Implied consent laws control.
Also pot stays in the body for at least a month.
Baked drivers are screwed. That’s a good thing.
Stays stored in fatty tissue for as long as a month - stays attached to neuroreceptors for only a few hours.
All that would prove is that someone smoked within the last month. They don't have any evidence of driving under the influence. If this is so cut and dried, why aren't they doing this now? There's already baked drivers everywhere (just like there's drunks). The real risk are the people who take regular prescription drugs - just about all say don't drive if you're taking these things but everyone does anyway. That's a bad thing.