The cause mechanisms would be inherently difficult to disentangle. Somebody could be particularly drunk and it's the phone that rings that ultimately happens to distract him or her from driving. Different people metabolize cannabis differently just as different people metabolize alcohol differently. I think the causal mechanism is going to be inherently difficult to discern, but I think we can all reasonably agree that driving high is probably a bad plan.
On September 12th, 2017. See this statement in context.