Certainly, you need temporary storage one way or the other. But I have come to picture road system with a fully coordinated self-driving car network where full system decisions can be made. If it’s a low-demand time, then there’s a need for storage while at the same time a reduced need for lanes. The coordinating software could outright shut down certain lanes (even in the city center) for car storage so that they’ll be right where they’re needed when demand picks back up. This is a reasonable argument predicting full obsolescence of parking decks… if the assumptions about a coordinated system become true.
But the system would keep humming 24 hours out of the day. A while ago I was looking into bulk traffic volume versus time of day, and the mid-day volume isn’t so radically different from rush hours. It’s a factor of 2 difference, and maybe less. Commute time are already naturally staggered due to general variation. One takeaway I got was that coordinated autonomous cars could be extremely active, averaging 10 hours or-so actively moving out of the day.