Planes routinely patrol highways and there's no way to detect them other than by sight. You can see them overtly on clear days, or a mass of patrol cars signaling people off the road. It would need to leave a 1 mile warning behind the line of sight since they usually gauge within that zone.
Planes routinely patrol highways and there's no way to detect them other than by sight. You can see them overtly on clear days, or a mass of patrol cars signaling people off the road. It would need to leave a 1 mile warning behind the line of sight since they usually gauge within that zone.