The Andrews government has decided their preferred option is to build a new port at Bay West(?). I think the difficulty of getting std gauge to Westernport may well have had some bearing on that decision.
I propose a new alignment through the Eastern suburbs, thus:
Leave the Melb - Syd mainline and pass Nth of the Wollert quarries; then,
through Sth Morang;
pass SW of Yarrambeet;
Cross Hurstbridge line between Diamond Ck and Wattle Glen;
pass SW of Kangaroo Ground;
Tunnel from Tacoma St, Park Orchards to Canterbury Rd;
Follow M3 to Rowville;
Follow Dandenong Ck;
Follow Cranbourne line to Western Port Hwy (M780);
Follow M780 to Hastings.
90km of new right of way through suburbia would be horribly expensive (esp with tunnelling and some significant bridges), and the NIMBYs would scream (some would be justified) yet I think it would be preferable to trying to use the existing corridors, which would entail:
Trying to find space for extra track;
Dual gauge where space can't be found;
Extra complication at junctions;
Mixing long heavy freighters with commuter traffic (even with freight curfews);
Apoplectic NIMBYs complaining about extra (supposedly noisy) freight trains.
What are your well reasoned thoughts on the topic?