So I’ve been reading up on this topic a bit more and I came across this

Problem Australia’s interstate freight rail network comprises many long sections of single track. This restricts the number of train paths, reducing rail’s competitiveness with road, and hindering rail’s ability to meet growing freight movement demand. The interstate freight rail network needs to be enhanced to accommodate growth in the freight and passenger task, and improve efficiency and safety.

From here, …gov.au/…/advanced-train-management-system-implem…

On the bright side it is a proposal to upgrade a lot of the rail corridors to support more freight than we have currently. Though it was added in 2016 and is still only in the ‘potential investment options’ phase