That last bit does not sound right. DUI laws are set at the state level on the threat of the DOT withholding federal funds for state level road construction and

That last bit does not sound right. DUI laws are set at the state level on the threat of the DOT withholding federal funds for state level road construction and maintenance. I'd be pretty surprised if the feds were okay with such a scheme. (Nor, frankly, do I think that it's morally defensible. Laws are better when everyone can predict whether or not what they're doing is legal. A clear cut BAC limit is easier for everyone to comply with than some nebulous concept of "tolerance").