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The Difference Between “Impaired” DUI and “Per Se” DUI

Posted on in DUI Defense

IL defense lawyerIf you have been charged with driving under the influence (DUI) in Illinois, your defense strategy will depend in part on whether your case is a “per se” DUI or “impaired” DUI.

Definition of DUI Per Se

A DUI per se (“by law”) means that your breath or blood tested over the legal limit for alcohol, marijuana, or another intoxicating substance.

If you test over the limit, the law assumes you were driving impaired, even if you exhibit no outward signs of intoxication and can pass the standardized field sobriety tests (the one-leg stand, the walk-and-turn, and the “follow my pen” horizontal gaze tests).

The legal limits are based on scientific studies that have documented the effects of varying levels of intoxicants on driver impairment. The “legal limit” varies by state, age, intoxicant, and what type of vehicle you are driving.

In Illinois, the legal limits for blood-alcohol concentration (BAC) are:

  • For adults driving a personal vehicle, a BAC of .08 or higher is over the limit.
  • For school bus drivers and anyone under age 21, a BAC above zero is over the limit.
  • For commercial vehicle drivers, a BAC of .04 or higher is over the limit.

Defenses for DUI Per Se

You might think that failing a BAC test guarantees your conviction for DUI, but that is not true.

Some of the possible defenses for DUI per se include:

  • The police officer did not have reasonable cause for the traffic stop.
  • The breathalyzer test is invalid because the proper testing procedure was not followed, the sample was contaminated, the machine was malfunctioning, or the operator was not licensed.
  • A blood test is invalid due to a break in the chain of custody of the blood sample or proper procedures were not followed. For example, a marijuana blood test is only valid within two hours of driving.
  • Involuntary intoxication, meaning that someone doctored your soda or in some other way you consumed intoxicants without your knowledge.

Definition of Impaired DUI

In Illinois, an adult driver (non-commercial) can be charged with DUI if your BAC is more than .05 but less than the legal limit of .08 and the arresting officer can show probable cause that you were driving impaired. Examples of probable cause include failure on the standardized field sobriety tests and other observational evidence such as how you were driving, open alcohol containers readily visible in the vehicle, slurred speech, and anything you say in response to questioning.

Defenses for Impaired DUI

Some of the possible defenses for DUI per se include:

  • Audio or video recordings contradict the police testimony, showing that the field sobriety tests were not conducted properly or that you did not really fail them.
  • There are other explanations for poor performance on one or more field sobriety tests, such as illness or tiredness.

Consult an Oak Brook Terrace DUI Defense Attorney

If you or a loved one has been charged with DUI in Illinois, you have two immediate issues. If you tested over the legal limit for alcohol or drugs or refused testing, you first need to try and fight the automatic (statutory) suspension of your driver’s license. Second, you need to fight the criminal DUI charge. The sooner you seek help from an experienced DuPage County DUI defense lawyer, the more time your attorney will have to investigate the details of your case and take steps to mitigate the damage that a DUI can do to your life. Call the attorneys at McMahon Law Offices at 630-953-4400 for a free consultation; we offer evening and weekend availability.





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