Depends. In St. Louis, for example, a fully electric vehicle produces the same pollution (via the power plant) as a 36mpg car [0]. That's about in line with a highly-rated compact like the Golf or Mazda3 these days.
Electric vehicles give us the capability to reduce emissions by building cleaner electrical infrastructure, but that does not mean we will do so.
[0] https://en.wikipedia.org/wiki/The_long_tailpipe#Carbon_footp...
Additionally, pollution concentrations matter for cities, specifically dumping the exhaust out right next to people vs. dumping it at remote locations where it has more area to dilute before encountering people.
The long tail pipe hypothesis seems to be a bunch of people trying to desperately prove that electric cars are no better, but they have to resort to extreme cases to try to justify their positions. 36mpg which pollutants? Certainly not all them. CO2 from pure coal is something like a 50 mpg car. And as we get rid of these inferior and more expensive sources of electricity, electric cars will only increase their lead over gas vehicles.
And when there's a surplus of self-driving cars, where do they go?
There will be an increase in miles driven per passenger mile in order to get the self driving cars to where they need to be, when they need to be.
No one wants to own a single person car, because even a single person wants to be able to carry passengers if they need to. But lots of people will be making single person journeys all the time, so it makes sense for a taxi company to own them.
But you are 100% right that congestion will be the problem. Cars simply do not scale well, as the amount of sqft/passenger/minute is huge. We seem to be unwilling to devote the huge amounts of land to highways that we would need to in order to make congestion go away. And in cities, intersections can only let so many vehicles through per minute.
As another commenter said, traffic is a good problem, however it's only good until it stops trips. It's great for people to be moving about, but when traffic prevents that, it's bad.
Autonomous drivers give people back their time in the car to do with as they please, but they will definitely increase congestion.