When a person is suspected of drunk driving in Connecticut, police officers will normally ask if they would be willing to perform roadside or field sobriety tests. While an officer may choose to administer a couple of additional tests, such as reciting the alphabet, counting or touching the tip of their finger to their nose, the three most reliable tests are ones that have been studied and standardized.
In order to provide some consistency in DUI investigations, the National Highway Traffic Safety Administration commissioned a study into the validity of certain types of roadside sobriety tests in the 1980s. From the study, three of the tests were determined to have a statistical correlation to intoxication. Those tests are called the horizontal nystagmus test, the one-legged stand and the walk-and-turn. They are the three tests that are most commonly used by DUI officers.
The walk-and-turn and the one-legged stand are both divided attention tests. They rely on the notion that an intoxicated person will have difficulty multitasking between performing a physical test and listening to verbal instructions. The one-legged stand involves the person standing with one leg raised off the ground about 6 inches while estimating 30 seconds in their heads. The walk-and turn involves the person walking heel-to-toe in a mandated manner down an imaginary line and back. The HGN is a test in which the officer will ask the person to follow his or her finger side to side while looking for involuntary jerking movements of the eye that are associated with alcohol and some other substances.
Although widely used, DUI sobriety tests are not infallible. There are certain conditions that may cause a person to fail even when they are sober. A criminal defense attorney may be able to attack performed sobriety testing through cross-examination.
Source: National Highway Traffic Safety Administration, "The Highway Safety Desk Book", November 30, 2014