Standardized Field Sobriety Tests

Standardized Field Sobriety Tests (often abbreviated as “SFST”) consists of three tests that are used to determine if a driver is under the influence of alcohol, drugs, or other substances which cause impairment, and thus establish probable cause for an arrest. 
 These tests are as follows:

1. HORIZONTAL GAZE NYSTAGMUS (HGN) TEST

The Horizontal Gaze Nystagmus test is a field sobriety test in which a police officer tests a driver’s eyes for evidence of “nystagmus” (or quick movement or jerking of the eye) to determine if the individual is impaired due to alcohol or drug use.

An officer will generally use a pen or some other
similar shaped object (such as a penlight or a finger) to conduct the HGN. 

 The officer will, after placing the object 12 – 15 inches from a suspect’s nose and slightly higher than eye level, move it from side to side.  An unimpaired person will be able to follow the movement of the object smoothly, while a person under the influence of drugs or alcohol will demonstrate a quick movement or jerking of the eye (known as a “nystagmus”) as the object moves from side to side.

There are three distinct things that the officer is looking for:

1) lack of smooth pursuit or motion;
2) distinct nystagmus at maximum deviation over a period of 4
secoonds (when the eye is looking at the farthest point, out towards the ear; and
3) angle of onset of nystagmus prior to 45 degrees (when the eye is looking at a point 45 degrees from center, or between ear and shoulder).

The test is repeated for both eyes.

There is some controversy over the reliability of HGN test.  Law enforcement firmly believes that the HGN test, if conducted properly, cannot be confused with any other type of nystagmus.  Defense lawyers, on the other hand, believe that nystagmus can also be caused by tiredness, eye strain, caffeine, nicotine, tranquilizers, pain medication, antihistamines, high blood pressure.  Nystagmus can also be caused by pathological disorders such as epilepsy, brain damage, brain tumors or inner ear diseases, but the prosecution contends that conditions display their own
unique  characteristics that are easily distinguishable from those of drugs or alcohol.  Finally, there are a very small number of people who exhibit a natural nystagmus.

2. NINE-STEP WALK AND TURN TEST

In this field sobriety test, the officer instructs the driver to take nine heel-to-toe steps in a straight line on a flat, hard surface, and then to turn around and walk back taking another nine heel-to-toe steps.  While performing this test, drivers are required to stay balanced without using their arms, must follow a straight line, must touch heel to toe, use the proper number of steps, or turn according to the officer’s instructions.

This test, when taken alone, is not always reliable.  People with middle ear problems or other problems maintaining their balance — the elderly, overweight individuals, or people with foot, leg, or back problems, for example — may not be able to pass this test.  However, this test is usually accompanied by other field sobriety tests or a breathalyzer test.

3. ONE LEG STAND TEST

This test requires a driver to stand on one leg with a foot approximately six inches off the ground while looking at your foot and with your arms at your side.  At the same time, you must count by thousands (one-thousand one, one thousand-two, one thousand-three, and so on).  If the driver hops, sways, or uses their arms for balance, this may be construed as evidence that they are under the influence of alcohol or illegal drugs.

Again, as with the Nine-Step Walk and Turn Test, there are many individuals who may not be able to successfully perform this test, so it is usually performed in conjunction with other SFST or a breathalyzer.

OTHER FIELD SOBRIETY TESTS

In the 1960’s and 70’s, the accuracy and reliability of several field sobriety tests — finger-to-nose, backward counting, and reverse-citation-of–the-alphabet tests — were successfully challenged.  As a consequence, most law enforcement agencies no longer employ these as field sobriety tests.

 

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