The Rising Blood Alcohol Level (BAC) Defense in DUI Cases

The rising BAC defense is also referred to as the "relation back" or "rising curve/BAC" defense argument. This defense acknowledges that under Virginia law there is a presumption (also referred to as a permissible inference) that a person's blood alcohol level at the time of driving is the same as the person's blood alcohol level at the time of the official breath test is taken at the Adult Detention Center or District Station hours after the driving. 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. This inference or presumption is rebuttable. That doesn't mean that the burden of proof shifts to the defendant, but the burden of producing 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, it is possible in certain cases 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. In other words, their BAC was rising at the time their vehicle was stopped. This often is the case where a person drinks a number of shots or concentrated alcohol shortly before driving. This can be a powerful defense and can be persuasive to both judges and jurors.
Where accepted by the fact finder, this defense would serve to rebut, or undermine, the results of the official breath test. In such a case, the fact finder would have to rely on the results of the field sobriety tests and general observations of the officer.
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