Information on Field Sobriety Testing
Field Sobriety Testing (FST) is a series of psychophysical tests administered by law enforcement designed to determine if an individual is Driving While Intoxicated (DWI) or Driving Under the Influence (DUI). More specifically, Field Sobriety Testing (FST) is used to determine if an individual is under the influence of alcohol.
Since the mid 1970’s, the National Highway Traffic Safety Administration (NHTSA) has conducted research resulting in the creation of three standardized field sobriety tests. Initially referred to as Improved Sobriety Testing, these tests were further validated by the Southern California Research Institute and relabeled Standardized Field Sobriety Testing (SFST). The tests were initially created by the Los Angeles
Police Department Training unit and are now the standard recommended by the Federal Government through the NHTSA. A formal training program has been developed and is available through the NHTSA to aid police officers in becoming more skillful at detecting suspects that may be Driving While Intoxicated (DWI) or Driving Under the Influence (DUI).
The Standard Field Sobriety Test (SFST) consists of a battery of three tests which are to be administered and evaluated in a standardized manner in order to obtain validated indicators of impairment and to establish probable cause for arrest. The three tests administered are:
- The Horizontal Gaze Nystagmus (HGN)
- The Walk-and-Turn
- The One-Leg Stand
Horizontal Gaze Nystagmus (HGN) Testing
Horizontal gaze nystagmus is an involuntary jerking movement of the eyeball that occurs naturally as an individual’s eye gazes to the side. Normally, nystagmus (jerking movement) occurs when the eyes are rotated at high peripheral angles. When an individual is impaired by the effects of alcohol, this jerking is exaggerated and can occur at lesser angles. Additionally, an individual Driving While Intoxicated (DWI) or Driving Under the Influence (DUI) will have greater difficulty tracking a moving object. As the test is administered, law enforcement personnel look for three indicators of impairment. The indicators are:
- If the eye cannot follow a moving object smoothly.
- If jerking is distinctly noticeable when the eye is looking as far to the side as it can (maximum deviation).
- If the jerking begins when the eye is within 45 degrees of center.
The officer tests each eye. If, between both eyes, four or more of the indicators are observed, research indicates that approximately 77 percent of suspects will likely have a Blood Alcohol Content (BAC) of .10 or higher.
Divided Attention Testing
The Walk-and-Turn test and the One-Leg Stand test are both “divided attention” tests that are easy to perform by most sober individuals. The goal of divided attention tests is to require an individual to both listen and follow instructions while performing simple physical movements. Individuals who are Driving While Intoxicated (DWI) or Driving Under the Influence (DUI) will typically have more difficulty completing these tasks than an individual who is not impaired.
In the Walk-and-Turn test, the individual is instructed to take nine steps, heel-to-toe, along a straight line. After taking the steps, the individual is instructed to turn on one foot and return in the same manner along the original path. There are seven indicators of impairment for this test. The indicators are:
- If the individual cannot maintain balance while listening to the instructions.
- If the individual begins before instructions are finished.
- If the individual stops while walking to regain balance.
- If the individual does not touch heel-to-toe.
- If the individual uses arms to balance.
- If the individual loses balance while turning.
- If the individual takes an incorrect number of steps.
Research indicates that 68 percent of individuals that demonstrate two or more of these indicators will have a Blood Alcohol Content (BAC) of .10 or higher.
One-Leg Stand Test
In the One-Leg Stand Test, an individual is instructed to stand with one foot approximately six inches off the ground and count aloud in thousands until instructed by law enforcement personnel to put the foot down. The individual is timed for thirty seconds. There are four indicators looked for during this test. The indicators are:
- If the individual sways while balancing.
- If the individual uses their arms to balance.
- If the individual hops to maintain balance.
- If the individual puts the foot down.
NHTSA research indicates that if two or more indicators are observed there is a 65 percent chance that the individual has a Blood Alcohol Content (BAC) of .10 or greater.
Effectiveness of Field Sobriety Testing in Court Testimony
The effectiveness of Field Sobriety Testing in court testimony depends largely on the total number of indicators observed during the three tests. If many indicators were observed during each of the three tests, the higher the effectiveness of the testimony. If the Field Sobriety Testing was administered according to national standards, it has greater credibility than purely subjective testimony. Only a qualified and competent DWI defense attorney can effectively assist in determining if the test was properly administered and build a solid defense to defend against incorrect administration or interpretation of the test results.