Signs of Impairment Police Look For That Create Reasonable Suspicion To Make A Traffic Stop

Understanding Reasonable Suspicion and Impairment in Chicago, Illinois

In Chicago, police officers are trained to look for specific signs of driver impairment that may justify a traffic stop under the legal standard of “reasonable suspicion.” Under Illinois law, an officer does not need probable cause to stop a vehicle initially. Instead, they need articulable facts suggesting that a traffic violation or criminal activity may be occurring. For DUI and related offenses, these facts often come from observations of driver behavior that indicate potential impairment.

Reasonable suspicion is a lower standard than probable cause, but it must still be grounded in observable facts. In the city of Chicago, where traffic enforcement intersects with DUI prevention, officers aggressively patrol areas near bars, clubs, and major roads like Lake Shore Drive, I-290, and I-90. Officers often initiate stops based on wide turns, lane drifting, delayed reactions at stoplights, and erratic braking. These seemingly minor observations can legally justify stopping a vehicle for further investigation.

Driving under the influence in Illinois is charged under 625 ILCS 5/11-501. A first-time DUI offense is typically classified as a Class A misdemeanor, punishable by up to one year in jail and a fine of up to $2,500. However, factors like high BAC, repeat offenses, or the presence of children in the vehicle can elevate the charge to a felony. Felony DUI offenses, such as aggravated DUI under 625 ILCS 5/11-501(d), carry prison time ranging from one to seven years depending on the classification (Class 4 to Class 2 felonies).

Common Signs Police Use to Justify a Stop Under Illinois Law

When initiating a stop, police officers must articulate specific facts leading them to suspect a violation of law has occurred. In DUI cases, these signs may be physical, behavioral, or vehicular in nature. For example, law enforcement often cites poor lane control, such as weaving or crossing lane lines, as a primary indicator of impairment. Failing to signal, tailgating, inconsistent speed, or striking curbs are also commonly used reasons for a stop.

Officers may also observe signs of impairment before pulling a driver over, such as loud music, erratic driving in parking lots, or even reports from other motorists. In some cases, surveillance or license plate scanning alerts officers to prior DUI-related suspensions, leading to heightened scrutiny. Once a stop is made, officers look for slurred speech, glassy eyes, the smell of alcohol, or confusion during questioning.

The Illinois Vehicle Code grants officers the authority to initiate a stop when there is a “reasonable belief” that a traffic violation has occurred. However, many challenges arise when officers rely solely on ambiguous driving behaviors. A defense attorney can analyze squad car footage, dashcam audio, and arrest reports to assess whether the stop was legally justified.

Relevant case law in Illinois, such as People v. Hackett, 2012 IL 111781, affirms that even minor infractions—like briefly touching the centerline—can justify a stop. Still, stops based solely on vague suspicion without clear evidence may violate the Fourth Amendment and result in suppressed evidence. That’s why it is crucial to evaluate the legality of every DUI stop in Cook County courts.

To see how these defenses work in real practice, visit our blog or explore the case outcomes shared on our main site.

How DUI Arrests Begin and the Investigation Process in Illinois

A DUI arrest typically begins with a traffic stop based on reasonable suspicion, but once the officer makes contact with the driver, the nature of the interaction quickly shifts toward a criminal investigation. Officers will ask questions, request identification, and observe the driver’s demeanor. In many cases, they will request field sobriety tests such as the walk-and-turn, one-leg stand, or horizontal gaze nystagmus. These tests are standardized by the National Highway Traffic Safety Administration (NHTSA), but their accuracy is heavily influenced by conditions like lighting, weather, and the driver’s physical health.

Officers may also request a preliminary breath test (PBT) on the roadside. Although PBT results are generally inadmissible in court, they provide further justification for arrest. If the officer believes there is probable cause, they will arrest the driver and transport them to the station for chemical testing, either via breathalyzer or blood draw.

Under Illinois’ implied consent law (625 ILCS 5/11-501.1), drivers who refuse chemical testing face automatic license suspension. For first-time refusals, the statutory summary suspension period is 12 months. If the driver submits and fails, the suspension is 6 months.

The formal criminal case begins when charges are filed in court. In Cook County and surrounding jurisdictions like DuPage, Will, and Lake Counties, a DUI charge will proceed through arraignment, pretrial motions, and possibly trial. At every stage, the quality of the evidence gathered by law enforcement is key to the prosecution’s case.

The Criminal Trial Defense Process and Example Case Strategy

The trial process in Illinois begins with arraignment, where the defendant hears the charges and enters a plea. A skilled criminal defense attorney may immediately file motions to suppress evidence if the stop was unconstitutional or if field sobriety tests were conducted improperly. Discovery is the next phase, where both sides exchange evidence. If the state’s case relies on questionable observations or improperly administered tests, the defense may seek dismissal or negotiate a favorable plea.

Consider a real-life example from a case we handled in Cook County. Our client was pulled over for “weaving within the lane.” The officer noted bloodshot eyes and a faint odor of alcohol. Our team obtained dashcam footage showing that the vehicle never left its lane, and no traffic laws were actually violated. Furthermore, the client’s performance on the field sobriety tests was steady and consistent. We filed a motion to suppress the stop and exclude all evidence gathered afterward.

After several hearings, the judge ruled the stop unlawful under the Fourth Amendment. All charges were dismissed, and our client avoided a DUI conviction, license suspension, and possible jail time. This outcome illustrates the importance of legal defense in every phase of the case.

You can learn more about our DUI defense strategies on our website at www.chicagocriminallawyer.pro and by reviewing recent case outcomes on our legal blog.

