Why BUI Field Sobriety Testing is Different from SFSTs

Recently, Tennessee lawmakers and law enforcement have been taking an increasingly more severe stance towards boating under the influence. Research has shown that boating under the influence of drugs and alcohol is dangerous and considerably increases the risk of boating accidents. The U.S. Coast Guard, who compiles nationwide statistics on boating accidents every year, reported that alcohol use contributed to 215 boating accidents, including 88 deaths and 148 injuries, in the year 2022 alone.

In response to the risk posed by impaired boating, Tennessee enacted a law making the penalties for BUI the same as those for driving a motor vehicle under the influence. Operating a boat while under the influence of any intoxicant is a Class A misdemeanor, punishable by up to 11 months, 29 days imprisonment for an individual’s first offense. (See T.C.A. §69-9-217, “Boating under the influence”).

Why BUI field sobriety testing is different from SFSTsTo show the public they’re serious about enforcing the new BUI law, the Tennessee Wildlife Resources Agency (the agency responsible for enforcing all the laws of the waters) launched Operation Dry Water in 2023. The goal of Operation Dry Water was to target BUI arrests right after the new BUI law went into effect, thus at a time when many people would be unaware that the penalties for BUI had increased. Best & Brock saw an influx of BUI cases in the summer of 2023, and we expect there to be even more during the summer of 2024. Whether or not TWRA launches another Operation Dry Water, law enforcement will almost certainly be focused on making more BUI arrests this summer.

With BUI arrests increasing, there’s a critical question at the heart of the trend: how do TWRA officers determine when to arrest an operator for boating under the influence?

Just like in a DUI case, officers will request a boat’s operator submit to field sobriety testing to determine if they are too intoxicated to operate a vessel. The trouble is, the Standardized Field Sobriety Test can almost never be conducted on a boat. The Walk and Turn and One Leg Stand tests require a flat surface for drivers to keep their balance. Because a boat bobs up and down on the water, officers usually cannot administer the Standardized Field Sobriety Test (SFST) on a boat. In addition, many people are unable to perform the SFST on dry land after being on a boat all day, because they have “sea legs” and feel unsteady when first returning to land.

The Standardized Field Sobriety Test is a critical factor in determining intoxication in DUI investigations because it is the result of decades of research by the National Highway Traffic Safety Administration. When the test is administered properly, it has a high accuracy rate for determining if a driver is impaired.

In the absence of a researched, validated, and standardized field sobriety test, TWRA officers have relied on a variety of less reliable sobriety tests. Seeking some uniformity and accuracy, the National Association of State Boating Law Administrators, or NASBLA, partnered with the Coast Guard to develop a seated battery of field sobriety tests for use in BUI investigations. The goal of their research was to scientifically test the seated field sobriety test to determine its usefulness in marine investigations, as well as its accuracy in determining BAC levels in participants.

Before we discuss how the field sobriety tests used in BUI investigations can be problematic, let’s briefly break down each test.

Horizontal Gaze Nystagmus

Horizontal Gaze Nystagmus, or HGN for short, refers to a lateral jerking of the eyeballs. While HGN has a number of causes, including head injury, one of the most common causes is alcohol consumption. The HGN test involves having the subject follow a stimulus with their eyes, so that officers can observe the onset and severity of horizontal gaze nystagmus. The angle at which nystagmus begins has been correlated to the occurrence of specific BAC levels.

The HGN test is the only seated field sobriety test that is also part of the Standardized Field Sobriety Test. With an accuracy rate of 88% (determined during NHTSA’s initial research), HGN is considered the most reliable field sobriety test for determining when a subject’s BAC has passed the 0.08% threshold. Although NASBLA’s tests only demonstrated an HGN accuracy rate of 67.4%, it was still the most accurate of the tests selected for the seated field sobriety test. This difference in accuracy may be due to a lack of proficiency in administering HGN amongst the officers that administered the seated sobriety test in NASBLA’s study – 5 of the 24 study officers had an overall accuracy percentage for HGN of less than 50% (Fiorentino et al., p. 89).

