One of the methods commonly used by officers to determine a driver's level of intoxication are the DUI field sobriety tests. This form of testing does not measure the driver's BAC levels, but rather their ability to pass tests that are presumed to be passable by a sober individual.
Illinois DUI Field Sobriety Tests
There are three main types of tests used by law enforcement officers to determine whether a driver may be driving under the influence. These are called "Standardized Field Sobriety Tests". The tests, or SFSTs, were developed over time and then "validated" by studies and adopted by NHTSA, an agency of the US Department of Transportation.
Walk and Turn
Sometimes called the "Heel-Toe" sobriety test, this is a divided attention test. In this test, the individual is instructed to take nine heel-to-toe steps along a straight line, and then pivot on one foot while taking small steps with the other, and returning with nine more steps to the starting point in the same way while keeping hands pressed against the sides of the body and counting each step aloud. The officer looks for eight indicators, or "clues" of possible impairment: unable to balance while listening to the instructions, begins before the instructions are completed, has to stop walking to regain their balance, steps off of the line, does not walk heel-to-toe, must use their arms to balance, does not turn properly, or takes too many steps.
One Leg Stand
Similar to the Walk and Turn, this test is meant to test the driver's ability to divide their attention, a task which is supposedly simple for a sober individual. The officer will instruct the driver to stand with one foot off the ground by approximately six inches, and then ask them to count aloud by thousands until they are instructed to place their foot back on the ground. The officer will time the driver performing this test for thirty seconds and look for four main indicators of intoxication during that time: using arms to assist balance, swaying, hopping to maintain balance, and putting their foot down before instructed to do so.
Horizontal Gaze Nystagmus (HGN)
HGN is the involuntary jerking of the eye that naturally occurs when the eyes are rotated at high peripheral angles. When a person is intoxicated, however, nystagmus becomes exaggerated and can occur when rotating at lesser angles, and they will have trouble smoothly tracking a moving object in front of them. To conduct this test, the officer will watch the driver's eyes as they follow a pen, small flashlight, or other object moving horizontally before them. The officer will look for three indicators of impairment: if one or both eyes cannot smoothly follow the object as it moves, if the eye is distinctly jerking when the eye is at the maximum deviation, and if the eye jerks when the angle of onset is within 45 degrees of center. If HGN is observed, officers then briefly check for VGN, or Vertical Gaze Nystagmus, which they are trained may indicate very high alcohol consumption.
Fighting the Evidence
Officers will claim that these tests are simple and expect that most people can pass without difficulty. In fact, there are so many instructions and requirements, these tests are extraordinarily difficult to pass even for the totally sober, and several factors may make performance of this test difficult in the absence of any alcohol or other intoxicating substance.
The standardization of these tests means the tests must be administered only to appropriate candidates for testing. The officer must therefore take specific steps to screen their test subject. Police are trained to give the tests only under satisfactory conditions, to only use the instructions they are trained to, and to demonstrate each test properly. Finally, the clues indicating impairment can only be registered based on certain trained standards. These tests are rarely administered in a manner that confirms to training, and are very often interpreted in a subjective, rather than objective manner.
If you were arrested for driving under the influence after taking DUI field sobriety tests, do not wait to discuss your case with a knowledgeable Chicago DUI defense attorney A talented and experienced lawyer from our team can thoroughly assess the circumstances that led to your arrest to determine your best defense options. The results of Illinois DUI field sobriety tests are highly subjective, and this evidence often rests on the officer's judgment of your actions during the test, rather than scientific evidence of your BAC at the time you were driving.