At what point do we replace humans with software here? Obviously we shouldn't remove humans from the loop entirely, but computers should be able to do a lot of the work of detecting and flagging collisions, directing traffic, etc.

At modern airports, a lot of that is in fact handled or assisted by computers.

The US's air traffic control is incredibly technologically outdated compared to its peers. Even 15 years old ATC technology would be an improvement in many cases. Other countries have a lot more automation, allowing them to make do with much fewer controllers.

Some of the systems in the states still use floppy disks!