Standardized Field Sobriety Tests

Posted by Craig Penrod | Oct 23, 2013 | 0 Comments

Standardized Field Sobriety Tests

One of the prosecution's major sources of evidence in a DUI case are the field sobriety tests (FST). Developed by police departments across the nation and standardized by the National Highway Traffic Safety Administration (NHTSA), the battery of field sobriety tests that are given in DUI stops by officers are the subject of legal attacks from defense attorneys around the globe.

Because of their subjective nature, coupled with the fact that they are administered by police officers in the field with little or no real training, along with their inherent bias towards believing everyone they stop is guilty, the field sobriety tests are the one part of the DUI investigation where you will do your case the most harm. Generally, an officer who has observed a traffic violation and then smells alcohol on your breath is not going to let you drive home and is simply using the FSTs to give himself a reason for arresting you.

There are two different types of field sobriety tests: standardized and non-standardized.  In this article we will discuss the methods and the meaning behind only the standardized field sobriety tests.

The standardized field sobriety tests have been evaluated by the US Department of Transportation's National Highway Traffic Safety Administration, or NHTSA, in a study conducted by the Southern California Research Institute in 1975.

The standardized tests that are available for the DUI officers to use are the Horizontal Gaze Nystagmus (HGN), the One Leg Stand (OLS), and the Walk and Turn (WAT) tests.


The Horizontal Gaze Nystagmus test, or HGN is perhaps the most scientifically relevant of the fsts, but also one of the easiest to mis-administer. 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 extreme 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.

When performing the test, the officer will generally hold a pen approximately 12-15 inches from the subject's face and slightly higher than eye level. The subject's eyes should be clearly visible and well lit for the officer. He should not however, position the subject so that the flashing lights from his patrol car are visible to the subject as this may cause nystagmus on its own.

The officer should have the subject remove his or her glasses.  Glasses and contacts do not allegedly affect the test results, but glasses may hinder the officer's observation of the eyes.

There are three parts of the test, or three things the officer is looking for:

  • Lack of Smooth Pursuit,
  • Nystagmus at Maximum Deviation, and
  • Onset Prior to 45 Degrees.

Lack of Smooth Pursuit - this is noted if the officer observes a jerkiness to the movement of the eye as it travels back and forth over a horizontal line.  Officers generally describe this to a jury as looking like a windshield wiper moving across a dry windshield.

Maximum Deviation - Nystagmus at maximum deviation occurs when the officer causes the subjects eye to follow his pen to the farthest angle possible.  The officer will allow the eye to rest in that position for at least four seconds and will note whether nystagmus is present in that position.  If nystagmus is present at maximum deviation, to the officer it will appear as if the eye rests for a moment and then begins a slight bouncing.

Onset Prior to 45 Degrees, or Angle of Onset - The officer moves the object at a speed that would take about four seconds for the object to reach the edge of the suspect's left shoulder. The officer notes this clue if the point or angle at which the eye begins to display nystagmus is before the object reaches 45 degrees from the center of the suspect's face. The officer then moves the object towards the suspect's right shoulder. For safety reasons, law enforcement officers usually use no apparatus to estimate the forty-five degree angle. Generally, 45 degrees from center is at the point where the object is in front of the tip of the subject's shoulder.

This test may result in up to six 'cues' of impairment.  You'll note the three possible examples of nystagmus listed above and they are checked in both eyes.

If an officer observes and testifies that he observed at least four of the above listed cues of impairment while administering the HGN test, he will follow his testimony with the supposition offered by NHTSA that this means there is approximately an 88 percent likelihood that the subject was at or above a .08 percent BAC at the time of the test.

As you can see the HGN test is one of the most powerful tools the prosecution has, aside from the blood, breath or urine test.  It will be offered as direct evidence of impairment, at or near the time of driving.

An experienced defense attorney will be able to attack the HGN test itself, the officer's qualifications to administer the test and the results offered at trial in order to discredit, and/or give the jury a reason to disbelieve the effectiveness of the test, minimizing its damage to the defense case.

