this is not worthy of HN and the concept has been touched on many times here. i only blogged it because it was too long for a tweet and i wanted to reference it in a discussion. please don't upvote.
The point could be taken further to work out how much people spend on average on a car and at what point they would get rid of their car.
Possibly for general use it is more applicable to self-driving cars than Uber but it's still interesting.