Horizontal gaze nystagmus, walk-and-turn and one-leg stand: how the standardized field sobriety tests work, what officers look for and the conditions that can skew results.
Few parts of a DUI stop are as familiar, or as misunderstood, as field sobriety tests. Many people picture reciting the alphabet backward or touching a finger to the nose. In practice, the tests most commonly described in DUI reports are three specific exercises standardized by the National Highway Traffic Safety Administration (NHTSA): horizontal gaze nystagmus, walk-and-turn and one-leg stand.
These tests were developed through research and are taught to officers through standardized training. Because they are standardized, the way they are administered and scored matters, and so do the conditions under which they are performed. This article explains each test in plain language and describes factors that can affect results. It is general educational information, not legal advice. Laws and procedures vary by state, and anyone with a specific situation should consult a licensed attorney.
What “standardized” means
A standardized field sobriety test is one with a defined set of instructions, a defined method of administration and a defined set of observable “clues” that officers are trained to look for. NHTSA training materials describe these procedures in detail. The idea is that when tests are administered consistently, results are more meaningful and comparable.
The flip side is that when tests are not administered as trained, or are given under poor conditions, the results may be less reliable. This is why reviewers pay close attention to instructions, demonstrations, surfaces, lighting and individual factors.
Test one: horizontal gaze nystagmus (HGN)
Nystagmus is an involuntary jerking of the eye. Horizontal gaze nystagmus refers to jerking that occurs as the eyes look to the side. Alcohol and certain other substances can make this jerking more pronounced or cause it to appear earlier as the eyes move.
How it is given: the officer holds a stimulus, such as a pen tip or fingertip, in front of the person’s face and moves it slowly from side to side while the person follows it with their eyes only, keeping the head still. The officer typically checks first for equal pupil size and equal tracking before looking for clues.
What officers look for: in each eye, training describes three clues: lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus before a certain angle. That makes six possible clues in total.
What can affect it:
- Certain medical and neurological conditions
- Some medications
- Eye conditions or injuries
- Flashing lights from patrol cars or passing traffic in the person’s view
- Wind, dust or fatigue
- Stimulus held at the wrong distance or moved at the wrong speed
HGN is difficult to verify from video because eye movements are rarely visible on camera. That means the officer’s administration and documentation carry extra weight.
Test two: walk-and-turn
The walk-and-turn is a “divided attention” test, meaning it requires a person to listen to and remember instructions while performing physical tasks.
How it is given: the person is asked to stand heel-to-toe on a real or imaginary line with arms at their sides while instructions are given, then take nine heel-to-toe steps along the line, turn in a prescribed way and take nine steps back, counting aloud and watching their feet.
What officers look for: training describes eight clues, including being unable to keep balance during instructions, starting too soon, stopping while walking, failing to touch heel to toe, stepping off the line, using arms for balance, making an improper turn and taking the wrong number of steps.
What can affect it:
- Uneven, sloped, wet, gravel or sandy surfaces
- Footwear such as heels, sandals or flip-flops
- Leg, back, hip or inner-ear problems
- Age and weight
- Cold, wind or rain
- Nervousness and confusion about instructions
- Poor lighting
Test three: one-leg stand
The one-leg stand is also a divided attention test.
How it is given: the person stands with feet together and arms at their sides, then raises one foot about six inches off the ground, keeps it parallel to the ground, looks at the raised foot and counts aloud in a prescribed way for about 30 seconds.
What officers look for: training describes four clues: swaying while balancing, using arms for balance, hopping and putting the foot down.
What can affect it: many of the same factors as the walk-and-turn, including surfaces, footwear, medical conditions, injuries, age, weight and weather.
Non-standardized tests
Officers sometimes use other tests: reciting the alphabet, counting backward, finger-to-nose, finger counting or the Romberg balance test. These are generally not part of the NHTSA standardized battery, and their reliability and weight may be argued differently in court.
Are field sobriety tests required?
