Field Sobriety Test Defense
In my practice, I often see clients who believe that their case was effectively over the moment an officer wrote “failed field sobriety tests” in a police report. That is not how I evaluate a Michigan drunk driving case. Field sobriety tests matter, but they are not magic. They are roadside investigative tools. They depend on training, instructions, scoring, surface conditions, lighting, footwear, medical history, age, weight, officer observation, and whether the officer actually followed the standardized procedures that give the tests whatever limited scientific value they may have.
The standardized field sobriety test battery, commonly called the SFST battery, consists of three tests administered in a fixed order: horizontal gaze nystagmus, walk-and-turn, and one-leg stand. Police officers are trained to use these tests during an OWI investigation to help decide whether to arrest the driver and request a chemical test. In many Michigan cases, the officer’s interpretation of these tests becomes the foundation for an arrest, a breath test, a blood draw, and a prosecution under MCL 257.625.
That is why field sobriety test defense requires more than simply asking whether a person “passed” or “failed.” The proper question is whether the officer administered the test in substantial compliance with the National Highway Traffic Safety Administration protocol, whether the officer scored only the standardized clues, whether the conditions were appropriate for the test, and whether the officer’s conclusion is supported by the video and the evidence.
Standardized Means Standardized
Michigan law recognizes the importance of standardization. MCL 257.62a defines a standardized field sobriety test by reference to tests validated by the National Highway Traffic Safety Administration. The statute provides that a field sobriety test qualifies as standardized if it is administered in substantial compliance with NHTSA standards. That phrase, “substantial compliance,” is critical. If the officer substantially changes the instructions, changes the scoring, changes the interpretation, or adds improvised corrections during the test, the prosecution should not be permitted to treat the result as though it came from the validated battery.
MCL 257.625s separately addresses testimony concerning standardized field sobriety tests. A person qualified by knowledge, skill, experience, training, or education in the administration of standardized field sobriety tests, including horizontal gaze nystagmus, may testify subject to a proper foundation. The same statute also preserves the admissibility of non-standardized field sobriety tests, but only if they comply with the Michigan Rules of Evidence. That distinction matters. A properly administered standardized test is one thing. An officer’s improvised roadside exercise is something else.
The legal framework is reinforced by MRE 702 and the reliability principles associated with Daubert v Merrell Dow Pharmaceuticals, Inc, 509 US 579 (1993), as adopted in Michigan in Gilbert v DaimlerChrysler Corp, 470 Mich 749 (2004). A party offering scientific, technical, or specialized testimony must establish that the testimony is based on reliable principles and methods and that those principles and methods were reliably applied to the facts of the case. A field sobriety test performed outside the standardized protocol raises a serious evidentiary problem because the claimed accuracy of the test comes from the standardized protocol, not from roadside improvisation.
The Walk-and-Turn Test
The walk-and-turn is a divided-attention test. The officer is supposed to instruct the driver to stand heel-to-toe, keep arms at the sides, listen to the instructions, and not begin until told to do so. The officer then instructs the driver to take nine heel-to-toe steps along a real or imaginary line, turn using a series of small steps with the other foot while keeping the lead foot on the line, and return nine heel-to-toe steps.
NHTSA identifies eight standardized clues for the walk-and-turn: inability to keep balance during the instructions, starting too soon, stopping while walking, failing to touch heel-to-toe, stepping off the line, using arms for balance, making an improper turn, and taking the wrong number of steps. Those are the clues. Counting quietly is not a clue. Asking a question is not a clue. Looking nervous is not a clue. Misunderstanding an unclear instruction is not proof of intoxication. When an officer scores non-standardized conduct as if it were a NHTSA clue, the testimony becomes vulnerable to challenge.
The walk-and-turn also depends on conditions. A person asked to perform the test on a sloped shoulder, loose gravel, snow, ice, uneven pavement, or near passing traffic is not performing the same test used in the validation studies. The officer should consider whether there is a reasonably dry, hard, level, non-slippery surface and enough room to complete the test safely. When those conditions are absent, the defense should examine whether the reported clues reflect alcohol impairment or the environment selected by the officer.
The One-Leg Stand Test
The one-leg stand is also a divided-attention test. The driver is instructed to stand with heels together and arms at the sides, raise one leg approximately six inches off the ground with the foot pointed out, look at the elevated foot, and count from 1001 to 1030 while the officer observes for thirty seconds.
NHTSA identifies four standardized clues for the one-leg stand: swaying while balancing, using arms for balance, hopping, and putting the foot down. Two or more clues are treated in the training curriculum as significant. But again, the officer must score only the standardized clues. The height of the raised foot is not itself a scoring clue. An officer who interrupts the test to demand that the driver raise the foot higher may be changing the test while it is being performed. That kind of intervention can affect the meaning of the result.
