This argument, commonly referred to as the "relation back" or "rising curve/BAC" defense argument, acknowledges that under Virginia law, the results of a breath test are rebuttable. In other words, if a person's BAC is .08 at the time of the test, Virginia law creates a rebuttable permissible inference/presumption that it was also a .08 at the time of driving. As mentioned, this inference/presumption is rebuttable. That doesn't mean that the burden of proof shifts to the defendant, but the burden of production of evidence does shift to the defendant on this issue once a BAC of .08 of more is shown. Through the use of an expert witness, many times it is possible to present evidence that based upon when a person drank, what they drank, what they ate, when the ate, their height and weight, and when the test was conducted that their BAC was below the legal limit at the time of driving even though it was above the legal limit when they were tested two to three hours later. Where applicable, this is a powerful defense and is very persuasive to both judges and jurors. You should consult with a Fairfax Virginia Drunk Driving / DWI / DUI / Driving Under the Influence Lawyer to discuss the details of your case. An experienced Virginia DUI attorney can help explore whther this defense applies in your case.