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Handedness of rail traffic: left hand and right hand operation world wide.
(upload.wikimedia.org)
Not visible in the map, but interesting to note, is that in France the trains normally drive on the left, except in Alsace where they drive on the right as a legacy of the time the province belonged to Germany.
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.