Chapter 4: DUI / DWI Laws

Driving Under the Influence (DUI) is one of the most dangerous and severely punished offenses a driver can commit. Alcohol and drugs impair judgment, coordination, and reaction time, turning a vehicle into a deadly weapon. Understanding Illinois’ strict DUI laws is critical for your safety and the safety of everyone on the road, and this knowledge is a major focus of the driver’s license exam due to the devastating consequences of impaired driving.

DUI & Implied Consent

In Illinois, a driver can be charged with Driving Under the Influence (DUI) for operating a motor vehicle while impaired by alcohol, cannabis (marijuana), other illegal drugs, prescription medications, over-the-counter drugs, or any intoxicating compound that makes them unfit to drive safely. DUI is not limited to just alcohol; any substance that impairs driving ability can lead to a DUI arrest.

Blood Alcohol Concentration (BAC) Limits

BAC is the percentage of alcohol in a person’s bloodstream. Illinois law establishes “per se” BAC limits, meaning that if a driver’s BAC is at or above these levels, they are considered legally intoxicated without any further evidence of impairment.

• Drivers Age 21 and Over: It is illegal to drive with a BAC of 0.08% or more.
• Drivers Under Age 21: Illinois has a Zero Tolerance Law. It is illegal for a person under 21 to drive with any trace of alcohol in their system (a BAC greater than 0.00%).
• Commercial Drivers (CDL): It is illegal to operate a commercial motor vehicle with a BAC of 0.04% or more.
• Cannabis (THC): It is illegal to drive with a THC concentration of 5 nanograms or more per milliliter of whole blood or 10 nanograms or more per milliliter of another bodily substance.

Common Mistake:
Believing that you can only get a DUI if your BAC is 0.08% or higher. A driver can be arrested and convicted of DUI with a BAC under 0.08% if they exhibit signs of impairment that prove they are unable to drive safely.

The “Implied Consent” Law

By operating a vehicle on Illinois roadways, a driver automatically gives their consent to submit to chemical testing (breath, blood, or urine) if arrested for DUI. This is known as the Implied Consent Law.

• Refusing a Test: If a driver refuses to submit to chemical testing after a lawful DUI arrest, their driving privileges will be automatically suspended. For a first offense, this suspension is for 12 months.
• Failing a Test: If a driver submits to testing and fails (shows a BAC of 0.08% or higher, or any illegal substance), their driving privileges will be suspended for 6 months for a first offense.

The penalties for refusal are more severe than for failing a test to discourage drivers from refusing.