Field Sobriety Tests


Criminal Defense

Field Sobriety Tests and Preliminary Breath Testing

You’ve been pulled over by the police and now you’re being asked to submit to some tests to make sure you’re alright to drive.  In this article, we’ll talk about what you can expect to happen next and some of the decisions you’ll have to make.

The tests the officer is offering you are referred to as Field Sobriety Tests, or “FSTs.”  If you’ve ever witnessed a DUI stop in real life or on TV, these are the tests that include following a stimulus with your eyes, walking a line, and holding your balance while standing on one leg.

Before we get too far into the tests, it’s important to understand why these tests are used and what credibility they have in the criminal justice system.  Back in 1975, the National Highway Traffic Safety Administration (“NHTSA”) funded research to create procedures for determining impaired drivers.  This research resulted in the creation of the standardized field tests that you will be subjected to if you agree to take part in the testing.  These tests are “standardized,” meaning that there is a universal method of giving the tests to a suspected impaired driver, as well as a universal method of scoring the results.  Any deviations from those standardized procedures are grounds for an attorney to challenge the validity of the results.

Three Types of Field Sobriety Tests

The three tests are the Horizontal Gaze Nystagmus (“HGN”), the Walk and Turn, and the One-leg Stand test.  In theory, these tests are somewhat accurate in determining whether a driver is impaired, although as you’ll soon see it’s not an exact science, not even close really.

The HGN is the test where the officer holds a stimulus in front of your face, usually a pen or his finger, and asks you to follow the stimulus with your eyes without moving your head.  Nystagmus is the involuntary jerking of your eyes, which can be an indicator of intoxication.  Although the officer will not usually mention the three subset tests, called “clues,” that he will be giving you, there are at least three “clues” that test your ability to track the stimulus.

The first HGN clue is called The Lack of Smooth Pursuit.  Quite simply, the officer is taught that as your eyes go from side-to-side, they should move like marbles rolling across glass.  If your eyes skip or stutter as they move, the officer will note this as a clue in his report.  Think of it as a strike against you.

The second HGN clue is called Distinct and Sustained Nystagmus at Maximum Deviation.  In this test, the officer will have you follow the stimulus until your eye is all the way to one side, otherwise known as maximum deviation.  He will hold the stimulus there for a required amount of time and will check for nystagmus.  If he says it’s there, it’s counted against you as a clue.

The third HGN clue is called Onset of Nystagmus Prior to 45 Degrees.  In this test, the officer will slowly move the stimulus horizontally to a maximum of 45 degrees from your nose.  If he observes nystagmus prior to 45 degrees, it will be counted against you as a clue.

How Are Field Sobriety Tests Scored?

Here’s how the scoring works:  for each test, you can have a maximum of one clue per eye.  In other words, for the first test, The Lack of Smooth Pursuit, if the officer observes nystagmus during that phase of the test in both eyes, he would mark down two clues for that test.  The same is true for the Distinct and Sustained Nystagmus at Maximum Deviation test, you can be scored a total of two clues, and the same is true of the third test, Onset of Nystagmus Prior to 45 Degrees.  So, there’s a total of three field sobriety tests, with two potential clues per test, which means if you fail every test in both eyes, the maximum score is six clues.

This might surprise you, but it is unusual, at least in my experience, to review a DUI arrest report where the defendant allegedly scored anything less than six clues n their field sobriety test.  To provide some context for this strange phenomenon, keep in mind the following. Even if the defendant is recorded on the dash-cam performing the HGN, 1) the video quality is too poor to be able to see the movement of the suspect’s pupils, and 2) the officers are actually trained to have the defendant look away from the dash-camera, due to the possibility of “optokinetic nystagmus,” which is naturally occurring nystagmus as a result of viewing objects that move suddenly or show rapid contrast changes, like the strobe lights on a police car, or the approaching headlights of cars.  So, you’ll never have video evidence to refute the results of the HGN test.  At this point, it’s the officer’s word against yours.  If you exhibit even just four of the six possible clues, according to NHTSA’s research in the 70’s, there is an 88% chance that your BAC is above .08.

What is the Most Difficult Test to Pass?

The second test, the Walk and Turn, is the most difficult to perform.  As a criminal defense attorney, this test is the one that I find exceptionally difficult for even sober people to perform, and I’m happy to tell you why.

The first part is called the Instruction Phase.  The officer will instruct you to assume a certain position and hold it throughout the rest of his explanation and demonstration.  Many people, sober or not, at some point, will take a more comfortable position as the officer’s instruction goes on and on.  I think it’s fairly normal, but the officer doesn’t have to announce to you that if you move your feet whatsoever while he’s giving the demonstration that you’ll have a clue counted against you.

Here are the directions from the NHTSA instructor guide:

  • Place your left foot on the line (real or imaginary).

  • Place your right foot on the line ahead of the left foot, with the heel of your right foot against the toe of the left foot.

  • Place your arms down at your sides.

  • Maintain this position until I have completed the instructions.

  • Do not start to walk until told to do so.

  • Do you understand the instructions so far? (Make sure subject indicates understanding.)

  • When I tell you to start, take nine heel to toe steps on the line, turn, and take nine heel to toe steps down the line.

  • When you turn, keep the front (lead) foot on the line, and turn by taking a series of small steps with the other foot, like this.

  • While you are walking, keep your arms at your sides, watch your feet at all times, and

  • count your steps out loud.

  • Once you start walking, don’t stop until you have completed the test.

  • Do you understand the instructions? (Make sure subject understands.)

  • Instruct the person to begin the test.

At the beginning of the second phase, called the Walking Phase, the officer will tell you to start, and now you have to get everything right the first time.  Make any mistakes and they’ll be interpreted as indications (clues) of intoxication against you.

