This is a fallacy - self-driving cars may reduce car ownership and may reduce traffic fatalities, but they could only reduce traffic if speeds were extraordinarily high.
That _might_ happen, but it'd also make every street a freeway. It's unlivable, and I will fight against that world.
That's not true at all. A ton of traffic congestion is caused by people making suboptimal decisions in traffic. Blocking intersections, not merging properly, stooping and going instead of coasting at a set speed, etc. really reduce the speed of traffic.
If you created a self driving only traffic system that guided the cars in an optimal path and speed you could increase traffic throughput by a lot.
But the current generation of self driving cars aren't even close to that task. If anything they will clog traffic even more when they panic and stop in the middle of traffic. That prevents accidents but it also will clog streets during rush hour.
But eventually they may solve traffic jams.
Not that you could increase speeds safely - SDCs still need to brake in time, and they're bound by the same laws of physics, and there are still blind corners in the future.