Both Queensland and Western Australia use a track gauge narrower than standard, which in turn, by the way, is a little narrower than the typical wheel track of modern road vehicles and even that of wagons of the 19th century. I wonder why Western Australia has that gauge given how flat that state is.
Anyway, cape gauge and standard gauge differ enough that dual-gauge track is possible with standard rails and without standard gauge users of the track facing a speed restriction. While there seem to be no plans to regauge even most railways in those states, would it be much less costly and less disruptive than converting from Irish gauge - in Adelaide metropolitan area and the state of Victoria?
Ummmmm...converting narrow gauge to standard gauge means replacing every sleeper, widening all formations, replacing most, if not all bridges and in the case of Queensland doing it under traffic with some lines carrying anywhere from 40 to 60 freight/coal trains per day. It is not simple, it is very expensive and with little chance of recouping costs through operational savings. You are looking at a minimum of $3-million per kilometre for conversion - in Queensland alone that would be a bill of about $30-billion.
Further to Silla1's reply:
When you say regauging the WA and Qld tracks to standard gauge are you referring to:
1: Just changing the gauge and retaining the existing allowable axle loads and rollingstock outline. Noting that these are different in WA and QLD.
or 2: Regauging and increasing the allowable axle loads and the allowable rollingsrtock ouline as allowed on the Defined Interstate Rail Network?
This the majority of the standard network east of Port Pirie.
or 3: To the ultimate Rollingstock outline adopted for the Defined Interstate Rail Network.
I once did a desktop study on converting the line from Tweed Heads to South Brisbane and the enormity of the task was beyond any imagination.
1: track centers on crossing loops, sidings and double track would have to be increased needing widening of the formation.
2: Platforms faces would have to moved back and raised to accommodate Standard Gauge rollingstock. In places where there is side platforms the widening of track centers would mean the platform faces would have to be moved back even further.
In some places not really feasible without major reconstruction.
3: Replacement of underlins bridges.
5: Raising of overehead bridges and enlarging of tunnels.
4: All this while maintaining traffic, it would be virtually impossible.
Thus the decision to provide a separate stand gauge track was the only feasible solution.
As far as converting from Irish gauge the works outlined above would not require any of the above works, just regauging as these tracks are built to the same axle loads and clearances as the standard gauge system.
Just to state my credentials, before I retired from QR, my area of oversight was axle loads and clearances, so I am familiar with these issues.
Just a pipe dream of someone with some very strange substance in their pipe.