In the early 90s the worn and out dated signalling arrangements were replaced by remote control and colour light signalling .
All signal boxes were closed between Lithgow and Orange from memory the last being Bathurst and then Orange .
National Rail Management decided to send most Adelaide and Perth traffic via Cootamundra and Parkes though a few AS/SA services did run initially .
With traffic levels falling SRA decided to "simplify" and "economise" on the western infrastructure by singling the above mentioned sections including Gresham to Newbridge .
I believe they usually improved whichever was the better line (up or down) and removed the opposite side once the single main was operational . West of Rydal it changes from one to the other slewed through the middle of the once double line formation .
In hindsight singling the lines was a bad move particularly between Wang and Tarana , it's a lengthy not particularly fast section with no crossing facilities and no follow on movements allowed .
The flip side was that SRA halved the length of line to maintain and closed three manned signal boxes . Many people said they could have just walked away from the then redundant rails and sleepers because it's easier to repair and reinstate existing infrastructure if needed in future .
The story I got was they reclaimed the unused rails to reuse elsewhere and I'd say the chance of NSW Trains/JH/ARTC ever recreating the double line sections is very remote - based on cost alone .
This is a problem you get from building a pretty railway and forsaking the reason it's there for in the first place - the efficient running of trains . The Governments care factors appears to be based on the voting publics perception of railways and the vast majority don't know or care how stone aged the alignments are and how poor the capacity limits is .
To be truthfull the main highway was shipfull between Lithgow and Bathurst in the early 1970s and try and imagine it today with single bi directional lanes in places .
Anyhow that aside it is 630 Km from Sydney Yard to Goobang via Coota and about 450 via Lithgow . On one hand you have less Sydney trains via SSFL (for freighters) and 1:40 grades - but it's 180 km longer and elec pass trains out to Lithgow .
Going west is faster time wise but the average speed is lower and - anything powered for the steeper 1:33 grades is overpowered beyond but often the tracks lower speed doesn't make it a huge advantage .