Impaired Driving is the first and most common type of DUI-DWI. This form of DUI-DWI has the usual components of a traditional (common law) drunk driving case involving these elements (essential parts of the crime that must be proven by the prosecutor to justify a conviction): (a) operating or being in actual physical control of a "vehicle;" (b) on a roadway, public way or other place prohibited by that state's laws (some states cover "any place within the state"); (c) while under the influence of an intoxicating beverage, substance, vapor or chemical, or some combination of these chemicals and substances. This type of DUI-DWI requires proof of impairment through testimony of one or more witnesses, and (where available) a quantitative breath or blood test result for alcohol content.
A second major type of offense now exists that has absolutely NO REQUIREMENT OF PROVING IMPAIRMENT of the driver. It is sometimes called "Driving UBAL" or "driving with an unlawful blood alcohol level" when the driver has consumed enough alcohol to exceed the applicable legal limit for the driver's age group and vehicle type.
For those who take the state's test and render a sample with an alcohol level at or over the state's legal limit, this alone (assuming the test result gets into evidence and is believed by the jury or judge hearing your case) constitutes the separate offense of DUI-DWI "per se"). Note that quantitative impaired driving limits for contraband drugs have not YET been "established" by the federal government, but that this legislation will be enacted within the next 2 to 5 years. Hence, today, only ALCOHOL has quantitative impairment guidelines limits for traditional DUI-DWI.