Anyway, TB’s idea of running airport trains via Newport is a fascinating one but really very little chance of actually happening given what’s already been planned.
As for running WV and Melton into the tunnel that just seems like a bad idea. Remember the theoretical capacity of a moving block line is 30tph but the practical capacity is 24tph to allow for minor delays. Then consider that every junction on a line reduces its effective capacity because you need to allow for merging delays even with flying junctions. Also, to my knowledge the current moving block plans are leaving fixed block in place for non-suburban service.
So you’d have fixed block Bendigo services merging with moving block Sunbury services at Sunbury and Sunshine, WV and Melton services merging at Deer Park junction, and then WV/Melton services merging with Sunbury services at Sunshine. I reckon you can forget about running more than about 20tph reliably on a line like that. Which is just not enough given the Sunbury is already under serious stress at peak 12tph.
"Given what’s already been planned", to be fair the route towards the city end is still under investigation. But I agree that they were thinking of the new rail tunnel through Footscray.
I guess the issue which you've note is capacity constraints by allowing the new electric lines converge together. Which is probably why an extra tunnel was announced.
So would it be cheaper building 2 seperate tunnels (2 tracks each)? Or maybe build one 4-track tunnel along the Metro 2 tunnel route?
But maybe that's a little overkill, as two seperate tunnels would probably be cheaper, as one tunnel goes under the Yarra and the other doesn't.
Someone noted the trains would be empty, but if the plans suggest creating Fisherman's Bend as an extended CBD, then perhaps there would be more demand in that area, which is currently lacking in services.
With a 2030+ date, you'd think you've built like another cross-city tunnel in that time. I'd really like if the Metro 2 tunnel project was accelarated, started sooner than later. Anyways a Newport-Sunshine orbital route would be nice to have and I'd think somehow instead build the 4 track tunnel via Metro 2, you could have the Werribee line use 1 tunnel, and Melton/Wydnham use the second tunnel. And have the Airport line use the Melbourne Metro Tunnel with Sunbury.
It's just something to keep note of.