests and Their Thresholds
Three tests carry NHTSA’s endorsement and have validated clue systems: the Horizontal Gaze Nystagmus test, the Walk-and-Turn, and the One-Leg Stand. They are meant to be used together as a battery, and combined accuracy runs about 91 percent when everything is administered by the book.1National Highway Traffic Safety Administration (NHTSA). Evaluation of the Effects of SFST Training on Impaired Driving Enforcement
Horizontal Gaze Nystagmus
The officer moves a pen or fingertip slowly across your field of vision and watches your eyes for involuntary jerking. There are three clues per eye, six possible in total:
- Lack of smooth pursuit as your eye tracks the stimulus
- Distinct and sustained jerking when your eye is held all the way to one side
- Onset of jerking before your eye reaches a 45-degree angle from center
Four or more clues across both eyes puts you over the threshold. NHTSA’s research puts this test’s accuracy at about 88 percent.2National Highway Traffic Safety Administration (NHTSA). DWI Detection and Standardized Field Sobriety Test Participant Manual You cannot suppress nystagmus by concentrating, which is why officers view this test as the most reliable of the three.
Walk-and-Turn
You walk nine heel-to-toe steps along a real or imaginary line, perform a specific turn, and walk nine steps back. There are eight possible clues:
- Losing balance during the instruction phase
- Starting before being told to begin
- Stopping mid-walk
- Failing to touch heel to toe
- Stepping off the line
- Raising your arms more than six inches for balance
- Making an improper turn
- Taking the wrong number of steps
Two clues is enough to fail. So is being unable to complete the test at all. Accuracy runs at about 79 percent, the lowest of the three.3National Highway Traffic Safety Administration (NHTSA). SFST Refresher Instructor Guide A sober person in dress shoes on gravel at night can hit two clues without any alcohol in their system.
One-Leg Stand
You raise one foot about six inches off the ground with both legs straight, look at the elevated foot, and count aloud for 30 seconds. There are four clues:
- Swaying while balancing
- Using your arms to balance
- Hopping
- Putting your foot down
Two clues is the failing threshold. Accuracy runs at about 83 percent.3National Highway Traffic Safety Administration (NHTSA). SFST Refresher Instructor Guide
Why Sober People Show Clues
The thresholds were calibrated against averages in controlled studies. They were never designed to account for the range of physical conditions, environments, and stress responses that show up on the side of a highway at midnight.
Medical Conditions and Medications
Inner ear disorders, back and knee injuries, and neurological conditions can produce clues on the Walk-and-Turn and One-Leg Stand for reasons that have nothing to do with alcohol. People over 65 or those who are significantly overweight often struggle with the balance tests as well.
The eye test carries its own vulnerability. Anti-seizure drugs like phenytoin, carbamazepine, and lamotrigine are known to cause nystagmus as a side effect.4National Center for Biotechnology Information. Antiseizure Medication-Induced Nystagmus During Eye Closure Identified by Electroencephalography Sedatives, certain antidepressants, and muscle relaxants can do the same. An officer looking at your eyes has no way to distinguish drug-induced nystagmus from alcohol-induced nystagmus. Officers are trained to ask about medical conditions and medications before testing, but many skip that step or ask without following up. If you have a relevant condition, say so clearly and early.
The Testing Environment
NHTSA’s training materials say testing should occur on a reasonably level, dry surface. Reality is often a gravel shoulder, a sloped road, wet pavement, or grass, with headlights and flashing lights in your face and traffic passing a few feet away. Every one of those conditions makes precise balance harder, and none of them changes the threshold the officer is counting toward.
Nerves
Being pulled over and evaluated by a police officer is inherently stressful, and stress disrupts balance and concentration. On the Walk-and-Turn, losing balance during the instructions counts as a clue. So does starting before the officer says “begin.” A nervous, sober driver can produce both before taking a single step.
Non-Standardized Tests
Some officers add roadside tests beyond the standardized three: the finger-to-nose test, the Modified Romberg Balance test (standing with your head tilted back and eyes closed while estimating 30 seconds), or alphabet and counting exercises.5National Highway Traffic Safety Administration (NHTSA). Advanced Roadside Impaired Driving Enforcement Participant Manual NHTSA researched these and found they were less accurate than the three standardized tests.6National Highway Traffic Safety Administration (NHTSA). DWI Detection and Standardized Field Sobriety Testing Participant Manual They have no validated clue system and no established accuracy rate, so results on them carry far less weight in court.
Your Right to Decline
In most states, field sobriety tests are voluntary. You can decline to perform them without triggering the automatic license suspension attached to refusing a post-arrest chemical test. Those chemical tests (breath, blood, or urine after an arrest) are governed by implied consent laws in every state and carry real penalties for refusal. The roadside sobriety tests generally are not.
Declining does not guarantee you drive away. If the officer already has enough evidence from your driving, your appearance, and your conversation to establish probable cause, an arrest can still follow. In some states, your refusal can be presented to a jury as evidence of “consciousness of guilt.” Others do not allow that. The rules vary significantly by jurisdiction.
Preliminary breath tests offered at the roadside before an arrest sit in a gray area. In most states these handheld devices are also voluntary for adults, and separate from the mandatory post-arrest chemical test. For drivers under 21, some states make the roadside breath test mandatory.
When You Can Challenge a Failed Test Later
Failing at the roadside is not the end of the story. NHTSA’s own training materials state that the validated accuracy rates apply only when the tests are administered in the prescribed, standardized manner, the standardized clues are used to assess performance, and the standardized criteria are used to interpret it. If any element changes, the validity is compromised.7National Highway Traffic Safety Administration (NHTSA). Standardized Field Sobriety Testing Participant Manual
Defense attorneys look for several categories of administration errors:
- Rushed or incomplete instructions, so that any resulting clues reflect confusion rather than impairment
- Failure to screen for medical conditions, injuries, or medications before testing
- Improper testing surface, such as a slope, gravel, wet pavement, or grass
- Subjective scoring, where officers count behaviors that are not on the validated clue list
Dashcam and bodycam footage often decides these challenges. An officer’s report might describe poor balance and missed heel-to-toe steps, and the video may show something quite different. When the footage contradicts the report, it undermines both the clue count and the officer’s credibility.
Passing a field sobriety test, then, is really two questions. At the roadside, it means keeping the clue count under the threshold on each of the three tests. In the days and weeks after, it can also mean showing that the count itself was never valid because of how the tests were conducted, where they were conducted, or who was being tested.