Most studies find that marijuana use doesn't actually significantly impair driving ability. The increased risk is somewhere between 1.0 - 1.3x. In comparison, there are several other drugs with up to a 4x increased risk that are completely legal with no limits.
It's a little bit counterintuitive since clearly you can be so intoxicated that you are whited out, but the results are very consistent across numerous different types of studies. I certainly wouldn't recommend driving after smoking, but epidemiologically speaking there is little to no increased risk when averaged out across the entire population.
Most studies find that marijuana use doesn't actually significantly impair driving ability. The increased risk is somewhere between 1.0 - 1.3x
Uh that meta-analysis of 9 studies you posted disagrees:
Specifically, drivers who test positive for marijuana or self-report using marijuana are more than twice as likely as other drivers to be involved in motor vehicle crashes. The increased risk of crash involvement associated with marijuana use is generally consistent across studies that were conducted in different geographic regions and driver populations, used different research design approaches, and were based on different methods for measuring marijuana use.
Further, one of those studies showed a 3.3x increase in crashes for high levels of THC-COOH in urine.
And as anyone who has been sufficiently stoned will tell you, there is no way in hell you should let them behind a wheel (or frankly, anyone who is mentally incapacitated). There is an upper limit just as there is for any number of prescription drugs that affect mental performance.
"Further, one of those studies showed a 3.3x increase in crashes for high levels of THC-COOH in urine."
That is the equivalent of something like half a beer, maybe one full beer at the most. And even the authors say that this is probably an overestimate, and most likely a substantial one.
If you look at the actual double blind studies, many of them can't even tell the placebo arm from the trial arm in terms of total accident risk.
Most studies find that marijuana use doesn't actually significantly impair driving ability.
I've conducted such studies, albeit in less than scientific environments. Truth be told, even without the bias of wanting to see the day where the vox populi regarding recreational use has swung the other way, driving after a few puffs of marijuana has always made me a more considerate driver.
This isn't the same as "I drive better when drunk" but instead "I tend to care less about some guy going before me at a four way stop when it's not his turn" et al
There isn't a scientific explanation, again but it's purely anecdotal; I become more relaxed and forgiving behind the wheel and honestly? Less angry drivers the better.
Your third link says:
"The results of this meta-analysis suggest that marijuana use by drivers is associated with a significantly increased risk of being involved in motor vehicle crashes."
Yes, they found a statistically significant increased risk, but the risk was lower (roughly half) than driving at .08, which suggests that it should not be illegal. Also, if you read the actual article including the discussion at the end they discuss why they think their combined risk is an overestimate. In fact the main reason I linked to that study is because of their arguments in the discussion, which are not only critical to understanding the paper at hand, but also for understanding the quality of the findings of other similar studies.
http://www.ncbi.nlm.nih.gov/pubmed/22785089
http://norml.org/library/item/cannabis-and-driving-a-scienti...
http://epirev.oxfordjournals.org/content/early/2011/10/04/ep...
http://www.biomedcentral.com/1471-2458/9/40
It's a little bit counterintuitive since clearly you can be so intoxicated that you are whited out, but the results are very consistent across numerous different types of studies. I certainly wouldn't recommend driving after smoking, but epidemiologically speaking there is little to no increased risk when averaged out across the entire population.