Standardized Field Sobriety Tests (SFSTs), which were developed by the National Highway Traffic Safety Administration, are the tools used by law enforcement officers to determine whether a person is impaired.
Horizontal Gaze Nystagmus
The first SFST that is typically administered is the HGN test. This is the “eye exam” test. During this test, a law enforcement officer requires you to follow a stimulus with your eye, such as the end of a pen. The officer will be looking for nystagmus, which is the involuntary shuddering of the eye. The officer moves the pen horizontally, and attempts to measure the onset of nystagmus. Nystagmus is a physiological indicator of impairment, but can also indicate other medical problems. After testing for Horizontal Gaze Nystagmus, the officer usually tests for Vertical Gaze Nystagmus. In extreme cases of impairment, there is Vertical Gaze Nystagmus, which is the shuddering of the eye when it tracks in a vertical direction.
Walk and Turn
Another Standardized Field Sobriety Test that is typically used is the Walk and Turn test, which measures your ability to listen to and comprehend instructions, and your ability to perform when your attention is divided. The officer will instruct you, and you are to follow his or her instructions. Typically the officer will have you stand on a line, which can be real or imaginary, and have you take “heel-to-toe” steps, counting as you go. After taking the pre-arranged number of steps, the officer will ask you to stop, and take small steps to turn around, at which point you count off the same amount of steps back to your starting spot.
One Leg Stand
Finally, there is the One Leg Stand Test. This test involves you standing and lifting one leg while holding your arms down by your side. You are to look at your foot and count out loud “one thousand one, one thousand two, and so on,” until the officer asks you to stop. If you sway, your hands come up from your side, or your raised foot touches the ground, you show clues that you may be intoxicated.
These three tests are the only ones that have been certified by the National Highway Traffic Safety Association. However, officers occasionally use other tests to determine impairment. An officer may have you recite a portion of the alphabet. Rather than have you do the whole alphabet, the officer will most likely have you start on a certain letter, and stop on a certain letter. This tests you ability to say the alphabet, and your ability to remember which letter to stop on.
Another non-standardized test is the counting test. Like the alphabet test, the officer has you start on a certain number, and end on a certain number. He or she will have you count backwards from the highest number, to the smaller number. Again, the purpose is to see if you can handle the task of counting down, while remembering the number that you are counting down to.
Finally, a third non-standardized test is the Finger Counting Test. This involves you touching your thumb to your fingers and counting “1-2-3-4, 4-3-2-1,” or some variation of this. This tests your fine motor skills. Beyond testing your dexterity, it makes you remember to count, and to count the correct finger with the correct number.
After giving the field sobriety tests, the officer will likely ask you to submit to a Portable Breath Test (PBT). He or she should ask you to provide two samples for the PBT. If you have a positive test for alcohol, the officer will then arrest you.
Your performance on the Standardized Field Sobriety Tests, whether positive or negative, may have an effect in how strong your case is for DWI. In close cases, the video from your sobriety test, if there is video, can help prove that you were not impaired while driving.