What Are Field Sobriety Tests?

Field sobriety tests are tests administered by law enforcement to determine if a driver is too impaired to drive. There are three standardized field sobriety tests. They are commonly known as SFSTs. These three—and only these three—have been validated for determining impairment due to alcohol. The three tests are Horizontal Gaze Nystagmus (the “eye test”), Walk and Turn, and One Leg Stand. If an officer attempts any test that is not one of those three, then they’re using something to evaluate impairment that has not been validated to determine impairment due to alcohol.

What’s the Horizontal Gaze Nystagmus Test?

Horizontal Gaze Nystagmus is conducted by a law enforcement officer who is looking for nystagmus in a person’s eyes. It’s commonly referred to as the HGN test. Nystagmus is the involuntary jerking of the eyes. It’s called horizontal gaze nystagmus because the officer attempts to determine if the eyes are jerking involuntarily horizontally. There are three clues that the officer will look for when administering the HGN test. These are lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmust prior to 45 degrees.

The officer must first evaluate the suspect for any medical conditions that could affect HGN. This involves asking the suspect if he or she has any head injuries or inner ear problems. The officer must check for equal pupil size and resting nystagmus. In addition to determining medical issues that cause nystagmus, unequal pupil size and resting nystagmus can also indicate that drugs could potentially be causing the nystagmus. Then, the officer is going to look for is equal tracking. The officer has to position a stimulus approximately 12”–15” in front of the suspect’s nose, slightly above eye level. A stimulus is typically the tip of the officer’s finger or a pen. The officer has to make one or two passes on each eye to see if both eyes are tracking the stimulus at the same rate. This test has to be performed by moving the stimulus from the center to the outside of the body at the rate of two seconds to reach the maximum distance.

The first HGN clue is lack of smooth pursuit. The officer must make two passes on each eye to see whether the eyes are following the stimulus smoothly. This test has to be performed by moving the stimulus from the center to the outside of the body at the rate of two seconds to reach the maximum distance.

The second HGN clue is distinct and sustained nystagmus at maximum deviation. The officer needs to position the stimulus to where there is no more white showing on the outside of the suspect’s eyes. The officer must hold the stimulus there for four seconds and determine whether there is any jerking at that maximum deviation point. The jerking must be both distinct and sustained.

The final HGN clue is the onset of nystagmus prior to 45 degrees. The officer moves the stimulus slowly from the center towards the outside of the suspect at a rate of four seconds to reach 45 degrees. Once the officer sees nystagmus, they must stop and hold the stimulus there to confirm that the eye is indeed jerking.

After completing all three tests, the officer totals the clues. There is a maximum of six possible clues, with three in each eye.

Somethig else an officer may do is check for vertical nystagmus. There are no points associated with vertical nystagmus; it is just to determine if there is any intoxication beyond the level detected by the first three HGN tests. The officer will move the stimulus vertically and hold it in position to determine if there is any involuntary vertical jerking of the eyes.

There is a blood alcohol content associated with the three HGN clues. If a suspect exhibits only lack of smooth pursuit, then they have a 0.04 blood alcohol content. A 0.08 BAC is associated with distinct and sustained nystagmus at maximum deviation, and a 0.10 blood alcohol content is associated with onset of nystagmus prior to 45 degrees. These tests are cumulative. This means that the onstet of nystagmus prior to 45 degrees can’t exist without both lack of smooth pursuit and distinct and sustained nystagmus at maximum deviation existing.

What Is The Walk And Turn Test?

The Walk and Turn is a divided attention test. This test has two phases. They are the instructional phase and the walking phase. Before the instructional phase, the officer must medically clear the individual. It is a fatal error in the administration of the test if the officer fails to do this. The officer must designate a line and tell the suspect to place their left foot on the line with their right foot in front of it touching heel to toe. The officer must demonstrate the stance. The suspect will then be told to maintain his position and not to start until told to do so. Finally, the officer is supposed to ask the suspect if they understand.

The suspect has to maintain his or her position while the officer demonstrates the walk-and-turn.The suspect must take nine heel-to-toe steps down the line, turn and take nine heel-to-toe steps back. The officer has to demonstrate three heel-to-toe steps and the turn. During the turn, the suspect must leave their front foot on the line and take a series of small steps. While walking, the suspect must watch their feet, keep their arms at their sides, count out loud, and not stop walking until they are told that the test is complete. At the end of all of the instructions, the officer must ask the suspect again if they understand.

There are eight clues of intoxication associated with the Walk and Turn. There are two in the instructional phase and six in the walking phase. The two in the instructional phase are inability to maintain balance and starting too soon. The six clues in the walking stage are as follows: stops while walking, does not touch heel to toe, steps off line, raises arms for balance, turns improperly or loses balance while turning, and takes the wrong number of steps. If a suspect takes a step that is more than half an inch away from the toe of the other foot, then that is considered a clue for the Walk and Turn.

The suspect may raise one or both arms to exhibit the “raises arms for balance” clue. The arm(s) must be raised more than 6” to qualify as a clue. The arms must be raised for balance. If somebody raises their arms to brush their hair out of their face or to scratch something, then that does not constitute raising arms for balance.

What Is The One Leg Stand Test?

Field Sobriety TestsThe One Leg Stand test is a divided attention test. This test has two phases. They are the instructional phase and the walking phase. The officer looks for four clues of intoxication. These are: puts foot down, raises arms for balance, sways, and hops. The officer has to first medically clear the suspect. During the instruction phase, the officer must tell the suspect to stand with their feet together and to place their arms at their sides. The officer must demonstrate this stance and tell the suspect not to start until instructed. At the end of the instruction phase, the officer must ask the suspect if they understand. While the suspect is in that position, the officer must tell them to begin only when they are told to do so and once they begin to raise one foot approximately six inches off the ground. The officer has to demonstrate raising one foot off the ground. The suspect may raise whichever foot they want.

The officer must tell the suspect to keep their raised foot parallel to the ground, keep both legs straight, keep both arms at their sides, look at the elevated foot, and count out loud in this manner: “One thousand one, one thousand two, one thousand three.” The suspect is to continue counting in that manner until told to stop. At the end, the officer must ask the suspect if he or she understands.

The suspect must raise both arms to exhibit the “raises arms for balance” clue. The arms must be raised more than 6” to qualify as a clue. The arms must be raised for balance. If somebody raises their arms to brush their hair out of their face or to scratch something, then that does not constitute raising arms for balance.

Source: NHTSA’s 2015 DWI Detection and Standardized Field Sobriety Testing student manual

For more information on the Field Sobriety Tests, call (405) 633-3420 to speak with an attorney.