Getting more out of the harbour bridge pair of tracks

[somebody]

A bit of an off the wall suggestion, but:

It has been suggested on Railpage that the airport line feed in to the harbour bridge, as well as what currently runs through Wynyard platforms 3 & 4.  If achievable, this is a plan worthy of considering.

That would also allow capacity for the NWRL.

[colinw]

What is the tightest headway across the bridge at present in peak?

Is it feasible to add an airport <=> NWRL pairing without diluting existing peak service on the north shore - or would construction of the NWRL effectively force a new harbour crossing to be built (even if its the eastern side of the bridge?)

[somebody]

It's about 18tph.  The idea depends on bifurcation Milson's Point-Chatswood really.  I would say that if you are going to do the bifurcation, you may as well quad it.

Should have mentioned that in the OP.

[colinw]

What do you propose - splitting Hornsby via North Shore & ECRL to separate pairs of tracks from Milson's Point?

If we assume 3 minute headways for each of the two tracks on the bridge, that only gives 10 tph to each of ECRL/NWRL & Hornsby via North Shore.

That should be reliable from the point where the lines split, but I wouldn't be relying on it over the bridge.

[somebody]

I was thinking more like this upgrade would allow 30tph over the bridge.  It's really the stations that limit the capacity - fix that, and more trains can use the bridge.  So 20tph proceeding to Strathfield, and 10tph proceeding to the Airport.

EDIT: So, new stations/platforms through the CBD - possibly using 20-23 or 26/27 at Central, and probably 1/2 at Wynyard with a quad Milsons Point-Chatswood.  Is it clear now?  I question the constructability of this, but if it can be done, maybe it should.