The Three Standard Field Sobriety Tests


The blue and red lights went on behind you, you pulled over, and the officer may have mentioned that you were speeding, made a wide turn, or perhaps were not staying in your lane. They asked for your driver’s license and other documents, while also inquiring if you had anything to drink, where you were going to, and where you were coming from. What you may not realize is that the police are asking things in such a way to initially gauge whether you may or may not be impaired. Officers are intentionally trying to see how you respond when your attention is divided between answering their questions, collecting specific items, and doing so promptly and without dropping them.

But this is usually only the beginning of these types of attention related tasks. When police are conducting an investigation to determine whether a driver is impaired or not, they will almost certainly request that the driver perform Standardized Field Sobriety Tests (FSTs), which were developed and “validated” more than thirty-five years ago by the National Highway Traffic Safety Administration (NHTSA). There are three tests that they studied all those years ago, Horizontal Gaze Nystagmus (HGN, the eye test), Walk and Turn, and One Leg Stand, and determined that a certain number of performance cues were correlated with alcohol impairment. Keep in mind: you do not have to agree to take these tests; there is no consequence for refusing the tests.

Both the Walk and Turn and One Leg Stand tests are “divided attention tests”; they are designed to examine whether an individual can sufficiently focus on two different things at once. Can you listen to the instructions that the officer has given to you and remember how to properly execute it? Can you perform a physical exercise (walking, maintaining a particular pose, and balancing) and simultaneously perform a mental exercise (counting up to a particular number)? When impaired by alcohol, studies have shown that the greater one’s impairment, the more and more difficult it will be for a person to divide his or her attention. However, there can be other explanations for poor performance on a test that have nothing to do with alcohol impairment. An individual’s physical aspects play into this along with more common factors such as physical exhaustion, stress and anxiety, and Attention Deficit Disorder.

Let’s look at each of these tests.

HGN: Nystagmus refers to an involuntary jerking of the eyeball in response to a stimulus. When a person’s central nervous system is affected by alcohol, other substance, or neurological condition, this involuntary jerking can be more distinct and easily visible. In this test, the subject is requested to follow a pen or a penlight (held about 12-15 inches away from the face and just slightly above eye level) with his eyes only, not moving his head. The officer will then look for “cues” of nystagmus, three cues in each of the subject’s eyes for a total of six cues. According to NHTSA publications and research, two types of cues in particular give evidence that alcohol is involved. If the officer observes Distinct and Sustained Nystagmus at Maximum Deviation, meaning that the jerking of the eye is observed when held all the way to either the right or left for more than four seconds, this is indicative that the nystagmus is caused by alcohol and not by some other source. Secondly, if the officer observes Onset of Nystagmus Prior to 45 Degrees, meaning that they observe the bouncing of the eye at the midway point between the person’s nose and the side of her head, NHTSA believes this is evidence that a person’s BAC is above a .08.

Although this examination is often considered the strongest evidence by officers and NHTSA, it is not foolproof! It is important to note that a number of these cues may be naturally occurring in some individuals and may occur in others because of a head injury, stroke, inner ear disorder, or even vitamin deficiencies. In other instances, the way that the officer holds and moves the stimulus could actually induce nystagmus. Further, most of the testing done for research purposes uses a featureless background (a blank wall, for example), but the vast majority of HGN tests are administered along a busy roadside outdoors because that is where traffic stops occur. Passing cars, flashing lights, bright sun, even birds flying through the air are commonly in a suspect’s field of vision while the officer is checking the eyes. These kinds of backgrounds featuring movement and distractions are called “optokinetic backgrounds,” and these can impact how the eye tracks the stimulus and may even result in “false positive” clues.

Walk and Turn: In this test, the subject must stand on a line with his feet in the heel-to-toe position with his arms at his sides. He must not start moving or taking steps until the officer instructs him to do so, nor should he alter how he stands while the officer gives him instructions. He must then take steps down a line in a prescribed manner, turn around in a very specific fashion, then take more steps back down the line until he has returned to his original position, all the while counting his steps aloud. In total, there are eight different behaviors that officers are looking for to decide whether a person’s performance is being impacted by alcohol. The NHTSA researchers determined that if a person demonstrated two or more problematic behaviors on this test, along with four or more cues on HGN, there was a strong correlation with having a BAC of .08 or greater 80% of the time.

One Leg Stand: In this test, the subject must stand with his heels together and arms at his sides. The subject must then stand on one foot and lift the other foot outwards approximately six inches off of the ground, keeping the raised leg straight, all the while counting aloud in the prescribed manner until the officer tells the him to stop. He must not raise his arms or use them for balance, nor should he let his foot drop to the ground or hop. In this test, there are four different behaviors that officers are looking for to decide whether a person’s performance is being affected by alcohol. The NHTSA researchers determined that if a person demonstrated two or more problematic behaviors on this test, along with four or more cues on HGN, there was a strong correlation with having a BAC of .08 or greater 65% of the time.

The Issues With Field Sobriety Tests


Although these tests have been researched by NHTSA, there are only certain persons who should be given the tests and only under certain circumstances, otherwise they lack scientific validity. In such circumstances, the guidelines have recommended that the tests should not be administered. One of the questions that often arises due to these two physical tests is whether the person asked to perform this test was a valid subject. NHTSA testing and research have found that people with injuries to their feet, legs, and back had difficulty performing the test even when completely sober. Persons over the age of 60 also had trouble with the test because of balance concerns due to aging and weakening muscle tone. The researchers also determined that these tests are difficult to perform if someone is wearing heels that are two inches or higher; they recommend that the person remove such shoes for these tests. The lighting of the area where the test occurred is another concern; it’s much more difficult for someone to walk perfectly on a straight line when it’s extremely dark. Additionally, if the area is not level or there is debris on the ground, the test will also be compromised.

From a practical standpoint, even if none of the above applies to you, these tests will be much more challenging for some people while sober versus being affected by alcohol. Are you an athlete or a trained dancer? On the other hand, would you describe yourself as uncoordinated or klutzy? Persons with excellent muscle memory, coordination, and those who are accustomed to regularly learning new physical movements will naturally be more adept at these tests. Similarly, as a general rule, the more one ages, the weaker their muscle tone and coordination becomes. Did you know that strength declines by 10-15% per decade of life up until the age of seventy, where it then accelerates to 25-40% loss per decade? Even though a fifty-five year old person would still be considered an “appropriate” candidate according to NHTSA, he will still have a much more difficult time performing these tests than would a twenty-five year old. Finally, have you been diagnosed with Attention Deficit Disorder or ADHD? These individuals face much greater challenges in listening to a variety of instructions and executing them, so these FSTs will, again, be much more difficult than for the average individual.

Another problem that often arises deals with the officer who is administering and evaluating the tests—has she been appropriately trained in how to give the instructions? Is she looking at the person’s behaviors in the way that NHTSA requires? Did she properly demonstrate the tests? Even though all officers receive instruction in these tests during their law enforcement training, that does not ensure that they can adequately explain and evaluate in a real life situation. There are advanced trainings and seminars that officers can attend in order to better understand these tests and DUI enforcement.

If the testing does not comply with the above referenced requirements, your DUI attorney will be able to dispute whether the officer should have given you the tests at all and also whether your performance can be used as evidence during trial.