The roadside interaction between a driver and the police follows a predictable legal timeline designed to gather evidence for an Operating While Intoxicated charge. The Michigan OWI traffic stop procedure has five phases: the stop, the officer’s observations, roadside tests, the arrest, and the chemical test. Knowing each phase shows what officers must do and where mistakes can occur.
How a Michigan OWI traffic stop procedure begins
An officer needs reasonable suspicion of a traffic violation or other crime to pull a driver over. Speeding, weaving between lanes, a broken taillight and running a stop sign all qualify. A Michigan State Police trooper or local officer must be able to state the reason for the stop, because a stop without one can later call the evidence into question.
What the officer looks for at the driver’s window
Within the first minute, the officer watches for an odor of alcohol, bloodshot eyes, slurred speech and fumbling with the license or registration. The officer also asks whether the driver has been drinking and where the driver was coming from. A driver may choose not to answer these questions, though the answers can become evidence. Taken together, these observations determine if the officer will ask the driver to exit the vehicle for roadside testing.
How roadside sobriety testing works in a Michigan OWI stop
NHTSA, the federal highway safety agency, standardized the voluntary, three-part roadside protocol that Michigan officers usually use:
- Horizontal gaze nystagmus: Moving a pen or finger from side to side before the driver’s eyes, the officer checks for involuntary jerking and scores up to six clues.
- Walk and turn: The motorist is required to walk nine steps heel-to-toe down a straight path, execute a specific pivot, and walk back identically. Meanwhile, the evaluating officer observes the performance to identify up to eight specific impairment clues.
- One-leg stand: With one foot raised off the ground, the driver counts aloud for about 30 seconds as the officer marks up to four clues.
Poor lighting, uneven pavement, footwear, age, weight and medical conditions can all affect performance. Officers often follow these tests with a preliminary breath test.
Michigan OWI breathalyzer rules and implied consent
A preliminary breath test, or PBT, is a handheld roadside device. Drivers age 21 and older may refuse it, and refusal is a civil infraction, not a crime. The result helps establish probable cause, but prosecutors generally cannot use it as proof of the actual BAC number.
After an arrest, the Michigan implied consent law applies. The Michigan Secretary of State suspends a driver’s license for one year when the driver refuses to give a breath, blood or urine sample for chemical testing. The officer may also seek a warrant for a blood draw. Breath tests at the station generally require at least a 15-minute observation period beforehand, and trained operators must use instruments approved by the Michigan State Police. Drivers may also request an additional test from a qualified person of their own choosing.
What blood alcohol content measures
Blood alcohol content, or BAC, measures the amount of alcohol in the body. Michigan law makes it a crime to drive with a BAC of .08 or higher. A BAC of .17 or higher carries enhanced penalties. Drivers under 21 face a zero tolerance standard, and commercial drivers face a lower limit of .04.
Several things affect a BAC reading. Alcohol takes time to absorb, so a test taken after the stop can show a different number than the level at the moment of driving. Food, body weight and the timing of the last drink also matter.
Why testing accuracy can change the outcome
Roadside investigation results are not always final, as the science behind the testing equipment depends on specific maintenance rules. Breath instruments need regular calibration, operators need current certification and officers need to follow the observation period. Gaps in any of these steps can weaken the reliability of a result. Blood samples raise additional questions about storage, labeling, and lab handling.
Each phase of the stop creates a record through reports, video and test data. Someone facing an OWI charge in Michigan may benefit from seeking legal counsel.