The car companies have another option for getting into the car sharing business with instant rentals. Daimler (car2go) already has about 750 cars here in Seattle and BMW (ReachNow) another 520, and they keep adding them. Or they can go the Lyft/GM's ExpressDrive route and provide a pool of rental cars to drivers. It will be far more profitable in the near term for other companies to jump into these markets than invest the billions it would take to build out a driverless fleet.