The offense of Driving Under the Influence is also known as DUI. Illinois DUI law provides that driving under the influence of alcohol is a crime. 625 ILCS 5/11-501(a)(2) In this type of DUI charge, the prosecutor will attempt to prove that your ability to act with reasonable care is impaired due to the consumption of alcohol.
Just as any competent person is able to do, a police officer can give opinion testimony about intoxication. This includes physical manifestations of intoxication, such as slurred speech, bloodshot eyes, poor balance, difficulty following directions and saying the same thing, or asking the same question, repeatedly.
Non physical manifestations of intoxication include extreme moods (crying or argumentative), confusion as to current location, destination, time and day, disheveled appearance (clothing messed up) and difficulty performing basic tasks such as locating and or removing a driver’s license, insurance card or proof of registration.
Furthermore, the National Highway Traffic Safety Administration (NHTSA) training manual for DWI detection identifies twenty cues of intoxication that police are trained to know. The most common cue is an overly wide turn.
NHTSA has also devised a set of three standardized tests that, according to NHTSA, are designed to demonstrate that a subject is over the legal limit for safe driving. These are known as the Standardized Field Sobriety Tests (SFST).
The first test administered is the Horizontal Gaze Nystagumus (HGN). In this test, the officer administering the test waves a pencil in front of your eyes. The reaction of your eyes supposedly gives clues as to whether you are intoxicated. As is the case with all the SFST, the results of the HGN are based upon the officer’s subjective interpretation of the tests.