Short-term car use doesn't appear to work in the market. I remember seeing a lot of advertising for Zipcar and thinking it'd be great to engage a zipcar in order to travel somewhere (say, to visit my family a couple hours away) and not have to pay the full cost of renting a car for the duration of the trip.

Except that's not allowed. Zipcar is (was?) exactly the same thing as a car rental. You pay for all the time you're in possession of the car. You're not allowed to return the car anywhere except the exact location you picked it up from.

What was the advantage supposed to be?