If you’ve ever been pulled over in Missouri and asked to get out of your vehicle to perform a few simple maneuvers, then you’re likely already familiar with what is known as the Standardized Field Sobriety Test (SFST). For those who have not yet been unlucky enough to have such an interaction, the SFST is a series of three tests performed during a traffic stop to determine if a person is driving with a blood alcohol level above the legal limit (0.08 in Missouri).
The field sobriety test was first developed back in the 1970s and has been tested so that it is admissible as evidence in a court of law. Though more basic field sobriety tests are done in certain situations, most officers rely on the SFST when a person is suspected of drinking and driving. The program was created by the National Highway Traffic Safety Administration which trains officers all across the country, including those here in St. Louis, on how to perform the tests.
The three parts of the SFTS are the horizontal gaze nystagmus test (HGN), the walk-and-turn (WAT) and the one-leg stand (OLS). The HGN refers to an involuntary motion of the eye that naturally happens as someone looks from side to side. When a person is sober, HGN occurs when their eyes turn horizontally. When a person is intoxicated, HGN movement is much more distinctive. Someone who is under the influence would also have a more difficult time following a moving object, such as an officer’s finger.
Officers performing this test look for signs that the suspect’s eyes cannot smoothly follow a moving object. Officers also check to see if the eye twitching is distinct, a good indication that the driver is intoxicated. In fact, research from the NHTSA reveals that this test, if done properly, is able to indicate intoxication correctly 77% of the time.
The next field sobriety test commonly given is the walk-and-turn test. Though the name largely explains things, there is a bit more to say. The WAT requires that the suspect listen carefully and follow instructions while performing simple movements. Drivers who are under the influence of alcohol typically have a much harder time performing tasks that require both physical and mental concentration.
The WAT involves taking nine steps, heel-to-toe, in a straight line. After walking the appropriate distance, the subject is asked to turn around on one foot and return in the same way. Officers are trained to look for lack of balance, halting steps, failure to fully listen to instructions, failure to walk heel-to-toe and improper turning. Research says that 68% of those who demonstrate two or more failures with the WAT are have a blood alcohol level above the legal limit.
Finally, the one leg stand is the field sobriety test perhaps most commonly seen in movies and on old episodes of Law & Order. This test requires that a suspect stand with one foot six inches off the ground and count aloud for approximately 30 seconds. If the subject sways, hops, or uses their arms for balance, the officer will note these as indications of intoxication. Though it may seem like this would be hard for most people to do sober, the NHTSA says that 65% of people who fail two or more indicators have a blood alcohol level greater than 0.10.
Though each test on its own is far from definitive, the NHTSA claims that research has proven the reliability of the package of tests. In fact, they claim that when each of the three tests is performed correctly, there is a combined 90% chance that officers will accurately assess a driver’s level of intoxication.
If you’ve had a run in with the law and find yourself in need of a Missouri DWI defense lawyer capable of aggressively protecting your interests, contact our St. Louis DWI law firm today at (314) 863-0500.
Source: “Standardized Field Sobriety Testing,” published at NHTSA.gov.