As self-driving cars come closer to being common on American roads, much of the rhetoric promoting them has to do with safety. About 40,000 people die on U.S. roads every year, and driver errors are linked to more than 90 percent of crashes. But many of the biggest advocates of autonomous vehicles aren't car companies looking to improve the safety of their existing products. Huge backing for self-driving technologies is coming from Silicon Valley giants like Google and Apple. Those of us who have studied the relationship between technology and society tend to look more carefully at the motivations behind any technological push.