My experiences are those of a driver, but I think about how the rides must feel from the passenger's perspective. Based on what some have told me, they feel uncomfortable during entirely silent rides. So I always start with a couple of generic conversation prompts. It's pretty easy to tell when someone wants a quiet ride. But other people are looking for someone to talk to, and I'm happy to oblige. Passengers also tell me about experiences with other drivers who've made them uncomfortable by hitting on them or going on political rants. I've also read about incidents where drivers have been assaulted by passengers, and passengers by drivers. Passengers and drivers are two strangers in a moving vehicle. Some of what seems to be passengers' indifference to me is probably their way of dealing with what is a potentially frightening experience.