Prosecutors often rely heavily on a defendant’s poor results on field sobriety tests to prove impairment in a case involving operating a vehicle under the influence (OVI). The field sobriety tests are supposed to evaluate whether the defendant was impaired. However, the results of the tests are often inaccurate, unreliable and inconclusive regarding the driver’s state of sobriety.
Standardized field sobriety tests include the:
The tests are administered on the roadway under a variety of conditions to people whose medical and personal histories are unknown to the officer.
The horizontal gaze nystagmus (HGN) test analyzes nystagmus, the involuntary jerking that occurs naturally when you rotate your eyes to the peripheral edges of the sockets. Under the influence of alcohol and certain drugs, nystagmus often becomes more exaggerated and happens at lesser angles. To conduct the HGN test, the officer slowly moves a pen or flashlight horizontally in front of your face and asks you to track the object with your eyes.
If the officer moves the object too fast or misjudges the angles of your eyes at the point that nystagmus occurs, the conclusions are flawed. In addition, a congenital birth condition, head injury or legal prescription, such as seizure drugs, may be responsible for pronounced nystagmus.
The walk-and-turn and one-leg stand tests are designed to assess divided attention — namely, that you can listen and follow directions while performing a physical task.
The walk-and-turn test involves taking nine heel-to-toe steps along a straight line, turning on one foot and returning in the same way in the opposite direction.
To perform the one-leg stand, you are told to stand while holding one foot about 6 inches off the ground and counting by thousands until the officer tells you to stop, after 30 seconds.
Uneven, sloping, rocky or icy terrain can put you off-kilter. Your footwear — such as high heels, flip-flops or uncomfortable shoes — can affect your ability to walk and balance. You may have medical issues — perhaps an inner ear infection, arthritis or a back injury — that make walking and standing difficult. Traffic noise may make it hard to hear the officer’s instructions, and the stress of standing on a busy highway or a dark, deserted back road may distract you from satisfactorily following directions.