Legal Limit in DUI Cases

When a person is stopped by a police officer under suspicion of for driving while intoxicated, the arresting officer has the discretion to make a determination as to whether the subject will be required to submit a breath, blood, and/or urine sample for testing. Testing for blood alcohol levels is not to determine whether or not the individual has reached the threshold for DUI in Illinois – a person can be convicted if any alcohol has impaired his or her driving ability. Blood alcohol testing and legal limits are in place to establish whether the individual will be presumed to be intoxicated at the time of testing.

The legal limit in Illinois for blood alcohol purposes is 0.08 grams of alcohol per 100 milliliters of blood. If you are under 21 years of old, there is a zero tolerance policy.

There are also special DUI laws that apply to commercial driver’s license (CDL) holders. When operating a CDL vehicle, the legal limit lowers to .04. If the CDL driver refuses testing, or if the CDL driver’s alcohol concentration is .04 or greater, the length of disqualification from operating a CDL is 12 months for a first-offense, and lifetime restriction for a second offense.


To a certain extent, there are exceptions. For people who consume alcohol as part of a religious ceremony (Passover Seder, Sacramental wine, etc.) or alcohol is in a prescribed medicine. However, even in those instances, .08 BAC will be the legal limit. Illinois law holds that there is simply no excuse for getting behind the wheel when your BAC is .08 or greater.

Knowing if You’ve Reached the Legal Limit

There’s no sure-fire way of knowing if a person has reached the legal limit. Some people can get up to .08 with just a couple of drinks. Others it may take hours. Factors include age, genetics, time, lifestyle, body-fat, and many other variables.

The only way to guarantee never having a DUI is to never drink and drive.

Understanding DUI and Testing for the Legal Limit

A person is considered “under the influence” when he or she no longer acts with ordinary care because of mental or physical impairment. Illinois is not a state that requires scientific proof of intoxication in order to uphold a conviction for DUI, provided that there is credible evidence from the arresting police officer or other witnesses.

Circumstantial evidence is proof of certain facts and circumstances from which the fact finder may infer other connected facts which usually and reasonably follow from the human experience and is not limited to facts that may reasonably have alternative, innocent explanations.”

If you are pulled over on suspicion of a DUI, you give your implied consent that the officer has the right to conduct a breathalyzer test, not unlike a field sobriety test. You can always refuse this, but it obviously won’t look very good, because the officer will still arrest you based on whatever circumstantial evidence led to you being pulled over. The prosecution can later use your act of refusal against you, arguing that it points to your guilt.

The point of this test is to establish – or refute – probable cause. If probable cause is established, the police officer may then arrest you and then conduct another type of test (of his or her choosing). And no, you do not have the right to speak to an attorney at this point.

The tests are as follows:

  • Another breathalyzer;
  • Urine test; or
  • Blood test.

The test must be conducted as soon as possible from when you were last driving, and you have the right to conduct your own tests, too. These tests have different evidential requirements and are different scientifically, so it’s important to distinguish between the two when talking to your attorney.

Limitations with the Breathalyzer Alone

Amazingly, even in this era of advanced testing and physical evidence, circumstantial evidence alone – including officer testimony – can convict a person of a DUI. Worse yet, prosecutors sometimes support unreliable officer testimony equally unreliable breathalyzer tests. Absent further BAC tests, the breathalyzer is highly problematic. Fortunately, of late the Illinois courts have come around, with the Illinois Supreme Court noting their inaccuracies recently.

Nonetheless, Illinois law requires that a person consent to taking a preliminary breath test in order for the police officer to determine probable cause. It’s the equivalent of letting the police officer search your vehicle for contraband.

There’s just one little problem. Breathalyzer’s are absolutely terrible at measuring a person’s blood alcohol level.

You may be well below the legal limit, with the breathalyzer showing otherwise. This could be true for a number of reasons, including:

  • Foreign substances in the mouth – substances in the mouth that have alcohol can lead to false positives because they often emit alcohol vapor, which may be much greater than what is being exhaled from your lungs. This is often the case with mouthwashes, mint, toothache medication, and other similar products.
  • Calibration Errors – Police officers forget to change batteries.
  • Human Error – How experienced was the police officer using the breathalyzer? Did he or she have a history of error?
  • Consistency – How many times was the test conducted? Was it consistent in its results – specifically, in its BAC levels?
  • Environmental Factors – External factors can trigger false results, such as fumes and chemicals in the area.

Imagine for minute that a 17-year-old boy is anxiously driving to pick up his first date. He’s just gargled a ton of mouthwash and loaded five minutes in his mouth, to the extent that his breath is oversaturated. He’s an inexperienced driver – and nervous for the date – so he forgets to signal when turning.

A police officer pulls him over for failing to signal, and he notices that the teen looks nervous. He asks him to consent to a breathalyzer, and the reading shows over a 1.0. This establishes probable cause to arrest the punk.

Maybe the teen gets it sorted out in the end, after calling his parents and hiring an attorney – then again, maybe not. But imagine the next year when the teenager applies to college and is asked on the application: “Have you ever been arrested, even if the arrest has not resulted in a conviction?” What is he going to answer?

How the Chicago DUI Attorneys with O’Meara Law Can Help

The Chicago DUI lawyers at O’Meara Law LLC have the requisite experience defending all types of DUI cases. We understand the intricacies of intoxication laws. As a former prosecutor, Michael O’Meara understands how to strategize from both sides and uses his former skills to his advantage. Our clients come first here, and we urge you to schedule a consultation with one of our Chicago criminal defense attorneys today at 312-909-0706.