After leaving the top deck and heading down the helix, the single main line will come out on the bottom deck and head into what will be basically a staging yard, that is a mixture of Hornsby and simply an area Beyond Gunnedah. A turntable will definitely be part of this yard, the exact location and layout I have not yet decided.
In this way trains that went through Gunnedah and beyond the upper deck heading towards Emerald Hill or Narrabri can have the engine and brake van swap ends in the yard and run back up the helix for a return trip through Gunnedah picking up and dropping off wagons as they pass the various industries.
This lower yard will also represent Hornsby so certain trains will start here and run north towards Gosford. They will go down the Cowan Bank where I will definitely model the disused No. 5 Boronio Tunnel and possibly one of the other tunnels for atmosphere.
Next they will run through Hawkesbury River Station, which also has a pair of sidings and in the steam days was the site of a coal stage, and another siding on the west side of the station where bank engines awaited duty. I found a track plan of Hawkesbury River circa 1959 which I have scaled into place on my drawing.
After leaving this area trains may go through a tunnel representing the Long Island tunnel and will then come out the other side and head into what will be a yard representing Gosford / Beyond Gunnedah.
If another helix is built, this staging area would represent trains coming from Werris Creek once they go up the helix to the top deck. Also as mentioned in my previous post having this helix would allow non stop running around the whole layout, and different coal trains could be run as a full and empty as they could go empty clockwise (down trains) through Gunndeah and full anticlockwise thrugh Gunnedah (up trains).
There may have to be some modelers licence used in as far as time periods go as I'd like to have the ovehead electric wires (or at least the frames that hold them up) representing the post 1960 period, but I'm not sure when the coal stage and banking steam engine siding was removed? In any case this is a case where it's my layout and I want t model the things that I find interesting and if it clashes slightly with reality so be it.
Having this section electrified will allow me to run 46 Class electrics and possibly the early stainless single deck interurban passenger trains if and when they are ever released.
Another possibility is having the 46 Class haul the W44 Concentrate train from Hornsby to Gosford where a Garratt would take over and haul it up the second helix towards Werris Creek. In this way even though the W44 never ran through Gunnedah, the top deck could be used simply to run it back around to the Hornsby yard where the 46 would once again take over.
So whilst everything will not be completely prototypical, there is flexibility there to have some interesting operation and run a good variety of trains.