Driving Under the Influence (DUI), more commonly known as drunk driving, is a crime of driving a motor vehicle while impaired by alcohol or other drugs. To determine a driver's level of intoxication from alcohol, officers use a breathalyzer that measures a person's blood alcohol content (BAC). In Florida, a BAC measurement of .08 or higher constitutes the criminal offense and is all that is needed to prove impairment. Further, officers may conduct a field sobriety test to determine whether a suspect is impaired.
In order to arrest a suspect for a DUI, the officer must have probable cause. To establish probable cause, police officers evaluate the performance of a suspect's field sobriety exercises. The US National Highway Traffic Safety Administration (NHTSA) recommends three roadside tests to be administered before making an arrest decision. The first test is the Horizontal Gaze Nystagmus test. The officer is looking for the involuntary jerking of the suspect's eyes as they gaze toward the side as the test is conducted. The next test administered is the Walk and Turn (WAT) test. This test is a divided attention test that also measures balance. The suspect must walk heel-to-toe on a line while following other instructions. The officer looks for the following clues to determine intoxication: cannot keep balance during instructions, misses heel-to-toe, uses arms to balance, makes an improper turn, steps off the line and takes an incorrect number of steps. The last test usually administered is the One Leg Stand (OLS). This test makes the suspect stand on one leg for 30 seconds. It measures balance and coordination.