One Leg Stand Test in North Carolina DWI Cases

The One Leg Stand, or “OLS,” is one of three “verified” Standardized Field Sobriety Tests (SFSTs) recognized by the National Highway Traffic Safety Administration (NHTSA), alongside the Horizontal Gaze Nystagmus and the Walk-and-Turn test. If pulled over on suspicion of impaired driving on the Outer Banks of North Carolina, there’s a reasonable chance the charging officer requested the suspect to submit to the One Leg Stand test.

The One-Leg Stand is a type of divided-attention test. The officer instructs a driver to stand on one leg, raise the other approximately six inches off the ground, keep the raised leg straight, point the toe of the raised foot, and count aloud until told to stop. Training materials direct the investigating officer to time the driver for 30 seconds. That sounds relatively straightforward. Like other field sobriety tests, however, the administration, interpretation, and reliability of the One Leg Stand can be far more complicated than the basic instructions suggest.

Whether the One Leg Stand is actually a reliable indicator of impairment depends on officer training, adherence to proper procedures and protocols, roadside conditions, and the individual being tested. SFST results are regularly used as evidence in DWI prosecutions. They support arrest decisions and the determination of probable cause to arrest. They get presented to judges and juries. In North Carolina, courts apply N.C.G.S. § 20-138.1 to evaluate impaired driving charges, and the use of OLS evidence in that process can make or break a case.

At a Glance | The One Leg Stand Test

Issue	Why It Matters
What OLS measures	Balance, coordination, and divided attention under standardized conditions
What officers look for	Up to four “clues” indicating possible impairment
Accuracy claims	NHTSA-sponsored research reports accuracy figures under specific conditions, but North Carolina courts may exclude those statistics as evidence
Physical limitations	Age, weight, physical fitness, prior injuries, and existing medical conditions can impact performance independent of impairment
Environmental factors	Road surface, weather, lighting, traffic, and footwear can all affect balance and test results
North Carolina law	OLS evidence may be admissible when offered by a properly trained officer, but the test’s administration, the underlying science, and alternative explanations can be challenged in court

1. What the One Leg Stand Actually Measures

The One-Leg Stand is a divided-attention test and is one of the three primary Standardized Field Sobriety Tests (SFSTs). The One Leg Stand DUI test involves maintaining balance while concentrating on a specific task, which requires cognitive and physical coordination. Alcohol and certain other substances can impair both balance and the mental focus necessary to perform the test.

What matters is what the test actually measures: balance and coordination at a specific moment. It is not a breathalyzer. It does not directly measure alcohol consumption. It measures physical performance.

A fair percentage of the general population cannot perform a perfect One Leg Stand test, even completely sober. In part, that’s because that particular SFST involves:

Static balance (standing on one leg)
Sustained attention (counting and maintaining focus)
Proprioception (awareness of body position)
Muscle control and coordination
The ability to perform the task while being observed, often in stressful circumstances

That combination is more demanding than many everyday tasks and, contrary to what is sometimes described, requires more dexterity than “walking up a flight of stairs” or basic balance. A sober person with poor balance, a sober person with prior leg or ankle injuries, a sober person who is more than 50 pounds overweight, or a sober person over a certain age will very likely have problems with and therefore perform poorly on a One Leg Stand test for reasons entirely unrelated to alcohol or drugs.

2. The One Leg Stand Test | Four Clues

According to NHTSA training protocols for standardized field sobriety tests, the officer should conduct a brief preliminary interview to assess whether the driver has any physical conditions that might affect performance.

Even after receiving information from the person suspected of impaired driving that there exist medical conditions that clearly will affect testing, officers regularly try to minimize the difficulty of SFST testing and further state, “Why don’t you just give it a try?” At best, that’s somewhat unfair. At worst, it’s downright misleading. When an officer ignores the voluntary disclosure of information in the screening aspect of the case, it calls into question whether they’re being fair.

Is the officer unbiased and fairly scoring performance? Is the officer purposely ignoring their training by asking someone to try a test when it’s obvious they’ll fail? And importantly, does that place the accused (and potentially an officer) in a position of danger, on the side of the roadway, and physically or medically unable to maintain balance?

The officer, per NHTSA training materials, is directed to demonstrate the test properly before asking the driver to perform it. During the One Leg Stand test, the officer looks for four clues:

Sway. The driver sways side to side or forward and backward while performing the test. Minor sway is normal; pronounced sway is what officers are trained to note.

Using arms for balance. The driver raises one or both arms away from the sides of the body (beyond a few inches) to maintain balance. This is typically one of the more obvious clues.

