In my city in Europe, my average speed is 23 km/h but I rarely go less than 40, more often 60-70 - meaning that I wait a lot, and I'm alone in the car. Yes, shared autonomous cars would help my city a lot.
Maybe TomMarius means that autonomous vehicles could negotiate intersections without stopping. No traffic lights required, only rules of precedence. It's going to be a slow procession but maybe the average speed would increase.
I'm not sure how that would mix with pedestrian crossings. In some dense areas there would be a non stop flow of people walking across the street and cars wouldn't be able to move.
The cars can work together to reduce riding distances, move faster in tandem when going in a green light, and so on. They virtually make the road much wider by eliminating human inefficiency in driving.