Field Sobriety Testing

The U. S. Department of Transportation designated the National Highway Traffic Safety Administration (NHTSA) as the agency to evaluate and issue directives for the administration of field sobriety tests. Beginning with their first study issued in 1977 NHTSA has promoted the three-test battery of “standardized field sobriety tests” (SFSTs). The tests that received NHTSA’s approval are the horizontal gaze nystagmus test (HGN), the walk and turn (WAT), and the one leg stand (OLS). The government claims that only these three tests have been “validated” and “standardized” for DUI detection. Other tests you may have heard about, such as touching your finger to the tip of your nose or closing your eyes and estimating thirty seconds, were rejected during that original study back in 1977.

The objective of field sobriety tests is ostensibly to check for both mental and physical impairment simultaneously. However, the chief proponent of the tests concedes that the ability to drive safely cannot be determined by administering these tests at roadside. Even the NHTSA training manual concedes this point but asserts that the SFST’s are accurate at predicting blood alcohol concentration. During the initial contact with a driver, police officers are trained to engage in a divided attention exercise to determine if field sobriety tests are necessary. The field sobriety testing manual suggests asking for a driver’s license and insurance at the same time. This divided attention task requires the person to remember the second request (providing proof of insurance) while complying with the first (handing the officer the license). If an officer decides that a driver should be ordered to get out of his car for field sobriety tests, the three-test battery will usually be employed if the officer has received sufficient training.

Summary of the Three-Test Battery

Horizontal Gaze Nystagmus

The horizontal gaze nystagmus test is regarded by many of its proponents as the most sensitive of the three tests. While this test is not admissible in any state other than possibly Georgia as evidence of blood alcohol concentration and is not admissible for any purpose in jury trials in states as far flung as Pennsylvania, Kansas, and Mississippi, the Georgia Court of Appeals has said that HGN is relevant as evidence that a person’s BAC was .08 or higher when that individual is prosecuted only for being under the influence of alcohol to the extent that he was a less safe driver.

The NHTSA protocol requires an officer to observe eye movements, taking particular note of any of the three clues that may be observed in each eye. These three clues are the lack of smooth pursuit as the person follows a stimulus (usually the officer’s finger, a pen, or a penlight) horizontally across the field of vision, nystagmus at maximum deviation (when the eyes are deflected so far to the left and then the right that the “white of the eyes” disappears), and the onset of nystagmus before 45 degrees, for which the edge of the shoulder is used as an indicator. NHTSA continues to claim that their original research revealed that when a test subject had four or more clues, there was a 77% probability that the individual had a blood alcohol level of .10 or higher.

Walk and Turn Test

The second of the three NHTSA approved standardized field sobriety tests, the walk and turn, is a divided attention test. After asking some screening questions, the law enforcement officer will ask the driver to get into the starting position by placing his left foot on a line (usually imaginary) and then putting his right foot on the line with the heel of the right foot touching the toe of the left foot. The officer should also tell the person to keep his arms at his side and not to begin the test until the officer directs him to start. The officer should demonstrate this starting position as he instructs the motorist on how to stand. Once the person is in the starting position, the officer should ask him if he understands the directions up to that point. The officer will then tell the driver how to take nine steps up and nine steps back as well as how to turn, and he should demonstrate the proper technique. If the person understands all of the instructions, the officer will tell him to begin. He will be looking for up to eight clues- not maintaining the starting position (which officers frequently characterize as “losing balance”), beginning the test too early, stopping during the walking phase, walking off the line, raising one or both arms more than six inches from the side, missing heal to toe, making an improper turn, and taking the wrong number of steps. Even if repeated, a clue cannot be counted more than once. For example, if a person steps off the line on steps 3 and 7, that only counts as one clue. Nowadays, most officers are taught that there is a 68% chance that a person with two or more clues has a BAC of .08 or higher.

One Leg Stand

The other field sobriety test is the one leg stand, which is also a divided attention exercise that requires the test subject to understand verbal instructions and complete a physical task simultaneously. According to the student manual, the test should be conducted on a reasonably dry, hard, level, and non-slippery surface. There are four clues. If the officer notes two or more clues or an individual fails to complete the test, the original NHTSA report claims there is a 65% chance that the test subject has a BAC of .10 or higher. These days officers are trained that the number is .08 and will usually testify to that lower number if permitted to.

In this test the person should stand with his hands by his side and with his feet together until he begins the test. When the individual starts, he raises one leg approximately six inches off the ground. The person should then look at the raised foot (losing the horizon?) and, while keeping both legs straight and his hands by his side, count out loud “one thousand one, one thousand two, one thousand three” until the officer tells him to stop. This is a timed test, and the officer should keep track of the time for thirty seconds, at which time he should tell the subject to stop.

Once again, there are four possible clues. They include swaying back and forth, using the arms for balance, hopping (to maintain your balance), or putting the foot down before the expiration of thirty seconds, at which time the officer should direct the person to put his foot down.

What does Allen Trapp know about field sobriety tests?

Allen Trapp has completed the NHTSA curriculum and been certified in the administration of the Standardized Field Sobriety Tests since 2003. He is well known in DUI defense circles for his statistical analysis of the field validation studies, which was published in a national magazine for criminal defense attorneys. He has also delivered presentations on this subject at meetings in Texas, Wyoming, and Georgia. His review of NHTSA’s own data reveals that false positive rates are far higher than the government has been willing to admit and that many people will be arrested because a certain number of “clues” have been observed by the police, although those clues are caused by something (such as clumsiness) other than excessive alcohol consumption.