The only way forward for the Gheringhap to Ballarat line is dual track between Gheringhap and Warrenheip Bank. Keep V/Line and the return of passenger services separated from SG freight and passenger.
No offence Bevans, but you're talking A-Grade rubbish here. That will not happen and if you think it through logically, you should be able to see why.
It would cost Billions to duplicate that track, and for what? Half a dozen trains each way each day? That doesn't stand a chance of passing muster with any of the decision makers, anywhere.
Has any other "damage" been done? Just wondering what would be required beyond sleepers, ballast and lengths of rail to reinstate a second line.
That isn't even scratching the surface. For a start, you have to consider that most of the line has been centred, meaning that to put a second line in many places you would be required to rip the existing track up and move it over, as this was done either when the line was singled, or in other cases, at a later date.
Then you would need to rebuild multiple bridges, culverts, drains etc. Earthwork would be required, especially between North Geelong and Moorabool, this section is double track, but it is ARTC track, as I stated earlier, for a regular suburban style service, ARTC would not appreciate loosing their capacity, so a 3rd track may well be required.
Then of course there is signalling. This would probably cost more than any of the above (except maybe for that viaduct over the Moorabool River, that is a doozy). Signalling is complex and expensive stuff, and to have the entirety of the Ballarat - Geelong line to be re-signalled would cost a bomb.
And then you have the cheap stuff like new fit for purpose stations at Bannockburn and Batesford, and anywhere else you want to stick one. Don't be thinking you can just re-activate the old stations, that would actually cost you more, why else do you think Creswick got a new station.
Add in the high cost of labour in Australia in the 21st Century and sleepers, ballast and lengths of rail are the least of your worries.
I mean it could be worse, the fact that you would be building it on an active rail corridor means at least you can probably avoid the costs of environmental impact studies and things like that, so hey, you're already half way there.