Standardized Field Sobriety Tests

On July 2, 1997, the BAC (blood alcohol content) limit for the state of Illinois was lowered to 0.08.  The National Highway Transportation Safety Administration (NHTSA) has developed three standardized field sobriety tests to assist officers in determining whether or not one suspected of DUI has a blood alcohol content in excess of .08 percent. The three Field Sobriety Tests (FST’s) are the Horizontal Gaze Nystagmus (HGN), the nine-step walk and turn, and the one leg stand. The nine-step walk-and-turn and the one-leg stand tests are considered “divided attention tests” because they test both a suspect’s coordination and the ability to remember and process information. Driving is a complex task that requires clear vision, focus, short-term memory ability, coordination, fine motor control, judgment, and decision-making. When a person is under the influence of alcohol, these abilities may be impaired.

SFSTa

1) Horizontal Gaze Nystagmus (HGN) Test

hgnHorizontal Gaze Nystagmus is a medical term describing the involuntary jerking of the eyes. An officer instructs a suspect to follow his or her pen, with only the eyes, as he or she moves the pen from side to side across the suspect’s field of vision. The officer instructs the suspect not to move his or her head, and to follow the pen only with the eyes. As the officer moves the pen from side to side, the officer watches the suspect’s eye movement. The officer observes whether or not the suspect’s eyes jerk involuntarily. According to the NHTSA, alcohol may cause this involuntary jerking.

There are three phases to the HGN test to detect this involuntary jerking of the eyes.

In the first phase of the HGN test, the officer will hold and move the pen 12-14 inches from the suspect’s face, from right to left. The officer observes the suspect’s eyes to determine whether or not the eyes move smoothly. If the suspect’s eyes do not move smoothly, the officer will record this as “Lack of Smooth Pursuit.”

In the second phase of the HGN test, the officer moves the pen to the far end of the suspect’s peripheral vision. Once a suspect’s eyes can move no further, the officer is to hold the pen in that position for at least four seconds. The officer then observes the suspect’s eyes to determine whether the suspect’s eyes remain still or jerk in a pronounced manner. If the officer observes a pronounced jerking motion, the officer will record this as “Distinct Nystagmus at Maximum Deviation.”

In the third phase of the HGN test, the officer moves his or her pen slowly from the center to the side of the suspect’s face. If the suspect’s eyes begin to jerk prior to the officer reaching a forty-five degree angle from the center, the officer will record this as “Onset of Nystagmus Prior to Forty-Five Degrees.”

2) Nine-Step Walk and Turn Test

The nine-step walk and turn test tests a suspect’s coordination and ability to comprehend and remember information. The first part of the test is instructional; the second is performance.

walk-the-lineThe officer first instructs the suspect to place his or her right foot in front of the left foot, touching heel-to-toe. The officer should instruct the suspect to remain in that position until receiving instruction to begin. The officer instructs the suspect how to perform the test, and observes to determine if the suspect is able to maintain his or her balance while receiving instructions. The officer will record if the suspect begins the test too soon.

While the suspect performs the test, the officer observes to determine whether or not the suspect follows instructions and whether or not the suspect is able to maintain his or her balance while walking a straight line. The officer will record if the suspect: misses heel-toe-while walking the straight line, fails to walk the straight line, uses his or her arms for balance, stops, takes the wrong number of steps, or turns in a manner other than what the officer directed.

3) One Leg Stand Test

one-leg-standThe one leg stand tests a suspect’s coordination and ability to comprehend instructions. The officer directs the suspect to raise whichever leg the suspect chooses, approximately six inches from the ground, with the toe pointed straight. The officer directs the suspect to hold the position, remaining balanced with arms down at the suspect’s sides. The officer directs the suspect to count, “one one-thousand,” “two one-thousand,” “three-one thousand” etc. & etc., usually to the count of thirty. The officer will record if the suspect hops, sways, uses his or her arms for balance, or places his or her foot down before the count of thirty.