Field Sobriety Tests

The Field Sobriety Tests offered by the police, or FST’s, are designed for you to fail. Most people can not perform these FST’s perfectly even when they are completely sober. The police are trained to notice the slightest things you do not “perform correctly” and they note it as evidence of intoxication. The three tests most commonly used are:

(1) the Horizontal Gaze Nystagmus test,
(2) the Walk and Turn test, and
(3) the One Legged Stand test.

According to the National Highway Traffic Safety Administration (NHTSA) these tests are only accurate in predicting BAC when:

  • The Tests Are Performed In The Prescribed, Standardized Manner
  • The Standardized Clues Are Used To Assess The Suspects Performance
  • The Standardized Criteria Are Employed To Interpret That Performance


  1. The Horizontal Gaze Nystagmus Test (HGN)Nystagmus is a natural, normal phenomenon involving the involuntary jerking of the eyes. Alcohol and certain other drugs do not cause nystagmus, but may exaggerate or magnify it. To conduct the test, the officer will hold a pen or a light 12-15 inches from your face and slowly movie it to the left and then right. The officer is checking to see if your eyes follow the item smoothly, at what point “nystagmus” occurs, and how “distinct” the nystagmus is.There are at least 38 possible ‘causes’ of nystagmus other than alcohol: problems with the inner ear labyrinth; irrigating the ears with warm or cold water; influenza; streptococcus infection; vertigo; measles; syphilis; arteriosclerosis; Korchaff’s syndrome; brain hemorrhage; epilepsy; hypertension; motion sickness; sunstroke; eye strain; eye muscle fatigue; glaucoma; changes in atmospheric pressure; consumption of excessive amounts of caffeine; excessive exposure to nicotine; aspirin; circadian rhythms; acute head trauma; chronic head trauma; some prescription drugs; tranquilizers; pain medication and anti-convulsant medication; barbiturates; disorders of the vestibular apparatus and brain stem; cerebellum dysfunction; heredity; diet; toxins; exposure to solvents; extreme chilling; eye muscle imbalance; lesions; continuous movement of the visual field past the eyes; and antihistamine use.

    Even when given perfectly, it is only 77% accurate in determining BAC over .10 and even less accurate in determining BAC over .08.

  2. The Walk and Turn TestThis test is even less accurate in determining BAC over .08 than the HGN test. The following are the NHTSA standardized clues which may indicate intoxication on the Walk-and-Turn Test:
    • Cannot keep balance while listening to instructions. Record this clue only if the suspect does not maintain the heel-to-toe position throughout the instructions. The feet must actually break apart. Don’t record this clue if the suspect merely sways or uses arm for balance.
    • Starts before instructions are finished. Record this clue if the suspect starts after being told not to start walking ‘until I tell you to begin’.
    • Stops while walking. The suspect pauses for several seconds. Do not record if the suspect is merely walking slowly.
    • Does not touch heel-to-toe. Record this clue if there is more than one-half inch of space between the heel and toe on any step.
    • Steps off the line. The suspect steps so that one foot is entirely off the line.
    • Uses arms to balance. The suspect raises one or both arms more than 6 inches from the sides in order to maintain balance.
    • Improper Turn. The suspect removes the front foot from the line while turning. Also record this clue if the suspect has not followed directions as demonstrated, i.e. spins or pivots around.
    • Incorrect Number of Steps. Record this clue if the suspects take more or fewer than nine steps in either direction.

    Two or more clues correctly classify 68% of the suspects as having a BAC of 0.10 or above.

    The Walk-and-Turn Test requires the test be performed on a line that the suspect can see, and should be performed on a dry, hard, level, non-slippery surface. If it is not performed on this type of surface, the results may be invalid. Research indicates persons with back, leg, middle ear problems, persons 50 pounds or greater overweight, and those over 65 years of age; have difficulty performing the test correctly.

  3. One Legged Stand TestOf the three tests, this is the least reliable in determining BAC content. When performing this test, the officer looks for the following clues:
    • The suspect sways while balancing. This refers to the side-to-side or back-and-forth motion while the suspect maintains the one-leg stand position.
    • Uses arms for balance. Suspect moves arms 6 or more inches from the side of the body to keep balance.
    • Hopping. Suspect is able to keep one foot off the ground, but resorts to hopping in order to maintain balance.
    • Puts foot down. The suspect is not able to maintain the one-leg stand position, putting the foot down one or more times during the 30-second count.”

    If the suspect scores two or more clues, research indicates that officers accurately classify 65% of the people tested. Again, these tests must be performed under strict conditions.

    Officers must remain relatively motionless and observe the suspect from a safe distance so as to not interfere.

    Again, the surface must be level, dry, and a non-slippery surface. Persons 65 years of age, 50 pounds or more overweight, and those with leg, back and middle ear problems will have difficulty performing the test. Adequate lighting is also required as in total darkness; the One-Leg Stand is difficult even for sober people.

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