Police officers who conduct a drunk driving traffic stop need to take steps to determine if the driver is impaired. They typically do this through a variety of methods, including a brief interview, a chemical test and a field sobriety test.
There are countless field sobriety tests that police officers can conduct. Only three of these are part of the standardized field sobriety test that’s endorsed by the National Highway Traffic Safety Administration. These tests are the only ones that are admissible in court.
Walk and turn
This test requires a person to take nine heel-to-toe steps along a straight line, pivot on one foot, and return in the same manner. While it may sound simple, it challenges both physical balance and mental focus. Officers look for signs of impairment such as stepping off the line, starting too early, miscounting steps or using arms to balance.
One leg stand
In this test, the individual must raise one foot approximately six inches off the ground and hold it steady while counting aloud until told to stop. The typical duration is 30 seconds. Officers note any hopping, swaying, putting the foot down or difficulty keeping balance.
Horizontal gaze nystagmus
The horizontal gaze nystagmus (HGN) test involves following a moving object—usually a pen or flashlight—with just the eyes. Nystagmus is an involuntary jerking of the eyes that becomes more pronounced when a person is impaired. Officers observe whether the eyes can smoothly follow the object, whether the jerking starts before a 45-degree angle, and whether the motion becomes exaggerated.
If these tests indicate impairment, the officer may arrest the driver. At that point, the driver has to think about their defense strategy. Working with someone familiar with drunk driving cases may be beneficial.