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Handedness of rail traffic: left hand and right hand operation world wide.
(upload.wikimedia.org)
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If you go by length instead of ridership it seems extremely plausible. Australia is a big place and building 2 lanes for mostly freight trains is an unnecessary expense.
Sidings/loops/passing tracks, allow trains to pass on a single track, and since things can be more regular scheduled (ideally anyway) with trains, they can work well enough and with much less track building needed.