Because HGN does not require a subject to stand or balance, it can easily be adapted to the marine environment, unlike the Walk and Turn or One Leg Stand. However, the bumping and bobbing of a boat may still impact HGN results during a BUI investigation. If, for example, an officer cannot keep their arm steady enough to smoothly move the stimulus, the subject may be forced to jerk their eyes to follow the stimulus. This may create an illusion of alcohol-induced nystagmus that is not there.

Finger to Nose

The Finger to Nose test was included in NHTSA’s original studies to develop the Standardized Field Sobriety Test in the 1970s and 1980s; however, it did not make the cut into

the finalized test, because the three final tests were more accurate. The Finger to Nose has since been adopted into the drug recognition exam and the seated field sobriety test.

In the Finger to Nose, the officer will instruct the subject to touch the tip of their nose with the tip of their index finger (either the left or right, per the officer’s instruction), and then bring the hand back down to the subject’s side with the index finger pointed out. The test is performed with the subject’s eyes closed and head tilted slightly back, which may challenge the subject’s balance.

On its own, the Finger to Nose test accurately predicted when the NASBLA laboratory research participants were at or over the legal BAC limit 59.9% of the time. There are thirteen clues in the Finger to Nose test that are purported to indicate impairment. If a subject exhibits nine clues, this is considered the “decision point” that indicates to officers that a subject is impaired. The purpose of the Finger to Nose test is to measure ataxia, or a lack of muscle control/coordination, which can be caused by alcohol. However, ataxia may also be caused by other factors. For example, many older folks lose coordination as they age and their muscles weaken.

Palm Pat

The Palm Pat is not part of any other validated sobriety test. This test requires subjects to extend their hands with one palm out and the other hand on top of it, touching palm to palm.

While the bottom hand stays still, subjects are instructed to alternate patting the bottom palm with the front and back of the top hand, counting each pat.

There are ten clues in the Palm Pat. After two of these have been exhibited, officers are instructed to make a decision regarding the participant’s impairment. These clues include stopping before instructed and rolling the hands. In NASBLA’s laboratory study, the Palm Pat was able to accurately predict whether participants’ BACs were below or above the legal limit only 57.2% of the time.

Hand Coordination

Like the Palm Pat, the Hand Coordination test appears to be unique to the seated field sobriety test. It involves asking subjects to perform a series of tasks with their hands, and is an attempt to mimic the Walk and Turn test. Subjects must move their hands fist-to-fist away from their chest in a steplike fashion, clap, then return their hands to a fist-to-fist position and “step” them back to the chest while counting aloud.

The decision point in the Hand Coordination test is three out of fifteen possible clues. A subject will be scored with a clue if, for example, they count improperly or forget to complete a segment of the test. With that criterion, the test accurately predicted BAC levels in 57.2% of the NASBLA study’s laboratory participants.

We know what you’re thinking: is there a scientific basis to these tests?

A three-year study on the seated field sobriety test was conducted by the Southern California Research Institute (a.k.a. SCRI), the same institution that conducted NHTSA’s research on the Standardized Field Sobriety Test. The study included laboratory and field research, such as analysis of actual on-water BUI investigations. Since the initial research was completed in 2009, further research on the test has been conducted, but not officially published by NASBLA. In contrast, NHTSA’s development of the Standardized Field Sobriety Test included two studies by SCRI, and three subsequent studies validating the results of the initial studies.

The first step in NASBLA’s research was to select which tests to include in the seated field sobriety test in a laboratory setting. With a study size of 157 participants, dosed out to a BAC (blood alcohol content) of either 0.00%, 0.04%, 0.08% (the legal limit), and 0.12%, the four seated field sobriety tests were selected in an experiment that tested the reliability of six potential tests. SCRI published their findings, which determined that the four selected tests, when their results were combined, were able to identify individuals with a BAC at or above the legal limit with 82% accuracy. The tests were only 67% accurate at determining when the participants had a BAC under the legal limit. This means that 33%, or one-third, of the participants whose BAC was actually under the legal limit were incorrectly identified as being over the legal BAC limit for operating a water vessel. The four tests that made it through the study had an overall laboratory accuracy of 72% for determining whether or not participants’ blood alcohol content was at or greater than 0.08%.

