For a fraction of the cost of developing self-driving cars we could have self-driving trains/trams/subways and most likely minibuses as part of public transportation networks.

And self-driving minibuses would basically provide 95% of the benefits of self-driving buses. They could offer 24/7 frequent service with huge coverage, we already have dedicated bus lanes in many places (and we could scale dedicated bus lanes much faster than dedicated self-driving car lanes), etc.

Now, I understand that in many places (especially the US) this is infeasible because public anything = communism.