Horizontal Gaze Nystagmus (HGN) Test
Horizontal Gaze Nystagmus (HGN) refers to an involuntary jerking of the eye which occurs as the person gazes towards the side and while following a stimulus. Police officers are instructed that this involuntary jerking becomes readily noticeable when a person is impaired. The police officer runs the individual through a series of exercises in which the officer looks for the eye to be jerking. The clues looked for are as follows: 1) as the eye moves from side to side, does it move smoothly or does it jerk noticeably?; 2) when the eye moves as far to the side as possible and is kept at that position for several seconds does it jerk distinctly?; 3) as the eye moves toward the side, does it start to jerk prior to a 45-degree angle? Each of these are checked on each eye for a total of 6 clues. 3 clues per eye. The police officers are taught that with 4 or more clues present, this test is 77% accurate in showing a suspect's blood alcohol concentration is above 0.10.
Walk and Turn (WAT) Test
The Walk and Turn (WAT) Test is divided into two parts: 1) The instruction stage; and 2) the Walking Stage. In the Instruction Stage, the suspect must stand with their feet in heel to toe position, left foot behind right foot, with their hands by their sides all while listening to the instructions. Two clues are possible in this position: 1) can't balance during instructions, and 2) starting two soon. The officer then instructs the suspect to take 9 heel-to-toe steps forward and nine heel to toe steps back. After the ninth step out, the person is to turn by keeping their front foot on the line and taking a series of small steps with the other foot. They then complete nine heel-to-toe steps back. During this whole time they are to watch their feet the whole time, keep their hands at your sides and count the steps out loud. There are 4 possible clues per step: 1) stepping off the line, 2) using arms for balance, 3) does not touch heel-to-toe, and 4) stops while walking. Continued.
Walk and Turn (WAT) Test Continued
There are two additional clues that the officers are looking for: 1) an improper turn, and 2) taking an incorrect number of steps. There are a total of 8 clues the officer is looking for. The police officers are taught that if the person demonstrates 2 or more clues on this test or fails to complete it, then there is a 68% accuracy in determining the suspect's blood alcohol content is above 0.10.
One Leg Stand (OLS) Test
During the One Leg Stand (OLS) Test, the officers instruct the suspect to stand with their feet together, hands by their sides, not to start until told, and ask if they understand so far. They are instructed to lift one leg (either leg) 6 inches off the ground keeping the foot parallel to the ground. Both legs are to be kept straight and arms kept by their sides. While holding this position, the person is to count "One thousand one, one thousand two, one thousand three..." until they are told to stop. The person is to keep their hands by their sides at all times and keep watching their foot. The Test is to be stopped after 30 seconds. The officer looks for 4 clues: 1) the suspect sways while balancing, 2) the suspect uses their arms for balance; 3) hopping, 4) the suspect puts their foot down. The officers are taught that if the suspect shows 2 or more clues or cannot complete the test then they can accurately determine the person's blood alcohol is above 0.10 65% of the time.
I intend to write additional guides outlining in more detail each of the specific tests. This guide is to provide general information about the exams so that you may know what "clues" the police officers are looking for in grading how you do on these exams. All of this information can be found in the Standardized Field Sobriety Testing manual. These tests will be used if one is prosecuted for Driving While Intoxicated (DWI). This guide is not intended to create an attorney/client relationship, is for informational purposes only, and will hopefully help you be better informed about this important aspect of Driving While Intoxicated (DWI) investigation and prosecution.