That does make sense and I think that's what regulators may do in some cases. However, there is a safety risk having drones flying over busy streets; if one we

That does make sense and I think that's what regulators may do in some cases. However, there is a safety risk having drones flying over busy streets; if one were to fall out of the sky, it could cause a traffic accident as cars swerve out of its way. (There really aren't any truly safe places for a drone to fly, as they could always crash into some unfortunate bystander. However, I think over roads would be higher risk than most.) I think these sorts of decisions are going to have to be made on a case-by-case basis, which means extending the notion of right-of-way into three dimensions and creating a machine-readable national database that can be easily queried by the drones themselves to determine if they're somewhere they're allowed to be. I expect these right-of-ways will, in some cases, need to be modified on-the-fly in response to things like forest fires, public events, and various kinds of emergencies. So, I don't think that static heuristics like "all roads have a drone right-of-way above them" will work well in the long run.