I reckon vibration would be just the thing you want in that geological environment! I suspect a metro tunnel would be cheaper to build per km (smaller profile), but it would extend between Miranda and Wollongong whereas the alternative would have to only join two ends of the existing line at Waterfall and Thirroul.

There are also Manildra trains on the line too.

What I was thinking about use of diesels in such a long tunnel is not gradients but the issue of ventilation.

I agree with you that I don't think I would see such a project in my lifetime either, even though this government is pretty gung-ho and supported by the Feds, so anything could happen. I think, as I said, there is a great need to focus on the performance on the great majority of the line, which is north of Waterfall and south of Thirroul. That's abysmal at present.

Tony are you looking at a single line Metro line, or double track or with the distance crossing like areas.

Depending on the length also the clearances of the tunnels there are options available that can clear the fume out, Ardglen and the Coal Cliff tunnel, depending on the wind direction or a totally still condition the fumes would more often then not overtake the engine, same with the waterboard crossing tunnel on the Unanderra-MV line. In fact very few tunnels even the shorter ones on double lines were quite unpleasant to be in both on steam and diesel when max loads were hauled.  Tickhole on the up was also a coughing nightmare if the wind was coming from the NCLE side of the tunnel. today its single line and a new one built next to it.

One thing I meant to put in my above post was that I doubt that Waterfall could be deemed a station where fast trains from the Gong and south of there should stop.  City bound interurban style trains from Kiama (Bomaderry) should have stops to the Gong, Thiroul, Helensburgh, Sutherland, Hurstville. Central,for primary peak hour services, the airport however could well be served by a train ex Mortdale following the coast train for the airport passengers changing at Wolli CK.

There are about three freights a day to and from Bomaderry. Manildra is a very busy customer.

Re a metro line - double track of course. Re fumes, I'm not just talking about freight crews gassing themselves, but what they leave behind in a tunnel of that gigantic length for passengers on other trains!

Your assumption is wrong and based on an assumption that Port Kembla is a one way port A6ET. Not only that but you have rail traffic that isn't just Port related running through the area to Bomaderry and other places south of Wollongong that send loaded traffic back up the mountains.

There are also the steel trains that have to climb.

Sims, yes I know there is other freight services on the coast, worked enough of them in my time..

The difference with Bomaderry is marked by the aspect of no longer milk, Co-op loading and the Petrol, also there was grain and other products that went out along the branch as well, don't believe any of that traffic is still going there.  Nor is there any metal on rail ex Bombo, not sure about Dunmore though.

While there is still loading that goes up the mountain, my post was primarily referring to the Waterfall (Central) to the Gong with some references to the M-D line.

• AFAIK, Bombo Quarry is still in operation.  
• There was some talk about Boral switching Dunmore to road last year IIRC, not sure what happened.
• Bomaderry still has grain to & product from Manildra

In regards to fumes I was reading about the tunnel on the inland at towoomba and apparently they will have doors at both ends.

https://www.youtube.com/watch?v=bCeCvTHkJ_c

Any tunnel from waterfall to thirroul would have to be similar to the old tunnels and not too deep as being suggested. Whether or not a cutting might be easier solution but I would prefer to see a tunnel just to not disturb the local wildlife. My issue was only with re using the old tunnels which just isn't going to happen because they are out of service and would never meet modern standards required. They are also only single tunnel and this tunnel is going to need to be able to run 2 tracks. Ideally the dive would probably have to start north of waterfall and not south with a new underground station for south coast passengers at waterfall.

I think I may have got the above link from the inland rail thread as well.

There are about three freights a day to and from Bomaderry. Manildra is a very busy customer.

Re a metro line - double track of course. Re fumes, I'm not just talking about freight crews gassing themselves, but what they leave behind in a tunnel of that gigantic length for passengers on other trains!

Re the metro, I can't see how a tunnel of that length without intermediate stations could be DAA compliant.  A 40km long evacuation platform?

Another issue with your scheme is I had heard (ie very apocryphal) the mine workings at Coal Cliff extend well below sea level, and some of the SC mines (it might only be Corrimal) also extend well out under the ocean.

I don't know if you've seen this @tonyp, but here is my "solution" - and like everything, it has issues.  (See here)  All of 5000m long.

Re the metro, I can't see how a tunnel of that length without intermediate stations could be DAA compliant.  A 40km long evacuation platform?

Another issue with your scheme is I had heard (ie very apocryphal) the mine workings at Coal Cliff extend well below sea level, and some of the SC mines (it might only be Corrimal) also extend well out under the ocean.

I don't know if you've seen this @tonyp, but here is my "solution" - and like everything, it has issues.  (See here)  All of 5000m long.

I would imagine a long tunnel without stations would have emergency exits along the way. There must be precedents for this around the world. There's also a possibility of a station at Stanwell Park in my scheme.

I have maps of the coal workings. Metropolitan extends to a little bit east of the line you have drawn on your aerial and west to a large area of newer workings west of the highway. Coalcliff extends from the seafront to west of Darkes Forest. Coalcliff is enormous. The whole of the scarp and Maddens Plains is undermined. Past governments didn't think the issue of protecting a railway easement out very well! When the south coast line was put through here in the 1880s, the mine had already been going below it for a decade. It was a long dry season and everything seemed very stable. When the rains came a few years later they realised what they had got themselves into.