The three standardized field sobriety tests (SFSTs), validated by the National Highway Traffic Safety Administration (NHTSA) and commonly used by law enforcement to assess impairment during DUI stops, are:
- Horizontal Gaze Nystagmus (HGN) Test
This test involves the officer asking the person to follow a moving object (like a pen or finger) with their eyes while keeping their head still. The officer looks for involuntary jerking of the eyes (nystagmus), which is more pronounced under the influence of alcohol. There are three key indicators in each eye: inability to smoothly follow the object, distinct jerking at maximum eye deviation, and jerking before the eye reaches 45 degrees off center
- Walk-and-Turn Test
This test evaluates balance, coordination, and the ability to follow instructions. The person is instructed to take nine heel-to-toe steps along a straight line, turn on one foot, and take nine steps back, all while counting aloud. Officers observe for signs of impairment such as losing balance, stepping off the line, starting too soon, or making an improper turn
- One-Leg Stand Test
The individual is asked to stand on one leg with the other foot raised about six inches off the ground and count aloud for 30 seconds. The officer watches for swaying, using arms to balance, hopping, or putting the foot down. These behaviors suggest impairment
These tests must be administered in a standardized manner to ensure their validity and reliability as objective indicators of impairment
. Results from these tests, combined with other evidence, help officers decide if a person is impaired and whether to proceed with further testing or arrest.
