Field Sobriety Exercises

Law enforcement uses a set of standardized tests developed by the Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) to determine a DUI suspect’s level of impairment. They are called “Field Sobriety Exercises” or “FSEs”.

Most officers use three tests standardized NHTSA: Horizontal Gaze Nystagmus (HGN), Walk-and-Turn, and the One-Leg Stand.


Horizontal Gaze Nystagmus (HGN): Impaired people experience an involuntary eye jerking known as nystagmus. Officers try to detect, and even measure the level of, impairment with this exercise. After the suspect is given a series of instructions and agrees that he understands them the officer will hold an object such as a pen approximately 12 inches from the suspect’s nose and slowly moves the object from side-to-side as the suspect tries to follow the object by moving only his or her eyes. The officer looks for three clues in each eye: lack of smooth pursuit of the eyes; distinct and sustained nystagmus (involuntary jerking) at the eyes’ maximum deviation; and, nystagmus starting before the eyes reach 45 degrees away from the nose. and then holding an object, typically a pen, uses a test called the Horizontal Gaze Nystagmus (HGN) to determine if a suspect is impaired. The test starts by simple holding an object 12 to 15 inches from the driver’s nose. Next, the officer will slowly move the object side to side while the driver is told to keep eye contact with the object. If the officer notices the driver involuntary jerking their eye or has issues tracking the object, he or she may be determined to be impaired.

The NHTSA Guidelines prescribe both the instructions the officer should give the suspect as well as for what the officer should be looking:

Horizontal Gaze Nystagmus Instructions (HGN)

    • I am going to check your eyes. (Please remove your glasses)
    • Keep your head still and follow the stimulus with your eyes only.
    • Do not move your head.
    • Do you understand the instructions?

Horizontal Gaze Nystagmus Evaluation

There are six cues or clues that a police officer is looking for on the Horizontal Gaze Nystagmus Test, they are as follows:

    • Lack of smooth pursuit
    • Distinct and sustained nystagmus and maximum deviation
    • Onset of nystagmus prior to 45 degrees

Total Cues: 6 Cues – Decision Point: 4/6 Cues

If the officer observes four of the six cues (six due to their being three potential cues for each eye), it indicates possible impairment.

Walk-and-Turn: The second exercise that the police usually ask the suspect to perform is the Walk and Turn. This exercise measures the suspect’s ability to maintain his or her balance, walk in a straight line, and follow directions. To perform the exercise, the suspect takes nine heel-to-toe steps along a straight line during which time he or she must keep their arms to his or her side and count each step out loud. While the suspect performs this exercise, the officer tries to observe if the suspect fails to follow instructions, has difficulty keeping his or her balance, stops walking in order to regain his or her balance, takes an incorrect number of steps, or fails to walk the line heel-to-toe.

A suspect asked to perform the Walk-and-Turn, according to the NHTSA Guidelines, should be told the following:

Walk-and-Turn test instructions

    • Put your left foot on the line, then place your right foot on the line ahead of your left, with the heel of your right foot against the toe of your left foot.
    • Do not start until I tell you to do so.
    • Do you understand? (must receive affirmative response)
    • When I tell you to begin, take 9 heel-to-toe steps on the line (demonstrate) and take 9 heel-to-toe steps back down the line.
    • When you turn on the ninth step, keep your front foot on the line and turn taking several small steps with the other foot (demonstrate) and take 9 heel-to-toe steps back down the line.
    • Ensure you look at your feet, count each step out loud, keep your arms at your side, ensure you touch heel-to-toe and do not stop until you have completed the test.
    • Do you understand the instructions?
    • You may begin.
    • If the suspect does not understand some part of the instructions, only the part in which the suspect does not understand should be repeated

The Guidelines also instruct the officer on what to look for while observing the suspect perform the Walk-and-Turn:

Walk-and-Turn test evaluation
There are eight cues or clues that a police officer is looking for on the Walk & Turn Test; they are as follows:

    • Can’t keep balance during instructions
    • Starts too soon
    • Stops walking
    • Misses heel-to-toe
    • Steps off line
    • Uses arms for balance
    • Improper turn
    • Incorrect number of steps

Total cues: 8 cues – Decision point: 2/8 cues

This last part means, that if the officer observes two out of the eight listed cues – say starts to soon and improper turn – the suspect may be impaired.

One-Leg Stand: The final exercise a suspect is typically asked to perform is the One-Leg Stand, which requires the suspect to stand on one leg for 30 seconds. This exercise also measures balance and coordination, as well as the ability to follow instructions. The officer loks for four cues: swaying, using the arms for balance, hopping, putting down the foot.
A suspect asked to perform the One-Leg Stand will be instructed, pursuant to the NHTSA Guidelines, as follows:

One-Leg Stand test instructions

    • Stand with your feet together and your arms at your side (demonstrate).
    • Maintain position until told otherwise.
    • When I tell you to, I want you to raise one leg, either one, approximately 6 inches off the ground, foot pointed out, both legs straight and look at the elevated foot. Count out loud in the following manner: 1001, 1002, 1003, 1004 and so on until told to stop.
    • Do you understand the instructions?
    • You may begin the test.

Here is what the officer looks for:

One-Leg Stand Test evaluation
There are four cues or clues that a police officer is looking for on the One-Leg Stand Test; they are as follows:

    • Sways while balancing
    • Uses arms to balance
    • Hops
    • Puts foot down

Total cues: 4 cues – Decision point: 2/4 cues

If the officer observes the suspect do any of these four actions, it indicates possible impairment.