Officers are trained to look for certain errors or clues which are believed to have a correlation to a persons blood alcohol concentration or content (BAC).
The Standard Field Sobriety Test (SFST) are frequently administered at roadside when police or state troopers come upon an individual who they believe to be intoxicated. Police use these tests in addition to observing a person’s pattern of speech, disorientation, odor of alcohol, and other movements. Unlike physical presentations (speech, odor, and movements), the scoring of the field sobriety test are subjective. Officers are trained to look for certain errors or “clues” which are believed to have a correlation to a person’s blood alcohol content (BAC). While failure on these tests isn’t required for police to have the probable cause to arrest someone the results are still important.
The prosecution will use the SFST to bolster the Commonwealth’s case if a person fails them. The defense should always focus on attacking the reliability of these tests and establishing alternative reasons for a driver’s poor performance or failure. Unlike chemical testing, a driver isn’t required to take a field sobriety test but keep in mind the prosecution could always use it as “consciousness of guilt” just as if a person ran from the scene of a crime.
I recommend that a person always submit to a field sobriety test because it’s much easier for the defense to argue that the tests are scientifically unproven or unreliable rather than a person has a constitutional right to refuse them. Refusing the test isn’t going to help your case! I believe that the prosecution’s “consciousness of guilt argument” is much stronger than the alternative defense argument. There are three types of field sobriety tests that are approved by the National Highway Transportation Safety Administration (NHTSA) and they are as follows:
- the horizontal gaze nystagmus test (HGN),
- the one leg stand test, and
- the walk and turn test.
I have written previous articles on these tests and I encourage you to read them. All of these tests are premised on the theory that impairment diminishes a person’s ability to perform mental and physical functions at the same time. To safely operate a car or motor vehicle, a person must be able to process mental data and perform physical functions contemporaneously.
The one leg stand test and the walk and turn test are divided attention or psychophysical tests. The goal of divided attention tests is to have the individual demonstrate two or more psychophysical skills such as the ability to process information, make decisions, use short term memory and maintain balance and coordination. Not all police officers are trained on field sobriety testing as training requires a specific certification.