The sky has capacity even when it looks empty
Safe separation, turning space, wake effects, battery margins and emergency alternatives consume invisible room. A corridor that works in clear weather may lose much of its capacity when visibility, wind or landing options change.
Every route needs a quiet budget
Average noise is not the only measure that matters. Repetition, time of day and the character of a neighborhood shape whether a route is tolerable. A city may need to allocate noise in the same way it allocates curb space or construction hours.
Failure must have somewhere to go
An air-road plan is incomplete until it maps safe descent, blocked landing sites, communication loss and priority for emergency services. The public should be able to understand those rules before traffic grows, not after the first serious incident.