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 (?)
Yes, and package delivery autonomous car can be made very small -- just big enough to carry the package. In fact, a ground-based autonomous delivery vehicle doesn't have to look anything like a car. Imaging an autonomous Segway-like 2-wheel cart. Segway is 4.5 times more efficient that Toyota Prius and 11 times more efficient than average American passenger vehicle.[1] Something like that would allow delivering packages very cheaply.
If everything is really well orchestrated logistically, your Segway solution could attach (piggyback) to a bigger autonomous vehicle for a certain duration for greater efficiency, higher speed and bigger radius. Of course, the fuel costs will have to be split, but that is just a matter of making smart accounting software.
I like that idea -- for less time-sensetive deliveries you could have a "mothership" truck loaded with mini-vehicles drive to a neighborhood center and then release them. However, for things like food delivery where you want to deliver in under an hour, it will be better to just use mini-vehicles.
