As far as Illinois DUI law is concerned, there are three general categories of offenses. The first and most common is DUI alcohol.
Alcohol-related DUI can arise from impaired driving evidence due to alcohol. That would come about by the police officer’s observations of your driving, your conduct during the arrest and your performance on what is known as Standardized Field Sobriety Tests (SFTS). 625 ILCS 5/11-501
DUI alcohol can also apply if a driver provides a chemical test that shows a blood alcohol level (BAL) of .08% or greater. This is known as “per se” (Latin for automatic) DUI. In a per se case, the state does not have to prove actual impairment but merely operation of a motor vehicle while having a BAL of .08% or higher.
The per se law can cause a great temptation for a driver to refuse to submit to testing. Since in Illinois a refusal is not a criminal offense, that can in some instances be a good strategy if you think you may fail.
The downsides of refusing are two. First of all, the judge will allow the prosecutor to argue to the jury that your refusal is evidence that you were afraid you were drunk and that is why you refused.