perhaps - only assuming that legalizing it would lead to an increase in it's use and also an increase accidents. I'm not aware of any statistics on this as it relates to MJ. I think the rampant and legal use of prescriptions drugs might be a bigger issue in this regard.
Is there any data from countries such as Canada where (I believe) it is legal or at least effectively decriminalized?
I think legalizing marijuana would lead to an increase in its use, don't you? I don't know about any stats either. And I agree prescription drugs are probably a bigger problem, but I'm pretty sure it's already illegal to drive while under the influence of things like oxycontin, vicodin, etc.