DUI Arrests in Chicago Often Rely on Bad Science—Don’t Let a Machine Decide Your Fate
If you were pulled over and arrested for DUI in Chicago, chances are the police relied on a breath or blood test to measure your blood alcohol concentration, or BAC. While these tests are often portrayed in court as infallible scientific proof, the truth is far murkier. Machines malfunction. Blood samples spoil. Officers skip steps. And innocent people face harsh consequences based on unreliable test results.
Under Illinois law—specifically 625 ILCS 5/11-501—it’s illegal to drive with a BAC of 0.08% or more. That level applies regardless of whether you felt drunk or not. If your BAC was over the legal limit, even slightly, you may be charged with a Class A misdemeanor DUI. But that’s just the starting point. If your BAC is exceptionally high or you have other aggravating circumstances, your misdemeanor DUI could quickly turn into a felony—a life-changing event with long-term consequences.
The problem? BAC tests are far from perfect. The devices used to collect these measurements are vulnerable to error, and the people administering the tests are human. That means your test result could be wildly inaccurate—and you could be paying the price unless you challenge it head-on.
How Illinois DUI Law Works—and Why BAC Tests Carry So Much Weight
Illinois DUI charges hinge largely on your BAC result. The legal limit is 0.08%, but charges can be filed even if your BAC is lower, as long as law enforcement claims you were impaired.
If you’re convicted of a first-time DUI with no aggravating factors, you’re looking at a Class A misdemeanor: up to one year in jail, fines of up to $2,500, and a driver’s license suspension. But if your BAC was 0.16% or higher, or if there were other people—especially minors—in the car, the penalties escalate.
For example, under 625 ILCS 5/11-501(d)(1)(H), having a BAC of 0.16% or greater while transporting a passenger under the age of 16 bumps the charge up to a Class 4 felony. If someone was injured or killed, or if it’s your second or third DUI, you could be facing years in prison.
With so much riding on a single test result, you would think the process would be flawless. It isn’t.
How Breath and Blood Tests Go Wrong—and Why It Happens So Often
There are three types of chemical tests Illinois law enforcement uses to measure BAC: breath, blood, and urine. Each method has flaws.
Breath tests are the most commonly used—and the least accurate. Machines like the Intoxilyzer 8000 used by many Illinois departments must be calibrated regularly and operated according to strict rules. If the machine hasn’t been serviced, if the operator isn’t trained, or if the driver has a condition like acid reflux, the results may be unreliable.
Blood tests are more accurate in theory, but they require proper storage and handling. If the blood isn’t refrigerated, if the vial contains the wrong preservatives, or if the lab technician was careless, the sample could be tainted. The result? A BAC reading that may not reflect your level of impairment when you were actually driving.
Urine tests are the least reliable of all and are rarely used unless breath or blood testing isn’t possible.
The Illinois Supreme Court has acknowledged that BAC tests must meet specific standards to be admissible in court. Even a small deviation from those standards can open the door for a defense attorney to challenge the results—and potentially get the evidence thrown out.
How BAC Evidence Is Introduced During a Criminal DUI Case
After your arrest in Chicago, your case will proceed through a series of stages: initial appearance, bond hearing, discovery, pretrial motions, and trial if necessary. At each stage, the BAC evidence will be front and center.
Prosecutors typically build their case around the chemical test result. The officer’s report, any video from the squad car or body camera, and field sobriety test results will supplement it—but the BAC number is often treated as the “proof” of guilt.
We don’t let that slide. Our defense team files discovery motions to obtain calibration records, maintenance logs, and video of the test administration. We may subpoena the person who administered the test to see whether they followed proper procedures. And we bring in toxicologists to evaluate whether the test result could be wrong.
We’ve seen too many people in Cook County convicted based on flawed BAC evidence. That’s why we question everything.
Real-Life Example: DUI Charge Dismissed After Breath Test Thrown Out
A young woman in Logan Square was arrested after leaving a holiday party. She submitted to a breathalyzer, which showed a BAC of 0.10%. She was charged with a Class A misdemeanor DUI.
We requested maintenance records for the breathalyzer. It turned out the device had failed an internal diagnostic check just days earlier—and had not been removed from service. The operator was also a new recruit who hadn’t completed all required training. We filed a motion to suppress the breath test results.
The judge granted it. Without the BAC reading, the case collapsed. Our client avoided a criminal conviction and a suspended license.
What Police Try to Collect During a DUI Stop—and How That Can Help or Hurt You
In a DUI investigation, law enforcement will gather multiple types of evidence:
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Field sobriety tests like the walk-and-turn or one-leg stand
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Observations about your speech, appearance, and behavior
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Breathalyzer or blood test results
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Dashcam and bodycam footage
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Witness statements, especially in crash cases
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Your own statements or admissions
Not all of this evidence is equally credible. Field sobriety tests are known to be unreliable, especially in poor weather or for people with medical conditions. Officer observations are subjective and sometimes contradicted by video. And even your own words may be inadmissible if you weren’t properly Mirandized.
As your defense attorneys, we review every piece of evidence to determine whether it can be suppressed, excluded, or discredited. We use that to build your defense.
Why a DUI Defense Attorney Is Essential From Day One
Illinois DUI laws are strict, and prosecutors aggressively pursue convictions. Without a defense attorney, you have no chance of holding the state accountable for poor testing practices or procedural errors.
A DUI attorney challenges the stop, the arrest, the testing process, and the evidence. We push back on assumptions. We argue for suppression when your rights are violated. And we negotiate alternatives like supervision or reduced charges where appropriate.
We understand the stakes: your license, your job, your freedom. You don’t have to go through this alone.
Potential DUI Defenses When BAC Test Results Are Questionable
There are several ways to attack the BAC evidence in a DUI case. Common defenses include:
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Improper calibration or maintenance of testing equipment
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Improper collection or storage of blood samples
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Mouth alcohol contamination from mouthwash, burping, or vomiting
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Medical conditions that interfere with breath testing
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Rising BAC—that is, alcohol still being absorbed at the time of the test
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Lack of probable cause for the traffic stop or arrest
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Chain of custody errors
Each case is different, but the common theme is this: BAC results are not bulletproof. A good defense can create doubt—and that’s all you need to avoid conviction.
What to Ask a DUI Attorney During Your Consultation
Your first consultation with a defense lawyer should give you a clear sense of your legal options and the attorney’s approach. Ask:
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Have you handled cases involving faulty BAC tests?
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Do you work with forensic experts?
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How do you challenge the legality of the stop or the test?
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Will you be the one handling my case in court?
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What are the best- and worst-case scenarios?
Look for honesty, transparency, and confidence—not empty promises.
Why The Law Offices of David L. Freidberg Is the Right Choice
At The Law Offices of David L. Freidberg, we understand that a DUI charge doesn’t make you guilty—and a BAC test doesn’t make the evidence reliable. We’ve represented thousands of clients in DUI cases across Chicago, Cook County, DuPage County, Will County, and Lake County.
We know what to look for. We know how to find testing errors. And we know how to fight back when the system tries to railroad you.
When You Need a Fighter, Call Us
Whether you’re charged in downtown Chicago, Skokie, Maywood, Bridgeview, or Rolling Meadows, we’re ready. We appear regularly in courtrooms throughout Cook, DuPage, Will, and Lake Counties. And we don’t treat aggravated speeding as just another moving violation.
If you were arrested in Chicago, 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.