Hopping. Instead of standing on one leg, the driver hops up and down. Hopping indicates an inability to maintain static balance.

Putting the foot down. The driver places the raised foot back on the ground before the 30-second period is over. This can happen once or multiple times during the test.

Two or more clues is the threshold prosecutors typically rely on. What that means in your actual case depends on how the officer conducted the test, what the conditions were, and whether video evidence contradicts what the officer claims to have observed.

The procedure seems simple in training materials. In practice, numerous factors complicate execution:

The driver’s initial stance and foot placement matter
The exact distance the raised leg should be from the ground (approximately six inches) is subjective
The proper pace of counting and the examiner’s instructions can affect performance
The officer’s timing and the exact duration of the test matter
The road surface, asphalt, gravel, and sandy shoulders, can affect balance
Weather conditions, including wind, rain, and temperature
Lighting conditions, especially if the test is conducted at night
Footwear (high heels, flip-flops, or worn-out shoes) affects balance
Traffic nearby, including headlights, emergency lights, and passing vehicles
Whether the driver’s shoes were removed or kept on
The driver’s posture and position relative to the officer’s instructions

Clearly, the existence of potential problem areas is not an automatic “win” for the defense. They are details that DWI lawyers regularly review, sometimes in coordination with body camera footage, to assess whether the test was properly administered and whether the clues the officer observed were actually clues or misinterpretations of normal balance variations.

3. The Accuracy and Reliability Question

Officers and prosecutors frequently reference the 1998 San Diego NHTSA validation study when OLS evidence comes up. The study is cited as evidence that the test works, specifically that two or more clues reliably indicate a driver with a BAC above 0.08. That narrative appears in police reports, training materials, and, in some jurisdictions, courtroom testimony.

In North Carolina, however, testimony pertaining to the number of clues and an estimated BAC concentration generally hits a legal wall. The state is generally precluded from introducing evidence that a validation study shows a particular accuracy rate or that a certain number of clues correlate to a specific BAC level. Those statistics and probability statements are problematic at best.

What that means in practice is that the prosecution can call an officer to testify about the clues they observed during the One Leg Stand test. The officer can describe sway, arm use, hopping, or the driver putting a foot down. What the officer cannot do, and the prosecution should not attempt to do, is cite the validation study’s percentages or tell the jury that “research shows two clues means you’re above 0.08.”

The State still bears the burden of proving impairment beyond a reasonable doubt under N.C.G.S. § 20-138.1. The OLS may support an officer’s opinion that a driver was impaired, but it does so without the statistical scaffolding of validation research, thus bolstering the officer’s opinion testimony. The officer’s testimony stands on the specific facts of what they observed, how they were trained, whether they followed protocol, and how the clues presented themselves, not on general accuracy rates or probability statements.

That limitation actually matters for the defense. It narrows what the prosecution can use against the accused. It also means the officer’s credibility, training, and procedure become the central issues, not abstract validation study numbers.

When reviewing a DUI case that includes OLS evidence, defense lawyers typically consider:

Whether the officer had current NHTSA certification and training
If refresher training occurred within the past two years (as NHTSA recommends)
Whether the officer asked about physical conditions before administering the test
If the officer actually demonstrated the test before asking the driver to perform it
What exact instructions the officer gave and whether they were consistent with protocol
Whether the driver was permitted to adjust shoes or other clothing that might affect balance
The actual length of time the test ran and whether it matched the 30-second standard
How the officer characterized each clue and whether it was a genuine observation or a subjective interpretation
What the surrounding conditions were like (uneven ground, wind, lighting, traffic activity)
Whether video evidence exists showing what actually occurred

In court, what matters is whether the test was performed correctly, whether the officer understood what they were looking at, and how defensible their interpretation actually is.

4. Medical, Physical, and Environmental Causes of Poor One Leg Stand Performance

Impaired balance is not automatically impaired driving. Multiple medical and physical conditions can result in poor OLS performance in completely sober people. Environmental circumstances can similarly affect results independent of alcohol or drugs.

Age-related factors can significantly affect balance. Older drivers naturally have lower balance confidence and control. NHTSA’s own validation studies noted that the test is less reliable for drivers over 65.

Weight and physical fitness affect balance. A driver who is significantly overweight (more than 50 pounds), out of shape, or with preexisting balance problems may perform poorly, regardless of sobriety.

Prior injuries to the legs, ankles, feet, knees, or hips, even injuries that occurred years ago, can permanently affect balance and proprioception. A driver with a prior ankle sprain, a knee replacement, or a hip injury may struggle with the One Leg Stand test even when completely sober.

