Standardized Field Sobriety Tests

In the late 1970s and early 1980s the National Highway Safety Administration (NHTSA) noticed that a high percentage of fatal vehicle crashes involved alcohol impaired drivers. Studies were implemented to devise roadside DUI tests that officers could administer to determine whether a driver was under the influence of alcohol.

As a McHenry County DUI lawyer, I am familiar with the tests that these studies examined and their findings.

After conducting studies there were three tests considered validated for determining whether a driver may be alcohol impaired. The Horizontal Gaze Nystagmus Test (HGN), the Walk and Turn Test (WAT) and the One Leg Stand (OLS). A 24 hour program was developed to train police in administering these standardized tests. Each test must be administered in accordance with NHTSA standards. There are two phases to the test: The instructional phase where the police officer explains how the test is to be performed and performance of the test by the driver.

The tests are designed to test the driver’s balance and rely upon the concept of divided attention. In my opinion as a McHenry County DUI lawyer, the tests are designed for failure and obviously used to further the officer’s ability to establish probable cause that the driver is DUI.

Horizontal Gaze Nystagmus

The first test, and most reliable if administered properly (88% validation), is the HGN. Nystagmus is the involuntary jerking of the eyes which may be a clue that the driver is DUI. Alcohol and other drugs can cause HGN. It is noteworthy that there are probably 45 or so medical conditions that may cause nystagmus other than alcohol, such as developmental, stroke, neurological conditions, certain medications for epilepsy and even fatigue.

In general, the officer has the driver stand straight with feet together and has the driver follow a stimulus that may be a pen, light or finger. The stimulus is held about 12-15 inches away and slightly above eye level. The driver is instructed to follow the stimulus with only his eyes, keeping the head still. The officer first must conduct a medical assessment by determining whether the driver has equal pupil size and no resting nystagmus. Unequal pupil size may indicate a neurological condition and resting nystagmus may be a medical condition or indicate that the driver is on a Dissociative Anesthetic drug such as PCP which could raise an officer safety issue. The officer then checks for equal tracking of the eyes by moving the stimulus to the left and then the right two times; both eyes should track together or there could be a medical condition.

The actual test then begins and consists of four parts, always starting with the left eye and always conducted twice. First the officer moves the stimulus to the left and back and to the right and back twice. Here he is checking for smooth pursuit of the eyes. Second, the officer checks for nystagmus at maximum deviation by moving the stimulus all the way to the left and right until the white of the eye cannot be seen. He must hold the stimulus at maximum deviation for 4 seconds and there must be a distinct and sustained nystagmus. Third, the officer will check for the onset of nystagmus prior to 45 degrees; if found, the test is considered accurate for a BAC of .08. The sooner the onset of nystagmus, the higher the degree of impairment. Finally, the officer will perform a test for vertical nystagmus by raising the stimulus vertically above the driver’s head. If there is vertical nystagmus it is indicative of a very high BAC.

Walk and Turn

Here the officer has the driver take nine heal to toe steps along an actual or imagined line while counting each step, arms at side, looking at feet and then turn as directed and return nine steps counting each step. Once the driver is told to start, he must complete the test without stopping. The officer is looking for the driver to start before told to start, not complete the test, not walk heal to toe, take the wrong number of steps, use arms for balance, not properly turn to return and walk off line.

One Leg Stand

The driver is instructed to stand with feet together and when told raise either foot parallel to the ground, look at the foot, arms at sides and count 1001, 1002 to 1030 or told to stop. The officer is looking for the driver to put foot down, use arms for balance, sway and hop.

As a practical matter, if asked to exit the vehicle to perform the field sobriety tests, the officer has already made up his mind to arrest for DUI and is only further building a case for probable cause to arrest and for the prosecutor to establish DUI beyond a reasonable doubt.


Defense against the field sobriety tests administered requires evaluating each test as performed and recorded in the police report and on available video. Each test must be reviewed to determine whether the procedures were followed exactly as required by the NHTSA Manual. For example, the officer often fails to administer the HGN correctly by failing to perform an initial medical assessment and then by failing to conduct each test twice. Also, officers often fail to hold the stimulus at maximum deviation for the required four seconds. In addition, having the driver facing the flashing police lights and passing traffic can cause Optokinetic Nystagmus.

The ground upon which the WAT and OLS are performed may be a basis for arguing the test is unfair. If the ground is slanted or covered with debris anyone would have a difficult time performing the tests. Moreover, older drivers have been noted to have a more difficult time balancing on one foot and walking heal to toe.

In addition, a person may have medical conditions with their feet, ankles, knees, etc. that may be used to cast doubt on the test with the assistance of a DUI attorney in McHenry County, Chicago.