The Types of Evidence Law Enforcement Tries to Collect

In DUI and traffic-related criminal cases, officers seek several forms of evidence to build their case. First is the officer’s own testimony regarding driving behavior and observations made during the stop. Next are the results of standardized field sobriety tests and preliminary breath test results. Chemical test results—either breath, blood, or urine—are central to proving intoxication under Illinois’ per se DUI law, which sets a BAC limit of 0.08.

Additionally, police will attempt to collect dashcam footage, squad car logs, witness statements, and sometimes social media or cellphone records. Surveillance video from nearby businesses or buildings may be used to corroborate or dispute officer claims. The state may also use booking room videos, medical records, or body camera footage.

Without proper representation, defendants may not even know which evidence exists or whether it was collected legally. An experienced Chicago DUI defense lawyer will fight to suppress unreliable or unlawfully obtained evidence, which can result in charges being reduced or dismissed.

Why Every Step in the Criminal Case Process Requires an Attorney

From the moment of the stop to the final resolution of the case, defendants are at risk of making mistakes that could lead to a conviction. Statements made to officers, the decision to refuse testing, or signing documents without understanding their implications can all harm your defense. A lawyer protects your rights at every stage—beginning with challenging the legality of the stop itself.

During arraignment, a defense attorney can negotiate terms of release or bail. At pretrial hearings, your attorney can argue motions that might eliminate key prosecution evidence. During trial, a lawyer cross-examines witnesses, challenges test results, and introduces reasonable doubt. Even if the case ends in a plea, having legal counsel ensures that the terms are fair and your record is protected as much as possible.

The risks of handling a DUI or criminal case without representation are significant. A conviction can result in license suspension, hefty fines, jail time, and a permanent criminal record that affects employment, housing, and professional licenses. Your defense attorney is your advocate in a system that often prioritizes conviction over fairness.

Potential Legal Defenses in DUI and Impairment-Based Stops

Several legal defenses can be raised in DUI and criminal traffic cases, including:

• The initial stop was unlawful because there was no reasonable suspicion
• Field sobriety tests were improperly administered
• Chemical test results were flawed or unreliable
• The driver had a medical condition that mimicked signs of impairment
• There was no evidence of actual physical control of the vehicle

An experienced attorney will identify the most promising defenses based on a detailed investigation of the facts, including officer conduct, testing procedures, and the chain of custody for evidence.

What to Look For in a Criminal Defense Attorney in Chicago

When facing criminal charges in Chicago, you want an attorney who is aggressive, thorough, and familiar with local courts. Look for someone who regularly appears in Cook County courts and understands how judges and prosecutors handle DUI and impairment cases. Trial experience, knowledge of Illinois statutes, and a strong record of motion practice are essential.

It’s also important that your attorney maintains clear communication, explains your options in plain language, and provides you with a realistic view of your case. You want someone who is strategic, responsive, and focused on achieving the best result for your situation.

Questions to Ask During Your Free Consultation

Before hiring a criminal defense lawyer, you should ask key questions to assess their fit for your case:

• How often do you handle DUI or traffic-related criminal cases in Chicago?
• What is your approach to challenging the legality of traffic stops?
• How do you evaluate whether field sobriety tests were properly conducted?
• Will you be the one personally handling my case?
• How accessible are you if I have questions or concerns?

These questions can help you determine whether the attorney understands the intricacies of your situation and is prepared to fight for your rights.

Chicago Criminal Defense FAQs

Can I Be Arrested for DUI in Chicago Without Failing a Breath Test?
Yes. Police in Chicago can arrest you based on observations such as slurred speech, bloodshot eyes, or failed field sobriety tests—even without a breath test result. However, these arrests are often easier to challenge, especially if your attorney can show the officer’s observations were subjective or unsupported.

Is It Legal for Police to Stop Me Just for Leaving a Bar?
No. Police must have a specific and articulable reason for the stop. Simply leaving a bar is not grounds for reasonable suspicion. If you were pulled over without a clear driving violation or suspicious behavior, any evidence obtained during the stop could be challenged.

How Long Will My License Be Suspended for a DUI Arrest in Illinois?
For a first DUI offense with a failed chemical test, your license will be suspended for six months. If you refuse testing, the suspension increases to 12 months. These are administrative suspensions that occur before any criminal conviction. A lawyer can help you request a hearing to contest the suspension.

What Happens if I Refuse the Field Sobriety Tests?
Field sobriety tests are voluntary in Illinois. You have the right to refuse, although the officer may still arrest you if other signs of impairment exist. Refusing can limit the evidence against you but may also trigger a license suspension if implied consent laws apply during later chemical testing.

Can I Beat a DUI Case if the Officer Says I Failed Sobriety Tests?
Yes. These tests are subjective and can be affected by fatigue, anxiety, or medical conditions. An attorney can review dashcam footage, cross-examine the officer, and argue that the results were not reliable indicators of impairment.

Why You Need Legal Help and Why We’re the Right Choice

If you’ve been stopped or arrested based on alleged signs of impairment, you need to act fast. From challenging the initial stop to suppressing flawed evidence, an experienced criminal defense attorney can make all the difference. Without representation, you face steep penalties, a criminal record, and the long-term consequences of a conviction.

At The Law Offices of David L. Freidberg, we provide aggressive, strategic defense for individuals throughout Chicago and surrounding counties. We’ve defended countless clients charged with DUI and other traffic-related offenses and have a track record of dismissed charges, reduced penalties, and favorable trial outcomes.

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.