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Standardized Field Sobriety Tests

Police use standardized field sobriety tests (SFSTs) to justify their arrests and prosecutors use the results to pursue OVI charges. A thorough understanding of the SFSTs is required to mount an effective challenge to the results.

Read the NHTSA SFST Participant Manual (2023)

What are SFSTs?

Police might conduct several tests at the side of the road to evaluate possible impairment. These might include an alphabet test, counting backwards, finger counting, a lack-of-convergence test, the modified Romberg test, horizontal gaze nystagmus, the walk-and-turn, and the one-leg-stand.

Only the last three are standardized, meaning there is research to support a finding that a person may be over the legal limit if they display sufficient clues.

Why correct administration matters

Those accuracy figures hold only when the tests are administered correctly. Officers must perform them properly for the results to be admissible, and in Ohio they need not be perfect but must substantially comply with the instructions in the current NHTSA SFST manual.

The Three Standardized Tests at a Glance

Horizontal Gaze Nystagmus
HGN
Clues to fail4 of 6
Accuracy*88%

Looks for an involuntary jerking of the eyes as they follow a moving stimulus.

Walk-and-Turn
WAT
Clues to fail2 of 8
Accuracy*79%

A divided-attention test of balance, memory, and following instructions while walking a line.

One-Leg-Stand
OLS
Clues to fail2 of 4
Accuracy*83%

A divided-attention test of balance while standing on one leg and counting.

*The probability that a person is at or above a 0.08 BAC when the test is administered correctly, per NHTSA validation research. These are the only three standardized tests, and the figures assume the officer substantially complied with the NHTSA procedures.

Validated for alcohol, not drugs

The accuracy figures above come from studies of alcohol impairment measured against a 0.08 BAC. The standardized tests were never validated to measure marijuana or other-drug impairment, so clues on these tests do not carry the same meaning in a THC or drug OVI case.

Horizontal Gaze Nystagmus (HGN)

Nystagmus is a distinct, involuntary jerking of the eyes, and horizontal gaze nystagmus is the jerking that appears as the eyes turn to the side. A person cannot feel it or control it, and alcohol and certain other drugs make it appear sooner and more sharply. It is the first test in the battery and the one NHTSA considers the most reliable, but it is also the most technique-dependent and the easiest to perform incorrectly.

HGN is not the only cause of eye jerking. Neurological conditions, head injury, inner-ear disorders, and certain medications can produce nystagmus that has nothing to do with alcohol, which is why the test is run in a strict sequence: an instruction phase, a medical evaluation phase, and only then the scored test.

Phase 1Instruction phase

The officer positions you and explains what to do before any checking begins.

  • "Put your feet together, hands at your side."
  • "Keep your head still."
  • "I am going to check your eyes."
  • "Keep your head still and follow this stimulus with your eyes only."
  • "Keep focusing on the stimulus until I tell you to stop. Do you understand?"
  • The officer should also have you remove any glasses before beginning.
Phase 2Medical evaluation phase

Before scoring anything, the officer has to separate alcohol from the many other things that make eyes jerk. This is a medical assessment, and skipping it departs from the standardized protocol.

The medical questions matter. First, the officer is supposed to ask about your eye and general health, including head injuries, neurological or inner-ear conditions, and any medications you take. Each of these can cause eye jerking that has nothing to do with alcohol, so the answers can decide whether the test means anything at all.
Equal pupil size
The officer compares the two pupils. Distinctly unequal pupils can point to a prosthetic eye, a head injury, or a neurological disorder, not alcohol.
Resting nystagmus
With the eyes looking straight ahead and the stimulus still, the officer watches for jerking. Resting nystagmus usually signals a medical condition or a drug such as a dissociative anesthetic, not alcohol.
Equal tracking
The officer moves the stimulus across both eyes, from center to far right, to far left, and back, at the same speed used for the smooth-pursuit check and usually a pass or two. If the eyes do not move together, it points to a possible injury or illness affecting the brain.

If any of these checks is abnormal, the officer may stop, and continuing anyway is outside the standardized protocol.

