Illinois DUI Law: Reasonable Suspicion & Probable Cause

In order to stop a vehicle, a police officer must have reasonable suspicion that the driver is committing a violation of Illinois law. The Fourth Amendment of the United States Constitution requires that law enforcement have specific and articulable facts that a crime has been committed, or is about to be committed, to justify the stop of a vehicle. An exception to this requirement is known as the community caretaking function, which allows a police officer to investigate if the driver appears to be in need of assistance.

Of course, there are a wide variety of offenses that can justify a vehicle stop. In DUI cases, the officer does not need to have a basis to believe that the driver is under the influence at the time of the stop. Minor moving violations or even equipment violations (i.e. a burnt out taillight or cracked windshield) are valid grounds to stop a vehicle. Most Illinois DUI investigations will begin with an allegation of improper lane usage, speeding or other common moving violations under the Illinois Vehicle Code.

When conducting an Illinois DUI arrest, the police officer must have probable cause to believe that a driver is under the influence. Probable cause is a higher standard than the reasonable suspicion necessary to stop a vehicle. Once a police officer has stopped a vehicle, that officer must be able to articulate specific facts supporting a belief that the driver is under the influence of alcohol, illegal drugs, medical cannabis, or another intoxicating compound in order to arrest the person for DUI. This can be based on factors relating to the driver’s speech, appearance, and odor. Specifically, officers will often point to sign of impairment including bloodshot and/or glassy eyes, slurred speech, soiled clothing, unusual actions, inconsistent responses and the odor of alcohol and/or marijuana.

The most compelling evidence of probable cause is usually the driver’s performance on field sobriety tests and the portable breath test (PBT) that is sometimes offered on the scene.

An Illinois DUI attorney can challenge the stop, investigation and/or arrest by filing a motion to quash arrest and suppress evidence. At the hearing on this type of motion, the defendant’s attorney can question the arresting officer on his or her grounds for probable cause.

The law surrounding probable cause and reasonable suspicion can be extremely complex. It is important that you have knowledgeable representation when facing a DUI charge in Illinois. The DUI defense attorneys at The Davis Law Group, P.C. evaluate all available evidence to determine potential challenges to probable cause. Our lawyers have years of experience, providing high-quality representation to our clients. Contact us to discuss your case.

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