Since we're doing fantasy lines & plans, I'll bore you all with the brief version of mine.
I should stress, the object of this plan is to address the problems of Sydney's greater rail network, as well as address the issues the NWRL and associated second crossing is (allegedly) supposed to solve. Primarily, it's intended to address to cost efficiency and cost recovery of the RailCorp network by increasing speed, load balancing, extending the range of peak loading and addressing load imbalances.
1) Terminate the NWRL at Epping rather than Chatswood. Single platform terminus for both system. The idea here is to move the NWRL/RailCorp interchange further upstream and away from the critical load point at Chatswood. Less convenient for PAX travelling Hills to Macquarie Park. More convenient for everyone else travelling to Macquarie Park and neutral for those travelling from the hills to the city. Even though the interchange is not as efficient as the one at Chatswood, it won't have the same load for the same system wide load.
Turning trains on a single platform would prevent through trains on the ECL from Hornsby, so this gets serviced by a shuttle. Peak load for this segment of stations is less than 2k PAX/hr.
My calcs suggest this alone will defer the need for the second crossing by ~5 years, perhaps more. But it actually decreases the cost of operations of CityRail over trying to cope with inadequate turning facilities on the Nth Shore.
2) Build this (for reasons which may become apparent later) at Redfern Jtn:
3) Create a 4th sector by Quadding from Central to St James:
All of 1.3km of new line, a third of which already exists.
Train Operations become:
Rt 4A Liverpool - Bankstown - St James
Rt 4B Lidcombe - Bankstown - St James
Rt 4C Homebush - Ashfield - St James
Rt 2A Campbelltown - Airport - St James - Wynyard
Rt 2B Leppington - Airport - St James - Wynyard
Rt 2C Reveseby - Airport - St James - Wynyard
Rt 2E Parramatta - (all to) Strathfield - Wynyard
Rt 2F (Glenfield) - Liverpool - Granville - Wynyard
Rt 2G Epping - Strathfield - Wynyard
Rt 3A Hornsby - Chatswood - Wynyard
Rt 3B Epping - Chatswood - Wynyard
Rt 3D Penrith - Blacktown - Parramatta (express) - Wynyard
Rt 3E (Richmond) - Schofields (all to) - Parramatta (express) - Wynyard
3) A BRT busway is built along the unused formation allowing Woolstoncraft & Waiverton to be closed as rail stations.
This presents an issue for interurban operations. This is dealt with by incorporating Springwood - Gosford into the Sydney Trains family. 3 peak trains from Wyong and Mt Vic (loading gauge permitting), but the rest of the time they get shuttles. The Capital improvements program is to
- add "high speed" deviations on the Cowan Bank
- tripling Hornsby to Mt Kuringai
- extra refuge/crossing loops at Brooklyn and Woy Woy
This will ultimately allow Sydney Trains to operate Gosford-Mt K single track, part/most of the Hornsby - Epping shuttle as single track, as well as the Parra river crossing single track. This delivers ARTC a (near) dedicated northern corridor into Sydney while reducing Sydney Train's perway maintenance burden.
The other problem this solves is the inadequacy of the H sets routes as long as the central coast interurban runs. It fixes this problem by reducing the run time to (hopefully) below 60 minutes.
- quading Chatswood - Hornsby, progressively replacing the island platforms with straight side platforms.
- upgraded signalling Westmead to Chatswood
- more entry/exit points at Town Hall platforms 2&3 (expensive)
- completing the 5th&6th sets of stairs at Wynyard 3&4 (planned by Bradfield but never built)
This plan should work till the early/mid 2030s, by which time Epping interchange will break. At that point through running of NWRL trains will be needed, and that will require fleet renewal of some sort - yet to be determined.
With only 4 sectors, my plan relied heavily on squeezing more out of the track pair between Chatswood and Parramatta - as does Sydney's Rail Future FWIW. It's certainly doable within the constraints of the current signalling system. Paris RER line A achieves 30tph using a similar (albeit slightly faster loading) form factor using conventional block signalling. In Sydney the same is possible with moving block.
Between 2040 and 2050 the system would need a 5th sector. I think the way to do this is convert the Inner West line to BRT, leaving just Burwood, Ashfield & Newtown on the HR system (Newtown & Ashfield generate more than 60% of the traffic on the entire line). The demographics make have changed by then. It might need to be an LRT system
But by then Sydney will be 10-15km larger in diameter again, and new lines to the north and west will be needed. I think a branch north from Rouse Hill toward Catai, a branch from Hornsby across Galstone Gorge toward Wiseman's Ferry, and perhaps a line south of the main west toward Wallacia. Sector 3 will need to be split to form a 5th sector. This could be a Western Express and terminating North Shore trains at Nth Sydney. It could have the two sector's sharing track across the Bridge as RER lines B&D do across the Sein. Or could even be a second crossing. But IMHO it's a project we'll need by 2040, not 2020.