Last week, we were discussing Field Sobriety Tests, (FST) and it turns out there are standardized types of these tests that most jurisdictions use. The most common are the Standardized Field Sobriety Test (SFST), which are recognized by the National Highway Traffic Safety Administration (NHTSA). They were created to enable law enforcement a method of determining impairment from drivers that would have more validity than merely the officer’s “gut feelings.”
The SFSTs are designed to allow an officer during your DUI stop in Tennessee a framework to accurately describe your behavior and to provide testimony in court that will be compelling enough for the judge or jury to return with a guilty verdict.
The three SFSTs created by the NHTSA are the Horizontal Gaze Nystagmus test, the Walk-and-Turn test, and the One-Leg Stand test.
Horizontal Gaze Nystagmus test is designed to provoke involuntary jerking of the eye as it tracks an object moving horizontally from side to side. If one is impaired by alcohol, this nystagmus is “exaggerated.” The officer will hold a pen or small flashlight in front of your eyes and watch your eyes as they follow the object. NHTSA claims this test is 88 percent accurate.
Walk and Turn is designed test your ability to walk a straight-line heel-to-toe for nine steps, and then turn on one leg and return. It is supposed to test your ability to follow directions while engaging in physical activity. The officer is watching for mistakes in following the instructions and inability to maintain balance, take the correct number of steps, make the turn correctly, etc. The officer is observing eight factors. NHTSA claims 79 percent effectiveness for this test.
The One-Leg Stand, unsurprisingly, demands you stand on one leg for 30 seconds. The officer will be watching to see how well you maintain your balance and if you sway or put your foot down. They claim failing two or more of these factors indicates a 0.08 BAC 83 percent of the time.
If you attempt either the walk and turn and the one-leg stand when you have had nothing to drink, you may find they are not that easy and that under the pressure and stress of a roadside stop, you may be even less confidant in your success.
Of course, with all of these tests, for all of their veneer of science, they are subjective observations by a human, not a measurement by a calibrated machine. And those humans are not without potential for error.