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What Are the Three Standardized Field Sobriety Tests?

In a DWI matter, after an officer stops and questions you, one of the next things they may do is ask you to step out of the vehicle for a pre-arrest screening. During this phase of the DWI investigation, the officer is trying to establish probable cause to arrest you for driving while intoxicated. Probable cause means that facts and information exist to believe that you have committed an offense. As such, the officer may direct you to perform a series of field sobriety tests.

The purpose of field sobriety tests is to determine whether the subject performing them is impaired. Essentially, the individual is put through different tasks that are difficult to accomplish when affected by alcohol. Law enforcement agencies might use different types of tests to detect inebriation, but only three are accepted as valid by the National Highway Traffic Safety Administration (NHTSA), as they have been validated by research.

Referred to as the Standardized Field Sobriety Tests (SFSTs), they include the:

  • Horizontal gaze nystagmus (HGN),
  • Walk and turn (WAT), and
  • One leg stand (OLS).

If you are directed to participate in the SFSTs, poor performance on them may be used as justification for the officer to arrest you for suspicion of DWI and may be presented as evidence against you in court. The troubling thing is that you can be facing serious consequences because of your performance on tests that are not 100% accurate and likely not administered under ideal conditions.

In this blog, we'll examine each of the three standardized field sobriety tests and what officers are looking for when administering them. Additionally, we'll explore factors that can affect performance and how results can be challenged.

The Horizontal Gaze Nystagmus Test

The first SFST you'll likely be directed to participate in is the horizontal gaze nystagmus. Nystagmus refers to the involuntary jerking of the eyes, which can be observed in people under the influence of alcohol.

As part of the HGN, the officer will instruct you to follow a stimulus, such as a pencil, flashlight, or finger. You must track the stimulus with your eyes only, keeping your head still. The officer will hold the stimulus just above eye level and about 12 inches away from your face. They will then move the stimulus from the center to one side of your face and repeat the process in the other direction.

The clues the officer will be looking for to determine whether you are intoxicated include:

  • Jerking or bouncing of the eyes: The inability of your eyes to smoothly follow the stimulus may suggest that you have a blood alcohol concentration at or above the legal limit of 0.08.
  • Consistent nystagmus: The officer will hold the stimulus at each side of your face for at least 4 seconds to see if your eyes jerk or bounce consistently during that time.
  • Onset of nystagmus: The officer will carefully watch your eyes to see when the nystagmus occurs. The earlier the jerking or bouncing begins, the higher your alcohol concentration level.

The Walk and Turn Test

One of the next SFSTs you'll be subject to is the walk and turn test. This assessment is referred to as a divided attention test because it requires you to do two things at once: mental and physical tasks. For the mental tasks, you must listen to, understand, and remember instructions the officer gives you. For the physical task, you will be required to maintain your balance and coordination.

Acceptable performance on the WAT includes the following:

  • Standing heel-to-toe on a line
  • Remaining balanced on that line while listening to the officer's instructions
  • Taking nine steps in one direction while touching the heel of your front foot to the toe of your back foot and staying on the line
  • Pivoting after taking the nine steps
  • Walking in the other direction while maintaining the heel-to-toe movement

As part of the instructions, the officer will tell you that having a gap of at least ½ inch between your heel and your toe indicates improper performance on the test. So too does lifting your arms more than 6 inches from your sides to balance yourself.

Clues suggesting that you have an alcohol concentration of 0.08 or more include:

  • Unable to balance while listening to the instructions
  • Starting before the officer tells you to
  • Stopping before taking the appropriate number of steps in each direction
  • Failing to touch heel to toe
  • Stepping off of the line
  • Putting your arms out to balance
  • Taking more or less than 9 steps in either direction

The One-Leg Stand Test

The one-leg stand test is also a divided attention test. Again, you must listen to, comprehend, and remember instructions while performing a physical task.

For this assessment, you will be required to lift one leg about 6 inches off the ground. Then, while balancing on the other leg, you must count to 30. As with the WAT, you cannot move your arms more than 6 inches from the side of your body to try to keep your balance.

The following clues suggest impairment:

  • Swaying side to side or back and forth while balancing on one leg
  • Putting arms out to balance
  • Hopping to remain balanced
  • Dropping the lifted foot

Challenging the SFSTs

As noted earlier, the standardized field sobriety tests are not entirely accurate.

According to the NHTSA, each individual test has the following accuracy scores:

  • HGN 77%
  • WAT 68%
  • OLS 65%

Additionally, a few different studies were done in Colorado, Florida, and California to determine the validity of the battery of tests. Although the findings suggest that an officer has a high probability of making a correct arrest after observing a person's performance on the SFSTs, some people may be arrested in error.

Below are the results of the validation studies:

  • Colorado: 86% accurate
  • Florida: 95% accurate
  • San Diego, CA: 91% accurate

The accuracy rates suggest that other factors can affect performance on the SFSTs. Thus, if they are not administered under ideal conditions or the subject has a health issue, the officer might think that they are observing signs of impairment when, in reality, poor performance was due to some other variable.

Some of the factors that can impact performance on SFSTs include, but are not limited to:

  • Physical impairments
  • Health conditions
  • Unsuitable attire
  • Anxiety
  • Fatigue
  • Unclear instructions
  • Insufficient officer training

If you participated in field sobriety testing after a DWI stop in or around Dallas, speak with an attorney about your case. They can review the details to determine whether the officer had probable cause to arrest you.

At Deandra Grant Law, Attorney Deandra Grant is well-versed in field sobriety testing procedures. She received training in Standardized Field Sobriety Tests and completed the NHTSA Field Sobriety Testing Instructor Course. Our team can use our insight and knowledge to challenge either the administering or results of the test and seek a favorable outcome in these cases.

To schedule a consultation, please contact us at (214) 225-7117 or submit an online contact form today.