Driving while intoxicated, driving while impaired or operating while under the influence of an intoxicant, is more than simply drinking alcohol and getting behind the wheel of a vehicle and driving.  Some of the acronyms used by the state to describe impaired driving are OWI, DUI, DWI, OMVWI, or OUI.  In all cases, an individual's ability to operate their vehicle must be impaired because of the consumption of alcohol or a controlled substance.  The individual must be less able to exercise the clear mind and steady hand necessary to operate a motor vehicle.  However, drunk driving is legally distinct from being over the limit (having a prohibited alcohol concentration (PAC)) or having the presence of a restricted controlled substance in your system.  In a drunk driving case, impairment is the relevant factor.  Conversely, in a PAC or restricted controlled substance case, the level of alcohol or drugs in the system is the relevant factor. In some multiple offense cases (4th or subsequent),  simply having a drink or two might put an individual over the legal limit (.02) resulting in a charge for operating with a prohibited alcohol concentration, one could be charged and convicted even if the individual was not impaired (less able to safely operate his vehicle).  I have seen many cases where an individual is found not guilty of operating while impaired (drunk driving) and guilty of being over the legal limit (PAC).  Unfortunately, being convicted of one or both results in the same set of penalties.  Likewise, operating a vehicle with even a trace of a restricted controlled substance in your system is separate and legally distinct from drunk driving.  It is not hard to imagine a situation where a person has a trace of marijuana (a restricted controlled substance) in their system, but they are not impaired.  Even a trace of a restricted controlled substance is sufficient to result in a charge.  Once again, a person could be convicted of having a trace of a restricted controlled substance in their system but found not guilty of being impaired.   Unfortunately, the penalties are still the same.

In terms of driving while impaired, just drinking a beer and driving does not translate into drunk driving.  What is illegal is consuming too much alcohol and driving.   To establish a driving while intoxicated charge, the state would need to show that the driver's ability to operate his vehicle was impaired.   Many times, the state will look at the driving, the field sobriety tests and normal motor coordination as well as the appearance of the individual.