What Factors Can Affect Performance on Field Sobriety Tests?

If an officer pulls you over on suspicion of drunk driving, they might ask you to participate in a battery of field sobriety tests (FSTs). Under ideal conditions, the tests may help the officer determine whether the driver was impaired. Still, performance on them can be affected by external factors, such as lighting conditions, as well as internal factors, such as a person's health. In this blog, we'll elaborate on the various things that can result in a failed FST even if you were not under the influence at the time.

What Are Field Sobriety Tests?

Field sobriety tests are measurements of a person's physical and physiological responses to certain stimuli and instructions. They are specifically designed to measure faculties that are typically impaired after a person has consumed alcohol.

Although police officers can administer several types of FSTs, generally, they use the standardized tests the National Highway Traffic Safety Administration considers reliable.

The three standardized FSTs include:

  • The Horizontal gaze Nystagmus test (HGN)
  • Walk and turn test
  • One-leg stand test

If you are unable to complete the tests correctly, it's considered a fail.

Why Are FSTs Administered?

Before an officer can arrest you on suspicion of drunk driving, they need probable cause to do so. Having probable cause means that the officer has some concrete evidence to justify taking you into custody. If you fail an FST, the officer has something they can point to that warrants your arrest.

What Can Affect FST Performance?

Officers should administer FSTs under ideal conditions. That means the area they are conducted in is well-lit and spacious enough to perform the tests, and the surface is level, free of debris, and dry. Any problems with the testing area can cause a sober person to fail the test. Additionally, physical and mental conditions may also play a part in a person's performance.

Some of the factors that can affect performance on a field sobriety test include, but are not limited to:

  • Poor lighting: Being unable to see the ground well can make it difficult for a driver to complete the walk and turn test or the one-leg stand test.
  • Uneven or cracked surface: Any changes in surface height, even subtle ones, and any fissures or holes in the ground can present challenges when a person is trying to balance.
  • Inclement weather: If the ground is wet or it is cold outside, the driver might have difficulty maintaining balance.
  • Auditory distractions/poor instructions: The driver should be able to hear what is required of them on the tests. However, if they can't make out what the officer is saying because of background noise or the officer does not give clear instructions, the driver may "fail" the test because of a misunderstanding.
  • Physical conditions: Leg, foot, or ankle injuries can make it difficult for a person to put their weight on the injured side of the body. While their balance may be off, it may not be due to alcohol impairment.
  • Mental conditions: Being pulled over and facing an arrest can cause fear and anxiety. When emotions are elevated, it may not be easy to process what's going on and do what is expected on the FST.
  • Unsuitable clothing: Baggy or tight-fitting attire or uncomfortable shoes can affect a person's performance on the FSTs.

Technically, if an officer requests that you participate in FSTs, you can politely refuse without facing criminal penalties. However, the officer may still arrest you and justify their actions based on other behavior they observed. Still, if they did not have a lawful reason to take you into custody, you can raise that as a defense in your case.

If you've been charged with a DUI, speak with our Salt Lake City attorneys. We will review the facts of your case to determine defenses for your situation. Contact Lokken & Associates, P.C. at (801) 829-9783 today.