https://www.atsb.gov.au/publications...ir/ao-2019-066
Controlled airspace is just as dangerous as OCTA if traffic information is not handled/understood and complied with. In this instance the only thing that saved a mid air collision (or at least a very close miss) between the ATR and PA-28 was TCAS, and even then it was only a TA, as the RA was inhibited at that altitude. Considering the position the PA28 was in below the ATR, it's unlikely the crew would have sighted them without the TA occurring. The Tower did not even see the conflict and was only alerted after the fact as they were dealing with a third aircraft.
There have been a number of actual collisions in CTA in the US in recent years.
This the result of one of them where both crews were lucky to survive.