The issue is that most of GOs platforms aren't capable of double berthing.. 24 through 27 certianly aren't and the platforms that are 660+ meters long are used by VIA.
I expect track-sharing to occur between GO and VIA.
It's quite obvious it will happen, with:
- massive GO concourse expansions (happening)
- signal upgrades happening (will be deployed)
- upgraded "train traffic control" centre (will be deployed)
- better trackside changeable-message video boards in VIA concourse (will be deployed)
- I see provisions for at least future
access to VIA's tracks from GO concourse AND teamways (look at the diagrams)
- all entrances (VIA+GO) to all tracks will have changeable-message video boards
- more track capacity upgrades will occur, than VIA expansions will bring.
When these happens, it wouldn't be too difficult of a stretch, to simply develop information technology capacity to on-the-fly reassign specific tracks between VIA and GO, once all entrances to all tracks have changeable-message video boards (like the ones you see for Platforms 25-27). Like the gate-sharing that happens at many airports nowadays. Those type of boards will also be in the renovated VIA concourse within a couple years. They can on-the-fly reassign tracks between GO / VIA. Even if GO passengers still have to board via the GO concourse, and VIA passengers still have to board via the VIA concourse, with alternate entrances 'discouraged' during peak (via turning off escalators, roping off, and crossed-out symbol on video board -- in order to prevent peak GO passenger traffic from crowding-out waiting VIA passengers). Though the future teamway entrances to platform #14-21 would probably be open to VIA ticketed passengers, too -- they already fare-inspect onboard anyway, and most VIA users buy tickets online anyway.
The new signal upgrades, new train traffic control system, and the all-entrance changeable video boards, makes it easy to reassign tracks on the fly. I actually saw it mentioned somewhere that it is part of the capacity-increasing plan, but I can't find it. I am pretty darn certain track-sharing is going to happen eventually, in the long term expansion through 2031.
What's the ownership of VIA's Union tracks? That wouldn't even be a dealbreaker at all! If VIA owns full rights -- then it may be a simple matter of Metrolinx cost-effectively dangling dollars to VIA to "conveniently rent some of their capacity whenever they don't need a track". Cash-starved VIA accepts, and uses the extra dollars to increase train frequency (the growing capacity pie serves both VIA and Metrolinx! Some of VIA's tracks are actually double-berthable by long 12-car gotrains and VIA probably won't run 8 trains per hour per track during GO's critical peak period times -- that is $$$$ sitting on the table!!!). Cheaper to dangle dollers that way than to accelerate digging a 4-track underground sooner than they need to. And VIA still gets to increase train service frequency, and they can still double-berth offpeak.
GO already pushes something like two dozens trains per hour through the limited GO trackage (look at GO's schedule between 4pm through 5pm) and they'll easily eat into VIA's expanded track capacity before 2031, just to fill up the triple-square-footage expansion of GO concourses.
Thusly, GO can double berthing only during peak, on the VIA tracks, for specific GOTrains/RER approaching Union from opposite directions. Once the capacity is increased, VIA doesn't need ALL of that capacity, and Metrolinx can simply reimburse VIA. That is very efficient use of trackage that VIA may not always use.
And we'd justify building Simcoe Street Teamways (And west-side York Street teamways) too as an alternate access to the west-side double-berth. Those too, will be accessible both by VIA passengers and GO passengers, via changeable video boards (already in use at some entrances), since track-sharing looks obvious.
