Field Sobriety Tests in Drunk Driving Cases

In a typical DUI investigation, the officer asks the DUI suspect to step out of his/her car and perform a series of "Field Sobriety Tests" (usually within a few minutes of the DUI traffic stop). These roadside exercises are meant to help the DUI officer determine whether the suspect may be drunk driving, and whether he/she should be arrested and taken for a blood or breath alcohol test. In DUI cases, the most common Field Sobriety Tests are (click on the links in this list to learn more about a given test):

• The Horizontal Gaze Nystagmus Test (follow the stimulus with your eyes)
• The Walk and Turn Test (9 steps each direction, on the line)
• The One Leg Stand Test (raise one foot for 30 seconds)
• The Rhomberg test (close eyes, tilt back head and count to 30)
• The Finger to Nose Test (close eyes, extend arms and touch nose with fingers)
• The Finger Count test (thumb to finger, 1-2-3-4 and 4-3-2-1)
• The Hand Pat Test (clapping palm and then backhand)

NHTSA Studies & The "Standardized" Field Sobriety Tests

The National Highway Transportation Safety Administration (NHTSA) conducted a series of laboratory and field studies to determine the accuracy of Field Sobriety Tests in signaling whether a DUI suspect is impaired. Of all the field sobriety tests, NHTSA found three to be the most reliable: The Horizontal Gaze Nystagmus, The Walk and Turn, and The One Leg Stand. These three became known as the "Standardized Field Sobriety Tests" (SFSTs). NHTSA claims to have quantified that the accuracy of the SFSTs in determining whether a DUI suspect's BAC is .10 or higher:

• Horizontal Gaze Nystagmus: 77% accurate in gauging DUI impairment
• Walk and Turn: 68% accurate in gauging DUI impairment
• Combined Horizontal Gaze Nystagmus and Walk and Turn: 80% accurate in gauging DUI impairment
• One Leg Stand: 65% accurate in gauging DUI impairment

Application of the FST Studies to DUI Defense

Even if these "accuracy rates" are correct, NHTSA's studies reveal several major problems with DUI enforcement and DUI prosecutions. First, if these SFSTs were used to convict people of drunk driving, then 20% to 32% would be wrongfully convicted.

Second, these numbers assume that the Standardized Field Sobriety Tests are administered exactly according to NHTSA's specifications. In reality, very few DUI officers are even aware of the specifications, let alone comply properly with them.

Finally, no studies have demonstrated the correlation between the remaining non-standardized field sobriety tests and DUI impairment. Opinions as to whether and to what extent the remaining field sobriety tests properly gauge the intoxication levels of DUI suspects are nothing more than speculation.

What we do know is that many factors can affect how well a DUI suspect performs on any of the field sobriety tests. Among these factors:

• Nervousness
• Fatigue
• Injuries
• Intimidation
• Weight, Age, Physical Condition & Natural Coordination
• The distraction of traffic and lights
• Weather conditions
• The clarity of DUI officer's instructions