Field sobriety tests

Table of Content

            Driving under the influence (DUI) is the act of operating and/or driving a motor vehicle under the influence of alcohol and/or drugs. In the United States, the National Highway Traffic Safety Administration (NHTSA) estimates that 17,013 people perished in 2003 due to alcohol related collisions, which represents 40 percent of total traffic deaths in the United States. More than 500,000 people were harmed due to alcohol related accidents in the U.S. in 2003.

            Given the blatant need to prevent DUI, an efficient program was formed to test a driver whether he is under the influence or otherwise. The Field Sobriety Test (FST) is a group of tests to verify if a driver is impaired. These tests assess balance, coordination, and the ability of the driver to multitask (Buddy, par. 1).

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            This paper deals with the use of Field Sobriety Tests as it is being applied to US traffic safety. It will describe the processes that drivers need to undergo if suspected of operating a vehicle under the influence of drugs and/or alcohol. The tests are mainly composed of standardized and non-standardized tests. The standardized tests are the following:

Horizontal gaze nystagmus test
One-leg stand
Walk and turn
However, the police officer may also opt to use non-standardized tests, these are the following:

Finger count
Standing with feet together and tipping the head backwards
Recitation of the alphabet or a portion of it
Counting backwards
Rhomberg stationary balance test
Finger to nose
Hand-pat test


In 1977, NHTSA commissioned the Southern California Research Institute (SCRA) to render the best methods of determining impaired motorists with the use of FST. This commission premised that better methods of detection would increase impaired driving arrest and conviction rates, therefore lowering impaired driving accidents. SCRI arrived with the conclusion that Horizontal Gaze Nystagmus (HGN) and alcohol consumption have a significant relationship. Moreover, the commission validated that HGN accompanied with Walk and Turn (WAT) and One Leg Stand (OLS), are the easiest tests to facilitate at roadside. It has also been proven to be the most accurate in determining impairment. SCRI standardized the administration of these tests in 1981. This made it certain for law enforcers throughout the country to administer a fast, easy, efficient, and uniform FST’s. HGN, WAT and OLS were combined to accurately determine a subject’s Blood Alcohol Content (BAC) during that time.

After the standardization of the FST’s, a third study was founded by NHSTA in 1983 to solidify findings.  With the use of the SCRI laboratory in 1981, the NHTSA research found out that WAT test was accurate sixty eight percent of the time. HGN was seventy seven percent precise in determining a subject’s BAC level of .10 or higher. Moreover, NHTSA learned that the combination of the two tests results eighty percent accuracy in detecting elevated BAC. Researchers predicted that OLS indicates impairment at sixty five percent accuracy during such time. NHTSA conducted a field study to confirm the validity of the tests’ capacity to differentiate a subject with .10 percent less BAC from a driver with BAC equal or higher than .10 percent. In conclusion, this field study determined that the HGN test was superior among the three tests regarding accuracy and effectiveness.

While the initial studies showed the significance of the HGN test, recent studies demonstrated increased accurate findings if it is facilitated by law enforcement officers trained and seasoned in administrating it. A study in 1986 justified this claim with an accuracy rate of ninety two percent. Another study during 1987 proved this finding to reach a ninety six percent accuracy in determining a .10 percent BAC or higher with the use of HGN test.

Finally, the outcome of these studies was the standardized field sobriety test battery (SFST). SFTS battery, especially the HGN test, aims to maximize the ability of law enforcement to: identify drivers with BAC’s in the .08 to .12 range that make up the bulk of the impaired subjects who do not necessarily exhibit exaggerated characteristics of impairment; and detect impairment in alcohol-tolerant subjects who may not display any gross coordination and balance problems.

The following will explain the context of Field Sobriety Test’s standardized measurements (horizontal gaze nystagmus, one-leg stand, walk and turn). It will also explain the procedures relative to the test.