Neurological conditions can affect balance and coordination, including:

Inner ear disorders and vestibular dysfunction
Multiple sclerosis
Parkinson’s disease
Cerebellar ataxia
The effects of prior stroke
Neuropathy affecting the feet or legs

Medications can affect balance and coordination, including:

Antidepressants
Antianxiety medications
Pain medications (even prescription-strength ibuprofen in some cases)
Antihistamines
Blood pressure medications
Certain antibiotics

Fatigue and exhaustion can impair balance and concentration just as significantly as alcohol. A driver who has been driving for 12 hours, who did not sleep well the night before, or who is dealing with illness or infection may perform poorly on a balance test.

Environmental factors can directly affect the driver’s ability to maintain balance:

Uneven road surfaces (gravel shoulders, potholed asphalt, sandy areas)
Inclined or sloped terrain
Wind and weather conditions
Cold temperatures (which can affect muscle control)
Wet or icy conditions
Emergency vehicle lights, flashing strobe effects, or oncoming headlights (which can affect spatial orientation)
Traffic and the stress of performing under observation on the side of a busy highway

Footwear significantly affects balance:

High heels or boots can make balance more difficult
Flip-flops or open-toed shoes provide less stability
Worn-out or damaged shoes may not provide adequate support

Pregnancy can affect a driver’s center of gravity and balance.

Medical history and physical condition do not erase the clues the officer observed. But they can help explain them. An older driver with arthritis performs differently from a younger driver. A tired driver performs differently from a rested one. These are not excuses. They are facts that may be proper for consideration by the finder of fact, whether that be a judge or jury.

If you are charged with DWI, understanding the full context of how the test was conducted and what might have affected your performance matters. That is one reason retaining legal counsel early in the process and giving your attorney time to investigate is valuable. Drivers do not always remember or immediately report relevant medical history, medications, injuries, or conditions when stopped. An attorney has time to dig deeper.

5. One Leg Stand Evidence | North Carolina Court

OLS results are used in two ways in North Carolina DWI cases, including support probable cause for arrest, and as evidence of appreciable impairment at trial. The State’s burden is to prove impairment beyond a reasonable doubt. Field sobriety test clues are one piece of that burden, not the whole thing. Everything about how the test was conducted, why it was administered, and what the clues actually meant is potentially open to challenge.

North Carolina Rule of Evidence 702 governs the admissibility of expert and specialized opinion testimony. An officer offering an opinion about impairment based on field sobriety test clues may be subject to cross-examination regarding:

Their training and qualifications
The specific procedure they followed
Whether the test was administered according to NHTSA standards
Alternative explanations for the observed clues
Environmental conditions that may have affected the test
The driver’s physical condition or medical history
The reliability of the underlying test itself

An officer’s description of OLS clues generally carries weight in the courtroom. The judge or jury hears “sway” or “foot down” and assumes those are objective observations. Cross-examination is where that assumption may be tested. Was the officer trained to NHTSA standards? Did they demonstrate the test first? How did they measure or estimate six inches? What was the road surface like? Details can matter because OLS clues are subjective interpretations made in real time by a human observer, who themselves are subject to errors, biases, and mistakes.

A police report stating that a driver “exhibited two clues on the OLS” may look very different on video, where the road surface is clearly uneven, the driver is standing on a slope, emergency lights are flashing, or the officer’s timing was imprecise. Conversely, a test result that seems weak on paper may be supported by other evidence the defense has to take seriously.

The bottom line: One Leg Stand evidence is one piece of a DUI case. Like any SFST result, it deserves careful scrutiny, not blind acceptance or automatic dismissal.

A Final Word | One Leg Stand Test

The One Leg Stand can have real limitations and real value depending on how it’s administered and what you do with the results. Blanket dismissal of the test is as wrong as treating it as dispositive proof of impairment. The question of reliability does not have a one-word answer.

If you are facing a DWI charges on the Outer Banks, whether in Dare County or elsewhere in North Carolina, the One Leg Stand evidence is ordinarily one piece of the broader case. Like the HGN test and the Walk-and-Turn test, it can be challenged, questioned, and placed in context.

If you’re facing a DWI charge involving an OLS test on the Outer Banks or elsewhere in North Carolina, Glover Law Firm represents clients in Dare County, Hatteras, Manteo, Nags Head, Kill Devil Hills, Kitty Hawk, Duck, and surrounding communities. The field sobriety test is just one piece of your case. Contact OBX Lawyer Danny Glover to discuss how the OLS evidence affects your specific situation.