Police officers in Colorado and elsewhere use three standardized field sobriety tests along with other clues to help them decide whether or not to arrest a driver on suspicion of driving under the influence of alcohol or drugs (DUI). These tests include the horizontal gaze nystagmus test, the one-leg stand test, and the walk-and-turn test.
These tests are difficult to pass, even if a driver is sober. However, police continue to use them because their ability to pick out drivers who are actually impaired is rated quite high by authorities such as the National Highway Traffic Safety Administration (NHTSA). For instance, a 1998 study cited by NHTSA concluded that in 88 percent of cases, the horizontal gaze nystagmus test will correctly identify an impaired driver; in 79 percent of cases, the walk-and-turn test will correctly identify a drunk driver; and in 83 percent of cases, the one-leg stand test will correctly identify a drunk driver. Overall, the study concluded, the standardized field sobriety tests will correctly identify drunk or impaired drivers 91 percent of the time if all three tests are used together.