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.
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.
Plus reduction of number of driving cars to roughly one third.