Unreliability of Field Sobriety Tests in California

Mar 3, 2014 @ 03:46 PM — by Myles L. Berman

You may have seen it done or actually done it roadside during a police stop…walking a straight line, touching your finger to your nose, or standing on one foot.  These tests, referred to as field sobriety tests or “FSTs”, are administered by law enforcement to exercise mental and physical ability to drivers who are suspected to be under the influence of alcohol and/or drugs.  The results are then assessed in attempts to determine an individual’s level of impairment and if they are too intoxicated to drive.  To increase the testing accuracy, police officers are trained in conducting these tests, however, the final results often depend on the administrator's subjective determination and other outside contributing factors, making them unreliable to some extent. 

Since the mid 1970’s, The National Highway Transportation Safety Administration (NHTSA) has been researching and analyzing the series of FSTs for the issuance of law enforcement protocols for driving under the influence (DUI) field sobriety testing.  Subsequently, the tests, along with federal funding, were turned over to the Southern California Research Institute for evaluation.  In effect, NHTSA validated a “standardized” battery of three roadside tests that are recommended to be administered in making an arrest decision.  These standardized field sobriety tests or “SFSTs”are:

  • One-Leg Stand (OLS) test
  • Walk-and-Turn (WAT) test
  • Horizontal Gaze Nystagmus (HGN) eye test

Incorporating balance, coordination, and doing two things at once, when done correctly, these tests are supposedly reliable enough to gauge sobriety in a suspected drunk driver.  The OLS test consists of standing on one leg approximately six inches from the ground for thirty seconds while counting aloud, the WAT test consists of walking heel-to-toe on a straight line, and the HGN test consists of following an object side-to-side to reveal involuntary jerking of the suspect's eyes that occurs naturally.  These tests have been challenged by various scientific studies. 

Although NHTSA has done several validation studies to support and establish a correlation between poor performance on the tests and DUI impairment, FST reliability can waiver due to many circumstances.  Since the tests rely on cooperation of the individual, how one performs on these tests can be impactful on whether they are arrested.

Law officials rely upon the scoring of one’s performance to aid in the DUI investigation process and an officer may opt to also administer non-standardized tests, which include:

  • Romberg's test
  • Finger-to-nose test
  • Finger-count test
  • Hand pat test
  • Alphabet recitation test
  • Counting numbers backwards

Other than one’s performance, there are several other factors, such as test conditions, that can affect the outcome of the battery of tests and lead to sobriety testing being unreliable.  These include, but are not limited to:

  • The surface setting
  • Lighting or visibility factor
  • Noise factor

FSTs should generally be conducted on a reasonably dry, hard, level, non-slippery surface, and with sufficient room for the suspect to perform the test.  They should also generally be done in adequate lighting, where the ground can be well seen and in a setting where a proper noise level exists, especially during the instruction, with little or no noise disturbances.  Despite being aimed to help officers to gauge one’s level of impairment, because the evaluation depends upon the officer’s judgment and interpretation, the tests are unreliable. 

It should also be noted that FSTs are voluntary in the state of California!

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