Why Field Sobriety Tests Can Be Inaccurate


Carefully walking in a straight line, reciting the alphabet backward: the various field sobriety tests police officers use to determine impairment are widely known, even if few people are aware of the scientific basis behind them. There are three field sobriety tests that the National Highway Traffic Safety Administration has standardized.

A field sobriety test is administered by a law enforcement officer in practically all DUI arrests, but how accurate are these tests? Why might a field sobriety test be inaccurate? The accuracy of a field sobriety test depends in large part on how carefully the arresting officer administers the test. It is crucial to your case to determine if the officer made any mistakes when administering a field sobriety test.


The first of the standardized tests is the horizontal gaze nystagmus (HGN TEST), colloquially known as the “eye test.” To administer this test, the officer will instruct the driver to look into a light and follow it as it moves. The officer will attempt to determine if there is a nystagmus (involuntary jerking motion) of the eyeballs; when a person looks sideways at an angle greater than 45 degrees, nystagmus is triggered. But in someone with high BAC, their eyes will twitch before reaching the 45-degree angle.

The eye test cannot be accurately administered to all individuals. Some people have a naturally occurring nystagmus, and certain head and eye conditions can also make the results of the test irrelevant. Therefore, it is generally checked as an indicator of possible impairment. Further tests are necessary to conclusively determine if a person is intoxicated or not.


The second standardized test is known as the “walk and turn” test. For this test, the officer will instruct the driver to take nine steps in a straight line, heel to toe, then perform an 180-degree turn and follow the same straight line back. The officer will then look for “clues” that indicate intoxication, which might include beginning to walk before instructed or taking normal strides instead of heel to toe steps. An intoxicated individual may also struggle to walk in a straight line or to turn without losing their balance. This test has not been validated as accurate for overweight or elderly people.


The final NHTSA test used to determine intoxication is the one leg stand. The driver must stand on one foot for thirty seconds with arms at their sides. As with the walk and turn test, this test has not been proved for overweight or elderly people.

Despite the many reasons that these tests may not be indicative of intoxication for all people, law enforcement officers require everyone to submit to them regardless.


Even just reading the descriptions of these tests, it is easy to see how they could be challenging for many people on the best day, much less in the highly stressful and confusing circumstances that they are usually administered in. Georgia DUI officers may also ask drivers to perform non-standardized tests such as saying the alphabet forwards and backward, counting backward from one hundred by sevens, or closing their eyes and trying to bring their index fingers to their nose. Although commonly administered and well known in pop culture, these tests have never been validated to indicate intoxication and do not have the scientific basis that the three NHTSA tests have.


Most patrol cars are equipped with a dashboard camera that can record the officer administering field sobriety tests on the driver. This video footage can be reviewed by expert DUI lawyers in Atlanta in order to identify whether or not the tests were administered properly.

If mistakes were made during the field sobriety test and the officer still used the test as grounds to make an arrest, they may be judged invalid by the court. The video might also reveal that a driver performed well on the tests and appeared to be behaving normally but was still charged with a DUI. This kind of video evidence can instrumental in a driver’s defense.


The standardized field sobriety tests recommended by the NHTSA must be performed according to the prescribed methods to produce valid results. Field sobriety tests have the potential be inaccurate due to something as simple as a person’s age, weight or existing medical conditions, but police officers often do not take these circumstances into account when administering the tests. An experienced DUI attorney in Cumming will be able to spot any mistakes during the test that may help you defend yourself against the state’s charges.