Ex FSO GRIFFO, one aircraft was certainly in the air. The point I am clearly making is that the highest risk is closest to the runway.
Further to this important scientific fact is the issue that the most likely airline accident we will have in the near future will be a runway (or close to runway) collision at an airport like Avalon – not a midair that ADS-B could have prevented in the high level airspace over Bourke or Birdsville.
The reason everyone seems to be obsessed with mandatory radio and ADS-B above 5,000 feet is because that is where (in the old days) Flight Service Officers could provide a service to both IFR and VFR with their existing staffing levels. Of course, where the risk increased at lower levels at airline airports such as Taree, there was no requirement for the VFR aircraft to be in the system – therefore traffic was not given by Flight Service.
This led to some people believing that the higher risk is above 5,000 feet, not below. Why else would the second stage of the ADS-B mandate for GA aircraft be talking about requirements above 5,000 feet, but not at lots of higher traffic density areas close to the ground?