In 2011, the Illinois Supreme Court handed down its decision in People. v. Martin, 2011 IL 109102. The issue involved a fairly technical legal question known as “causation”.
Causation refers the notion that in the criminal law, a person is responsible for the outcome of an event only if the state is able to prove that something he did in an illegal manner caused the outcome. For instance, if your headlight is not operating properly and someone rear ends you, the state cannot say that you were the cause of the collision even though your car was not in proper working order. In other words, your non-functioning headlight, while illegal, was not in any manner responsible for your being hit from behind.
This idea came into play in the Martin because of the manner in which certain DUI laws are written. Under 625 ILCS 5/11-500, you can be charged with Driving Under the Influence (DUI) in a number of ways.
One way is prove you were “under the influence” of alcohol, drugs, or a combination of the two. Another is to prove that you were driving with a blood alcohol content of .08 or greater. A third is to show that you were under the influence of other intoxicants (huffing for instance).
One can make an argument that if your blood alcohol content is above .08, you are potentially a dangerous driver. The state should not be limited to proving your impairment by reference to your physical condition, actions and conduct at the time of the alleged offense.
Your blood alcohol content alone should be sufficient to show you ought not to have been driving. It would seem that since the purpose of the DUI laws is to keep dangerous drivers off the public roadway, this is a reasonable law.
However, there is one situation in which the state need merely show that you were operating your motor vehicle at a time you had any amount, no matter how small, of a prohibited drug in your system. 625 ILCS 5/11-501(a)(6) Unlike alcohol, which leaves your system relatively quickly, some drugs remain in your body long after (sometime for weeks) you ingested them and well after their presence in your system would impact the mind and body in ways that could make you an unsafe driver.