How accurate are field sobriety tests?

| May 16, 2019 | Field Sobriety Tests |

If you’re suspected of driving under the influence in Massachusets, you’ll likely be subjected to a field sobriety test. These tests are designed to determine whether a person is under the influence of alcohol or other substances behind the wheel and are considered a reliable way to determine a person’s sobriety. But are they truly accurate? Very Well Mind explains how field sobriety testing works, as well as define their level of accuracy. 

Walk and turn test

This test entails taking nine steps in the heel-to-toe formation while walking in a straight line. Upon reaching the ninth step, you’ll be asked to turn on one foot and return using the same directions. While the test is being conducted, the officer will look for certain things. For instance, loss of balance is considered an indication of intoxication, as is stopping in order to regain balance. Your form will also be assessed, as well as whether you take the accurate number of steps. The walk and turn test is considered 68% accurate at determining BAC of 0.10% when two or more signs of impairment are witnessed. 

Horizontal gaze nystagmus (HGN)

HGN testing looks for abnormal jerking of the eyes when the test subject is following an object, such as a flashlight. These abnormalities include an inability to follow the object smoothly or when the eyes make these movements at lesser angles. This is thought to indicate inebriation. HGN testing is thought to be accurate up to 77% of the time, provided there are four or more indications of abnormal eye movements. 

One leg stand test

This test involves standing on one foot and counting from 1,001. The test usually takes 30 seconds, during which time the officer looks for balance issues or whether the person puts the elevated foot down to prevent falling. This test is considered to be 65% accurate at judging a BAC of 0.10% or higher. Medical conditions or other factors can cause the failure of a field sobriety test, so it’s important to inform the officer if you have a disability or other problem. Failing a field sobriety test usually calls for a follow-up breathalyzer.