[lostcolony]

That's true with alcohol, too, though, it effects people differently. .08 was basically just resolving legal ambiguity by picking a reasonable BAC; it's not like at .079 you can operate a car safely but at .08 you're a danger to everyone on the road.

You can actually be arrested for an 'OUI' in some states, an Operating Under the Influence, for when you are clearly impaired, but fall below the legal cutoff for a DUI. This would likely necessitate being the same sort of thing, a legal recognition that you were driving recklessly, and you exhibit the signs of recent marijuana usage (or if we have some way of actually measuring it, then that too).