Accuracy of Field Sobriety Tests
U.S. police officers have been using the three standardized field sobriety tests (FSTs)–the horizontal gaze nystagmus, the walk-and-turn, and the one-leg stand—since the late 1970s. The purpose of FSTs is to determine whether a driver is too intoxicated to drive his or her motor vehicle. The results are often used as a basis of probable cause for an OUI arrest.
However, the reliability of these tests is typically questioned. While police and prosecutors alike depend on FST results for ascertaining a driver’s level of intoxication, many criminal defense attorneys believe these tests can sometimes be inaccurate.
How Reliable are Field Sobriety Tests?
To determine the accuracy of FSTs, the NHTSA performed various studies involving officers. Police officers were tested to see how they could properly identify a person with a BAC of .1% or higher.
The results of these NHTSA-sponsored tests are the following:
- The accuracy rate when all three tests were used together – 82%
- The accuracy rate of the horizontal gaze nystagmus – 77%
- The accuracy of the walk-and-turn – 68%
- The accuracy of the one-leg stand – 65%
When these tests are correct, they only indicate a driver’s BAC level and not his or her ability to drive a vehicle. Overall, the FSTs are not a scientifically-proven method to determine intoxication.
There are expert witnesses who study FSTs and understand their vulnerabilities. Any individual arrested for drunk driving on the basis of a field sobriety test score is encouraged to challenge their results in an effort to obtain a favorable outcome in their OUI case.