I can drive safely if I am high to a point that I cannot recognise that I am stoned - not sure if that makes sense. If I am proper stoned I find driving very difficult in that I am short of being overcome by paranoia and anxiety; cars, especially those on the other side of single-lane road, feel very close, as does the curb. As such I avoid driving, even as a passenger with someone sober, when freshly stoned, treating it the same way I would when consuming alcohol.
I would rather take my stash with if we go somewhere and get high at the destination, waiting until I feel sober enough to be relaxed before driving back or elsewhere.