One Leg Stand (OLS)

The One Leg Stand test is another of the Standardized Field Sobriety Tests established by NHTSA. The test itself is neither scientific nor complicated, but the officer must make sure that the subject understands the instructions.  He or she does so by both explaining the test and demonstrating it.

In performing the test the subject is instructed to stand with his feet together, hands at his sides.  He must raise one foot off the ground 6-8 inches, toe pointed and maintain that position while counting from 1001-1030.While the subject performs the test, the officer looks for four signs that indicate the person may be intoxicated:

  • 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.

The one-leg stand test must be performed on dry, hard, level land. If a person is wearing heels above two inches, he or she is allowed to remove them. The elderly, people with back, leg, or middle ear problems, and overweight people often have difficulty with this test when sober. It is, therefore, difficult to determine for certain if they have been drinking. In these instances, officers usually substantiate the one-leg stand test with the horizontal gaze nystagmus field test or a breathalyzer test.

Of course, the one leg stand test can be difficult even for a completely sober person to complete without mistakes.  And most defense attorneys will attempt to prove that to the jury and that this test is basically just designed to fail.

Yet this test is typically administered on the side of a road, often at night, when the distractions can be numerous. For example, the shoulder of the road might be uneven or covered in gravel; cars may be passing at a high rate of speed; the blue lights on the police officer's patrol car might be glaring in your eyes; etc. Additionally, people who are overweight, people over the age of 65 and people who have any kind of physical limitation may be unable to perform the one-leg stand test.

Of course, NHTSA contends that if you fail the OLS, there is a 65 percent likelihood that your BAC is above a .10 percent.

Walk and Turn (WAT)

The walk and turn test is the third and final field sobriety test that was standardized by NHTSA. In the walk-and-turn test, you are instructed to take nine steps in a heel-to-toe fashion in a straight line.  After the ninth step, you then must turn on one foot and return in the opposite direction in a heel-to-toe fashion.  While you are completing the walk-and-turn test, the police officer is making note of the presence of the following seven indicators of impairment:

(1) whether you are unable to maintain your balance while listening to the officer's instructions;

(2) whether you begin walking before the officer has completed the instructions;

(3) whether you stop while walking in order to regain your balance;

(4) whether you actually touch your feet heel-to-toe;

(5) whether you use your arms to maintain your balance;

(6) whether you lose your balance while turning; and

(7) whether you take an incorrect number of steps.

The presence of two or more of these indicators is evidence of impairment. That is to say, if you exhibit two or more of these indicators, your blood alcohol content (BAC) will, according to NHTSA, be over .10, at least with a 68 percent likelihood.

In many instances, if you have not been stopped in an area where the pavement is actually marked with a line, and since many officers do not carry tape to lay down a line for you to walk on, the test becomes even more subjective in that you are instructed to walk an IMAGINARY line.

As you can see, the standardized field sobriety tests, though relied upon heavily by the prosecution to prove that you are 'impaired,' are largely subjective and hinge mainly on the officer's ability to accurately reflect results, ideal conditions and the assumption that the officer will not bring his own prejudices into the testing procedure.  As such, they are a dangerous and misleading weapon in the hands of the state, but ones that can be deflected by a skillful defense attorney.

Keep in mind, that in Arizona these tests are strictly voluntary.  You are not required to submit to any of them, and a refusal carries with it no penalty, other than the officer's annoyance.  In fact, most attorneys would advise you to refuse to submit to any of the above tests, no matter how much you've had to drink.

If you are stopped and subsequently cited for a DUI anywhere in the Phoenix area, you will need the guidance on an experienced DUI defense attorney. If you find yourself at risk of being charged any kind of DUI, call The Law Offices of Craig W. Penrod, P.C. for a free consultation at (480) 753-5888 or visit our website at

About the Author

Craig Penrod

Craig W. Penrod was born and raised in Arizona and has practiced criminal defense for over 30 years. Mr. Penrod is a member of the State Bar of Arizona, Maricopa County Bar Association, State of Nevada Bar Association, American Bar Association, American Trial Lawyers Association, Arizona Trial Lawyers Association, Nevada Trial Lawyers Association, Arizona Attorneys for Criminal Justice and the National Association of Criminal Defense Lawyers.


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