Put it this way @dan. If SRL(west) and MARL do not share track then its not a 30 year wait for the SRL last piece, its never.Bit late with the reply sorry.
I entirely agree that the SRL will not be 3 seperate lines or systems, doing so would be incredibly stupid for costs logistics and passenger convenience.
However, I doubt that the SRL will share any tracks with the exisiting BG network based on whats been announced. Share the Same corridor for a section of it? Most probably. Do I think they will let trains intermingle? no, and I cannot see them ordering dual voltage stock in the short, or long term with SRL. My guess is that some sort of provision will be left in place on part of the airport rail link for the SRL's alinement and Future station. If intermingling with the exisiting network was planned, we would have heard already.
, a bit of reality check.
Melbourne Metro trains are served by 3 companies - Alstrom, Downer, Bombardier. All of which have build/repair facilities on the BG network.
Iintroducing a 4th player, on the SG
network is fanciful.
At some point SRL trains will have to get to/from the factory, so why make life difficult with SG.
Sharing corridor only sounds easy, until you consider that mean SIX tracks on the Albion detour, including 55m above the Maribyrnong.
And FOUR tunnels under the Airport.
A very expensive excercise for max 6 tpa.