There would likely be vehicle sharing benefits, but self driving cars are apt to make traffic worse. Your average 8 lane freeway will still only be able to carry 11k cars an hour assuming everyone has minimal stopping distance & is driving at 40mph for ideal throughput.
Traffic lights are also unlikely to disappear, as self driving cars do not magically get perfect traction or stopping abilities, and they will have to share the road with the other humans that exist on our streets, whether they be pedestrians, bikers, joggers, skateboarders, etc.
In contrast, a light rail alignment can move 20k people an hour. It also won't reduce traffic, but it'll slow traffic growth by reducing latent transport demand and allow cities to remain economically viable as traffic increases.