If an officer pulls you over under suspicion of driving under the influence (DUI), you may be asked to perform one or more field sobriety tests. These are intended to help determine if you are impaired and may provide probable cause for an arrest.
Here is what you should know about these tests and their accuracy:
What Are Field Sobriety Tests?
Field sobriety tests are preliminary roadside evaluations that a police officer may ask you to perform during a DUI stop. If you fail, you may be placed under arrest. Further testing, such as with a breathalyzer, can confirm impairment. Failing one of these evaluations can have a negative impact on your case.
Standardized Field Sobriety Tests (SFSTs)
Although officers may use a combination of different tests, the National Highway Traffic Safety Administration (NHTSA) recognizes three standardized field sobriety tests (SFSTs).
Horizontal Gaze Nystagmus
Nystagmus is an involuntary twitch in your eyes that happens when you are tracking an object in your peripheral vision (greater than 45 degrees). While this twitch is normal even when someone is sober, it may be a sign of impairment if nystagmus occurs when looking at an angle of less than 45 degrees or is more pronounced.
To perform the horizontal gaze nystagmus (HGN) test, the officer will ask you to remove any glasses if necessary. You will need to keep your head still and follow a light with only your eyes. The officer watches for lack of smooth pursuit, distinct nystagmus and maximum deviation, or an onset of the twitch before 45 degrees.
Walk and Turn (WAT)
During the walk and turn (WAT) test, you will need to walk nine heel-to-toe steps in a straight line with your hands at your sides, then turn around and walk back to the starting position. In addition to testing your ability to balance yourself, the evaluation also tests your ability to follow directions as the officer will tell you not to start until they tell you to.
One Leg Stand (OLS)
For the one leg stand (OLS) test, the officer will ask you to keep your hands at your sides and stand with one foot six inches off the ground with the toe pointed upward. You will need to look at that foot while counting. Like the WAT test, this evaluates your balance as well as your ability to follow instructions.
Are These Tests Accurate?
The NHTSA has scientifically evaluated the three standardized tests listed above and have deemed them the most accurate. Under ideal circumstances, officers correctly identified impaired individuals 88% of the time with HGN, 79% of the time with WAT, and 83% of the time with OLS. However, the evaluations are rarely performed in a perfect situation and many factors can influence their accuracy. In a DUI case, your lawyer will likely question the reliability of any tests you were given. It’s also important to note that any tests other than HGN, WAT, and OLS have not been verified as accurate.
Refusing to Take Field Sobriety Tests
Unlike blood alcohol concentration (BAC) tests, field evaluations are not mandatory under Arizona law. In most cases, it is beneficial to respectfully refuse to take them. You should remain polite throughout the entire DUI stop but it is also important to know your rights.
Need Help After a DUI Arrest?
If you were arrested for DUI, our attorneys can help. We will use our experience and dedication to help you achieve the best possible outcome.