DWI investigations: Officers can avoid field sobriety tests missteps with practice

Attention to timing, instructions and demonstrations help reveal intoxication clues during pre-arrest screening

This is the third article in a series that focuses on tips, techniques and methods front-line officers can use to improve their intoxicated driving interdiction abilities. Click here to read part one and click here to read part two.

Odds are that if you are reading this article, you are already somewhat proficient with intoxication investigations and techniques for pre-arrest screening. Therefore, I am not going to spend a great deal of time discussing standardized field sobriety tests (SFSTs) except for a few things.

You should be well versed in the administration of SFSTs, and if you aren’t, consult the National Highway Traffic Safety Administration (NHTSA) manual and commit it to memory.

With that said, I find a great number of officers face difficulty primarily in two areas of SFSTs: instruction and demonstration, and timing. We will start with timing, and what I mean by this is timing during horizontal gaze nystagmus (HGN) testing.

Officers typically tend to move way too quickly when checking for horizontal gaze nystagmus.
Officers typically tend to move way too quickly when checking for horizontal gaze nystagmus. (Getty Images)


Officers typically tend to move way too quickly when checking for HGN. The consensus on timing is that slower is better, and nobody expects you to be exactly spot-on. Moving the stimulus too quickly during HGN can cause false negatives because you are not granting yourself enough time to see nystagmus if it is present. Conversely, moving slower affords you more opportunity to see nystagmus if it is present.

When checking for lack of smooth pursuit, the stimulus should move from center to maximum deviation smoothly in two seconds. This is the easiest clue to spot, but for some reason, it is also one that officers blaze through most often. Lack of smooth pursuit should take no less than 16 seconds from start to finish.

When it comes to distinct and sustained nystagmus at maximum deviation, I find officers move the stimulus very quickly from center to maximum with a sudden stop. This causes the subject’s eye to track it quickly and the eye to “bounce” off the edge at maximum deviation. The eye may bounce a few more times as it tries to refocus on the stimulus. Inexperienced officers may mistake this for nystagmus.

Best practice is to move smoothly and avoid sudden, jerky movements or stops. Furthermore, officers tend to cut their timing short when checking for this clue, generally around the two- or three-second mark. Instead, try counting to “one-thousand five (or six)” in your head before moving the stimulus. Distinct and sustained nystagmus at maximum deviation should take about 20 seconds to complete.

Lastly, the onset of nystagmus prior to 45 degrees is the most difficult clue to spot and doing so requires excellent timing and a sharp eye. NHTSA says the stimulus should be smoothly moved from the center to 45 degrees in a minimum of four seconds.

That is not very far and for a lot longer time than you may think, roughly 11 degrees per second. This is one that simply takes practice to master but should also take about 20 seconds to complete. Remember to move slow enough to allow you to see any existing clues.


As far as instruction and demonstration is concerned, this mainly applies to the walk and turn test and, to a lesser degree, the one-leg stand. Giving the instructions and demonstrations is also something that takes considerable practice, but luckily NHTSA has provided us with a way to do it.

You should develop a method of delivering instructions and demonstrations and stick to it. When I do this, I give them in the exact same way with the exact same wording every single time. Doing so helps to mitigate error. I generally give the instructions first and then provide the demonstration, rather than doing both at the same time.

Something of note pertains to demonstrating the “turn” for walk and turn. Often, officers will demonstrate the first three steps, and then they will stop walking to instruct and demonstrate the turn. Do not do this!

Your demonstration should be as fluid as you expect the driver’s performance to be. If you stop walking prior to the turn and then they do it too, you cannot count that clue against them because they did the same thing you demonstrated. Avoiding this takes practice but can be done. Make sure to give the instructions completely and concisely.


After administering SFSTs, make the decision to arrest or not. If you feel unsure if the violator is intoxicated, but you are not OK with letting them drive away, then clearly you believe they are intoxicated, and an arrest needs to be made! Trust the tests and trust your instincts.

In the next article of the series, we will take a look at obtaining specimens and determining drug impairment in the post-arrest phase. Click here.

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