Phase 3The test

Only now does the officer check for the three scored clues, and the stimulus must be handled to exact tolerances.

  • Hold the stimulus about 12 to 15 inches from the nose, slightly above eye level.
  • Check each eye, beginning with the left.
  • Smooth pursuit: move to the side at a speed of about two seconds out, at least two passes per eye.
  • Maximum deviation: hold at the far corner for a minimum of four seconds.
  • Onset: move slowly, about four seconds to reach 45 degrees, and stop when the jerking begins to confirm it is before 45 degrees.
Scored Clues: HGN One per eye for each check, six total
4 of 6 clues = BAC 0.08+
1
Lack of smooth pursuit
The eye cannot follow the slowly moving stimulus smoothly and instead jerks as it tracks, like a windshield wiper on a dry window.
2
Distinct and sustained nystagmus at maximum deviation
Clear, sustained jerking when the eye is held as far to the side as it will go.
Must be distinct and sustained for at least four seconds. The manual is explicit: if the officer has to convince himself the jerking is there, it is not. This is different from fatigue nystagmus, which only appears after 30 or more seconds at maximum deviation.
3
Onset of nystagmus prior to 45 degrees
The jerking begins before the eye reaches a 45-degree angle from center.
At 45 degrees, some white is usually still visible in the corner of the eye, which is how the angle is estimated. The officer must stop and confirm the jerking continues at that point.
Each clue is scored once per eye, for a maximum of six. Four or more classifies the subject at a BAC of 0.08 or above. HGN is reported as roughly 88% accurate, and the most reliable of the three tests, when administered correctly per NHTSA validation research.
A note on vertical nystagmus. After the three checks, officers also look for vertical gaze nystagmus by holding the stimulus at maximum elevation for at least four seconds. It is associated with high doses, but it is not one of the six scored HGN clues.

How we challenge HGN results

A field sobriety test is only valid when it is administered correctly, so the officer's performance is on trial too. We obtain any available video and the officer's report, then review, analyze, and time each step against the NHTSA standards. The officer graded you; we get to grade the officer.

The required medical checks (equal pupil size, resting nystagmus, equal tracking) are often skipped or rushed, and the health questions go unasked, which by NHTSA's own manual departs from the standardized protocol.
Many conditions unrelated to alcohol cause eye jerking, including neurological disorders, head injury, inner-ear disease, and certain medications.
The stimulus was positioned or moved incorrectly, too fast, too slow, or too far, rather than at the required distance and speed.
The stimulus was not held for the time the particular pass requires, such as the four-second hold at maximum deviation, which can create or hide a clue.
Flashing cruiser lights, strobes, and passing traffic can cause a different kind of nystagmus when the test is not done properly.

Walk-and-Turn

The walk-and-turn is a divided-attention test, not a simple walking test. It is built to split your attention between a physical task and a mental task at the same time, and the officer scores how you perform against a precise set of standardized instructions.

The manual divides it into two stages. Each stage has its own instructions, and a clue counts only when very specific conditions are met.

Phase 1Instruction stage

You balance heel-to-toe on the line while listening to and remembering the instructions.

  • "Place your left foot on the line."
  • "Place your right foot on the line ahead of the left foot, with the heel of the right foot against the toe of the left foot, and place your arms down at your side."
  • Officer demonstrates the stance.
  • "Keep this position until I tell you to begin."
  • "Do not start to walk until I tell you to do so."
  • "Do you understand the instructions so far?"
Phase 2Walking stage

You walk the line, turn, and walk back while counting out loud and watching your feet, dividing attention among balance, counting, and memory.

