You forget transportation of goods. Pretty much all over-land cargo in the U.S. and most of that elsewhere (less so, because trains) could be transported by self-driving cars/drones. Not sure if that is larger or smaller than transportation of people at this point, but it's still an astronomically huge market.
Mostly because, freight and passenger trains interfere badly. No passengers = easier freight. A big wave of deregulation of the market a few decades ago helped, too. The Economist ran a special about the US market a few years ago.