In many states, roadside field sobriety tests are voluntary, and implied consent laws typically apply to chemical tests rather than field tests. However, laws differ, and refusing tests can have consequences or be described in reports. Anyone wanting to understand their rights in a specific state should speak to a local attorney. This article does not advise anyone whether to take or decline any test.
How results are documented
Officers usually record the clues observed on each test in their report or on a standardized form. Reviewers compare that documentation with video, if available, and with training standards. Questions often include:
- Were the instructions given completely and correctly?
- Was a demonstration given where training calls for one?
- Was the person asked about medical conditions, injuries or footwear?
- Was the surface reasonably level, dry and lit?
- Does the video match the documented clues?
- Was the officer trained and current on standardized field sobriety testing?
Why conditions on the coast matter
Coastal areas present particular conditions: sand blown onto pavement, sloped shoulders, wind off the ocean, humid nights and people wearing beach footwear. Busy tourist strips can have flashing lights and heavy traffic nearby. All of these can affect balance and concentration, and all can be relevant when results are reviewed.
A field sobriety test review checklist
- Which tests were given, standardized and non-standardized
- Instructions as documented and as recorded
- Surface, lighting, weather and traffic
- Footwear and clothing
- Medical conditions, injuries, age and weight
- Clues documented for each test
- Video comparison
- Officer training records
Common questions
Can a sober person fail field sobriety tests?
Performance can be affected by many factors other than impairment, including nerves, medical conditions and conditions at the scene. That is why administration and context are examined.
Do field sobriety tests measure blood alcohol content?
No. They are designed to help officers assess signs of impairment, not to measure a specific alcohol level.
Are field sobriety test results always admitted in court?
Admissibility depends on state law, court rulings and the circumstances of the case.
Instructions are part of the test
Because the walk-and-turn and one-leg stand are divided attention tests, the instructions themselves are part of what is being evaluated. A person who starts too soon, for example, may be scored with a clue. That makes the clarity and completeness of the instructions especially important. Were instructions given in a language the person understood well? Was there background noise? Was the person asked whether they understood? Did the officer demonstrate the test as training describes? Were the instructions interrupted by radio traffic or passing cars?
Body camera audio can often answer these questions more precisely than a report can. Reviewers sometimes compare the recorded instructions, word for word, with the standardized instructions described in training materials.
Officer training and updates
Officers are typically trained in standardized field sobriety testing through courses based on NHTSA curricula, and training materials have been revised over the years. Training records may show when an officer completed initial training and any refresher courses. In some cases, the training an officer received, and whether the tests were administered consistently with it, becomes a topic of examination.
Validation research and its limits
The standardized tests were developed and validated through research studies conducted under particular conditions. Courts and experts sometimes discuss how closely the conditions of a specific roadside stop match the conditions in that research, and what that means for how much weight results should receive. These are matters for attorneys and, where appropriate, expert witnesses, and the answers depend on the facts and on the law in each state.
Documenting conditions at the scene
Conditions change quickly. A road surface that was wet on the night of the stop may be dry the next day, and temporary lighting from businesses may change with the seasons. Photographs, video and notes made close to the time of the stop are the most reliable record of what the person was asked to perform on. Reviewers often note the slope of the surface, the presence of sand, gravel or debris, the nearest light sources and the flow of traffic.
Field tests in Myrtle Beach and Horry County cases
Many DUI stops on the Grand Strand happen on roads near the beach, in parking lots or on highway shoulders where sand, slopes and wind are common, and many drivers are visitors wearing sandals or flip-flops. Those facts may be worth examining in a particular case. Anyone charged with DUI in the area can consult Johnny Gardner, a Grand Strand DUI lawyer, about how field sobriety tests were administered in their case and what that may mean under South Carolina law. Only a lawyer reviewing the actual file can give advice.
This article is general educational information about legal processes, not legal advice. DUI laws and procedures vary and change. If you are facing a charge or a license suspension, speak with a licensed South Carolina attorney promptly.