How Police Identify Alleged Impairment Behind the Wheel in Chicago

Police officers in Chicago and throughout Illinois are trained to identify certain behaviors and driving patterns that, in their view, may suggest that a driver is under the influence of alcohol or drugs. These signs—however minor or subjective—can form the basis for a traffic stop under Illinois law. Once that stop occurs, it can escalate quickly into an arrest, formal criminal charges, and life-altering consequences.

At The Law Offices of David L. Freidberg, our DUI defense lawyer in Chicago understands how DUI arrests unfold in the real world and how law enforcement builds its case. What’s often overlooked by many drivers is that the entire criminal prosecution rests on whether the original stop was legally justified. That means if the officer didn’t have lawful grounds to pull you over, then any evidence obtained afterward may be inadmissible in court.

This article will explain what officers in Chicago typically claim to observe to justify a DUI stop, how those observations are challenged in court, and why having an experienced criminal defense lawyer is critical from the moment your case begins.

What Police Say They See: Behavior That Raises Suspicion in Illinois DUI Cases

Under Illinois law, an officer can stop a motorist if they have “reasonable suspicion” that a traffic violation or criminal activity is occurring. That standard—outlined in court decisions interpreting the Fourth Amendment—doesn’t require definitive proof of wrongdoing, just observable facts that suggest possible unlawful behavior.

In the context of suspected impaired driving, officers often cite the following as reasons to initiate a traffic stop:

Drifting within the lane
Frequent or unnecessary braking
Delayed response to traffic signals
Turning too wide or abruptly
Driving without headlights at night
Failing to stay within the lane
Tailgating or inconsistent speed
Nearly striking other vehicles or objects

These behaviors may seem mundane or even explainable by road conditions, fatigue, or unfamiliarity with the area. Yet police officers often report them as the first sign of possible DUI and use them to justify the stop. From that moment, every move the driver makes is scrutinized—speech, eye contact, mannerisms, and interaction with law enforcement.

In a congested city like Chicago, particularly on routes like the Dan Ryan Expressway or during weekend nights in River North or Wicker Park, law enforcement may rely on minimal infractions to stop a driver and begin investigating for DUI.

Field Sobriety Tests and the Subjective Nature of Police Reports

After stopping a driver, officers often ask them to step out of the vehicle and perform standardized field sobriety tests (SFSTs). These tests include:

Horizontal Gaze Nystagmus (HGN)
Walk-and-Turn
One-Leg Stand

These tests were developed by the National Highway Traffic Safety Administration (NHTSA) and are widely used across Illinois. However, they are far from perfect. Success on these tests can be affected by age, weather conditions, footwear, inner ear issues, or even nervousness.

Still, officers typically write in their reports that a driver “exhibited signs of impairment,” even if the driver complied fully and wasn’t unsteady. This language becomes part of the foundation for an arrest and for the prosecution’s case in court. Many drivers don’t realize they’re under investigation until the officer tells them they’re being arrested—usually after these field tests are completed.

If you’re charged with DUI under 625 ILCS 5/11-501, your defense starts with a detailed analysis of how and why you were stopped, what you said or did, and whether any of that rises to the legal threshold required for a charge to be sustained.

How a DUI Case Unfolds in Cook County Courts

After an arrest, you’ll be taken to a police station for a chemical test—typically a breath test, but in some cases a blood or urine test. You’re then processed, possibly held overnight, and given a court date.

The criminal court process begins at arraignment, where you hear the charges against you and enter a plea. DUI cases proceed through pretrial hearings, where your attorney can file motions to suppress evidence, challenge the arrest, and cross-examine officers.

Every stage of the criminal case—from initial stop to trial—offers an opportunity to fight back. Your attorney can argue that the stop lacked reasonable suspicion, that field tests were administered improperly, or that chemical tests were flawed or tainted.

