Field sobriety tests in Michigan: the three standardized tests and how courts treat them

Field sobriety tests are the physical and eye tests an officer may ask a driver to perform at the roadside during an OWI investigation. Michigan law defines a "standardized field sobriety test" as one of the tests validated by the National Highway Traffic Safety Administration (NHTSA), and a test counts as standardized only if it is given "in substantial compliance with the standards prescribed by" NHTSA.^[1]

This page covers the three standardized tests, how NHTSA teaches officers to score them, what the scores are meant to show, and how Michigan courts treat testimony about them. The eye test has its own page: the horizontal gaze nystagmus (HGN) test.

The three standardized tests

NHTSA's participant manual says there are three standardized field sobriety tests (SFSTs): horizontal gaze nystagmus, walk and turn, and one leg stand. It says scientifically validated clues of alcohol impairment have been identified for each, and that they are "the only Standardized Field Sobriety Tests for which validated clues have been identified."^[2]

The figures below come from NHTSA's 2013 participant guide (HS 178 R5/13), the edition read for this guide.^[5][6][7]

Test	What the officer looks for (NHTSA clues)	NHTSA decision point
Horizontal gaze nystagmus	In each eye: lack of smooth pursuit; distinct and sustained nystagmus at maximum deviation (held at least four seconds); onset of nystagmus before 45 degrees. Maximum 6 clues.[5]	4 or more clues; NHTSA says this classifies about 88% of subjects accurately as at or above 0.08.[8]
Walk and turn	Can't keep balance during instructions; starts too soon; stops while walking; doesn't touch heel to toe; steps off line; uses arms to balance; improper turn; incorrect number of steps. 8 clues.[6]	2 or more clues, or failure to complete; NHTSA says 79% accurate.[6]
One leg stand	Sways while balancing; uses arms to balance; hopping; puts foot down. 4 clues.[7]	2 or more clues, or failure to complete; NHTSA says 83% accurate.[7]

What the accuracy numbers measure

Each NHTSA percentage is stated as the share of subjects classified correctly as having a BAC at or above 0.08 using that decision point.^[8][6][7] The manual's words are about predicting an alcohol level, not a direct measure of driving ability. Michigan's OWI statute can be violated either by being "under the influence" or by having a 0.08 or higher alcohol content, so the two ideas are related but not the same.^[9] The guide on what "under the influence" means explains the difference.

Not a pass/fail test

NHTSA's manual instructs officers: "Remember that the SFSTs are a tool to assist you in seeing visible signs of impairment and are not a pass/fail test."^[3] A common belief is that a person either "passes" or "fails" the roadside tests. The training material itself describes clues and decision points instead.

Conditions and people the tests may not fit

NHTSA's manual sets out conditions for the balance tests. Walk and turn should be done, whenever possible, on a reasonably dry, hard, level, non-slippery surface.^[10] For one leg stand, the original research recommended a dry, hard, level, non-slippery surface and relatively safe conditions; if not, the research recommends the test be done elsewhere or only HGN be given.^[11]

• The original studies suggested that people over 65, or with back, leg or inner-ear problems, had difficulty with walk and turn; less than 1.5% of the original subjects were over 65.^[10]
• For one leg stand, the same groups and people overweight by 50 or more pounds "may have difficulty performing this test," although the manual adds that the final report contained no data on the test subjects' weight.^[11][12]
• People wearing heels more than 2 inches high should be given the opportunity to remove their shoes.^[10][11]

The manual also says, for each of the two balance tests, that recent field validation studies indicated varying environmental conditions have not affected a subject's ability to perform the test, and it tells officers to "consider all factors when conducting SFSTs."^[12] Under Michigan's definition, a test counts as standardized only if it was given in substantial compliance with NHTSA's standards.^[1]

Who is trained to give them

The Impaired Driving Safety Commission reported in March 2019 that since 2010 the Michigan Commission on Law Enforcement Standards (MCOLES) has required all basic police academy students to complete NHTSA's DWI Detection and SFST program.^[13] The same report said about 20% of licensed Michigan officers had the more advanced ARIDE training, which sits between SFST and drug recognition expert training.^[13] Drug recognition experts use divided-attention tests as one step of a longer protocol, covered in the drug recognition expert guide.^[14]

How Michigan courts treat field sobriety test evidence

The statute on testimony

MCL 257.625s says: "A person who is qualified by knowledge, skill, experience, training, or education, in the administration of standardized field sobriety tests, including the horizontal gaze nystagmus (HGN) test, shall be allowed to testify subject to showing of a proper foundation of qualifications."^[4] The same section adds that it "does not preclude the admissibility of a nonstandardized field sobriety test if it complies with the Michigan rules of evidence."^[4] Both provisions were added by 2016 PA 242, effective September 22, 2016.^[1][4]

Officers as expert witnesses

The Evidence Benchbook summarizes People v Peebles (1996): an officer may testify as an expert about field sobriety test results if the evidence shows the officer has knowledge, training and experience with the tests at issue.^[15] In Peebles, an officer with one year and seven months on the job, four or five hours of training on the tests and on-the-job training was allowed to testify.^[15]

Nonstandardized tests

Tests other than the three NHTSA tests are not barred by Michigan's statute; it says nonstandardized tests may be admitted if they comply with the Michigan Rules of Evidence.^[4] Because MCL 257.62a defines "standardized" by NHTSA validation, those other tests are not "standardized" under Michigan's definition.^[1]

Field tests and the arrest decision

Field sobriety tests are part of the roadside investigation, along with the officer's observations and any preliminary breath test. An officer may require a PBT on reasonable cause to believe alcohol or drugs may have affected the person's ability to operate, and may arrest based in whole or in part on a PBT result.^[16][17] The legal standard for the arrest itself is explained in the guide to probable cause for an OWI arrest, and the full sequence is in what happens at an OWI traffic stop.

Field sobriety tests are separate from the roadside PBT. Refusing a lawfully requested PBT is a civil infraction for most drivers, and a misdemeanor for commercial-vehicle drivers.^[18][19] This guide has not found a Michigan statute or court rule that states whether a driver may decline field sobriety tests or whether declining may be mentioned at trial, so it does not state a rule on those points.

Field tests in marijuana and drug cases

Michigan has no numeric THC limit in the Vehicle Code.^[20] In its March 2019 report, the Impaired Driving Safety Commission recommended against a THC threshold and "instead recommends the use of a roadside sobriety test(s) to determine whether a driver is impaired."^[21] The THC blood tests guide explains why.

Common misunderstandings

Belief	What the sources say
"I passed the field tests, so I can't be charged."	NHTSA says the tests are not pass/fail, and Michigan's chemical-testing rules do not limit other admissible evidence of impairment.[3][22]
"88% accurate means 88% of people who fail are drunk."	NHTSA states the figure as the share of subjects it classifies accurately as at or above 0.08 using four or more HGN clues.[8]
"Only the three NHTSA tests can be used in court."	MCL 257.625s allows a nonstandardized test if it complies with the Michigan Rules of Evidence.[4]

Challenges to the stop, the arrest or the evidence are raised by motion; see the motions to suppress guide and the evidence guide.