I agree with your second point (self-driving cars might make more efficient use of roads), but I don't see how cheaper taxis is going to reduce road congestion?
Also, with self-driving cars that are cheaper, I expect that people who now drive a car to the suburbs will move further out of town to get cheaper housing because a) driving is cheaper and b) self-driving would mean they can do things on their commute (work, watch Netflix, etc)
I think the uncomfortable truth is that, to fight climate change, we must give up some luxuries. Flying, driving a car, electricity, low priced almost disposable clothing, electronics gadgets, etc. must get more expensive.
In any case this article was about road congestion; not about saving the planet. When it comes to that, I don't really believe in technical martyrdom where people voluntarily choose to not do lots of things they would like to do as a solution. And making you feel good about you through voluntarily declining to do certain things is nice and nobel but more of a form of hedonism than a practical solution. Nothing wrong with that but it's not a scalable solution in the sense that in the bigger picture of 7-9 billion people not following your lead, it's going to be statistically meaningless/irrelevant unless you convince them otherwise at unprecedented scale.