A first-time DUI is typically a Class A misdemeanor, punishable by up to one year in jail and up to $2,500 in fines. However, if you have prior DUI convictions, a high BAC, were involved in a crash, or were driving on a suspended license, the charge can be elevated to a felony. Felony DUIs in Illinois carry years of imprisonment, hefty fines, and long-term license revocation.

Visit our blog at www.chicagocriminallawyerblog.com for legal updates and to read more about real cases we’ve handled involving suppression of DUI evidence and police misconduct.

A Real Example of How We Beat a DUI Stop

In one case we defended in Cook County, our client was stopped just after midnight on Clark Street for “lane deviation.” The officer claimed the vehicle touched the center line several times. Our client submitted to field tests and was arrested for DUI based on the officer’s interpretation of “clues” from the walk-and-turn test.

We immediately requested dashcam and bodycam footage. The video revealed that the vehicle never exited its lane, and our client performed the tests steadily. We filed a motion to suppress the stop, citing lack of reasonable suspicion and improper administration of SFSTs. The judge granted the motion, and the entire case was dismissed.

This outcome protected our client from jail time, license suspension, and a permanent record. It also reinforced how vital it is to have legal representation from the very beginning.

Why Implied Consent and Summary Suspension Laws Make Quick Action Critical

Under Illinois’s implied consent law (625 ILCS 5/11-501.1), drivers are considered to have agreed in advance to submit to chemical testing if arrested for DUI. Refusing the test leads to an automatic 12-month driver’s license suspension (for a first offense), while failing the test leads to a six-month suspension.

This is a civil penalty separate from the criminal charge and goes into effect 46 days after notice is served. You have a limited window to contest this suspension by requesting a hearing. If you miss this deadline, you could lose your license even if you’re never convicted of DUI.

That’s why it’s critical to contact a lawyer immediately. At The Law Offices of David L. Freidberg, we can help you file the necessary petitions and defend both your criminal case and your driving privileges.

Why You Should Never Face DUI Charges Without a Criminal Defense Attorney

Police officers and prosecutors are trained to pursue convictions, not to offer you the best outcome. When you’re charged with DUI, everything you say and do will be used against you. Without an attorney guiding your steps, you could unknowingly damage your own defense.

A lawyer protects your rights, challenges the legality of the stop, investigates flaws in chemical testing, and works to suppress weak or unlawfully obtained evidence. We can negotiate alternative sentencing, request court supervision, or fight the case at trial if needed.

Even if you think the evidence is stacked against you, there are often legal and procedural defenses available. The officer may have lacked training, the testing device may have been improperly calibrated, or the initial stop may have been illegal.

Without experienced legal counsel, you may miss these opportunities—and that could cost you your future.

Learn more about the criminal case process on www.chicagocriminallawyer.pro, where we break down the process step by step.

Legal Defenses to DUI Stops in Chicago

There are several defenses available to individuals charged with DUI in Illinois. Common strategies include:

Arguing that the stop was not based on reasonable suspicion
Demonstrating that field sobriety tests were administered incorrectly
Showing that the chemical test was invalid due to improper calibration or procedure
Establishing that medical conditions explained alleged signs of impairment
Challenging the chain of custody for blood or urine samples

Each case is different, and the most effective defense depends on the unique facts of your situation.

Call Now – The Law Offices of David L. Freidberg Is Ready to Help

If you’ve been charged with DUI in Chicago and have a medical condition that may have impacted your arrest or test results, call The Law Offices of David L. Freidberg for a free 24/7 consultation.

If you were arrested in Chicago for DUI, protect your future by contacting The Law Offices of David L. Freidberg. We have decades of experience handling DUI cases in Illinois. Our firm is available 24/7 to provide the legal defense you deserve.

Contact us today at (312) 560-7100 or toll-free at (800) 803-1442 for a free consultation. We’re available 24/7 to serve clients throughout Illinois, Cook County, DuPage County, Will County, and Lake County.