The one-leg stand also has limits. NHTSA training materials identify categories of people for whom the walk-and-turn and one-leg stand are not validated, including individuals over 65, individuals more than 50 pounds overweight, persons with back, leg, or middle-ear problems, and persons wearing heels more than two inches high. A person’s inability to perform a roadside balance exercise may say more about age, weight, footwear, injury, medical condition, or anxiety than alcohol impairment.
Horizontal Gaze Nystagmus
Horizontal gaze nystagmus, or HGN, is usually the first test in the standardized battery. It is different from the walk-and-turn and one-leg stand because it involves eye movement rather than balance and coordination. The officer looks for lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus before 45 degrees in each eye, for a maximum of six clues.
HGN can be powerful evidence when it is presented without context, but it is also highly technical. Proper stimulus position, speed, distance, lighting, medical screening, equal tracking, resting nystagmus, and correct angle estimation all matter. HGN also raises distinct vision-science questions, which is why I generally analyze it separately from the physical performance tests. The central point is the same, however: the officer’s conclusion is only as reliable as the administration, scoring, and interpretation that produced it.
Non-Standardized Roadside Tests
Many Michigan OWI investigations include non-standardized exercises such as alphabet recitation, counting backward, finger counting, finger-to-nose, or improvised number tasks. These exercises are often presented in police reports as though they carry the same significance as the standardized battery. They do not.
The original research that produced the SFST battery rejected many of these exercises as insufficiently useful for inclusion in the validated test battery. NHTSA materials may discuss some verbal tasks as pre-exit interview techniques or screening devices, but they do not replace the standardized field sobriety tests. When the prosecution seeks to rely on non-standardized roadside exercises, the admissibility question should be addressed under the Michigan Rules of Evidence, including MRE 702 and MRE 703. The proponent should not be allowed to borrow the scientific reputation of the standardized battery for tests that were not part of that battery.
Field Sobriety Tests and Drugged Driving Cases
Another common problem arises when officers use alcohol-oriented field sobriety tests in cases involving marijuana, prescription medication, or alleged drug impairment. The standardized field sobriety test battery was developed and validated primarily to assist in alcohol-impaired driving investigations. It was not validated as a reliable roadside method for identifying impairment by every drug or medication.
That distinction is important in Michigan drugged driving cases. The presence of a drug does not always establish impaired driving, and the signs associated with alcohol do not always translate cleanly to marijuana, prescription medication, or mixed-substance cases. People v Bowden, 344 Mich App 171 (2022), recognized the difficulty of proving marijuana-impaired driving through the kinds of tools available for alcohol cases. In practice, a careful defense must examine toxicology, driving behavior, officer observations, medical issues, timing, and whether the field sobriety evidence actually supports the conclusion being urged.
How I Evaluate Field Sobriety Test Evidence
When I evaluate field sobriety test evidence, I do not begin with the officer’s conclusion. I begin with the video, the instructions, the surface, the weather, the lighting, the footwear, the timing, the subject’s medical history, the officer’s training, and the scoring. I compare what the officer did with what the standardized protocol required. I look for added instructions, omitted instructions, improper demonstrations, premature scoring, non-standardized clues, unsafe conditions, and conclusions that are stronger than the facts support.
Body camera and dashboard video are often decisive. A police report may say that a driver failed to walk heel-to-toe, used arms for balance, or made an improper turn. The video may show something more nuanced. It may show that the officer gave unclear instructions, selected a poor surface, interrupted the test, counted a non-clue, or exaggerated the driver’s difficulty. Conversely, the video may confirm that the officer administered the test correctly. Either way, the defense analysis should be grounded in the actual record, not in assumptions.
Why This Matters in Court
Field sobriety testing can affect several legal issues in an OWI case. It may influence whether the officer had reasonable suspicion to extend a traffic stop into an OWI investigation. It may affect whether the officer had probable cause to arrest. It may influence the admissibility and weight of chemical test evidence. It may also shape how a judge or jury views the driver’s physical condition at the roadside.
A defense challenge does not require claiming that every field sobriety test is worthless. That would overstate the issue. The better approach is more precise. The standardized battery has defined rules, defined clues, defined limits, and defined assumptions. When those rules are followed, the prosecution may argue that the results have significance. When those rules are not followed, the defense should explain exactly why the result is less reliable, less probative, or not supported by the validation studies.
Conclusion
Field sobriety test defense is not guesswork. It is a disciplined comparison between the officer’s roadside investigation and the standards that govern the test. The issue is not whether a driver looked nervous, awkward, tired, confused, or imperfect. The issue is whether the officer administered and scored a validated test in substantial compliance with NHTSA standards, under conditions that allow the result to mean what the prosecution says it means.
In Michigan OWI cases, I treat field sobriety evidence as a technical subject requiring careful review. The officer’s opinion may be important, but it is not the final word. The video, the protocol, the statutes, the rules of evidence, and the science all matter. A proper defense begins by slowing the case down, separating standardized evidence from non-standardized impressions, and testing every claimed clue against the procedure that gives the test its claimed reliability.
