Don't forget the original idea was spawned in the pre privatization days meaning freight and pass under the one State Govt umbrella .
If some here think MD is a great freight path into Sydney have a closer look .
PITA journey from Pt Kembla Yards to Unanderra then climb a steep grade just to get to Dombarton . The diesels are going to be working hard just to get into the proposed tunnel so heat and exhaust issues would be a problem even if the tunnel was level - which it won't be . Think Illawarra range tunnel west bound if you've ever work trains up to Moss Vale that way .
After all this you're dumped out at Mauldon which is still a considerable distance from the Enfield area and the SSFL is a single line with only two crossing opportunities .
By comparison the distance from say Unanderra North/Conniston to Enfield is much shorter .
The things that cost freight trains so much time on the Illawarra are reasonably easy to fix .
1) Pathetic slow speed junction at Meeks Road , spare me - 15 km/h - in 2017 ...
2) Pathetic signal sighting going into the down refuge at Waterfall , makes a mockery of the 50 km/h turnout .
3) Pathetic 25 km/h departure speed at the south end of Waterfall down refuge .
4) Pathetic speed for all traffic on the down main through Waterfall station .
5) Pathetic practice of Sydney/NSW trains standing their tin cans for extended time periods on the mainline platform roads at Wollongong .
Fix some / all of these issues and the freighters feed through the Illawarra a lot faster . Win for everyone .
The operators could also consider spending on things like ECP brakes for unit trains and then have a chance of asking for higher operating speeds - in places where Sydney Trains has pathetic low speed boards to limit freight train speeds because they don't think they can stop otherwise .