  • "Take nine heel-to-toe steps down the line, turn around, and take nine heel-to-toe steps back up the line."
  • Officer demonstrates three heel-to-toe steps.
  • "Keep the front foot on the line, and turn by taking a series of small steps with the other foot."
  • Officer demonstrates the turn.
  • "Watch your feet at all times."
  • "Count the steps out loud."
  • "Keep your arms at your side at all times."
  • "Once you start walking, do not stop until you have completed the test."
  • "Count your first step from the heel-to-toe position as number one."
  • "Do you understand the instructions so far?"
Scored Clues: Walk-and-Turn Eight total
2 of 8 clues = BAC 0.08+
Instruction stage
1
Cannot keep balance while listening to the instructions
The subject does not maintain the heel-to-toe position throughout the instructions.
Counts only if the feet actually break apart or step off the line. It does not count if the subject merely sways or raises the arms but keeps the heel-to-toe position.
2
Starts too soon
The subject begins walking before being told to start.
Walking stage
3
Stops while walking
The subject stops while walking.
Does not count if the subject is merely walking slowly.
4
Does not touch heel-to-toe
The subject leaves a space of one-half inch or more between the heel and toe on any step.
5
Steps off the line
The subject steps so that one foot is entirely off the line.
6
Uses arm(s) to balance
The subject raises one or both arms six or more inches from the sides to maintain balance.
7
Improper turn
The subject removes the front foot from the line while turning. It also counts if the subject spins or pivots, or loses balance during the turn.
8
Incorrect number of steps
The subject takes more or fewer than nine steps in either direction.
Two or more clues, or an inability to complete the test, classifies the subject at a BAC of 0.08 or above. Reported as roughly 79% accurate when administered correctly per NHTSA validation research.

How we challenge walk-and-turn results

On this test the score only means something if the officer satisfied every definition behind each clue, so we rebuild the stop from the video and the officer's notes and measure the conditions, the instructions, and every called clue against the NHTSA standards. A test graded loosely is a test that comes apart under a careful eye.

The walking area was not dry, hard, level, and non-slippery, or there was no room for nine heel-to-toe steps.
There was no actual line to follow.
The instruction-phase balance clue was marked for swaying or raised arms, although the manual records it only when the feet break apart or step off the line.
"Stops while walking" was charged for merely walking slowly, "does not touch heel-to-toe" without the half-inch gap, or "steps off the line" without a foot entirely off.
The demonstration was incomplete or skipped, or understanding was never confirmed.
Age, a back, leg, or inner-ear condition, or heels over two inches that were never removed made the test unreliable for reasons unrelated to alcohol.

One-Leg-Stand

The one-leg-stand is also a divided-attention test. It asks you to balance on one foot while counting out loud for about thirty seconds, splitting your attention between a physical task and a mental task.

Like the walk-and-turn, it has two stages, and the four clues are narrowly defined.

Phase 1Instruction stage

You stand with your feet together and arms at your sides while the officer explains and demonstrates the test.

  • "Stand with your feet together and your arms down at the sides, like this."
  • Officer demonstrates.
  • "Do not start to perform the test until I tell you to do so."
  • "Do you understand the instructions so far?"
Phase 2Balance and counting stage

You raise one foot and count out loud while the officer times thirty seconds.

  • "Raise either leg with the foot approximately six inches off the ground, keeping your foot parallel to the ground."
  • "Keep both legs straight and your arms at your side."
  • "While holding that position, count out loud in the following manner: one thousand one, one thousand two, one thousand three, and so on until told to stop."
  • "Keep your arms at your sides at all times and keep watching the raised foot."
  • "Do you understand?"
  • Officer times the full thirty seconds and discontinues the test at thirty seconds.
Scored Clues: One-Leg-Stand Four total
2 of 4 clues = BAC 0.08+
1
Sways while balancing
Side-to-side or back-and-forth motion of the body, or a swaying motion of the foot, while holding the position.
Slight tremors of the foot or body should not be interpreted as swaying.
2
Uses arm(s) to balance
The subject moves one or both arms six or more inches from the side of the body to keep balance.
3
Hopping
The subject keeps the foot off the ground but hops on the standing foot to maintain balance.
4
Puts the foot down
The subject cannot hold the position and puts the foot down one or more times during the thirty-second count.
Two or more clues, or an inability to complete the test, classifies the subject at a BAC of 0.08 or above. Reported as roughly 83% accurate when administered correctly per NHTSA validation research.

How we challenge one-leg-stand results

So much of this test rides on precise timing and narrow definitions that a small lapse by the officer changes the outcome, which is why we put the administration itself under the microscope, timing the count and comparing the video against what the manual requires. When the procedure drifts from the standard, the result loses its footing.

