Field Sobriety Tests Used for DWI Investigations in Mecklenburg County

Standardized Field Sobriety Tests

Standardized field sobriety tests (SFSTs) were introduced in the 1970s based on scientific research sponsored by the National Highway Traffic Safety Administration to identify roadside sobriety tests that were accurate indicators of impairment. From this research, three tests were recognized as tests that were reliable, if administered in a standardized manner, in determining when individuals were under the influence of an impairing substance.

The three standardized field sobriety tests include:

Horizontal Gaze Nystagmus (HGN)

One Leg Stand (OLS)

Walk and Turn (WAT)

Each of these SFSTs has an instruction phase and a performance phase. During the instruction phase, you are asked to maintain a stance while listening to the test instructions and the performance phase involves you performing the test as instructed. We've outlined each of these tests below.

Horizontal Gaze Nystagmus (HGN)

Horizontal Gaze Nystagmus (HGN) is by far the most complicated Standardized Field Sobriety Test (SFST) to understand. It’s the test where the officer moves a stimulus, typically a pen, back and forth in front of the DWI suspect, who must follow that stimulus with his or her eyes only. The officer is looking for nystagmus or an involuntary jerking of the eyes. HGN is type of nystagmus that occurs as a person’s eyes gaze toward the side. Officers investigating a DWI conduct this test because HGN is believed to be a sign of impairment by alcohol or certain drugs.

During the instruction phase of HGN testing, you will typically be asked to stand with your feet together, hands at your side, and instructed to look straight ahead. The officer should begin the HGN evaluation by giving you information and instructions, including the following:

I am going to check your eyes.

Keep your head still and follow the stimulus with your eyes only.

Keep your eyes on the stimulus until I tell you to stop.

Before actually administering the HGN test, an officer will conduct certain preliminary tests in order to detect medical disorders or head injuries to the DWI suspect. Certain medical disorders and head injuries can impact the accuracy of HGN testing. If the officer discovers any signs, the test should not be administered. These preliminary tests check for equal pupil size, equal tracking of the eyes, and ensure there is no resting nystagmus.

During the actual administration of the HGN test, the officer is looking for the following three clues in each eye; thus, there are a total of six clues of impairment.

Lack of smooth pursuit. During this portion of the testing the officer will slowly move the stimulus from side to side. If your eyes jerk, or bounce, as they move left and right in pursuit of the object, a clue is noted.

Distinct and sustained nystagmus at maximum deviation. For this part of the testing your eyes are moved to the point where there is no more of the white of the eye visible. If your eye jerks at this point, another clue is noted.

Onset of nystagmus prior to 45 degrees. If an officer observes the eye jerk prior to reaching the 45 degree point, a clue is again noted.

It should be noted that while not an HGN clue, failure to abide by the officer’s instructions may be used against you in a DWI trial. For example, if you choose to take this test and do not keep your head still during the test, the prosecutor will argue that the reason you did not keep your head still was because you were too impaired to follow these simple instructions.

One Leg Stand (OLS)

The One Leg Stand (OLS) test has you try to keep your balance while standing on one leg for a period of 30 seconds. Like the other standardized field sobrity tests, the OLS begins with an instruction phase. Here, the officer will provide you with the following instructions:

Stand straight with your feet together, arms by your side, and remain in that position until you are told to begin the test.
When you are instructed to begin, stand on the leg of your choice, raise one foot six inches off the ground with your toes pointed forward, both legs straight, and the raised foot parallel to the ground and look at your foot and count out loud until you are told to stop.
Do you understand the instructions?

The officer evaluating your performance on the OLS is trained to look for the following four clues:

Using the arms for balance (6 inches or more)
Swaying
Hopping
Putting the foot down before the 30 seconds is up

While not considered validated indicators of impairment, the evaluating officer will also make a note of other clues that the State will argue demonstrates drunk driving, such as not counting out loud, not looking down at feet, and raising arms, but less than 6 inches.

Walk and Turn (WAT)

The WAT makes you attempt to walk a straight line. Before beginning the WAT, you will be provided an extensive list of instructions, including:

Place your left foot on the line and your right foot in front of the left with the right heel against the left toe. Keep your arms by your sides and remain in the position until told to begin.
When you are instructed to begin, walk nine heel to toe steps down the line. On the ninth step, keep your front foot on the line and take small steps to turn around.Walk nine heel to toe steps back. Count each step out loud and watch your feet. One you start the test, do not stop the test until it is completed.
Do you understand the instructions?

Officers conducting the WAT are trained to look for eight clues during this test, two during the instruction phase and six during the performance phase. During the instruction phase, an officer looks to see whether you:

Start the test too soon
Lose your balance

Throughout the performance phase, the officer marks a clue if you:

Stop walking
Miss heel to toe (by more than ½ inch)
Step off the line
Use your arms for balance (6 inches or more)
Take the wrong number of steps
Make an improper turn

Even where you demonstrate the same clue more than once, the officer investigating the DUI should only count that clue one time. Additionally, while not considered clues, the officer will make note of other observations that the State will argue are indicators of impairment, such as not counting out loud, swaying, not looking down at your feet, and raising arms not more than six inches.

Other Field Sobriety Tests Used in DWI Investigations

In addition to SFSTs, there are other field sobriety tests an officer may ask you to perform. These tests are not standardized, have not been validated by NHTSA or any other credible agency, and are not required to be performed in a uniform manner.

Vertical Gaze Nystagmus (VGN)
Romberg Balance Test
Finger-to-Nose Test
Finger-Count Test
Hand Pat Test
ABC Test
Numbers Backward Test

You Can Refuse to Perform Field Sobriety Tests

When an officer stops you for DUI, they will likely make you think you have perform these SFSTs; the truth is that you don't. You can refuse to perform field sobriety tests and you probably should. While classified by some as "standardized", SFSTs are still slanted in favor of law enforcement. Considering the hectic and confusing conditions you face while being investigated for DWI, it would be difficult for a completely sober person to pass these tests - if there is even a way to actually "pass".

In North Carolina there are no driver's license implications for refusing to perform these tests. By refusing, you will keep your driving privileges and you will also strengthen your case if you are charged with DWI by limiting the amount of evidence the police and prosecutor have to use against you.

Challenging a Field Sobriety Test

It is worth noting that per North Carolina General Statute (N.C.G.S.) 20-139.1(f), where a person charged with DUI refuses to perform field sobriety tests at the request of an officer, evidence of that refusal is admissible in any criminal, civil, or administrative action against that person. Even so, it is important to remember that poor performance on field sobriety tests is one way an officer builds a DUI case against you when charging you with DUI. Without evidence of such poor performance on the SFSTs, the State’s case is undeniably weakened.

DWI Case Results

Field Sobriety Tests Used for DWI Investigations in Mecklenburg County

Standardized Field Sobriety Tests

Horizontal Gaze Nystagmus (HGN)

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One Leg Stand (OLS)

Walk and Turn (WAT)

Other Field Sobriety Tests Used in DWI Investigations

You Can Refuse to Perform Field Sobriety Tests

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