The Standardized Field Sobriety Test (SFST) or Field Sobriety Test (FST) is a group of three physical activities that a law enforcement officer can administer at the scene when a driver is stopped for possible Driving While Intoxicated, DWI (or in some states Driving Under the Influence, DUI). These tests measure a person’s coordination and balance, which are impaired when a person has been drinking. The expressed purpose of the SFST is to assess if the driver is impaired and should be arrested. In some states, there is an observation period of 15-20 minutes for police to observe the driver prior to FST. The three physical activities are: Horizontal Gaze Nystagmus (HGN), Walk-and-turn (WAT) and One-Leg Stands (OLS). The SFST was developed by the Southern California Research Institute for the National Highway Traffic Safety Administration.
The HGN test instructs the suspect to follow an object such as a pen or a small flashlight with their eyes. This test measures the involuntary jerking of an individual’s eye, which is exaggerated when one is drunk. An alcohol-impaired person will have difficulty smoothly tracking a moving object.
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The Walk-and-turn test involves the suspect taking nine heel-to-toe steps in a straight line usually on the side of the road. (The heel of suspect’s right foot touching the toe of the left foot).The suspect must then turn around on one foot and return along the same line. The officer looks for the suspect to lose balance, to start before all the instructions are given, the suspect stops to balance, uses arms to balance, takes an incorrect number of steps or does not put his foot down in heel-to-toe fashion. There are many ways a suspect can fail this test.
In the One-Leg stand, the suspect must stand on one leg and hold the other leg six inches off the ground for 30 seconds while counting from one thousand. The officer looks for lack of balance, using arms to steady themselves, and touching the held up foot to the ground. It is known that people over 60 or 50 pounds or more overweight or those with back or leg problems have difficulty with the test. It should not be done in total darkness and must be administered on a dry, level surface. In addition to these three tests, some law enforcement personnel might use non-standardized field sobriety tests as well – such as touching a finger to one’s nose, counting finger test or ABC test.
FSTs are “divided attention exercises”, that is, they test an individual’s ability to listen to instructions and then carry them out.
The International Association of Chief of Police (IACP) and NHTSA publishes a manual for conducting SFSTs and also conduct a three-day course around the country for law enforcement officers on “how to” conduct a DWI/DUI traffic stop and SFST including writing the report. The manual was formerly called the Driving While Intoxicated Detection and Standardized Field Sobriety Test but is now known as the Advanced Roadside Impairment Driving Enforcement.
Because the results of SFST can be used as evidence in a drunk driving case with possibly severe consequences, there has always been intense interest in the validity of the SFST. Defense attorneys have argued the subjectivity of some of the observations, especially the Horizontal Gaze Nystagmus (HGN). Many people find the Field Sobriety Tests difficult to do even if they have not been drinking! Any driver suspect can refuse to do the FST. The refusal, however, can be used against someone at trial as evidence that the driver did not want to incriminate themselves. Many DUI/DWI defense attorneys advise against participating in the FST, or any other act which would corroborate the officer’s suspicion that the driver is intoxicated. In almost all cases, submitting to a FST simply gives the prosecution more evidence to use against you. In Florida, as in most states, there are no laws which state who must take a FST. A suspect must submit to a blood, breath or urine test once they have been arrested for DUI/DWI.
In 1977 and 1981 the NHTSA tested the validity of the SFST. The tests range from 65-80% reliable in establishing that a driver is in fact intoxicated or impaired by drugs as determined by the driver’s Blood Alcohol Content (BAC). In 1986, IACP recommended that law enforcement adopt the training on FST by NHTSA. The standards were drafted and presented to the voting membership of IACP. According to NHTSA, laboratory research revealed that the One-Legged stand test was 65% accurate in identifying subjects whose blood alcohol concentrations were 0.10 or higher, the Walk-and Turn was 68% accurate, and the HGN was 77% accurate. The reliability of the FST results depends on strict adherence to the standardized procedures. A large scale field valuation study was then performed in 1982 and 1983. +
“suspicion of DWI’, A field evaluation of the three SFSTs recorded data on 1,506 drivers stopped for as well as a review of data recorded on an additional 1,000 drivers stopped for DWI in other states. The results of that field evaluation were reported in This study reported that the HGN test was 82% accurate, the One-Leg Stand 78% accurate and the Walk-and-Turn 83% accurate in the detection of DWI offenders.
Stuster and Burns repeated the study in 1998, they found greater accuracies in arrest decisions at 0.08% BAC on the basis of SFSTs: HGN 88%, WAT 79% and OLS 83%. The greater accuracy was attributed to 17 years of implementation of the tests, and a lower BAC.
In 1997, a very thorough test was done in Florida where BAC was compared to the results of the SFST and subsequent officer’s decision to arrest or release the driver. The study showed 95% of the officers’ decisions to arrest drivers were correct decisions. Furthermore, 82% of their decisions to release drivers (and not arrest them) were correct (Burns and Dioquino 1997). Although these tests of accuracy are criticized, the general perception is that the FST is 90-95% accurate.
In many jurisdictions, the police car dashcam or body camera is being used routinely for traffic stops and FSTs. A defendant can obtain a copy of the video prior to a court appearance. This can be a check on the arresting officer’s written report of the FST, and eliminates some of the subjectivity in the FST report.
FSTs will continue to be routinely used in prosecuting DWI/DUI cases. Knowledge of recommendations for administering the test and limitations of the test is necessary in interpreting and using the results.
