The Standardized Field Sobriety Test (SFST) is a series of three tests used by police officers in the United States to determine if a driver is impaired by alcohol or drugs. The SFST consists of the horizontal gaze nystagmus (HGN), walk-and-turn, and one-leg stand tests.
Each test evaluates different aspects of a driver’s physical and cognitive abilities. These three tests are often a part of obtaining probable cause that leads to an arrest. The law does not mandate that motorists must submit to these tests when asked.
Horizontal gaze nystagmus (HGN) test
The HGN test involves an officer observing a suspect’s eyes as they follow a slowly moving object, like a pen or flashlight, horizontally with their eyes. The officer looks for signs of nystagmus, an involuntary eyeball jerking. Alcohol and certain other drugs can cause nystagmus to become exaggerated and may cause the jerking to occur at lesser angles. The eye will twitch or jerk in an impaired person before reaching a 45-degree angle.
This test assesses a person’s ability to complete tasks requiring divided attention, similar to what’s needed for driving. In the walk-and-turn test, the subject is asked to take nine steps, heel-to-toe, along a straight line, turn on one foot and return in the same way. Officers look for signs of impairment, such as inability to keep balance, starting before instructions are finished, stopping while walking, not touching heel-to-toe, stepping off the line, using arms to balance, making an improper turn or taking an incorrect number of steps.
One-leg stand test
In the one-leg stand test, the individual is instructed to stand with one foot approximately six inches off the ground and count out loud by thousands until they’re told to put their foot down. The officer times the subject for 30 seconds. Indicators of impairment include swaying while balancing, using arms to balance, hopping to maintain balance and putting the foot down.
Non-standardized tests and court evidence
Non-standardized field sobriety tests, such as asking a person to recite the alphabet backward or touching the nose with a finger, aren’t included in the SFST and aren’t generally admissible as evidence in court. This is primarily because these tests have not undergone the same rigorous scientific evaluation as the standardized tests.
Anyone facing drunk driving charges should work closely with someone who understands how to handle these situations. Developing a defense strategy is critical in these cases, so defendants should seek legal guidance sooner rather than later.