NHTSA (National Highway Traffic Safety Administration) over thirty years ago researched and determined that out of numerous filed sobriety tests used by law enforcement, the most reliable are the One Leg Stand Test, the Horizontal Gaze Nystagmus Test, and the Walk and Turn Tests.
Here, I will discuss One Leg Stand Test (OLS) and its reliability (or rather unreliability), during a DUI stop in Los Angeles.
NHTSA determined that 83% of people who exhibit two more “clues” during poor performance on One Leg Stand Test will have a blood alcohol content of .08% or higher.
First off, that means that 17% of people who fail this test are not under the influence. But more importantly, other factors that intoxication can affect performance during One Leg Stand Test. For example, investigating officer might not give complete or proper instructions. Despite being trained to do so, most officers do not give complete instructions or direction for this test.
The proper instructions involve the following:
(1) raising whichever foot you want;
(2) holding foot 6 inches from ground;
(3) keeping foot parallel to the ground;
(4) count out-loud one thousand one; one thousand two; one thousand three etc.;
(5) do not lower foot until instructed by the officer;
(6) keep the eyes on the raised foot.
The “clues” that investigating officer have to pay attention too are:
(1) hopping to keep balance,
(2) using hands to balance,
(4) putting foot down.
Two or more of such clues will fail the test. Notice that such things like slow counting or breaking the count is not a clue that NHTSA uses to determine intoxication.
But also, because our ability to balance depends on three separate sensory perceptions working together – removing two will affect balancing ability of of any individuals drunk or sober. By requiring individuals to stand on one foot while looking down – the test removes two of the three ways which we use to balance: observation of horizon and use of two legs. The remaining sensory perception from temporal bone in our ear is in effect tested by One Leg Stand. So, NHTSA in effect tests how we can balance using only temporal bone. The theory is that if it does not work, there is 83% chances that you are above .08% BAC. Clearly, despite some correlation between intoxication and ability to balance, other things can affect performance. For example: uneven surface, nervousness, weather. Professional DUI defense attorney in Los Angeles will help you point out the unreliability of this tests and prove that performance on this test is not evidence of intoxication.