Officers who suspect drivers of impairment at the wheel often move quickly to gather evidence supporting their allegations. For example, they may ask someone to exit the vehicle and perform a series of field sobriety tests.
Those tests can lead to someone’s arrest or a request for chemical testing. How reliable are field sobriety test results for detecting intoxication?
Standardized tests are the most reliable
In theory, police officers could make up any strange tests that they personally think might show whether someone is under the influence or not. Typically, only standardized field sobriety tests hold up under close scrutiny during criminal proceedings. There are three field sobriety tests recognized as standard and relatively reliable.
The first is the walk-and-turn test. The officer instructs someone to walk in a straight line, turn 180° and walk back along the same line. Officers may also have someone perform a one-leg stand test. Having someone balance on one leg, possibly while moving their arms or performing minor mental tasks, can help an officer evaluate an individual for signs of intoxication.
Finally, officers may ask someone to follow their finger, a flashlight or a pen from side to side with their eyes without moving their head. This is the horizontal gaze nystagmus test. This test helps an officer look for signs of an involuntary muscle twitch in the eyes that becomes more pronounced when someone has had too much alcohol. Depending on how someone performs on those standardized tests, an officer may have the probable cause they need to arrest someone for an alleged impaired driving offense.
There are reasons people fail beyond impairment
Even with standardized field sobriety tests, there could be numerous other reasonable explanations for someone’s poor performance on one or all of those tests. Certain medical conditions, including conditions that affect muscle spasticity, could impact someone’s performance on field sobriety tests. So could mental health issues, like anxiety or post-traumatic stress disorder.
People who can safely drive might display functional limitations during field sobriety tests that raise questions about their chemical impairment. If they have medical records documenting conditions that may explain their poor performance, those drivers may have an easier time challenging the drunk driving charges they face.
Other times, there may be issues with the legality of the initial traffic stop. A lawyer could challenge the inclusion of certain evidence during criminal proceedings if a police officer illegally stopped someone or otherwise violated best practices. Performing non-standard tests or failing to record field sobriety tests are among the mistakes that might raise questions about their usefulness as evidence later.
Understanding that a field sobriety test is not a guarantee of evidence of chemical impairment might help people feel empowered to fight back against drunk driving allegations.