The Standardized Field Sobriety Test (SFST) is a series of three tests administered and evaluated in a standardized manner to obtain valid indicators of impairment and establish probable cause for arrest. These tests were developed as a result of research sponsored by the National Highway Traffic Safety Administration (NHTSA). A formal program of training was developed and is available through NHTSA to help police officers become more skillful at detecting DUI suspects, describing the behavior of these suspects and presenting effective testimony in court. Formal administration and accreditation of the program is provided through IACP. The three tests of the SFST are:
· the horizontal gaze nystagmus (HGN)
· the walk-and-turn
· the one-leg stand
These tests should be administered systematically and objectively evaluated according to measured responses of the suspect. (Sullivan, 2004)
a. HGN Testing
Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as a pen or small flashlight, horizontally with his eyes. (Wanberg, 2004)
The examiner looks for three indicators of impairment in each eye: 1) if the eye cannot follow a moving object smoothly, 2) if jerking is distinct when the eye is at maximum deviation, and 3) if the angle of onset of jerking is within 45 degrees of center. If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.10 or greater....................
