It is likely that most Massachusetts drivers have heard of field sobriety tests; however, they may not know what the most common tests are. The Standardized Field Sobriety Test is comprised of three main tests that are used by authorities to look for impairment: the horizontal gaze nystagmus test, or HGN test, the one-leg test, and the walk-and-turn test.
When a police officer uses the HGN test, they are looking for nystagmus, or involuntary jerking, of the eye, at a horizontal level. The officer may conduct this test by slowly moving a pen or a flashlight horizontally in front of the eyes while instructing the person to follow the object without moving their head. In the one-leg test, the person must stand on one foot with the second foot held 6 inches above the ground. They must then count in thousands for thirty seconds. Finally, in the walk-and-turn test, the person must take exactly nine steps, heel-to-toe. Then, they must turn on one foot and continue back the way they came.
In each test, officers may look for indicators of impairment, such as loss of balance, failure to follow instructions and failure to focus on objects. The tests have a certain degree of accuracy, with 77 percent of people who exhibit HGN found to have a BAC of .10 percent or higher. For the one-leg test and the walk-and-turn, 68 percent of people and 65 percent of people are found to have a BAC of .10 percent or higher, respectively.
While the field sobriety tests do provide indicators of impairment, not everyone can do the tests due to physical or mental impairments. If someone is taken into custody on suspicion of drunk driving, it is recommended that they seek advice from an attorney to potentially determine if the case can be challenged due to the field sobriety tests being improperly conducted.
Source: National Highway Traffic Safety Administration, "The Highway Safety Desk Book", November 30, 2014