Texas law only provides that the crime of DWI occurs when a person drives, and at that time, has an alcohol concentration of .08 or more in their body. It is not a crime to have an alcohol concentration of .08 in the body either before or after one has driven, as long as the driver still had the normal use of their mental and physical faculties while driving. However, depending on the time the test is conducted, such an alcohol concentration may be relevant, but not necessarily accurate, in determining if the person had a .08 or more alcohol concentration when the actual driving occurred.

The timing of the particular test in question can present significant problems for both the prosecution and the defense in the trial of a DWI case. This dilemma arises because .08 alcohol concentration testing is hardly ever done at or immediately after driving. Generally, an alcohol concentration test is usually administered approximately 45 minutes to 1 hour and 15 minutes after driving. Consequently, unless there is information about the number of alcoholic drinks consumed, the type of drinks consumed, and knowledge of when the drinks were consumed, it is scientifically impossible to determine if the person was over, or more importantly for the innocent, under a .08 alcohol concentration at the time of driving.