Thinking a little further. In the future, we will have autonomous cars, and a user will probably not "own" the car, but will simply order it. And the user can specify if (s)he would like to share their ride. This car can easily have additional functions, for example package-delivery (a package is nothing more than a shared ride with a non-human passenger). Of course the logistics will be run from a central computer system. Perhaps this could be a more cost-effective solution to the whole package-delivery problem (?)