After pulling you over for possible impaired driving, authorities may perform field sobriety tests. These are tasks you have to complete to demonstrate skills required to operate a motor vehicle.
There are no rules requiring that law enforcement use particular field sobriety tests. Authorities can use any assessments on you they want. There are only three assessments that research has shown to be reliable in demonstrating driving impairment. Together, they comprise standardized field sobriety tests.
What are the three standardized field sobriety tests?
The three standardized field sobriety tests are the one-leg stand test, the walk-and-turn test and the horizontal gaze nystagmus test. The first two are fairly straightforward. The one-leg stand test requires you to stand on one foot with the other stretched out in front of you. You do this until the authorities say to stop. The walk-and-turn test requires you to take nine steps, heel to toe, in a straight line. Then you turn around and come back.
The horizontal gaze nystagmus test requires you to follow a moving object, such as a pen or a flashlight, with your eyes without moving your head. The law enforcement officer is looking for an involuntary eye twitch that becomes more pronounced when you are under the influence of alcohol.
How accurate are the standardized field sobriety tests?
SFSTs are more accurate when used in combination with one another than any individual assessment is by itself. Together, the three assessments are 90% accurate. Individually, however, the one-leg stand test is 65% accurate, the walk-and-turn test is 68% accurate and the horizontal gaze nystagmus test is 77% accurate.
While there is no rule preventing law enforcement from using non-standard sobriety tests when pulling you over, authorities may choose not to do so because the results may not be admissible in court.