Interesting that smart cars (even a modest percentage) could elminate congestion. As you say, factors at work are:

1) Computers drive better than humans, can anticipate and plan for macroscopic traffic trends, plus

2) Online education, Zoom meetings, work at home, better delivery systems etc are eliminating some driving needs

3) Robo taxis may eliminate the need for some to own cars, changing city planning patterns.

Some frontiers that might remain are:

4) Making highway traffic more "electrified" and "frictionless" (to compliment electric cars, compete with rail travel) My article:

https://medium.com/p/c3e260916d9d

5) Getting more people to share rides (which may not be necessary if cars get smaller and more efficient).

1-3 are rather threatening to those loving the freedom of driving, while 4-5 are not favored by rail fans, my article:

https://medium.com/p/fb0db319bda9

It's kind of sad/startling to predict the demise of rail/bus travel at some level. I suppose they will always have a place in congested urban areas, perhaps not in Suburbs and beyond. The thing about rail/bus, they are only efficient if they are close to full capacity; https://medium.com/p/e6c07f12a3ed