In California, as is the case in most states, Field Sobriety Tests are used to determine probable cause to arrest for driving under the influence. The “tests” are also used as substantive evidence of impairment for purposes of proving whether the driver was guilty of driving while “impaired” under the legal definition of “under the influence” in criminal court. But are these tests reliable?
To answer this question we have to first understand the origin of these tests. Back before per se laws were enacted the government had to prove the driver was actually impaired or affected by alcohol to the degree they could no longer drive a vehicle with the required caution characteristic of a sober driver under the same or similar circumstances. Cops were often scant in the evidence they had collected to prove this so the government embarked on a mission to provide law enforcement with tools they could use in the field to collect evidence of this nature. This was the birth of the SFST which stands for Standardized Field Sobriety Test. These exercises were created in a way that every police officer could administer the tests in the same manner whether they are in California or some other state. Thus, the name ”Standardized” Field Sobriety Test.
The government entity behind the tests was NHTSA, the National Highway Traffic Safety Administration. It sponsored studies that would back up and bolster the efficacy of the SFST. In early testing the SFSTs were found to be about 70-80 percent accurate in predicting blood alcohol levels above .10 which was the national BAC limit in most states at that time. The tests were comprised of a “3 test battery” consisting of the Horizontal Gaze Nystagmus (HGN), the Walk and Turn (WAT), and the One Leg Stand (OLS). What is important to understand is that the tests were never validated to measure impairment. Let me repeat that: The SFST’s were never designed to validate or measure impairment. They were validated only to predict or determine whether a subject was above the legal limit at the time, .10 BAC. [ See “Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent” NHTSA Study 1998]. The following is a direct quote from the study: ”…… SFST results help officers to make accurate DWI arrest decisions even though SFSTs do not directly measure driving impairment.” (pg. 28, Ibid.)
With all this being said, here is the crux of the issue. FST exercise results can be very incriminating when the observations show obvious signs of physical and mental impairment due to alcohol intoxication. However, police will often report the driver did not perform well when subtle ”clues” are observed. it is in these cases where the administration of the test must be in strict accordance with the training and standardized procedures. Particularly when it involves the HGN test, cops will oftentimes not conduct the test properly. As a DUI Attorney with over 30 years experience, I personally can attest to the fact these tests are done too fast and certain critical steps are often skipped.
When field sobriety testing is conducted in a manner that departs from established methods and procedures, the results are inherently unreliable. In an extensive study, the National Highway Traffic Safety Administration (“NHTSA”) evaluated field sobriety tests in terms of their utility in determining whether a subject’s blood-alcohol concentration is below or above the legal limit. The NHTSA concluded that field sobriety tests are an effective means of detecting legal intoxication “only when: the tests are administered in the prescribed, standardized manner,……the standardized clues are used to assess the suspect’s performance,….. [and] the standardized criteria are employed to interpret that performance.” National Highway Traffic Safety Administration ., U.S. Dept. of Transp., HS 178 R2/00, DWI Detection and Standardized Field Sobriety Testing, Student Manual (2000), at VIII-3. According to the NHTSA, “[i]f any one of the standardized field sobriety test elements is changed, the validity is compromised.” Id.