Driving on highways is far easier than driving in cities because it's a more controlled environment. There aren't supposed to be pedestrians, bikers, traffic lights, and it's generally a more constrained problem. Logistically, you can just have truckers drive in cities, get out at certain waypoints, and then have truckers take over again at waypoints (mostly located just outside cities).

I'm not saying it's an easy problem, but it's a much easier problem. You also don't have to be as concerned with public perception, as you aren't asking a consumer to get inside of it.