No need to wait while we figure it out. The study I posted says, as pointed out in a previous post:
"In blind ratings, police officers rated drivers with a BAC of 0.08% as more impaired than those who had taken moderate to high doses of cannabis, and driving instructors rated subjects with a BAC of 0.04% as impaired, while those who had consumed a dose equivalent to 7 mg of THC were rated as unimpaired."
and
"...suggests that a serum of THC concentration of 12-16 ng/ml may correspond to the same accident risk as a BAC of 0.05% [12]."
So, again, just because you aren't the exact same as someone who is totally drug free, it doesn't mean your driving is dangerous enough to make the substance illegal. High doses of marijuana tend to make people drive like someone who is still legal under the alcohol driving laws. Way under the legal alcohol limit, actually. And driving instructors were not able to detect any impairment at all.
People need to get past the generalities of saying "You are impaired, therefore your driving must be." It's not that simple. Not everything that impairs you, the person, will also make your driving more dangerous.