Do a mental experiment. Suppose that you have technology that can make buses drive themselves.

First, you want to solve the problem of long bus intervals. It's still not economic to just buy more buses because they require a lot of power to run and do tons of road damage.

But you can make buses smaller! And by making them smaller, you can run them faster without incurring a lot of useless overhead.

Heck, you can just idle, dare I say _park_, these unused small buses when there is no demand. And since it's so easy to manage the fleet this way, you can make personalized buses for every passenger.

Hmm... It really reminds me of something...