People don't want to be underground for extended periods. If I were building an autonomous world from scratch, I'd want to design it so people are always above ground but "things" travel below ground.

There's an Amazon patent for an underground delivery system via tunnels that would mitigate against some problems that autonomous cars will bring. Once we have fully autonomous cars that don't need people, most cars on the road won't have anyone in them. Rather than pizza delivery people, shipping delivery, etc -- even something like "oh let me send my friend a key to my apartment while I go on vacation."

It will completely take over the roads unless we do something drastic. So send THAT traffic underground. We are going to need traffic lanes for "stuff." Let somebody commuting to work see the sun during their commute.

Edit: One thing I'd add is that New York and other places used to have a basic version of this - a series of pneumatic tubes that connected the city. There's a city in the U.S. that does trash via pneumatic tubes. I don't think that's the ideal delivery system for other reasons, but worth pointing out that this isn't an entirely new idea. Here's a map: https://untappedcities-wpengine.netdna-ssl.com/wp-content/up...