I should have said Manhattan. 23% is "scarce" in that, on the island, there are relatively few gas stations, parking is expensive, and getting your car serviced reasonably encumbering. It's also a four-fold reduction from the U.S. average.

How much cheaper would a driverless Lyft or taxi be? 50%? How many more people would forego driving, in Manhattan, if ridesharing were half as expensive as it is today? If half do we're at 11.5% car ownership, a 7-fold reduction from the present-day U.S. average. If 2/3 do, we get to 10-fold.