250below10 - You are correct however a parallel taxiway is probably more expensive than a small (privately run) Class D control tower. Proof of this can be seen at airports such as Cairns, Gold and Sunny Coasts, Hobart, and so on, all of which have large (Government monopoly) Towers, but either limited or no parallel taxiways. In these cases the Tower is in fact a mitigator for the lack of a parallel taxyway as anyone who has operated through Cairns should be able to work out. The parallel taxiway only provides a mitigator against runway occupancy issues; this is only one factor in the complexity problem. A single person Class D Tower controller can mitigate against many other issues in on the ground, and in the air, as well as contributing to the smooth running of the airport. This, in my view a reason why the ATCs should be working for the airport, not the Government. There is, by the way, no reason why a privately run Tower should not operate as part of the overall ATC system and be able to provide clearnces, SSR codes, etc. The fact that this does not occur at Ballina and Ayres Rock is an artificial constraint imposed by the Federal Government (Airservices and CASA) in order to be able to claim that a CA/GRS is not an ATS.
Should anyone claim that a privately operated ATC service is not possible or unsafe, I would only ask them to consider whether privately operated airlines are safe, and why do the British CAA and US FAA allow them? Is it too expensive? The costs would be mainly ATC salaries, but the CA/GRS guys at Ballina are all retired ATCs, if that is affordable than so would be a Tower