Standardized Field Sobriety Tests Used by Law Enforcement

 Posted on July 15, 2014 in DuPage County criminal defense attorney

When a driver is pulled over by law enforcement on suspicion of driving under the influence (DUI), the police will usually have the driver go through a series of field sobriety tests.

There are three standardized field sobriety tests used by police across the country, which were developed at the Southern California Research Institute, with support from the National Highway Traffic Safety Administration (NHTSA). These tests are the Horizontal Gaze Nystagmus (HGN), Walk-and-Turn (WAT), and One-Leg Stand (OLS).

When there is a disturbance to the brain’s ability to control eye movements, an involuntary bouncing or jerking of the eye occurs when a person tries to look sideways. This is referred to as nystagmus. Alcohol affects the brain’s ability to control the eye muscle, so a person who has been drinking will show signs of nystagmus. The more the person drinks, the more pronounced are the eye movements. For the HGN test, an officer will hold a penlight about a foot away from a person’s face and tell them to follow the light.

For the WAT test, the person walks in a straight line, heel to toe, for nine steps. On the ninth step, they are instructed to turn around on one foot and then walk back the same way, heel to toe. The officer will look for several signs that indicate impairment, which include:

• The person not being able to keep their balance;
• Whether or not the person begins walking without waiting for the officer’s instructions;
• The person needing to stop walking in order to regain their balance;
• The person not walking heel to toe;
• The person stepping off the line;
• The person needing to use his or her arms to stay balanced;
• The person not turning around correctly; and
• The person taking more or less than nine steps.

When using the OLS test, the person is instructed to stand with one foot approximately six inches off the ground. They are then to count, out loud, by the thousands until they are instructed to put their foot down. The officer will time the person for 30 seconds. Indicators of impairment an officer looks for include swaying, an inability to keep the foot off the ground, hopping in order to stay balanced, or using arms to stay balanced.

According to national statistics provided by NHTSA, when law enforcement use results from the three tests combined, they are correct 91 percent of the time regarding a person’s impairment. However, there are circumstances that could affect a person’s ability to perform these tests and could lead to an improper arrest. If you were arrested for driving under the influence and failed the field sobriety tests, please contact an experienced DuPage County criminal defense attorney to make sure that your constitutional rights are protected in the courtroom.