Field Sobriety Testing

Standardized Field Sobriety Tests, abbreviated as SFST, are a battery of 3 tests that are performed during a traffic stop. The tests help determine if the person suspected of impaired driving is intoxicated with alcohol or drugs. Research was started by NHSTA (National Highway Traffic Safety Administration) in 1975 to make tests that would help them determine whether the suspect was impaired due to the use of alcohol or drugs. By 1981, officers started using the standardized sobriety tests to determine whether or not to arrest an impaired driver.

There are three parts of the SFST tests, as given below:

Horizontal Gaze Nystagmus (HGN) – This test is carried out to see the involuntary jerking of the eyeball when the suspect gazes to the side. In a normal person, nystagmus occurs when the eyes are rotated at high peripheral angles, but with someone who is impaired by alcohol, nystagmus occurs at much lesser angles. An impaired individual will also have difficulty tracking any moving object smoothly.

When an officer conducts an HGH test, the officer observes the eyes of the suspect and how they follow a slow moving object such as a pen or pencil. Three indications are checked for in the suspect:

  • If the eye can easily follow any moving object
  • If the jerking is distinct and is it is sustained when at maximum deviation
  • If the onset of jerking is before 45 degrees of center

Walk-and-turn Test – The suspect is asked to take nine steps along a straight line and also asked to touch heel-to-toe. In this test, the officer looks for eight indications of impairment as listed below:

  • If the suspect can keep balance while walking on a straight line and listening to the instructions
  • If the suspect begins before the officer has done giving the instructions
  • If the suspect stops midway to gain balance
  • If the suspect fails to touch heel-to-toe
  • If the suspect uses arms to balance themselves
  • If the suspect takes an incorrect number of steps
  • If the suspect walks off the straight line
  • If the suspect makes an improper turn

One-leg stand test – The suspect is instructed to stand on one leg with the foot approximately six inches off the ground. The suspect also has to count aloud while standing until told to put the foot down. The officer will time the subject for 30 seconds.

Four indicators are checked by the officer when conducting the one-leg stand test which are listed below:

  • Swaying while balancing
  • Using arms to balance themselves
  • Hopping to maintain balance
  • Putting their foot down

The suspects performance on the field sobriety tests is recorded by the officer and is used as evidence in DUI cases. If the suspect fails to complete the tests, they may be charged and arrested for DUI. The purpose of the field sobriety tests is also to give enough evidence to the officer to arrest someone for driving under the influence, also known as probable cause.

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