The pre-arrest screening consists of field sobriety evaluations and sometimes a preliminary roadside breath test to establish whether the impairment is alcohol or drug related. The number associated with the preliminary breath test is not admissible due to the unreliability of the portable machine. So, when the officer talks about the number, the only appropriate response is positive or negative for alcohol.

The National Highway Traffic Safety Administration (NHTSA) has put together the three most reliable evaluations for detecting alcohol impairment. These evaluations have been standardized to establish exact protocols for administering the evaluations and criteria for grading the performance on the evaluations. However, these tests still produce false positives which means that even sober people can fail these tests under ideal circumstances. The idea of reliability and false positives are addressed in NHTSA’s own studies so the officer will have to acknowledge that these are imperfect evaluations if they have any understanding of DUI law. In non-alcohol cases, these evaluations are even more unreliable or flat out do not work for some categories of drugs. To detect drug impairment, the officer must have advanced training, and the most reliable tests must be conducted in a controlled environment which means they occur after your arrest when you have been transported to the jail or precinct. Like all field sobriety evaluations, these tests are voluntary. The three standardized tests present in almost every case are the Horizontal Gaze Nystagmus (HGN), Walk and Turn (WAT), and One Leg Stand (OLS).


The HGN evaluation is the designed to detect nystagmus as the eyes gaze from side to side. Nystagmus is an involuntary jerking of the eyes. This evaluation is rarely captured from an angle that shows the eyes jerking. So, a simple defense to this evaluation is that the officer is both the administrator and the grader of the evaluation. First, the jury must believe that the officer conducted the evaluation properly. Then, the jury must believe that the officer honestly evaluated your performance on the HGN. This defense works best when the officer has already been caught in some inconsistencies that would hurt their credibility.

If you choose to dive into the specifics of the evaluation, then the first part of HGN is medical qualification. The officer must rule out any medical impairment and confirm that you are a good candidate for the evaluation. Medical conditions such as brain tumors, some inner ear diseases, head injuries or neurological disorders can make you a poor candidate to perform HGN and deem any results unreliable.

If you are medically qualified to perform HGN, then the officer will then begin checking for three different “clues” of impairment. The test is performed by having you track a stimulus with your eyes without moving your head. The stimulus is usually a pen or the officer’s finger which is held about 12-15 inches from your face and slightly above eye level. The first clue is a “lack of smooth pursuit” which means that instead of flowing smoothly from side to side, the eyes bounce like windshield wipers on a dry windshield. If present, the officer will mark one clue for each eye for a total of two possible clues for lack of smooth pursuit. The next clue is “distinct and sustained nystagmus at maximum deviation” where the eyes look to the far left or far right and hold their gaze on the fixed stimulus. Again, the officer is looking for one clue in each eye here. Finally, the officer checks for “onset of nystagmus prior to 45 degrees” where the stimulus is moved slowly, and the officer marks the first point at which the eyes begin to jerk. If the eyes begin to jerk prior to 45 degrees, then this is the final clue of impairment on the HGN evaluation. Of note, if one eye shows a particular clue, so will the other eye. Likewise, if one eye exhibits nystagmus as 30 degrees, so will the other eye. Therefore, be looking out for situations in which the officer stops the stimulus at your shoulder on one side but then goes several inches past your shoulder on the other side. This would be an indication that the officer did not see nystagmus prior to 45 degrees. Otherwise, they would have stopped at the same spot on each side. If the jury believes the officer and trusts the reliability of this evaluation, then four out of six clues mean you were impaired.


The second field sobriety evaluation is the Walk and Turn (WAT) evaluation. In this evaluation, you walk a straight line, turn around and walk back. Easy enough, right? Well, the physical performance is only part of the evaluation. This is a divided attention test which means that you are given a mental task and a physical task. The officer explains the evaluation and then demonstrates. During these instructions, you are supposed to stand with one foot in front of the other in a heel-to-toe position without breaking this position until the officer tells you to begin.

The evaluation should be performed on a smooth, level and dry surface. Most of the time these evaluations are done on the side of the road, so the surface is not ideal. Any incline, debris or other irregularities with the walking surface may undermine the reliability of the evaluation so they must be brought to the attention of the jury.

The evaluation really has two distinct parts, the instructional phase and the walking phase. In the instructional phase, there are two possible clues: starting too soon and losing balance. In the walking phase, there are six more possible clues: stopping while walking, not touching heel-to-toe, stepping off line, using arms to balance, an improper turn and incorrect number of steps. If you show at least two of the eight possible clues, then the officer will say you are impaired. It is important to explain what justifies each clue and how many opportunities there are to show each clue. When broken down into its separate parts, you can point out some commonsense problems with the evaluation such the fact that you can “fail” the test during the instructional phase alone, even if you perform the walking section perfectly. Another issue is that one misstep can show up to four clues even if every other step is perfect.


The third field sobriety evaluation is the One Leg Stand (OLS) evaluation. The OLS is also a divided attention test and should be performed on a smooth, level and dry surface. The officer will instruct you to stand with your feet together and hands down by your side until told to begin the evaluation. You are instructed to raise the leg of your choosing approximately six inches off the ground while counting out loud. The officer is looking for four clues: swaying while balancing, using arms to balance, hopping, and putting foot down. Unknown to you at the time, the officer is timing this evaluation for thirty seconds. If you put your foot down even one time, that is a clue. Oddly, if you put your foot down multiple times, it is still one clue. However, if you keep your foot up the whole time but raise your hands once and sway once, then you have shown two clues and are deemed impaired. These tests are imperfect, and these imperfections should be brought to the attention of the jury. Even more important, the jury must be told that these tests are known to produce false positives. When you are talking about proof beyond a reasonable doubt, tests that are prone to failure are not the best evidence to establish someone’s guilt.

For more information on DUI Field Sobriety Evaluations in Georgia, call or text (470) 728-1725 to speak with attorney Carl Chapman.

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