The standardized field sobriety test (SFST) is a series of three tests used by law enforcement to determine if a driver is impaired. Each test assesses different physical and cognitive functions to identify signs of intoxication.
These tests are often used as an initial gauge for determining if a driver is impaired. After these tests are administered, a driver who appears to be impaired may be asked to take a chemical test to determine if they’re intoxicated and provide a quantifiable result that can potentially be used in a criminal complaint.
These three tests are endorsed by the National Highway Traffic Safety Administration because they’re considered reliable enough to be admissible in court.
Horizontal gaze nystagmus
The horizontal gaze nystagmus (HGN) test examines the involuntary jerking of the eyes. This is typically more pronounced when a person is impaired by alcohol. During this test, an officer will ask the driver to follow a pen, flashlight or another easily identifiable object with their eyes as it moves horizontally. The officer looks for specific indicators in the movement of the eye that suggest impairment.
One-leg stand
The one-leg stand test assesses balance and concentration. The officer instructs the driver to stand on one leg while raising the other about six inches off the ground and count out loud by thousands until told to stop, usually for 30 seconds. The officer watches for things like putting the foot down, hopping or using the arms to balance because those can indicate impairment.
Walk-and-turn
The walk-and-turn test evaluates a driver’s ability to follow instructions, balance and perform tasks simultaneously. The officer asks the driver to take nine heel-to-toe steps along a straight line, turn on one foot and return in the same manner. The officer looks for several signs of impairment, including failing to maintain balance during instructions, starting before the instructions are finished, stopping while walking or being unsteady on the feet.
While the SFST is often a good indicator for possible drunk driving cases, many facets of it are subject to interpretation. This reality can become a central focus of a drunk driving defense.