A field sobriety test (FST) is a battery of tests that police officers administer in the case of a driver who is suspected of being under the influence of drugs or alcohol. How the driver performs on these tests is one of the ways an officer will initially decide if the driver has been driving while under the influence, and if he or she should be arrested.

If the driver has difficulty with the exercises, or difficulty following the police officer’s instructions, it could be a sign that the driver is mentally or physically impaired by alcohol or drugs. Since the field sobriety test is so subjective to police when deciding to arrest or not to arrest, it would be ideal if the test could be delivered consistently and without variation. Unfortunately, this is rarely the case. Field sobriety tests are often flawed and unreliable, with accuracy levels of only around 70% in detecting intoxication.

What this means is that nearly one out of every four people getting arrested for being under the influence are actually NOT under the influence.

The National Highway Traffic Safety Administration (NHTSA) has three standardized field sobriety tests to detect intoxication. Here are their names and descriptions:

  1. The Horizontal Gaze Nystagmus test (HGN) – Horizontal gaze nystagmus is an involuntary jerking of the eyes as the eyes are gazing to the side. You are unaware it is happening when it does occur. During the HGN test, an officer has the driver follow a pen or a penlight with his eyes to the left and right, without turning their head. If nystagmus (the jerking of the eye) happens before the eyes get to a 45-degree angle, it is highly indicative of a high blood alcohol concentration. The NHTSA has performed studies showing the HGN test to be 77% reliable in determining whether blood alcohol concentration is above 0.10.
  2. The Walk-and-Turn test – The purpose of the walk-and-turn test is two-fold. First, this test is administered to see if the driver suspected of being under the influence is able to split their attention between a mental and a physical task. The suspect must listen and follow the instructions while performing the test of walking nine heel-to-toe steps, turning around on a pivot, and walking back nine heel-to-toe steps. The instructions are specific for a reason. The officer will watch the suspect for eight clues:
    1. Does the suspect keep his/her balance while being given instructions?
    2. Does the suspect start the test too soon?
    3. Does the suspect stop while walking?
    4. Does the suspect perform the correct heel-to-toe action?
    5. Does the suspect step off the line?
    6. Does the suspect use his or her arms to balance?
    7. Does the suspect perform the turn around correctly?
    8. Does the suspect take the proper number of steps?
  3. The One-Leg Stand test – This is another test given to detect if a suspect can divide his or her attention. An officer will instruct the driver to raise his or her foot six inches off the ground, and hold it in that position while counting from 1001 to 1030, and also while looking down at his or her foot. The officer will watch to see whether clues show up that will indicate impairment, such as:
    1. Hopping to keep from falling or putting foot down
    2. Swaying
    3. Using arms for balance
    4. Putting foot back down on ground

The NHTSA requires that these three tests be performed in a safe and appropriate manner. If conditions are not ideal, the tests can become very difficult to perform and result in errors. The conditions under which the FST should be given include:

  • Surface conditions that are dry, hard, level and non-slippery. The suspect should not be in danger of falling because of the surface on which they are performing the tests. The area should be free of heavy traffic where the suspect may fall and get hit by a car.
  • Light conditions where the suspect can perform the tests while being able to see the officer, and the ground below them. An officer may use a flashlight to illuminate the ground, but in complete darkness, even sober people cannot correctly perform the FST.
  • Audial conditions should be such that the suspect is able to clearly hear the instructions they are being given by the officer present. If there is too much noise in the place where the suspect has been stopped, an alternative location should be considered.

The reliability of field sobriety tests is being seriously questioned. There are several weaknesses within the procedures and the administration of those procedures that may be exposed during a DUI case, such as:

  • Physical and mental impairments – An older-aged suspect; a suspect who is ill; a suspect with inner ear issues, back, leg, or foot problems; a severely overweight suspect – these along with many other ailments and/or conditions – can skew the results of the FST to show a false failure. Mental impairments also need to be considered.
  • Officer distraction – When administering the FST, the officer is to remain as still as possible so as not to interfere with the testing. If he or she walks around, gets on their radio, or any other distracting behavior, it can taint the test results.
  • Suspect’s clothing – If a suspect is wearing high heels, boots, very tight pants, or any other clothing that may limit their ability to maneuver their body, it can make taking the test difficult.
  • Less than ideal conditions – Conditions such as bad weather, dim or no lighting, uneven surfaces, and lights and sounds from traffic and spectators can all skew the test and result in false failures.
  • Coordination issues – Many people have balance problems, or are simply physically uncoordinated. Coordination problems can also occur when one is physically exhausted or on certain medications.

As you can see, field sobriety tests have many issues that may result in a false failure. If you’ve been arrested and charged with DUI, contact an experienced DUI attorney and allow them to do the research into your FST and whether it was administered correctly and fairly.