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What Is the Purpose of the Field Sobriety Test?


Interviewer: Today we’re going to be talking about DUIs and specifically, the whole concept of the field sobriety test. My first question with regards to the field sobriety test is what is its purpose?

Probable Cause and Evidence

James Abate: There are two purposes for the standardized field sobriety test. The first purpose is for the officer to investigate whether there is probable cause for you to be arrested for driving while intoxicated. What I mean by that is can you be taken into the station to take the Alcotest. There is a very low standard for probable cause.

The Tests Were Designed by the National Highway Transportation Safety Administration (NHTSA)

The second purpose of the field sobriety test is for evidence. The evidence is based on whether the officer can testify as an expert based on your performance of the standardized field sobriety test. There are two factors that go into this. First of all, the standard field sobriety tests are promulgated by the United Stated Department of Transportation by the National Highway Transportation Safety Administration (NHTSA).

There Are 3 Core Tests

There are really three core tests. The first test is the horizontal gaze Nystagmus test. That is when a stylus is brought across your eyes and the officer is measuring whether your eyes evidencing Nystagmus.

The second test is the walk-and-turn test where you walk nine steps, turn around and walk nine steps back. The last test is the one-legged stand where you are given instructions on how to raise your one leg a certain amount off the ground and seeing if you can hold your balance.

If All Tests Are Performed by the Driver, Statistically, the Officer Has a 66% Chance of Observing Intoxication

If you perform all three tests, the officer has a 66% chance according to NHTSA to be able to detect an intoxicated driver. Based on that the officer can then testify as to whether or not you were intoxicated. Even if they lose on the machine results for some reason, the fallback is on the officer to then testify as an expert. In some cases we have to contend with both the machine and the officer.

The Tests Are Designed as an Evaluation, Not as a Pass or Fail

Interviewer: If the person actually passes them they still have a chance of getting arrested and charged with DUI?

James Abate: Well technically there is, it’s not a pass-fail thing. It’s an evaluation based on the performance of the test. If the officer thinks that based on the fact that you performed the field sobriety test properly, that you passed the test, he will not be arresting you. This is because if he comes into court and he testifies that you did a good job in the field sobriety test and he still arrested you, then he didn’t have probable cause for the arrest and he’d be in a whole world of trouble now.

There are many times when the officers do not do the test according to the DWI Detection and Standardized Field Sobriety Testing Manual. That should be the way they are trained to and if they don’t perform the test properly then we can eliminate that as evidence. But he’ll still have the probable cause that based on the way he did evaluated the evidence that they can still support probable cause.

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