In the one-leg stand, you raise one foot about six inches off the ground and count out loud while the officer times 30 seconds and watches for four specific behaviors. Two of the four are enough, under the National Highway Traffic Safety Administration's (NHTSA) training, for the officer to conclude you are likely over 0.08. This page describes the test as the 2023 NHTSA manual teaches it, including the groups the research says have difficulty. It is part of our Montana DUI Guide.
The Instructions You Should Hear
Like the walk-and-turn, the one-leg stand has an instruction stage and a performance stage. The officer is trained to say, with demonstrations:
- Stand with your feet together and your arms down at the sides.
- Do not start to perform the test until told to do so.
- The officer asks whether you understand so far.
- When told to start, raise either leg with the foot approximately six inches off the ground, keeping the foot parallel to the ground.
- Keep both legs straight and your arms at your side.
- While holding that position, count out loud: "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.
- The officer asks whether you understand, then tells you to begin.
The manual explains the design. Counting divides your attention between balancing and processing information, which is the point of a divided attention test.
The Four Scored Clues
| Clue | How the manual defines it | What does not count |
|---|---|---|
| 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 |
| Uses arms to balance | Moves one or both arms 6 or more inches from the side of the body | Smaller arm movements do not meet the definition |
| Hopping | Keeps one foot off the ground but resorts to hopping to maintain balance | |
| Puts foot down | Is not able to maintain the position and puts the foot down one or more times during the 30-second count | The officer is told to have the person pick the foot up and continue counting from where they left off |
Each behavior is one clue, and the maximum is four. The manual states that if a person shows two or more clues or cannot complete the test, "there is a good chance" the alcohol concentration is at or above 0.08, and that officers using that criterion will accurately classify 83% of the people they test. It cites a 1998 field study for that figure. The manual also reports that NHTSA's analysis of the original laboratory data found the one-leg stand, by itself, 65% accurate.
Notice what is not on the list. Miscounting, counting too fast or too slow, and looking away from the foot are not among the four clues the manual lists.
Why the 30 Seconds Matters
The manual calls the officer's timing "an important part" of the test. It explains that the original research showed many impaired subjects can stand on one leg for up to 25 seconds, but few can do so for 30. That is why the officer, not the subject, keeps time, and why the test is to be discontinued after 30 seconds.
In a case review, the video timestamp settles this. A test that ran well past 30 seconds asked for more than the protocol does, and a clue that appeared only in the extra time is open to question. A test cut off early did not measure the part of the interval the research considered most telling.
Who Has Difficulty With This Test
The manual does not create exemptions, but it is candid about the research. It says the original studies suggested that these groups "may have difficulty performing this test":
- Individuals over 65 years of age.
- People with back, leg, or inner ear problems.
- People who are overweight by 50 or more pounds.
It then adds two qualifications that cut in the driver's favor. Fewer than 1.5% of the test subjects in the original studies were over 65. And "there was no data containing the weight of the test subjects included in the final report." In other words, the original data on older and heavier people was limited.
The manual also says the original studies suggest that people wearing heels more than 2 inches high should be given the opportunity to remove their shoes.
Surface, Weather, and Safety
The stated test conditions are a reasonably dry, hard, level, and non-slippery surface, "whenever possible," with the subject's safety considered at all times. The original research recommended that if those conditions were not available, the person be asked to perform the test elsewhere or only the eye test be given. The manual then notes that field validation studies indicated varying environmental conditions did not affect performance, and that standardizing the test for every road condition is unrealistic.
Both halves of that passage get quoted in court. The prosecution points to the second. The defense points to the first, and to common sense about ice, slush, sloped shoulders, and wind. If a person cannot do the test, the officer is told to record the observed clues and "document the reason for not completing the test."
What to Tell the Officer, and What to Write Down
Officers are trained to ask whether you are sick or injured, under a doctor's care, or taking medication. If you have a condition that affects your balance, saying so at that point puts it on the recording.
Afterward, while it is fresh, write down the surface, the slope, the weather, your shoes, any injury or condition that affects your balance, and what you told the officer. Those details are what a lawyer compares against the report.
How the Test Is Used in Montana
The one-leg stand is evidence an officer may rely on for an arrest and later describe at trial. A report of a physical or psychomotor assessment is admissible if made by a person trained by the Department of Justice or with training it recognizes (MCA § 61-8-1018(1)(c)). The manual itself reminds officers that the standardized tests are "not a pass/fail test" and that their validation applies only when they are given in the prescribed, standardized manner.
For the eye test, see the HGN eye test. For exercises outside the standardized battery, see non-standard field tests. Our field sobriety tests page covers how the tests fit into a DUI defense, and challenging field sobriety tests explains how they are contested.
This page describes NHTSA's published training materials (2023 curriculum) and explains Montana law in general as of October 9, 2026. It is not legal advice about your specific case.