[ericlevine]

Of course I'm way late to the game here, but thought I'd add one more voice of dissent:

The real estate costs can be extremely low for self-driving cars. Imagine a tower of, say, 10 cars stacked vertically with an elevator mechanism to bring them to and from ground-level. Since each autonomous car is interchangeable, you can just treat the vertical parking lot as a stack. When demand is high, pop off the stack. When demand is low, push back onto the stack. No need for ramps or anything else that existing parking garages use. And just to be totally clear, humans don't interact with this tower, it's just a storage mechanism for empty cars after they've unloaded passengers.

[maxerickson]

If demand is low traffic should be low too, why not just use empty lanes of streets for the same purpose? Or at least, some variation on that theme. Maybe things work out so well that streets usually only have 1 lane.