From Hornsby to Lindfield you can probably get away with sharing the tracks with locals and some easy curve easing. South from Lindfield/Chatswood realestate becomes increadibly expensive and you will need a dedicated pair of tracks as the existing track capacity is approaching 20t/hr. The propose UG Metro is UG because cost wise its not worth the effort to go surface. Then there is the bridge and tunnels and stations to Central, all of which are fairly crowded.
Meanwhile on the main north, there alignment is more readily expandable, some of which is already 4 tracks or was previously made ready for 4 tracks. Newcastle expresses could share a pair of tracks with freights leaving a pair of tracks for local traffic. The bridge over the river is much easier to expand than HB or short enough with low enough traffic to simply leave as a single pair. It would far more easier and cheaper to get sparks holding +90km/hr from Hornsby south than getting another 20km/hr on NSL.
Cityrail clearways projects was designed to segreate intertwinned services and keep trains from A to B not mixing with C to D and elimnate where possible A to C's etc To me running express CC/Newcastle trains down the NSL especially post NWRL is clashing with the clearwats concept. You could easily build a double pair of tracks from Hornsby to Nth Straithfield excluding the bridge where you have two tracks for local, two tracks for express, CL and freighters or some other combination.
having commuted the route from Straithfield to Gosford for some years although a while back. The route screams of "realign me".
- From Asquith to Berowa, should be no issue and you would probably cut 500-1000m of trackage. stick a 3rd track down the middle for NSFL.
- Berowa to Hawsberry River (costly, lots), almost a completely new route going east of the F3 and direct via a series of long tunnels to teh River probably using the last few km of existing route. The current line nth of Cowan would be removed. the route from Bewora to Cowan maybe even reduced to part single track with Cowan station Plat 1 increased to 8 cars. The current freight stowage loop could be used for storing sparks. Suspect 2-4km of route distance would be eliminated. I've seen reports that leave the freights on the current route, if if single tracked and alignment improved to take advanatage of the wider ROW, I cannot see how this makes sense when you are building a new alignment, it won't cost that much more to do it properly as 3 tracks or even as two tracks as freighters will move through faster. Modern bi-di design will enable sparks to pass freighters on the move or even stalled. QR can manage this quite well with 80km/hr coalies, 100km/hr freighters and 160km/hr TT on the dual Gladstone-Rocky section. Not uncommon to have trains changing back and forward enable passing.
- Hawsberry to Woy Woy tunnel, again this route screams straighten me. Just nth of the nth side river tunnel, use modern machinery to build the route straight rather than have train holding 50-70km/hr around the endless bends. There will be impacts on the national park, but the final result will see trains more away from the trees and water front than now with less sqr metreage used for the rail alignmemt. Proberly pull out 1-2km of track here.
- Limited options along the Brisbane Waters, perhaps some curve easing near Tascott/Point Clair.
- Nth of Gosford to Tugg, shouldn't be hard to achieve a bit here.
- nth of Wyee, again there are plenty of low cost options.