Addiction Alcohol Use Drunk Driving Field Sobriety Test to Assess Drunk Driving By Buddy T facebook twitter Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism. Learn about our editorial process Buddy T Medically reviewed by Medically reviewed by Daniel B. Block, MD on March 09, 2020 twitter linkedin Daniel B. Block, MD, is an award-winning, board-certified psychiatrist who operates a private practice in Pennsylvania. Learn about our Review Board Daniel B. Block, MD on March 09, 2020 Print DarrenMower/Getty Images Field Sobriety Tests are groups of three tests used by police to determine if a driver is impaired. The tasks assess balance, coordination, and the ability of the driver to divide his attention to more than one task during the field sobriety test. The tests have been scientifically proven to validate legal intoxication in drivers suspected of drunken driving in 90% of cases if administered by a trained officer. Results of the test are admissible as evidence in court. The Field Sobriety Test National Highway Traffic Safety Administration defines and describes the three parts of the SFST in detail. If the driver fails any of the field sobriety tests, the officer will then ask the suspect to take a breath test or a chemical test to confirm their blood-alcohol content. The Standard Field Sobriety Test (SFST) is a battery of 3 tests that include the horizontal gaze nystagmus (HGN), the walk-and-turn, and the one-leg stand tests. Horizontal Gaze Nystagmus Horizontal gaze nystagmus is an involuntary "jerking" of the eyeball which happens to everyone when the eyes are rotated at high peripheral angles. When a person is intoxicated, however, the jerking of the eyes becomes more exaggerated and occurs at lesser angles. Turning the HGN test, the officer will ask the driver to follow a moving object, such as a pen or flashlight, slowly from side to side. The officer looks to determine: If jerking is distinct when the eye is at maximum deviationIf the angle of jerking onset is within 45 degreesIf the eye cannot follow the object smoothly If four or more clues appear between the two eyes, the driver is likely to have a blood-alcohol content (BAC) 0.10 or greater. NHTSA research shows this test to be accurate in 77% of test subjects. Walk-And-Turn Test For the walk-and-turn test, the officer asks the driver to take nine steps, heel-to-toe, along a straight line, turn on one foot and return nine steps in the opposite direction. During the test, the officer looks for seven indicators of impairment. A subject may be impaired if they: Begin before the instructions are finishedCannot keep balance while listening to the instructionsDoes not touch heel-to-toeLoses balance while turningStops while walking to regain balanceTakes an incorrect number of stepsUses arms to balance If the driver exhibits two or more of the above indicators during the test, there is a 68% likelihood of at BAC level of 0.10 or higher, according to the NHTSA. Impairment Begins Long Before You Are Legally Drunk One-Leg Stand Test For the one-leg stand test, the officer asks the driver to stand with one foot about six inches off the ground and count from 1,001 (one-thousand-one, one thousand two, etc.) until the officer says to put the foot down. During the next 30 seconds, the officer looks for these four indicators: Hopping to maintain balancePutting the foot downSwaying while balancingUsing arms to balance If the driver exhibits two or more of the above indicators, there is a 65% chance they have a BAC of 0.10 or greater, according to the NHSTA. Can You Fail the Test While Sober? There are many reasons that people who are not intoxicated might not be able to perform the above tests successfully, including certain medical conditions, disabilities, age, injury, and taking a certain medication. Wearing contact lenses, for example, could affect the HGN test results. The officer usually will ask the driver if there is a reason that they may not be able to pass the test and makes a note of their answer in his arrest report. If there is a legitimate reason, medical or otherwise, why you might fail one or more parts of the field sobriety test make sure you mention it to so that the officer makes a note of it in the official record. It might be helpful to you in court later. Was this page helpful? Thanks for your feedback! Learn the best ways to manage stress and negativity in your life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Stuster J. Validation of the standardized field sobriety test battery at 0.08% blood alcohol concentration. Hum Factors. 2006;48(3):608-14. doi:10.1518/001872006778606895 National Highway Traffic Safety Administration (NHTSA). Instructor Guide DWI Detection and Standardized Field Sobriety Testing Refersher. October 2015.