Here are the ways you will have clues counted against you per the NHTSA standard:

  • Cannot keep balance while listening to the instructions.  If you move your feet from the heel to toe starting position, regardless of whether you’re trying to get a better view of the officer’s demonstration, or if you just naturally move your feet apart while listening and watching the officer, that’s a clue against you.

  • Starts too soon.  Even if you acknowledge that you understand the officer’s explanation and do not have any questions, if you start performing the test before the officer actually tells you to start, that’s a clue against you.

  • Does not touch heel to toe.  If you leave more than one half of an inch between the heel and toe on any step, that will count as a clue against you.

  • Steps off the line.  Keep in mind, 99 out of 100 times there is not a “line” for you to follow, the officer will simply instruct you to imagine a line in front of you.  I’ve never understood how the officer is able to see the line you are imagining, but you better believe they will testify in court that you stepped off of your imaginary line…

  • Uses arms to balance.  If you raise an arm more than six inches from your side, that’s a clue against you.

  • Improper turn. Any deviation from the exact procedure for turning will be marked as a clue against you.  Keep in mind that this is probably the most cumbersome procedure they could have created, so much so, that I’ve had cases where the police officer explained and/or demonstrated the turning portion incorrectly.  I’ve had clients that practically did a perfect pirouette and they were assessed a clue for not turning correctly.

  • Incorrect number of steps.  It’s easier than you might think to get confused as to whether your ninth step should be the one you start to turn on, the one before the turn, etc.  Also, at times the person will finish the test and take another step or two with their arms up in the air in an effort to show the officer that it was no big deal.  They will get a clue assessed against them for taking those extra steps, and another clue for raising their arms.

Considering all of the above clues you can be assessed, keep in mind that if you score two, JUST TWO clues, NHTSA ‘s research indicates there is a 79% chance you are impaired at a level at or above .08.

The third test, the One-leg Stand test, is a far simpler test to understand, but is also difficult for sober people to perform.  Like the Walk and Turn test, there is an instruction phase and a Standing/Walking phase.  During the instructions stage, you’ll be instructed to put your feet together with your arms at your side and to remain that way.

Here are the instructions from the NHTSA manual:

  • When I tell you to start, raise either leg with the foot approximately six inches off the ground.

  • Keep both legs straight and your arms at your side.

  • While holding that position, count out loud in the following manner: “one thousand one, one thousand two, one thousand three,” and so on until told to stop.

  • Keep your arms at your sides at all times and keep watching the raised foot.

  • Do you understand?

  • Go ahead and perform the test. (Officer should always time the 30 seconds. Test should be discontinued after 30 seconds.)

Here are the ways you can be assessed clue on the One-leg Stand test:

  • Subject sways while balancing

  • Uses arms to balance

  • Hopping

  • Puts foot down

According to the NHTSA manual, a person with a BAC above .10 can maintain their balance for up to 25 seconds, but “seldom as long as 30 seconds.”  Two or more clues, or failing to complete the test, is indicative, at least according to NHTSA, as having an 83% chance of having a BAC of .08 or higher.

The officer may ask you to perform other field sobriety tests, such as the Vertical Nystagmus test, have you count, or say the alphabet from one letter to another, but these tests have not been vetted in the same way as the first three.  In other words, the results of those tests as compared to a level of intoxication will be difficult for the officer to articulate in court.

How Does The Preliminary Breath Test Work?

The last test you will be asked to perform will be the Preliminary Breath Test (PBT).  This can be the nail in the coffin in cases where the results of the HGN, Walk and Turn, and One-leg Stand tests could otherwise be suppressed for flaws in their instructions, demonstration, etc.  The PBT is not admissible in court to prove you were DUI, but it is instead used to support the probable cause needed for your DUI arrest.  This distinction will be explored further in a subsequent article.

The PBT itself is simple; you blow into a plastic tube and within a few seconds the portable breath testing device will display a readout of the blood alcohol content (BAC) it detects in your breath sample.  If the amount is .08 or higher, the officer will make it a point to hold the device up to the dash-cam to make sure the result is videotaped.  When this happens, your arrest is only seconds away…

The FSTs have one purpose: providing the probable cause necessary for your arrest for DUI.  I have seen one case, only one, where taking the PBT and subsequent breathalyzer was beneficial to a client.  In that case, the PBT indicated a BAC of higher than .08, however, when the client took the breathalyzer at the station, it registered 0.0.  Obviously one of the devices was malfunctioning, and it was for this reason that the DUI was dropped, and another charge, something like open container or consumption of alcohol by a minor if I remember correctly, was brought against my client.  That case represents a very small number of those where performing the FSTs resulted in a suspect avoiding a DUI charge.

That said, when you’re on the side of the road an officer, who suspects you may be under the influence of alcohol, asks you to do some Field Sobriety Tests, such as the Horizontal Gaze Nystagmus, Walk and Turn, and the Stand on One Leg test, you can refuse without penalty.  Some officers will become fairly aggressive if you refuse and will try to get you to admit that you’ve had some drinks, or you’re worried about the results, etc.  Others will not even ask you to participate, they will bluntly tell you “what you’re going to do…”  You can dismiss these attempts with a simple “I’m declining to participate without an attorney present.  Am I free to go?”  If they insist on asking you to participate repeatedly, you can simply repeat your position.  Whatever you decide, just remember that the results of the field sobriety tests will be used as evidence against you.

Still need help? Reach out to an experienced Belleville DUI lawyer today.

This article is in no way intended to be, nor should it be construed as, legal advice and you should not rely on the information herein.  I’m simply sharing some random thoughts and ideas, my experience, and I’m certainly not touching on every issue that is necessary to consider for any serious legal analysis.


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