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What You Need to Know about DUI Field Sobriety Tests

No matter how law-abiding and well intentioned you may be, you could one day find yourself sitting in your vehicle on the side of the road during a traffic stop that turned into a driving under the influence (DUI) investigation. If so, the law enforcement officer will likely ask you to exit the vehicle and perform “field sobriety tests.” To prepare you for that possibility, a Murfreesboro DUI lawyer at Bennett, Michael & Hornsby explains what you need to know about field sobriety tests.

When a Traffic Stop Turns into a DUI

A police officer may initially stop a motorist on suspicion of drunk driving, or a simple traffic stop may turn into a DUI investigation. Before a law enforcement officer can arrest a motorist,Murfreesboro criminal defense attorney however, the officer must have probable cause to make the arrest. One way an officer can ascertain that probable cause is to ask the driver to perform field sobriety tests. Although a law enforcement officer can use additional “tests” to determine if you are sober, most agencies encourage, if not require, officers to use the following standardized field sobriety tests:

  • Horizontal Gaze Nystagmus test. According to the NHTSA, “Horizontal Gaze Nystagmus is an involuntary jerking of the eye that occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object.” The HGN test involves the officer using a pen light, or similar instrument, and asking the subject to track it as it is moved from the center of the subject’s field of vision over to one side and back. When administered properly, and graded objectively, the HGN test can be relatively accurate at detecting impairment. The examiner looks for three indicators of impairment in each eye: 
    • if the eye cannot follow a moving object smoothly
    • if jerking is distinct and sustained nystagmus when the eye is at maximum deviation
    • if the angle of onset of jerking is prior to 45 degrees of center.
  • Walk and turn. A subject it required to take nine steps, heel-to-toe, along a straight line. After taking the steps, the suspect must turn on one foot and return in the same manner in the opposite direction. The examiner looks for eight indicators of impairment:
    • if the suspect cannot keep balance while listening to the instructions
    • begins before the instructions are finished
    • stops while walking to regain balance
    • does not touch heel-to-toe
    • uses arms to balance
    • steps off the line
    • takes an incorrect number of steps
    • makes an improper turn
  • One leg stand. A subject must stand with one foot approximately six inches off the ground and count aloud by thousands until told to put the foot down. The officer times the subject for 30 seconds. The officer looks for four indicators of impairment including: 
    • swaying while balancing
    • using arms to balance
    • hopping to maintain balance
    • putting the foot down.

Am I Required to Perform the Field Sobriety Tests?

You cannot be forced to perform the FSTs that you will likely be asked to perform during a DUI investigation. More importantly, the results of those tests cannot be used against you in a court of law.  The results can only be used to provide the probable cause necessary to arrest you. Taking into consideration the fact that the officer both administers the tests and decides if you passed, there is very little to be gained by agreeing to perform the FSTs unless you are completely sober, and the conditions (including everything from the road and weather conditions to the shoes you are wearing and your emotional state) are ideal.

Contact a Murfreesboro DUI Lawyer

If you have been charged with driving under the influence in Tennessee, consult with an experienced Murfreesboro DUI lawyer as soon as possible to discuss your legal options. In Tennessee contact a Murfreesboro DUI lawyer at Bennett, Michael & Hornsby to discuss your legal options. Contact the team today by calling 615-898-1560 to schedule your free appointment.


Stan Bennett