Originally Posted by Hetman

You don't need to blow .08 or over to be convicted of DUI. It only needs to be proven the driver was impaired. The law is not about the BAC; the law is "driving under the influence."

In most states, .08 BAC is considered prima facie evidence that the driver is impaired. In the strict legal sense, this means that unless the defendant is able to impeach the evidence provided by the BAC test, that alone is sufficient evidence to convict. BAC, however, is only one piece of evidence. It can still be proven through other evidence that the driver is impaired, resulting in a DUI conviction even with a BAC below .08.

If you are pulled over or are in an accident and the police find probable cause (e.g., open container, smell of alcohol, erratic driving, field sobriety test) for a breath test on which you blow .06, the police have a a lot of evidence and a strong case against you. Not the prima facie evidence of blowing at or over .08 but still enough evidence to build a strong case.