Horizontal Gaze Nystagmus

            According to Burns, Nystagmus is an involuntary bouncing of the eyeball that occurs when there is a disturbance of the vestibular (inner ear) system or the oculomotor control of the eye. Moreover, the horizontal gaze nystagmus refers to a lateral or horizontal jerking when the eye gazes to the side (par. 1). In the context of impaired driving, alcohol consumption or consumption of other central nervous system depressants, inhalants or phencyclidine, creates a barrier that hinders the ability of the brain to control eye muscles, which causes the jerking. As the degree of impairment becomes greater, the nystagmus becomes more obvious. This is assesses by the horizontal nystagmus test.

            Alcohol causes two types of nystagmus, the alcohol gaze nystagmus and the positional alcohol nystagmus. As the term suggests, the former is a nystagmus caused by alcohol. It occurs as the eye moves from looking straight ahead, to the side, or up. Alcohol is a nervous system depressant affecting higher and lower control systems of the body. It causes incoordination, sluggish reflexes, and emotional stability. On the other hand, positional alcohol nystagmus (PAN) occurs when alcohol is the foreign fluid. The two types of PAN are PAN I (the alcohol concentration is higher in the blood than in the vestibular system fluid and occurs when a person’s blood alcohol content is increasing) and PAN II (the alcohol concentration is lower in the blood than in the vestibular system fluid and occurs when a person’s blood alcohol content is decreasing).

Administering the Horizontal Gaze Nystagmus

            The police officer administering the test must be able to see the driver’s eyes clearly. That is, in a well lit area or by using a flashlight to illuminate the subject’s face. The subject should not face toward blinking lights of passing cars. The subject can be tested standing or sitting down. As the police officer looks at the eyes of the subject, he must check for the physical manifestation of HGN. The officer should also ask the subject if the subject has any medical impairment, which may hinder effective testing. The subject needs to follow an object with his eyes. The head should remain still. Usually, the officer makes the subject hold his head by pressing on his cheeks or holding his chin. After settling with the subject’s position, the officer must check for medical impairment. The officer primarily checks for equal tracking. This is by moving an object rapidly across the subject’s field of vision. This is to check whether the eyes follow the object simultaneously or not. Equal pupil size also needs to be checked. Lack of equal tracking and/or equal pupil size may indicate blindness in one eye, a glass eye, a medical disorder or an injury. If the subject displays these symptoms, the police officer would need to discontinue the test and proceed to seeking medical attention.

            Given that the subject doesn’t need any medical attention, the officer should proceed with the test by looking for six clues of impairment—that is three for each eye. These clues are: Lack of smooth pursuit; distinct nystagmus at maximum deviation; and angle of onset of nystagmus prior to forty five degrees.

            The lack of smooth pursuit can be seen by moving an object slowly and steadily from the center of the subject face towards the left ear. If the left eye doesn’t smoothly follow the object (or if the eye shows nystagmus), the officer should note the clue. The same process should be done to the right eye.

            A distinct nystagmus at maximum deviation can be seen by starting again from the center of the subject’s face. The same process goes as with the former. But this time, it tests where the eye can go as far over as possible. The officer must hold the object on the farthest the eye can see.  The officer must hold the object for four seconds to ensure that quick movement doesn’t cause nystagmus. If a nystagmus is apparent while holding the object, the officer notes the clue.

            The angle of onset of nystagmus prior to forty five degrees can be seen if the officer moves an object, starting from the center of the face, to the subject’s left shoulder, at a speed of not more than four seconds. The officer notes the clue if the point or angle at which the eye begins to display nystagmus is before the object reaches forty-five degrees from the center of the suspect’s face. The same goes for the right eye, moving the object to the right shoulder.

            Aside from these three, the officer can also check for vertical nystagmus. The officer should check for vertical nystagmus by raising an object several inches above the subject’s eyes. Vertical nystagmus is not a clue for HGN but serves as a tool for indicating high doses of alcohol intake, nervous system depressants and drugs like phencyclidine.

