How Field Sobriety Tests Can Impact Your DUI Case in Michigan

When a law enforcement officer stops a driver suspected of impaired driving, the field sobriety test is one of the first tools they rely on. In Michigan, as in many states, the results of these roadside tests can become pivotal in shaping the DUI case. But these tests are far from infallible, and an experienced defense can often challenge their reliability, administration, and admissibility in court.

What Are Field Sobriety Tests?

Field sobriety tests (FSTs) are on-site physical or cognitive exercises officers may ask a driver to perform. The goal is to detect signs of impairment in balance, coordination, mental function, or eye movement. The classic three tests derived from National Highway Traffic Safety Administration (NHTSA) protocols are:

1. Horizontal Gaze Nystagmus (HGN) – The officer asks the driver to follow an object, like a pen or flashlight, with their eyes, watching for involuntary jerking at certain angles.
2. Walk-and-Turn (WAT) – The suspect takes several heel-to-toe steps in a straight line, turns on one foot, and returns the same way while being observed.
3. One-Leg Stand (OLS) – The driver must stand on one leg and count aloud for a period, while the officer watches for swaying, hopping, or balance corrections.

Officers may ask drivers to recite the alphabet, count backwards, estimate elapsed time, or perform other nonstandard tests. In Michigan, only the NHTSA‐sanctioned tests carry the weight of legitimacy in many cases, and the defense may challenge deviations from protocol.

Are Field Sobriety Tests Mandatory in Michigan?

Many drivers don’t realize that FSTs are voluntary in Michigan. Unlike the implied consent responsibilities that attach to chemical tests after arrest, Michigan law does not require a person to submit to them, and there is no direct statutory penalty for refusing them.

Declining an FST may influence how the officer proceeds and may become part of the case narrative. Some drivers hesitate to refuse out of fear that noncompliance will look like consciousness of guilt or make the officer more aggressive. Because field sobriety tests are not legally mandatory, your refusal cannot trigger statutory penalties like license suspension.

How Field Sobriety Tests Influence Your DUI Case

1. Forming Probable Cause for Arrest

One of the most significant roles FSTs play is helping an officer justify probable cause to arrest the driver for DUI. A poorly performed or failed test may bolster the officer’s assertion that impairment was present. If the tests and observations of slurred speech, red eyes, the smell of alcohol, and erratic driving are combined, they create a narrative of impairment.

If a defense can show the tests were improperly administered, or that the officer lacked sufficient reasonable suspicion or probable cause, it may weaken the state’s argument for a lawful arrest or for admitting specific evidence later.

2. Evidence Admissibility in Court

While FSTs are not definitive proof of intoxication, prosecutors often use their results to support DUI charges. Their admissibility is not automatic. Defense attorneys can challenge FST evidence on several grounds, including whether the officer followed proper testing protocols, had the necessary training and certification, or accounted for external conditions such as weather, pavement, lighting, or personal factors like footwear, medical conditions, injuries, nervousness, or fatigue that could have affected performance. Challenges may also target whether the officer documented the test adequately through notes or video, or whether nonstandard tests were misapplied or conducted improperly. If the court finds these challenges valid, it may suppress the evidence or reduce its weight in the case.

3. Strengthening or Weakening the Prosecutor’s Case

Because FST results are often portrayed as scientific evidence, they can add persuasive weight in the eyes of juries or judges, especially when combined with chemical test results or other observations. A failed FST can support the state’s claim of impairment. Conversely, if the defense can show that the driver performed acceptably or that the test was unreliable, it can reduce the credibility of the state’s overall narrative.

Even if the FST results are allowed, defense may argue that their probative value is weak given known error rates. For example, NHTSA estimates that the three standardized tests correctly identify impairment about 80 % of the time.

Because FSTs test coordination and balance, many non-alcoholic factors such as inner-ear issues, age, footwear, uneven surface, medical conditions, fatigue, and anxiety may degrade performance independent of intoxication. The defense can present expert testimony or medical evidence to show that the test was unreliable in that particular case.

How to Challenge Field Sobriety Test Evidence in Michigan

If you face a DUI case in Michigan and FSTs were used, there are several strategies your defense team may employ.

1. Attack the officer’s training, certification, or experience. If the officer cannot prove they were adequately trained, their observations may be deemed suspect.
2. Show deviations from the protocol that can undermine the test’s validity.
3. Exposing environmental or physical hindrances, such as slick pavement, darkness, uneven surfaces, wind, or medical/physical limitations, may explain poor performance absent intoxication.
4. Use video/dashcam/bodycam evidence that may reveal that the officer misrepresented or exaggerated, gave poor instructions, or observed environmental difficulties.
5. Because FSTs are inconclusive, defense may present expert testimony about their statistical error rates and limitations, emphasizing that they cannot reliably measure exact blood alcohol content.
6. Before trial, counsel may file motions to exclude or limit FST-based evidence based on improper administration, jurisdictional defects, or a violation of due process.

Don’t Let Unfair Field Sobriety Tests Decide Your Future

A failed field sobriety test does not automatically mean a conviction. Don’t let mistakes or improper tests affect your driving privileges. Manley & Manley will review your case, examine evidence, and build a strong defense strategy. Call us today at 810-374-0240 to schedule a consultation. We aggressively defend clients facing DUI charges, focusing on every detail of your case to protect your rights.