Automation on the roads could be the great public-health achievement of the 21st century. If driverless cars deliver on their promise to eliminate the vast majority of fatal traffic accidents, the technology will rank among the most transformative public-health initiatives in human history. But how many lives, realistically, will be saved? By the end of this century, there’s good reason to believe that tens of millions oftraffic fatalities will be prevented around the world. This…