When a police officer initiates a traffic stop for the suspicion of drunk driving, they have to figure out what’s going on. They have several tools that they can use to determine whether a driver is impaired or not.
They may rely on the standardized field sobriety test when assessing potential impairment in drivers.
1: One-leg stand
The one-leg stand checks balance and concentration. During this test, the individual stands with one foot approximately six inches off the ground and counts by thousands for 30 seconds. Officers look for signs of impairment, including swaying, hopping or using arms for balance.
2: Walk and turn
The walk-and-turn test measures a person’s ability to follow directions and execute tasks requiring divided attention. In this test, the individual is instructed to take nine heel-to-toe steps along a straight line, turn on one foot and return in the same manner in the opposite direction. The officer assesses the person’s ability to maintain balance, follow directions and walk in a straight line.
3: Horizontal gaze nystagmus
This component involves the involuntary jerking of the eyeball, which can become exaggerated when a person is impaired by alcohol. In this test, the officer checks a suspect’s eyes as they slowly move a finger or another object horizontally in front of the person’s face. The officer looks for three indicators of impairment in each eye that occur when alcohol and certain other drugs impair the nervous system’s control of eye movements.
While these tests are standardized and widely used, they aren’t foolproof. Factors like physical impairments, nervousness or weather conditions can affect a person’s performance on these tests. Those factors may be considered as part of a drunk driving defense.