What is a DUI?

 In Washington State, the Prosecution must prove three elements before you can be convicted of Driving Under the Influence.  The first two elements are generally pretty easy to prove and the last element comes in two flavors.

You were the Driver.  In the case of a traffic stop, the police officer can testify that he or she saw you driving.  However, this element can sometimes be disputed.  For example, the case of one car accidents often raises proof issues with this element.  Since Washington State still follows the "Corpus Delicti" rule - your statement "I was the driver" cannot be used against you unless the Prosecutor can independently prove each element of the crime - including the element of who was driving.

You drove in the State of Washington.  This element is generally easy to prove however there is a related issue called venue.  For example, a driver who drove in King County would have to be prosecuted in that county.  If the charge were prosecuted in Snohomish County then the driver would be able to get the case thrown out under an "improper venue" challenge - even though both counties are in Washington State.

You took the breath test and got a .08 or higher, within two hours of driving.  In this case, we need to make sure that the breath test itself was reliable.  If there are any problems with how the test was performed or who performed it then the results may not be persuasive evidence against you.  The "within two hours of driving" language is called the "per se" prong of DUI i.e. if you're above the legal limit then you're guilty.  If the results are older than two hours then they can still be used against you but can only be used as evidence that you were affected by the alcohol.  

OR

Your ability to drive was affected to any appreciable degree by the alcohol (or drugs) you consumed.  Under this part of the third element, the Prosecutor must show that you were literally "under the influence" of alcohol or drugs.  The difference between this prong and the .08 prong is that approximately 20% of drivers will show no outward signs of intoxication with a breath alcohol concentration of .08.  Field sobriety tests, observations of driving and observation of the driver are the main tools used by Prosecutors to satisfy this prong.