Field Sobriety Tests – You Do Not Want to Fail . . .

Field Sobriety Tests -Pass these and you probably won’t be arrested.

Field Sobriety Tests (FSTs)are how law enforcement determine if you should be brought in on suspicion of drunk driving. These tests are used to gather evidence against possibly impaired drivers and to send unimpaired drivers on there way. Generally speaking, if you get asked to take a field sobriety test the officers think you are driving while intoxicated.  These tests help them to better gauge how alcohol-impaired you might be and are used as evidence against you if you are arrested.

Field Sobriety Tests


Most lawyers will tell you not to take these tests. That you only have to take the breathalyzer test. Most lawyers, however, aren’t with you when you get pulled over. Also; most lawyers aren’t afraid of legal problems and most people are. They come along after the fact to tell you how badly you’ve screwed up.  Nevertheless, if you can remember what you’ve been told you might save yourself some problems.

The Standardized Field Sobriety Tests (FST)

The information below is excerpted from either the National Highway Traffic Safety Administration (NHTSA) or the DUI/DWI Foundation.

Horizontal Gaze Nystagmus is an involuntary jerking of the eye that occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as a pen or small flashlight, horizontally with his or her eyes. The examiner looks for three indicators of impairment in each eye: if the eye cannot follow a moving object smoothly, if jerking is distinct when the eye is at maximum deviation, and if the angle of onset of jerking is within 45 degrees of center. If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.08 or greater. NHTSA research found that this test allows proper classification of approximately 88 percent of suspects (Stuster and Burns, 1998). HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.

Problems for police:

Even though this field sobriety test has proved quite accurate and is widely used by law enforcement in assessing a person’s blood alcohol content, many lawyers still try to challenge its credibility in court. In fact, many states to not allow the test to be used as evidence against a person in a court of law.

One of the main complaints is that the officers who administer the test are not medically trained. Therefore, their ability to asses the angle at which nystagmus begins is often skewed. Consequently, law enforcement officials tend to use the test in conjunction with other field sobriety tests, breathalyzer tests, or urine or blood tests to build a stronger case against a driver.

FST – Horizontal Gaze Nystagmus Test

The Walk-and-Turn test and One-Leg Stand test are “divided attention” tests that are easily performed by most unimpaired people. They require a suspect to listen to and follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises.

In the Walk-and-Turn test, the subject is directed to take nine steps, heel-to-toe, along a straight line. After taking the steps, the suspect must turn on one foot and return in the same manner in the opposite direction. The examiner looks for eight indicators of impairment: if the suspect cannot keep balance while listening to the instructions, begins before the instructions are finished, stops while walking to regain balance, does not touch heel-to-toe, steps off the line, uses arms to balance, makes an improper turn, or takes an incorrect number of steps. NHTSA research indicates that 79 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.08 or greater (Stuster and Burns, 1998).

Indicators to police:

  • Inability to stay balanced while receiving instructions
  • Starting or stopping the test before indicated
  • Failure to touch heel-to-toe
  • Stepping off of the line
  • Using arms to balance
  • Improperly turning
  • Using the incorrect number of steps

FST – Walk and Turn Test

 In the One-Leg Stand test, the suspect is instructed to stand with one foot approximately six inches off the ground and count aloud by thousands (One thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for 30 seconds. The officer looks for four indicators of impairment, including swaying while balancing, using arms to balance, hopping to maintain balance, and putting the foot down. NHTSA research indicates that 83 percent of individuals who exhibit two or more such indicators in the performance of the test will have a BAC of 0.08 of greater (Stuster and Burns, 1998).

FST – One Leg Stand Test

FST – Combined Measures

When the component tests of the standardized field sobriety test battery are combined, officers are accurate in 91 percent of cases, overall, and in 94 percent of cases if explanations for some of the false positives are accepted (Stuster and Burns, 1998).

The original NHTSA research found different accuracies for the standardized field sobriety tests battery than reported in the more recent study. Tharp, Burns, and Moskowitz (1981) reported accuracies of 77 percent for the HGN, 68 percent for the Walk and Turn, and 65 percent for the One Leg Stand components; 81 percent of officers’ arrest decisions at 0.10 BAC were correct when all three measures were combined. In contrast, Stuster and Burns (1998) found greater accuracies in making arrest decisions on the basis of standardized field sobriety tests results in their study at 0.08 percent blood alcohol concentration, as described previously and summarized in the following table.

Indicators to police:

  • Swaying while balancing – Although it is natural for humans to sway slightly in order to keep their balance, the officer is trained to look for marked swaying, such as a back-and-forth movement.
  • Using the arms to keep balance – If the subject raises his or her arms more than six inches from the side of the body, then this is a sign that he or she is having significant difficulties maintaining balance.
  • Hopping on the anchor foot in order to maintain balance – It is permissible for a person to move the anchor back and forth slightly, but raising it off the ground is now allowed.
  • Resting the raised foot on the ground three or more times during the required thirty seconds – The person is considered unable to complete the test.

Except for my personal observations the information on field sobriety tests comes from the two following sources.
DUI/DWI Foundation

I was given permission to use the field sobriety  tests videos from the Michigan based Maze Law Group  so long ago I cannot remember who gave it to me.

Here is what one looks like out in the field.

See my post on drinking and driving facts
Stop Drinking Alcohol Naturally
Home: Am I An Alcoholic