As excited as I am for robotaxis, nothing beats the raw people moving capacity of trains. The places where robotaxis offer the greatest benefit is in providing first and last mile services getting people to the train station and back in sprawling suburban areas where adequate transit service isn't feasible.

You'd need to have some very smart, and tough public policy in place, though, to constrain robotaxis to instances where they provide maximal societal benefit. It will more likely be a free for all that makes traffic worse, not better, because that's just the way these things tend to go.