Field Sobriety Tests (FSTs) are some of the evidence prosecutors use in order to convict someone of driving under the influence.

Field Sobriety Tests, in one form or another, have been around for a very long time. Police officers use these tests as an aid in determining if someone is impaired for the purposes of operating a motor vehicle. Field Sobriety Tests are basically coordination tests; they do not test a person’s blood alcohol level. Since these tests are coordination tests, they can be failed for any number of reasons. It is not uncommon for people in an alcohol–free state to fail these tests and, since these tests are given under the worst possible conditions, late at night, on the side of the road with cars flying by and a very nervous and tired defendant, results should be reviewed very carefully. Many peace officers, however, view these tests as simply a way to build up evidence against the defendant.

Further, some peace officers believe that FSTs can be used to show a person’s lack of divided attention (a person’s ability to perform more than one task at a time). FSTs, however, are not really the best measure of divided attention, driving is. When a person drives a motor vehicle, he/she must do many things at one time. He/she has to stay in the lane, maintain speed, etc. Lack of divided attention can show mental as well as physical impairment.

When reviewing performance on FSTs, an attorney must be intimately familiar with each of the individual tests used and what defines a failure of said tests.

A chemical test, blood or breath, is the evidence of a person’s actual blood alcohol level. These tests are usually very accurate, however, mistakes can be made. Even if these tests were 100 percent accurate, which they are not, they still do not show what the blood alcohol was at the time of driving. This must be done by a complicated process called retrograde extrapolation. Any good criminal defense attorney must know this and also must know how the State as well as the Defense will present this.