Of all the things that could be automated on roads garbage collection and street cleaning seem ideal. They operate at slow speeds, have far fewer edge cases e.g. cars aggressively cutting in and out and people already move out of their way when they come by.

And you don't want to dismiss Japan's (a) technology ability and (b) commitment to robotics. Sony, Panasonic and Toshiba lead the world in many sensor technologies in particular visual that would be relevant to cars, robotics and other automated systems.

Most importantly their culture is more conducive to it, case in point the robot run hotel:

http://www.abc.net.au/news/2015-08-19/japanese-hotel-run-by-...