On their own, the three new tests (excluding HGN, which has been validated in multiple other studies), have an accuracy rate averaging at 58% for indicating if an individual is below or above the legal limit. The SCRI study’s authors even stated in the publication of their findings, “FTN, PP, and HC did not improve the prediction [of participants’ BAC levels] beyond that of HGN” (Fiorentino et al., p. 88). This introduces a considerable risk for BUI investigations where an officer is not able to conduct the entire seated field sobriety test. If a suspect is unable to complete a test, or refuses to participate in further testing, officers’ determination of that suspect’s BAC level may be less accurate. Given the seriousness of a BUI charge, it’s concerning that officers are instructed to make an arrest decision based on tests that are only accurate about half the time.

In comparison, the three tests that make up the Standardized Field Sobriety Test have an accuracy rate of 88% (Horizontal Gaze Nystagmus, which is also part of the NASBLA test), 79% (Walk and Turn), and 83% (One Leg Stand) for determining whether a driver’s BAC is at or greater than 0.08%. (DWI Detection and Standardized Field Sobriety Testing Participant Manual, NHTSA, 2023).

After the seated field sobriety’s finalized tests were selected and their accuracy quantified, the SCRI research team conducted a field study that involved 331 study cases on the waters of Missouri. The combined accuracy of the tests fared slightly more poorly in the field setting than they had in the laboratory setting, with an overall field accuracy rate of 68%. In the absence of HGN, the remaining four tests could only accurately predict subjects’ BAC status 66% of the time on the waters.

This introduces some concerns for those of us working in the criminal justice system, as well as for anyone who goes out on the waters. It is possible that individuals are being arrested for boating under the influence while being well under the legal BAC limit for boat operation, based on potentially inaccurate field sobriety tests. Furthermore, it is possible that intoxicated boat operators may perform well on the seated field sobriety test, and thus be allowed to regain operation of their vessel. In a criminal justice system that is supposed to strive for fairness and due process, a field sobriety test that has demonstrated poor accuracy rates can foster injustice.

Let Best & Brock Guide You to Shore

In the evolving legal landscape of boating under the influence cases, you need an experienced criminal defense attorney on your side. Best & Brock may not be with you when TWRA officers lead you through the seated field sobriety test, but we will stand by your side in the court proceedings that follow. By rigorously investigating every detail of your case and staying up to date with field sobriety procedures, we will navigate to a fair resolution to your BUI case. If you or a loved one has been charged with boating under the influence, reach out to Best & Brock at (423) 829-1055 or by filling out our online contact form to set up a FREE consultation with one of our experienced attorneys.

Sources referenced in this blog:

  •  Fiorentino, Dary D. et al. (Southern California Research Institute), “Development of Sobriety Tests for the Marine Environment,”, Transportation Research Record: Journal of the
  • Transportation Research Board, No. 2222, Transportation Research Board of the National Academies, Washington, D.C., 2011, pp. 85–89.
  • Fiorentino, Dary D. (Southern California Research Institute), “Validation of sobriety tests for the marine environment,” Accident Analysis and Prevention 43, Association for the Advancement of Automotive Medicine, 2011, pp. 870-877.
  • Lawrence, Bruce A. et al., “Recent Research on Recreational Boating Accidents and the Contribution of Boating Under the Influence,” United States Coast Guard Inspection and Compliance Directorate, Washington, D.C., 2006.
  • SFST DWI Detection and Standardized Field Sobriety Testing Participant Manual, National Highway Traffic Safety Administration, Washington, D.C., 2023.