Travel in the country will go back to rail as the price of oil rises.
ex Shell CEO says $100 a barrel by next year and $150 later.

People are already complaining loudly about the cost of driving to work.
They will be forced onto the train by cost pressures.
Country rail bus services will become uneconomic and require too many
busses and that will force the return of rail, even diesal powered
trains will be more efficient.

Its coming, its just we do not know how soon.

Freediver, the main role that I could see for the rail system in the case of national defence is not one that would involve the army, but a system to move masses of people south, west or east. Assuming that the price and availability of petrol would make it impossible for individuals to travel far under their own steam, rail is the best bulk option. Of course it is very vunerable, and the reason it is normally the first thing to be targetted in war is due to its usefulness. Despite the army not owning many (any?) trains, trains could easily be commandeered for military purposes, and could play large role in helping shift supplies to where they are needed. Again, I dont see any immediate threat, but prudence is always wise.

Bazz you make a good point about transport and the rising cost of fuel.

The good thing about an invader is that if he is coming en masse he has a problem with supply lines. If its China, then they have a long way to come with supplies before the first soldiers, they would probably parachute in, would get their back-up ammunition and food. Though Australia is open she's a long way to come from the Far East, which gives us time. If its Indoesian then their syupply lines are not so long. An army friend says that some years ago defence dept. people found a large pile of automatic guns and ammunition under camorflage just in behind one of the beaches up the Northern Territory way that they thought might have been a prelude to an invasion; but the invasion never happened. For a surprise invasion from Indonesia that kind of pre-dumping thing would probably have to occur. Theres time for Australia yet with those railway lines and their maintanence. War is coming. We can see it building with all of the regional unrest, Islam and their frenzy and Chinas build-up isnt for nothing...its just a matter of time. Sure hope they put some guns in the Defence cupboard for the citizens.

But what if the invaders arrive by flying saucer?

Seriously, I'm in general agreement that rail transport will come back into its own once road transport becomes too expensive - but it will have virtually nothing to do with defence. Instead, rail will replace the scandalously wasteful road transport of freight, and mass air transport of passengers.

In a time of crisis we want resilient systems, not complex fragile ones. Rail lines, power stations etc are all soft targets for attack. A more resilient system would be more modular and distributed. For power, this means solar on our roofs or small wind farms. This is going to be especially important as future wars are far less likely to have identifiable front lines. It will look more like coordinated terrorist attacks.

While there are plenty of good reasons for maintaining our railways, potential invasion is not one of them. If a railway line is not being used at the moment, it certainly won't be used in a time of war.

I don't think an invasion will be in the form of a conventional army.
I notice the Federal Police Commissioner Kelty stated what must
certainly be government belief in that he said "they" will come as a
mass of people looking for food.
Thats what he believes is the big security risk.

The risk with China is if we don't sell them the coal and gas they might just come and get it.
At present they are running around the world buying all the oil, gas
and coal they can lay hands on.
We will have oil problems quite a bit earlier because of China's long
term contracts.
It is obvious they have heard of peak everything, they didn't need
Richard Heinberg's book to tell them about it.

So to sum up, start building steam locos and refurbish all those
branch lines.