I wonder how much of that code is the old code compiled for the new platform.
That being said, it's pretty common in retrofits for the older system to still be around as a fallback if the CBTC fails.
This is different from Sydney, where the Metro lines are physically disconnected from the traditional rail lines. (Apparently there is still some track linking the Northwest metro line to the Main Northern line underneath Epping station, legacy of the old Epping-Chatswood Rail Link, but it is blocked with off with stops; there is no plan for any rail connection between the new Metro West line and the traditional rail network, despite the fact that remnants of the old Carlingford line are directly adjacent to the site of the new Metro West maintenance facility, meaning they could create such a connection if they wanted to.)
I have heard it said that the level crossing removal program is associated with a goal of moving to driverless trains network-wide. Presumably there is a network-wide CBTC migration plan.
The old trains wouldn’t work with the platform doors, so no. But the other way around: those lines continue beyond the tunnels on the surface, and some of those surface sections may be shared by both old and new trains, which would require some form of interoperability between CBTC and non-CBTC, until they move the whole network to CBTC.
Also, I would expect that maintenance trains (track inspection, etc) will likely be shared between CBTC and non-CBTC and so have to support both
It is also, where provisions have been made, possible to put CBTC equipment on old trains. That is what NYC is doing, for example.
Wikipedia's article on CBTC [0] seems to want to limit the term to moving block systems only, not including fixed block – I'm not sure if that is correct or if that is just some agenda some Wikipedia editor has.
But it seems to me that even in a fixed block system, the train could operate (semi-automatically) if it knew its location and the location and current state of signals – and the current signal state could be broadcast to it via radio. Would you call such a system CBTC or not?
Also, it seems to me that fixed block with physical signals and moving block CBTC could coexist on the same line. Moving block CBTC trains are authorised to disregard red signals, and instead get their movement authority via radio; fixed block trains are not. If a fixed block train is in a fixed block, that locks the block out for all trains (both fixed and moving); if a moving block train is in a fixed block, that locks the block out for all fixed block trains; but two moving block trains can coexist in the same fixed block provided their moving blocks are non-overlapping.
[0] https://en.wikipedia.org/wiki/Communications-based_train_con...
Both types of systems can be automated. And yes they do often coexist, like i mentioned in my grandparent comment. But brand new rail lines that install CBTC often don’t, to simplify maintenance; trackside equipment gets exposed to pretty hard operating conditions and can’t be fixed without some kind of shutdown of the rail line.
Urbalis Fluence works as you describe, but that is a very new approach to CBTC and as far as I'm aware has only one installation.
Trains runnin have been running this way in normal passenger service for months now, though I think it’s only in the last few weeks they’ve been testing it with HCMTs entering the tunnel at Hawksburn with diesels behind them instead going to South Yarra. (Currently, the trains with actual passengers take the South Yarra route at that junction.)
The HCMTs run only on this line, from Sunbury to East Pakenham/Cranbourne. They have their own new depot at East Pakenham so they don’t have to go elsewhere for stabling and maintenance. And they probably can’t; just for them to go through the City Loop as is temporarily required that tunnel had to be resignalled (the old location wasn’t visible from the cab.)
They did run an old Comeng train through the Metro Tunnel, without any signalling, to test clearance for a track maintenance train.