One of the great things about a fleet like this would be that you could change your car depending on where you were going and what you were doing. For example you take a 1-seater to get around a city but if you go a longer drive you take a larger, more powerful car. This is one of the things I enjoy about using zipcar, you get to drive fancy cars some days but only pay for the cheaper ones most of the time.

The great thing about an automated fleet is that you could actually switch cars during the journey. Take a small car to leave the busy urban areas and than switch to a larger car when you get to the motorway.

I love the idea of smaller, more efficient vehicles, but I think we hold too much hope in the fact that they could be "self driving". Why would a smaller self-driving car be more likely to gain in popularity over what most people choose to drive today? Why is it more likely to be electric? Those are two independent characteristics that haven't taken off on their own; I don't see how the self-driving aspect is going to change many of the existing problems we have with car-based transportation.

Robo-cars in taxi mode won't stop, they'll go from one job to the next, and they won't park except at times of low demand. Unlike drive-it-yourself cars, they won't eat up urban space for parking lots, and the total car fleet will be much smaller because the allocation only has to be "one per currently travelling commuter", more or less, rather than "one per human".

This is the harm-reduction debate. For example, Swedish snus and electronic cigarettes are much less harmful than smoking, but the argument goes that quitting nicotine altogether is less harmful than anything. Yet people still smoke and use nicotine, so switching the stalwarts over to less-harmful methods of nicotine consumption would save lots of lives and money.

Likewise, it may not be possible in the short term to convince everyone to stop driving cars. Self-driving cars won't fix the long-term problem of efficient transportation, urban sprawl, or emissions, but they can reduce its harm by efficiently providing car-like service to the public.