Prosecutors rely on field sobriety tests to build a DUI / DWI case, but many drivers don’t realize that they are vitally important to the defense as well. Prosecutors will attempt to show that any variation between the manner in which the officer explained the tests, and the way in which the subject performed the tests, is proof of mental or physical impairment.  However, a Florida DUI defense lawyer Michael J. Kessler will use the same field sobriety tests to demonstrate that the driver was not physically or mentally impaired.

Florida DUI / DWI cases are made up of two different elements – the allegation that the driver was driving under the influence, meaning he or she was mentally and physically impaired, and the “per se” charge, which focuses on whether the driver’s blood alcohol content (BAC) was .08 percent or greater.

The allegation of driving under the influence hinges on circumstantial evidence of the driver’s physical or mental impairment due to alcohol and/or drug consumption.  Police use field sobriety tests to obtain evidence that supports this allegation. They are divided attention tests, meaning they are designed to force drivers into focusing on two tasks at once. Although field sobriety tests are optional, most officers don’t advise drivers of that fact.

Physical and mental impairment is the heart of every DUI / DWI case.  Forensic experts, whether they testify for the prosecution or the defense, agree on certain points regarding alcohol intoxication.  For example, experts agree that alcohol consumption can cause both mental and physical impairment. However, mental impairment always occurs before physical impairment takes place. 

Drivers with a high tolerance for alcohol can often disguise signs of physical impairment.  However, it is impossible to mask symptoms of mental impairment.  If a driver displays physical impairment, but not mental impairment, that impairment must come from a source other than alcohol.

Physical impairment can be caused by any number of issues that have nothing to do with alcohol intoxication.  Injuries or other physical disabilities can impair a person’s ability to perform on field sobriety tests.  Fatigue can impact a driver’s performance, as can nervousness.  Thus, field sobriety test performance fuels arguments for both the prosecution and the defense in DUI cases.

Field sobriety tests in drunk driving cases have been researched and studied extensively. Three tests have been standardized by the National Highway Traffic Safety Administration (NHTSA).  These are the horizontal gaze nystagmus test, the walk and turn test, and the one leg stand test.  These tests are standardized because they have precise instructions to follow, and an objective scoring system.

Despite the availability of NHTSA-standardized tests, many officers use non-standardized tests to evaluate drivers for signs of mental or physical impairment.  These tests include the Rhomberg balance test, the finger-to-nose test,  reciting the alphabet, the hand-pat test, the finger-tap test, and other tests as simple as dropping coins in the roadway and asking the subject to pick up those coins that are “heads” or “tails.”