An article published earlier this month addresses the accuracy of field sobriety tests (FSTs). A team of researchers set-out to evaluate the effectiveness of FSTs for identifying drivers under the influence of THC. The researchers conducted clinical trials involving THC use, field sobriety testing, and driving simulations. The clinical trials showed the FSTs do not effectively discriminate between people who are impaired and people who are not impaired.
Law Enforcement Use of Field Sobriety Tests
In the 1970s, the National Highway Traffic Safety Administration (NHTSA) developed three standardized field sobriety tests: Horizontal Gaze Nystagmus test, Walk And Turn test, and One Leg Stand test. NHTSA published the manual “DWI Detection and Standardized Field Sobriety Testing”, which is used to train law enforcement officers how to administer FSTs. NHTSA materials also provide training for additional tests: Finger-to-Nose test, Lack of Convergence test, and Modified Romberg test. Although the FSTs are designed to predict a person’s blood alcohol concentration, the tests are also used by law enforcement officers to detect impairment from drugs other than alcohol.
The Recent Study
As the most prevalent drug in DUI cases is THC, a team of researchers endeavored to “examine the classification accuracy of FSTs with respect to cannabis exposure and driving impairment”. The accuracy of a test includes the test’s ability to distinguish between impaired drivers and non-impaired drivers. As the article states, “validation of objective, unbiased, and effective methods for discriminating between drivers who are or are not impaired by cannabis is critical in ensuring equitable enforcement of driving-under-the-influence laws.”
To examine the accuracy of SFSTs, the researchers conducted clinical trials. The trials involved 184 participants who used cannabis in the past 30 days but did not use cannabis for at least two days before the trial. During the trial, 121 participants smoked cigarettes with THC, and 63 smoked placebo cigarettes. Trained law enforcement officers administered FSTs to the participants. The officers then predicted whether each participant received real marijuana or a placebo, and the officers classified each participant as being impaired or not impaired. The participants then drove on a driving simulator and were scored on key driving variables.
Results of the Study
The ‘THC group’ performed worse on FSTs and the driving simulator than the ‘placebo group’. This could lead to the conclusion that FSTs reliably predict whether a driver is impaired. However, the clinical trials showed the FSTs do not reliably distinguish between impaired drivers and non-impaired drivers. According to the article, “a substantial proportion of the placebo group performed poorly on the FSTs, and officers classified 49.2% of the placebo group as FST impaired.” The placebo group was subjected to blood testing, so it was clear they were not under the influence of alcohol or drugs during the FSTs.
This is a huge problem. In a real-world situation, an officer who administers FSTs and classifies a person as impaired arrests that person. That means 49.2% of drivers who are not under the influence of alcohol or drugs would be arrested and charged with OVI. This applies not only to drivers suspected of THC impairment, but also to drivers suspected of alcohol impairment. The FSTs do not work: half of sober drivers who take FSTs would be arrested for OVI.
This is not the first study to conclude FSTs do not accurately predict THC impairment. A U.S. Department of Justice study reached the same conclusion. The most significant implication of this study is the FSTs are not effective for predicting driving impairment from any cause because sober people perform poorly on them.