To me, this just highlights what a big white elephant the NWRL & 2nd crossing are. All of this work is essentially to solve the problems created by the incompatible format.
My alternate solution:
- Upgrade Sector 3 to support 24tph (and ultimately 10car 200m trains) with improvements to Town Hall & Wynyard Stations (ie more platform egress points) ... ie 30kPAX per hour to start with, increasing to 36kPax/hr. (NB this is sort of planned anyway, to cope with the NWRL metro prior to the second crossing), with express operation Central to Parramatta (hopefully down to 15min, though this would require some track upgrades & removal of)
- Re-align the tracks west of Redfern so Sector 3 takes the Mains, Sector 2 the suburbans & locals, but the locals feeding the east side of the circle rather than the west.
- Bring Gosford - Springfield into the SydneyTrains Zone, and operate them exclusively through Sector 3 across the SHB. (With peak services starting at Lawson & Wyong, the latter to keep Shane happy ).
- Shift Epping-Strathfield to Sector 2. Hornsby - Epping runs as a 4 car shuttle.
To create the 4th sector:
Stage 1: quad Central to St James by extending the Eddie ave viaduct to Wentworth Ave then under Oxford St connecting with Bradfield's existing tunnels into the original platforms 2&3 at St James. This takes Inner West & Bankstown trains - could be operated as a Metro - or existing format prior to the second crossing.
Stage 2: extend the tunnels beneath Macquarie to a new station beneath Bridge Street
Stage 3: extend to Barangaroo
Stage 4: extend beneath the harbour to Chatswood to connect to the NWRL - but only *after* Nth Sydney - Hornsby is quaded.
In the interim, have the NWRL/CityRail interchange at Epping (with a peak capacity of 12tph on CityRail being fed by a similar metro service from the NWRL).
The advantage of building underground as SD is basically its cheaper per km, 20% more dirt to add another 0.5m radius, hence I don't see major new works being done as DD unless its too intergrated, like the airport line and this is similar to OS experience and probably the main driver for making the NWRL metro as much of its UG and and the extension to the city is going to be near 100% UG. Had it been on the surface it would have probably been alot different.
You are quading the NSL and building a tunnel to Chatswood? Expensive? Just so yo can run on the Central Coast services?