Liability: It'll be interesting to see how automated driving technology performs in the hands of the common folk. While under development, you've got technically skilled individuals with the best training available checking prototype vehicles out on a regular basis. What happens when they're out in the wild? There are quite a few people out there that can't be bothered to change their headlight bulbs or get an oil change on time, let alone maintain a complex computer system that requires a variety of sensors and other equipment be working for the technology to function correctly. How many people drive around with a check engine light? I'm sure the dealership will be able to simply summon the car back overnight and send out a loaner if it's not ready in time, but is it wise to have a malfunctioning vehicle driving itself in for service while it is malfunctioning? Will the dealer's mechanics have the appropriate skills to maintain such systems? Self-driving vehicles still have the same properties as other vehicles, including causing serious property damage and bodily injury if they hit you.
Capacity/Energy: Automated vehicles driving around on the road will take up space and use energy, with or without an occupant. Here's a scenario: Dad's at work for a few more hours, Mom needs to visit a client. Jane wants to go to a friend's house on the other side of town. Rather than drive across town twice, Mom decides to summon Dad's car so that Jane can use it while Mom is out taking care of business. Once Jane is at her friend's house, the car drives itself back to work to pick up Dad. Meanwhile, Mom's done and Dad isn't home yet, so she sends her car back out to pick up Jane. In this scenario, instead of Mom running around town in a single car, both cars are on the road for an extended duration. Multiply this times millions of large families that are drooling over such a possibility. Yes, there will be an increase in cars on the road, either from vehicles deadheading (see below), or families that will be encouraged to take trips separately to save time.
I'm not saying that driverless technology isn't going to work out. EV/hybrid and automated tech will likely become the standard in taxi and rental car service, where vehicles can be dispatched and returned to a garage for maintenance/fueling as needed, with fleets maintained by dedicated mechanics with access to appropriate resources and detailed maintenance histories. Given enough time, automation will probably replace some forms of rubber wheeled transit services as well. After all, an automated vehicle that is summoned by the touch of a button, that can go anywhere on a door-to-door basis is the main premise of personal rapid transit. How will the average person use this technology? Will they use it responsibly?