Standardized Field Sobriety Test

Driving under the influence, is the crime of driving a motor vehicle while impaired by alcohol or other drugs, to a level that renders the driver incapable of operating a motor vehicle safely. The name of the offense varies from jurisdiction to jurisdiction and from legal to colloquial terminology. Other terms include: drink-driving, drunk driving, drunken driving, impaired driving, operating under the influence, drinking and driving, over the prescribed limit .

With alcohol, a drunk driver 's level of intoxication is typically determined by a measurement of blood alcohol content or BAC. A BAC measurement in excess of a specific threshold level, such as 0.05% or 0.08%, defines the criminal offense with no need to prove impairment. In some jurisdictions,

A police officer in the United States must have probable cause to make an arrest for driving under the influence. In establishing probable cause for a DUI arrest officers frequently consider the suspect 's performance of Standardized Field Sobriety Tests. The US National Highway Traffic Safety Administration has established a standard battery of three roadside tests that are recommended to be administered in a standardized manner in making this arrest decision. The first test typically administered is the Horizontal Gaze Nystagmus test. When this test is conducted the officer is looking for the involuntary jerking of the suspect 's eyes as they gaze toward the side. The officers check for three separate clues in each eye. The clues for each eye are: lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation and onset of nystagmus prior to 45 degrees. They also then check for vertical nystagmus. Another test that may administered is the Walk and Turn test. This test is a divided attention test and also measures balance. It requires the suspect to walk heel-to-toe on a line along with other instructions. There are eight clues that the officer is looking for when conducting this test. The officer looks for the following clues: cannot keep balance during instructions, starts the test before the instructions are finished, stops while walking to steady themself, misses heel-to-toe, steps off the line, uses arms to balance, makes an improper turn and takes the incorrect number of steps. The other standardized test is the One Leg Stand . The OLS test requires the suspect to stand on one leg for 30 seconds and also measures balance, coordination, and similar to the WAT test, divides the suspect 's attention. The officer is looking for any of the four possible clues: Sways while balancing, uses arms for balance, hopping and puts their foot