Field sobriety tests are used by police officers to determine if a driver may be impaired. While field sobriety tests are one tool used by police officers, they are not the only, or the most effective, way to determine if someone has been drinking enough for their blood alcohol to be .08%, the official designation for driving under the influence.
Field sobriety tests are limited in their effectiveness in several ways. The tests must be completed exactly as developed in order for the police officer to get accurate data. Given that the officer may be conducting the test during bad weather, along a busy or dark stretch of road, or any other variables that make the tests a challenge, it can be difficult to trust the test results. In addition, some individuals will have issues completing these tests even while sober. Individuals who are overweight, have certain health problems or injuries, or are 65 or older may not perform well on field sobriety tests regardless of whether or not they have been drinking.
The purpose of field sobriety tests is to determine how an individual performs in a divided attention state, which is generally an indicator of how they would also perform while operating an automobile. The National Highway Traffic Safety Administration has validated three particular field sobriety tests for use by police officers. These are the horizontal gaze nystagmus test, which involves following an object with your eyes while it is being moved by the police officer, the walk and turn test, and the one-leg stand. Other field sobriety tests, such as touching your finger to your nose, reciting the alphabet and counting backwards are not validated as effective field sobriety test methods.
An individual who fails a field sobriety test will typically be taken into the police station for further testing. Officers will use a breath or blood test to accurately determine the level of alcohol in the individual’s blood. While failing a field test is not a positive determination that someone has been drinking, it is considered probable cause that allows the officer to pursue further testing.