I have always wondered how they would contend with weather, it seems to me, this factor alone would put a large percentage of flights at risk especially at the distances needed to fly. Here in Florida weather changes so quickly in the summer months I couldn't see them successfully completing 20% of scheduled flights with a UAV unless they had the ability to switch delivery methods at the point of distribution.
Pat
This from a link in the referenced article:
The application, originally filed last spring, proposes that the drones save energy, recharge, and seek shelter by riding on top of other vehicles for part of their journey. In addition to utilizing its own trucks for the purpose, Amazon is hoping to form partnerships with other shipping companies and even public transportation agencies to give drones permission to land on trucks and public buses. The drones would use identifying markings and GPS coordinates to find vehicles to land on if they were in trouble or out of battery life. This fits in with Amazon’s earlier suggestion that partnerships should be utilized to help in other methods of delivery; such as fitting products into underutilized space on newspaper delivery trucks already scheduled along similar routes.