The same sort of problem occurs on the other end when you try to compare the risk of driving vs walking. Cars are 5 times faster in the city and 20 times faster

The same sort of problem occurs on the other end when you try to compare the risk of driving vs walking. Cars are 5 times faster in the city and 20 times faster on the highway than walking. The trips are almost always shorter on foot, you drive to the far away big box store but would walk to the neighbourhood store. Better metrics than risk per unit of distance would be risk per unit of time spent or risk per trip. I would point out that in a similar way few people drive between continents but flight is common.