Can Americans Handle Legal Weed?

So Andrew Sullivan seems to have convinced himself that legalizing marijuana is a real possibility. I haven't been paying all that much attention to developments on that front, but I'll believe it when I see it. In fact, I might not even believe it then.

But I wonder: can Americans handle legal weed? I mean, we can't handle legal alcohol--this is a country with about fourteen thousand booze-related automobile fatalities per year. Conventional wisdom seems to indicate that weed impairs driving ability less than booze does. And I'm all for legalizing weed in principle. But when I sit down and think about adding a bunch of high morons speeding around in SUVs to the drunk morons we already have speeding around in their SUVs, it gives me pause.

The smart solution would be to make penalties for impaired driving more severe, but for some reason that escapes me, we seem to be unwilling to do that.