A field sobriety test is a series of tests used by police officers to determine if a person is impaired, most commonly from alcohol, while operating a vehicle. The National Highway Traffic Safety Administration developed the standardized field sobriety test in the United States. Standardizing these tests was to provide a validated and consistent method for law enforcement officers to detect impairment.
The SFST comprises three tests intended to assess a person’s physical and cognitive impairment. The three tests are the horizontal gaze nystagmus, walk-and-turn and one-leg stand.
Horizontal gaze nystagmus
This test involves an officer observing a suspect’s eyes as they slowly move a pen or small object from side to side. The officer is looking for involuntary jerking of the eye, known as nystagmus, which can become pronounced in an impaired individual.
The walk-and-turn test assesses a suspect’s ability to perform tasks with divided attention, which are typically difficult for impaired individuals. The suspect is asked to take nine steps, heel-to-toe, along a straight line, then turn on one foot and return in the same manner in the opposite direction. The officer is looking for indications of impairment.
In the one-leg stand test, the suspect is instructed to stand with one foot approximately six inches off the ground and count out loud by thousands until told to put the foot down. The officer times the subject for 30 seconds and looks for signs of impairment.
Some police departments use other tests, but other tests aren’t admissible in court. If you’re charged with impaired driving that involves these tests, it’s crucial to work with someone who understands this area of the law so you can learn your options for presenting a defense.