Lead - While I agree with alphacentauri's argument, I worry about "paralysis by analysis". If figures such as he/she wants do exist then let us apply them to Ballina and make a decision.
In the 2017 CASA OAR supplementary study of Ballina, Paragraph 6.6 is entitled Safety Assessment. This contains two highly scientific statements:
6.6.1 Analysis of aerodrome activity at BBGA determined that the risk to airspace users in the BBGA area was highest between 0800 and1800 hrs which primarily covers daylight hours.
6.6.2 The likelihood of a safety incident between two aircraft after 1800 hrs was assessed as extremely low because all passenger transport movements are separated by time in their flight schedules and there are very few airspace users around BBGA after 1800 hrs.
In 6.6.1 CASA uses the words "determined" and "was highest" and in 6.6.2 "likelihood" and "assessed as extremely low". There is no evidence attached as to how OAR reached these conclusions, normally I would expect a hazard analysis and scoring based on a qualitative assessment matrix ranging from extreme to acceptable. If this is the standard that is acceptable to CASA when making decisions about the operating hours of a facility they believe will improve air safety then alphacentauri's suggestions are impossible in Australia. CASA further states that the airspace is "fit for purpose" (by the way CA/GRS is not airspace) so clearly they do not believe Class D airspace would be cost-effective. They are willing to wait for something - but what that something is we do not know.
My guess is that they are waiting for Airservices to say they are willing to open a Tower, and then CASA will write a report saying they should. In my view, as currently managed and operated, OAR is a waste of space.