A person who police officers stop for the suspicion of drunk driving may be asked to take a field sobriety test. While there are many types of tests that an officer can conduct, there are only three that the National Highway Traffic Safety Administration endorses. These are known as the standardized field sobriety test (SFST).
The three tests in the SFST are considered reliable enough to be used in court. The three components include:
One-leg stand
The one-leg stand evaluates a person’s balance and physical control by requiring them to stand with one foot approximately six inches off the ground and count by thousands until they’re told to put their foot down. The officer watches for signs of impairment, including swaying, using arms to balance, hopping to maintain balance and putting their foot down before being instructed to.
Horizontal gaze nystagmus
During the HGN test, an officer will ask the individual to follow an object, like a pen or flashlight, with their eyes without moving their head. The officer looks for three indicators of impairment in each eye:
- If the eye can’t follow the object smoothly
- If jerking is distinct when the eye is at maximum deviation
- If the angle of onset of jerking is within 45 degrees of center.
If the officer sees these indications of impairment, they may deduce that the driver is impaired.
Walk-and-turn
The walk-and-turn test assesses an individual’s ability to complete tasks requiring attention, balance and coordination. The subject is instructed to take nine steps, heel-to-toe, along a straight line, turn on one foot and return in the same manner. This test is designed to divide the subject’s attention between physical and mental tasks, revealing potential impairment.
Even though they’re considered reliable, these tests are still subjected to the interpretation of the person conducting the test. This, along with other information, can be used as part of a defense strategy in court.
