A New Way to Rent a CarTwo San Francisco-based startups, RelayRides and Getaround, have teamed up to create a new kind of car-rental company -- one that allows car owners to rent out their vehicles.

There are few investments less sensible than car ownership. A new purchase loses close to 9 percent of its value the minute it leaves the dealer's lot, according to automotive-information site Edmunds. Further, most cars sit idle the majority of the time.

Two San Francisco-based startups,RelayRidesandGetaround, are working to change these inefficiencies--and snag a piece of the nation's $20 billion car-rental market. Similar to Airbnb, both companies facilitate peer-to-peer transactions through which car owners can rent out their vehicles to those who need them by the hour, day or week. Owners set the rental price for their vehicles; both companies say the average rental runs $8 to $12 per hour and lasts 40 hours.