Ohio law enforcement uses several factors to charge motorists with DUI/OVI charges, one of which involves field sobriety testing. Field sobriety tests help officers determine if their suspicions are valid (probable cause) and the level of intoxication or impairment a driver is experiencing.

According to the Insurance Institute for Highway Safety, Highway Loss Data Institute, law enforcement officers can also use preliminary blood alcohol content results in conjunction with field sobriety tests to determine if alcohol impairment is an issue. The three common types of field sobriety tests police use at DUI checkpoints and traffic stops are the horizontal gaze nystagmus, one-leg stand, and walk-and-turn.

Horizontal nystagmus

Alcohol and drug impairment reduce drivers’ ability to control their movements, especially their eyes. Officers use the horizontal nystagmus assessment to determine if there is enough impairment to affect normal nystagmus (repetitive eye jerking) function and pupil size. When drivers are suffering from impairment, their pupils are larger or more unequal in size than normal, unable to smoothly follow objects and they may exhibit repetitive, involuntary eye movement when looking at certain angles.

One-Leg stand

The one-leg standing assessment measures an impaired person’s ability to maintain balance while standing on one foot. During the test, the administering officer has the person count while he or she observes the driver’s ability to hold balance without making excess movements, i.e., waving arms, swaying, dropping the other foot and hopping around.

Walk-and-turn

The walk-and-turn test involves walking in a straight line, using a heel-to-toe stance. An impaired individual experiences challenges with this particular test because it requires him or her to perform multiple functions at once. To successfully pass the walk-and-turn, drivers must maintain their balance, focus and follow all directions.

Neurological issues, health conditions, medications and other factors can affect a person’s ability to pass field sobriety testing without impairment, states Alcohol.org. The officer administering the tests must have proper training. Many successful DUI defenses counter the credibility of the field sobriety tests and law enforcement’s use of probable cause.