[throwaway729]

> This is the reason that an impairment standard, rather than a chemical standard, makes more sense for criminal liability.

Impairment standards are far too subjective given the stakes. How exactly are you supposed to completely objectively measure "70% impairment"? You need a baseline, and the baseline driving ability of a person varies radically based upon time of day, emotional state, etc.

Impairment standards also lack any mechanism for differentiating between actors who know and don't know they're behaving recklessly. A cop friend of mine gave me a roadside sobriety test after a week-long period of intense work and very little sleep; I failed miserably. Now, should I have been driving? No. (And I wasn't!) But should "driving while tired" be treated the same way as "driving while piss drunk"? I'd argue not. Now, what about "got a cell phone call telling you that your parents just died, and you think you're OK, but you're not"? Jail time again?

Or, consider this case, which IMO amounts to "cut off the wrong person".

If this were a $20 ticket, I might be more sympathetic to your viewpoint. But the penalties baked into DWI laws are usually significant. We shouldn't be throwing people in jail because they were a little off-balance and jittery when pulled over on their way home from work. And especially not because they were perfectly fine but pissed off the wrong person who then lied about the results of an entirely subjective test.