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.
If my fried could have just summoned the nearest self driving car, an entire one way trip wouldn't ever occurred.
A self driving car takes the pain out of driving so unless society changes a lot we will see more cars driving around (often empty) and people will have longer commutes while sleeping their car.
[1] https://en.wikipedia.org/wiki/Sanisette
[2] http://www.eatmedaily.com/wordpress/wp-content/uploads/2009/...
In addition to this, on surface streets, traffic lights meter traffic through intersections. With self-driving cars, the cars will be able to go through intersections without the need for a traffic light, eliminating that metering effect.
In my cynical opinion SDCs will likely precipitate a ten year pause in new road construction as drive times drop dramatically. But at some point we'll catch up to the additional capacity and spend another five or six years suffering as roads are built and expanded.
But the newly constructed roads will be more efficiently utilized than roads at present, so it will be cheaper per passenger mile.