is Mise,
I suppose the ignorant/arrogant elite of the day thought they could buy culture by building the Opera House. The rest didn't occur to them as imortant. Very much like the ALP nowadays.
Cultural longevity & progressive cultural content can only be achieved in the same way as sensible infrastructure. This high speed train proposal is not a practical high speed, it is a fad, an ultra high speed game. It has absolutely nothing to do with commercial long-term efficiency. It's all about some egoists trying to spend other peoples' money with of course a nice Superannuation at the end of the line.
What would be some of the benefits of an ultra high speed train network in comparison to a say 120 Km/h train ?

“What would be some of the benefits of an ultra high speed train network in comparison to a say 120 Km/h train?”

The benefits are it would be able to compete with air traffic along the east coast of Australia and might eliminate the need for a new airport in Sydney.

For example Melbourne, Sydney by rail is 870 Ks, by air the flight time is 45 mins but there is a substantial time overhead.
Very roughly:-

1 Travel time to airport 45 mins
2 Book in and get through security 1 hour
3 Flight time 45 mins
4 Deplane and retrieve luggage from hold 15 mins
5 Travel time to final destination 45 mins

So if a train can do the trip in less than 3½ hours it will be a better option than flying.

1 Because it should be cheaper.
2 Weather delays should be less frequent
3 It should be more comfortable and less cramped

To do Melbourne Sydney by train in 3½ hours you need to average about 250 Kph.
This suggests you would need a top speed of around 300 Kph.

Warmair, a little information;
The current XPT trains in NSW are capable of 200km/hr and they are the
same trains as the 125s used in the UK.
The only thing that limits their speed here is the track layout, the
way the line winds around the hills instead of having cuttings.
The track was built with horses and scoops, no earth moving machines.
The trackwork itself needs to be brought up to UK standards.

If you have traveled on the 125s in the UK you will know the difference.
I went from London to Edinburgh on the East Coast line and that is what
we need here. A Fast Enough service.

If that was done then Sydney to Melbourne could be done in a little over 5 hours including stops.

If that was done then Sydney to Melbourne could be done in a little over 5 hours including stops.
Bazz,
if that's not satisfactory then nothing will ever satisfy some. what they really want is a "Beam me up Mr Scott". And even then it wouldn't be fast enough for some.
I really think people have had it so easy for so long that they have lost all sense of reality.
Faster, better, more cause more problems than they solve.

Indeed Individual, we are all in for a rethink on a whole range of
taken for granted features of our current lives.

For instance Warmair showed some times a couple of posts back.
His time to the airport will be wrong, because Kingsford Smith airport
will be closed and if he can afford the airfare he will have to go to
Badgery's Creek where the remaining services will operate.
In a zero growth economy we may not be able to rebuild into a fast enough rail system.

Not many of us can work out just what things will change dramatically.
Aviation is an easy one as we can see it happening now.
Cars are another one that we can see problems with, as electric cars
would not solve all problems in that area of transport.
It maybe that the cost of materials to build cars will put them out
of the affordability of the average person.

Things will be different for electricity supply in other countries
as they will reach peak coal around 2025/2030. Remember what the
Chinese premier said;

"We will burn all our coal then we will burn all yours !".

What if we said, "Oh no you won't !"

Hmmm

Our real problem will be employment,we need to get on with reorganising
for a very different energy system and we need to do it now while we
have the energy needed for major adaptations. We will have the people
to do the job, but if we do not get a move on we may be attempting
the impossible.

That is where governments are letting us down, they have been told
what the problem is by their own experts as well as many other
organisations but they just cannot accept it.
They are like roos in the headlights.

What we need is a bit of common sense in creating ongoing jobs in this country.

Example:
I live in a country town and the streets are swept by a mechanical sweeper truck that was imported from Germany, it is one man operated.

Its drawbacks are that it cannot sweep the gutters where there are parked cars nor can it sweep right angled internal corners such as where there are culverts or over the gutter driveways. Spare parts are imported as is the pollution producing fuel.

It replaced a couple of horse drawn drays with two men crews.

Now that's progress, but the men sweeping the gutters could sweep where there were parked cars and get their brooms into corners and nooks and crannies, thus more efficient sweeping and less rubbish into the drainage system.
The horses were locally bred, the drays were locally built as were any needed spare parts and the fuel was locally grown.
Moreover the horses and drays could be used for other purposes whereas the mechanical sweeper is a dedicated vehicle that has only one use.

Thus there was more money spent locally, there were three more men locally employed which would normally mean three more families in the town, more children in the school and more money spent in the town.

A study was done on this very scenario and the conclusion was that overall the dray system was more efficient and less costly.

It had one great drawback however, it was not seen as progressive and modern!