The officer did not time, or mistimed, the full thirty seconds the test requires.
A slight tremor of the foot or body was scored as swaying, though the manual says tremors are not swaying.
The foot-down clue was recorded when the foot never came down, or the arm clue without the six-inch movement.
The surface was uneven or unsafe, or the subject's safety was not considered.
The demonstration was improper or rushed, or understanding was never confirmed.
Being over 65, more than fifty pounds overweight, or having a back, leg, or inner-ear condition, or wearing heels over two inches, made balance difficult for reasons unrelated to alcohol.

Conclusion

These tests can look authoritative at the roadside, but each one is only as reliable as the officer's administration of it. As a general rule, it is reasonable to decline a request to take them.

An experienced OVI attorney will evaluate how the tests were performed, the instructions, the demonstrations, the conditions, the performance on the tests and the various research studies regarding the tests. At our firm, our attorneys have completed the same NHTSA Standardized Field Sobriety Testing and Advanced Roadside Impaired Driving Enforcement (ARIDE) course that the police receive, and we are certified to perform the tests ourselves.

What this means for your case

Because we know exactly how each test is supposed to be given, we can pinpoint the administration errors that undermine the results and, where the evidence warrants, move to keep them out of your case.

Ohio statutes referenced

  • R.C. 4511.19 – Operating a vehicle under the influence (OVI), including the field sobriety test admissibility standard in 4511.19(D)(4)(b)
  • R.C. 4511.191 – Implied consent and the administrative license suspension for refusing or failing a chemical test
  • R.C. 4511.192 – Arrest and the request to submit to a chemical test

Frequently Asked Questions: Field Sobriety Tests in Ohio

Do I have to take field sobriety tests in Ohio?
No. Field sobriety tests are voluntary in Ohio, and there is no license suspension or separate criminal charge for declining them. They are designed to gather evidence the prosecution can use against you, so as a general rule it is reasonable to politely decline. This is different from a chemical test of your breath, blood, or urine after an arrest, which is governed by Ohio's implied-consent law and can carry an administrative license suspension for refusal.
What are the three standardized field sobriety tests?
Only three roadside tests are standardized: the horizontal gaze nystagmus (HGN) test, the walk-and-turn test, and the one-leg-stand test. Other roadside tasks an officer may ask you to perform, such as reciting the alphabet, counting backwards, or a finger-count test, are not standardized and do not have validated accuracy. The standardized tests are scored by counting specific clues.
How accurate are field sobriety tests?
According to NHTSA validation research, when the tests are administered correctly, the horizontal gaze nystagmus test is about 88% accurate at 4 of 6 clues, the walk-and-turn is about 79% at 2 of 8 clues, and the one-leg-stand is about 83% at 2 of 4 clues for indicating a blood alcohol concentration at or above 0.08. Those figures assume proper administration. Medical conditions, footwear, road conditions, nerves, and officer error can all affect the results.
What happens if the officer administers the tests incorrectly?
The validated accuracy of the tests depends on the officer following the standardized procedures. In Ohio, the officer does not have to be perfect, but must substantially comply with the instructions in the current NHTSA manual for the results to be admissible. An experienced OVI attorney reviews the instructions given, the demonstrations, the conditions, and how the test was scored to challenge results that were not gathered properly.
Can a medical condition affect a field sobriety test?
Yes. Many conditions unrelated to alcohol can affect performance or mimic clues. Eye conditions, neurological issues, inner-ear and balance problems, injuries, age, and weight can all influence the results, and the horizontal gaze nystagmus test in particular can show clues for reasons other than alcohol. The officer is supposed to screen for some of these before testing, and a failure to do so can be a basis to challenge the results.
Should I refuse field sobriety tests if I have been drinking?
These tests are voluntary and exist to build evidence against you, so as a general rule it is reasonable to decline them politely. Declining the roadside tests is not the same as refusing a chemical test after arrest, which can carry an administrative license suspension under Ohio's implied-consent law. Every situation is different, so if you have been charged after an OVI stop, it is best to speak with an attorney about your specific facts.

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