Nearly every Michigan drunk driving case is built on the same short sequence: the officer's observations at the window, a set of roadside tests, a handheld breath test, and then an evidentiary test after arrest. Each of those links can be attacked, and each of them fails more often than the report makes it sound.
The Standardized Field Sobriety Tests
Three tests make up the battery the National Highway Traffic Safety Administration standardized. They are only meaningful if they are administered exactly the way the training requires — which, in practice, they frequently are not.
Horizontal Gaze Nystagmus (the "eye test")
Nystagmus is involuntary jerking of the eye. The officer stands in front of you and moves a pen, finger, or flashlight across your field of vision, watching for three clues in each eye: lack of smooth pursuit, distinct jerking at maximum deviation, and the onset of jerking before 45 degrees.
What is rarely mentioned at the roadside is how many ordinary things produce nystagmus that has nothing to do with alcohol — inner ear conditions, head injuries, eye strain, certain prescription medications, and neurological conditions among them. Passing headlights and flashing overhead lights interfere with the test. And the officer's own technique — how fast the stimulus moves, how long it is held, whether the eyes were checked for equal tracking first — determines whether the result means anything at all.
Walk and Turn
Nine heel-to-toe steps along a real or imagined line, a specific turn, nine steps back, while counting aloud. The scoring begins during the instruction phase, before you take a step — the officer is already watching whether you keep your feet in the required position and whether you start too soon. Uneven pavement, a sloped shoulder, gravel, boots or heels, weight, age, and injuries all affect performance, and none of that is captured in a report that simply records the number of clues.
One Leg Stand
You raise one foot roughly six inches off the ground and count aloud until told to stop. There are two phases: the instruction stage, where the officer watches how you stand and listen, and the balance stage, where the clues are swaying, using your arms for balance, hopping, and putting your foot down. Balance testing on a roadside at night, in traffic, on an uneven surface, under stress, is difficult for plenty of sober people — and any leg, back, knee, or inner-ear problem makes it close to meaningless.
The Preliminary Breath Test (PBT)
The PBT is the small handheld device offered at the roadside, before arrest. It is a screening tool and it is not reliable enough to prove a specific blood alcohol level at trial — its results are limited in what they can be used for in court. PBTs are thrown off by other substances, by weather and temperature, by residual mouth alcohol, and by officers who have not been properly trained on the device.
Refusing a PBT is a civil infraction for an ordinary driver under MCL 257.625a — a ticket, not a crime, and not a license suspension. For a commercial driver, refusing is a misdemeanor punishable by up to 93 days or a fine of up to $100, or both.
The Evidentiary Test — a Different Thing Entirely
The breath, blood, or urine test administered after arrest is the one that carries real evidentiary weight, and it is the one governed by Michigan's implied consent law. Refusing it means a 1-year license suspension and 6 points, and you have only 14 days to request a hearing. That is covered in full on implied consent and refusing a chemical test.
Evidentiary breath results are challenged through the machine's calibration and maintenance records, the required observation period before the sample, the operator's certification, and the presence of interfering substances. Blood results are challenged through the draw itself, the chain of custody, storage and preservation, the delay between driving and testing, and the laboratory's own procedures.
What This Means for Your Case
Field sobriety and chemical testing is the part of an OWI case where careful work pays. The tests are not magic and the numbers are not beyond question — they are procedures performed by people under time pressure at the side of a road, and procedures can be shown to have been done wrong. Related: drunk driving defense, DUI traffic stop basics.
Frequently Asked Questions
Do I have to take field sobriety tests in Michigan?
The standardized roadside tests — the eye test, walk-and-turn, and one-leg-stand — are not backed by the license penalties that apply to the evidentiary chemical test after arrest. What you should understand is that they are voluntary in a way the post-arrest test is not, and that an officer who has already decided to investigate you for OWI is looking for clues to record. If you are unsure what applies to your stop, ask a lawyer about your specific facts.
What is the eye test the police do during a DUI stop?
It is the horizontal gaze nystagmus test. The officer moves a stimulus across your field of vision looking for involuntary jerking of the eye. Alcohol can cause it — but so can inner ear problems, head injuries, eye strain, some prescription medications, neurological conditions, and even passing headlights, which is why administration technique matters so much.
Can field sobriety test results be thrown out?
They can be undermined, and sometimes excluded. These tests only carry weight when administered the way the training requires, on a suitable surface, and scored correctly. Uneven ground, footwear, injuries, weight, age, weather, traffic, and improper instructions all affect the result, and the officer’s report rarely records any of it.
What is the difference between a PBT and a Datamaster test?
The PBT is the handheld screening device used at the roadside before arrest; its results are limited in what they can be used to prove in court, and refusing it is a civil infraction for an ordinary driver. The evidentiary test after arrest carries real weight at trial and is governed by the implied consent law, where a refusal means a 1-year license suspension and 6 points.
Talk to Me Before You Talk to Anyone Else
I am Shawn Haff, and I defend drunk driving cases across Kent, Ottawa, Allegan, Barry, Ionia, Muskegon, Newaygo, and Van Buren counties. The call is free, I answer my own phone, and on an OWI the clock starts running the day you are arrested. Call 616-438-6719 or send me a message.