I was thinking about this the other day, quadroptors could be designed to latch on to cars, trucks, bus and trains going in the direction they need to go. They would jump between vehicles getting closer and closer to their final destination.
I had two ideas about how to make that work.
In one situation, especially if the quadropters were smallish, I would suggest that the quadropters need no permission to hitch a ride on a vehicle. They would be designed with none-damaging landing gear, suction cups or magnets. As well they would be designed with some sort of security protocol that would allow them to fly off if they noticed that they were stopped and in danger of being attacked
I suspect they could act almost like a skittish pigeon that doesn't let anyone get too close. They would also be able to find a safe place to rest during periods of limited traffic or high danger. They could simply land on a deserted rooftop and use the same security system to leave when danger is present.
Now another alternative, that would probably work in conjunction with the previous description, would be a unified protocol of communication and utilities that would facilitate the quadroptor delivery network. For example, a city bus system could be outfitted with bus roof landing zones that would provide better aerodynamics, a recharge station and a reliable route of travel. The landing zone and quadroptor could communicate and the quadroptor would be able to pay for the services in crypto-currency ( or normal currency I guess).
People would also be able to set up recharge and security stations on their own property and roofs and be paid for their services by the robots.
I really can't wait for the day that I get a package delivered by quadroptor.
I guess we could call it OWL mail.