I'm not sure that this is a helpful way to look at things. Cars are much safer than they could be and the risk per mile is low, but driving is still one of our big sources of risk, precisely because we do it so much.

Similarly, I estimate ~2 deaths per million cigarettes smoked (~1000 cigarettes/year/person >= age 15, 480k deaths/year), and while driving a hundred miles in a day is unremarkable, smoking 100 cigarettes in a day is pretty astonishing, but I wouldn't say that cigarettes are not that risky. The total deaths per capita are high.

(To be clear: cigarettes are more dangerous than driving any way you measure it. I'm just showing that you get to weird places if you look at risk/unit, without looking at total volume).