One-Leg Stand Test

            In the one-leg stand test, the subject is instructed to stand in one foot that is approximately six inches off the ground. While standing, the subject must count by thousands (e.g. one thousand-one, one thousand-two, one thousand-three, etc.) until told to put the foot down. The process should be timed for 30 seconds. The one-leg stand test indicates several symptoms of DUI. That is, the following: swaying while balancing; using arms to balance; hopping to maintain balance; and putting the subject’s foot down. National Highway Traffic Safety Administration research indicates that 65 percent of individuals who exhibit two or more such indicators in the performance of the test will have a BAC of 0.10 or greater (par. 6).

Walk and Turn

            In this test, the subject is instructed to take nine steps on a straight line, and walking should be by heel to toe. After which, the suspect must turn on one foot and return in the same manner in the opposite direction. The officer should look for seven indicators of impairment. These are the following: subject cannot keep balance while listening to instructions; subject begins before instructions are finished; subject stops while walking to regain balance; subject’s feet does not touch heel-to-toe; subject uses arms to balance; subject loses balance while turning; and subject takes an incorrect number of steps. NHTSA research indicates that 68 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.10 or greater (par. 5).


The following will explain the context and procedures on non-standardized testing. It would include finger count, Rhomberg stationary balance test, finger to nose, and hand-pat test. Other tests like standing with feet together and tipping the head backwards, recitation of the alphabet or a portion of it, and counting backwards are self explanatory

Finger Count

The DUI finger count assists officers in proving the conditions of the following criteria: information processing; short-term memory; judgment and decision making; steady sure reactions; clear vision; small muscle control; and coordination of limbs.

The officer instructs a subject to put one hand in front of the face with the extended palm facing upward. The top of the thumb is then touched with the tip of the index, middle, ring, and little finger. The finger and thumb are separated after each touch. The subject then need count out loud in relation to each finger-thumb connection. This should be done in reverse on three complete sets.

Rhomberg Stationary Balance Test

            In this test, the officer just needs to instruct the subject to stand with feet together. The subject must also lean his head back to look up at the sky while holding the arms out to the side. The officer should look for an indication of loss of balance.

Finger to Nose Test

            The finger to nose test evaluates upper-limb coordination. In this test, the subject is instructed to touch the officer’s forefinger at full extension. While the subject’s eyes are open, the officer moves his finger to alternate positions. The subject should repeat the process of touching his nose and then the officer’s finger as fast as possible. The officer should fix his forefinger at one location while the patient repeats the process. It should be done both with eyes open and with eyes closed, as fast as possible.

Hand Pat Test

            In the Hand Pat Test, the officer would need to instruct the subject to place one hand extended, palm up, out in front of him. The other hand is placed on top of the first, with the palm facing down. The top hand should then begin to pat the bottom hand. The top hand rotates 180 degrees alternating between the back of the hand and the palm of the hand. The bottom hand should remain fixed to its position. The officer should instruct the subject to count out loud (one-two,one-two) for each pat.

The FST’s and the Law

            The effectiveness of FST in court testimonials and evidentiary support depends on the cumulative total of impairment indicators provided by these tests. The greater number of indicators, the more convincing the testimony. The FST is administered according to national standards and is supported by significant research, it has greater credibility than mere subjective testimony.


United States. Department of Transportation. Traffic Safety Facts 2004. DC: NCSA, 2004

Humphrey Belton, Lateral Nystagmus: A Specific Diagnostic Sign of Ethyl Alcohol Intoxication, 100 N.Z. Med. J. 534, 535 (Aug. 1987).

Gunnar Aschan, Different Types of Alcohol Nystagmus, 140 Acta Oto-laryngol 69, 76 (Sweden 1958); Goldberg, supra note 10, at 128.

Buddy T., Alcoholism and Substance Abuse.


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Field sobriety tests. (2016, Dec 09). Retrieved from

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