Field Sobriety Tests

Field Sobriety TestsField sobriety testing is vitally important for both the prosecution and defense in a DUI arrest and prosecution. Field sobriety tests are divided-attention tests, which are designed to test for both mental and physical impairment. Prosecutors will attempt to show that any variation between the manner in which the officer explained and demonstrated the tests, and the manner in which the subject performed the tests, is proof of mental or physical impairment. A skilled California DUI defense lawyer will be able to highlight the absence of mental or physical impairment based on the same field sobriety tests.

Driving Under the Influence cases are usually prosecuted using one (or both) of two different theories. One charge usually leveled in California drunk driving cases is the “per se” charge, which is unconcerned with the alleged impairment of the driver. The sole concern in the per se charge is whether or not the accused is above the legal limit at the time of driving. The legal limit for driving is now .08 percent blood alcohol content (BAC) in all 50 states.

Another charge is driving under the influence, which relates to impairment of the driver at the time he or she is driving. This type of drunk driving charge hinges on circumstantial evidence of the driver’s physical or mental faculties being impaired as the result of consuming alcohol or other drugs. Police often use field sobriety tests to gather evidence that supports the theory that a suspected DUI driver was mentally and physically impaired. Although field sobriety tests are optional, most police officers don’t share that information with drivers.

Mental and physical impairment is at the heart of every DUI / DWI prosecution. Both prosecution and defense experts agree on certain points relating to impairment as the result of consuming alcohol. For example, all experts agree that impairment can be either mental or physical. But when it comes to impairment from alcohol, mental impairment always takes place before physical impairment.

Any lawyer experienced in the prosecution or defense of drunk driving cases will also tell you that it is possible to mask physical impairment as the result of drinking alcohol through the phenomenon known as “tolerance”. However, it is impossible to mask symptoms of mental impairment.

If a subject is exhibiting physical impairment, but not mental impairment, that impairment must come from a source other than alcohol. Physical impairment can stem from a variety of sources. 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. Certainly, being forced out of one’s car in the middle of the night by armed officers under the threat of being carted off to jail can provoke the kind of nervousness that will negatively impact performance on field sobriety tests. Thus, field sobriety test performance fuels arguments for both the prosecution and the defense in DUI cases.

Field sobriety testing in DUI / DWI cases has been the subject of much research and study. There are three tests that have been “validated” 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. Each of these three tests has precise instructions to be followed in the administration of the test, and precise scoring to be performed during the performance phase.

In addition to the NHTSA validated field sobriety tests, many officers use non-standardized tests to show 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”.

The bottom line is that no matter how a driver charged with DUI / DWI feels he or she performed on a field sobriety test, an experienced drunk driving attorney can use the results to show that any physical impairment came from sources other than alcohol.

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