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What 3 tests are commonly used for field sobriety tests?

The Standardized Field Sobriety Test is a series of three assessments that South Carolina law enforcement officials administer to help them determine whether a driver suspected of impairment is in fact impaired. The series consists of the horizontal gaze nystagmus, the one-leg stand and the walk-and-turn test. Reportedly, the National Highway Traffic Safety Administration helped in the research used to develop these assessments.

The horizontal gaze nystagmus is when the human eyeball involuntarily jerks while gazing from side to side. This is a natural occurrence, but the jerking is exaggerated in alcohol-impaired people, making it hard for them to smoothly track a moving item. During HGN tests, officials observe the horizontal movement of the driver's eyes as the driver follows a slowly moving object.

The one-leg stand and walk-and-turn tests evaluate the drivers' capacity for paying attention and performing acts of balance. During one-leg stand tests, officers instruct drivers to stand with one foot about 6 inches above the ground while counting until they are told to stop. The duration of the test is 30 seconds.

During walk-and-turn tests, officers direct drivers to walk in a heel-to-toe manner for nine steps along a line. Then, the drivers must pivot on one foot and repeat the process going back to where they started.

When drivers are charged with DUI, the impairment indicators that police record from these field sobriety tests may be used as evidence. However, drivers may retain a criminal defense lawyer following the traffic stop, who might argue that the indicators were the result of a health condition and not impairment. By invalidating such purportedly incriminating evidence, defense lawyers may cast doubt on impaired driving charges. This blog post is not meant to be substituted for legal counsel.

Source: National Highway Traffic Safety Administration, "The Highway Safety Desk Book", November 22, 2014

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