First, there's traffic, and there's parking. The claim you're making is that the lack of need for parking in dense areas creates traffic while the SDCs go to park. That may be true, but if the SDCs are delivering say, 5-9 people to work every day between shared rides and multiple trips, the fact that one SDC then has to make an extra drive out of the business district, at the end of the morning rush hour is not that significant.

The hope is also that SDC driving behavior is also a lot more consistent and predictable, leading to more smoothly flowing traffic. Sometimes a few crazy drivers, or worse, drivers that cause accidents, can foul up traffic massively. I'd expect that this would be reduced in a mostly SDC world.