I have no idea. But in general, with modern signalling you can get a lot of capacity out of a two-track rail line. A third track can be added in certain sections too.
That’s true, but some of that capacity is lost if you are intermingling trains with different performance and scheduling attributes.
It's 16 miles from Scarborough Jct to Major Mackenzie by rail. Track speed is 50 mph north of Agincourt, with a 25 mph slow order through Markham. I assume a 50 limit is possible south of Agincourt once construction ends. Maybe speed could be bumped higher once the current project ends, but it's pretty curvy from Milliken to Mount Joy.
At current scheduling, even under optimum timings an HFR departing Scarboro Jct will overtake the previous RER around Markham, assuming 15 min headways. So yes a third track will be needed, to overtake. The same dynamics will work in the other direction, and with 15 minute RER headways in 2 directions one can't overtake in double track without conflicting with the other direction. So you are probably needing an overtaking track in each direction. As noted, the 401 underpass is not expandable beyond 2 track, nor is the trench at Underwood.
Can't say it can't be done, but there will be $$$ and the result will require careful coordination of schedules. In particular, it would be challenging for VIA to coordinate westward trains with RER, since there will inevitably be some variability in actual performance over the course of a run from Ottawa. To my mind, it's not the kind of flexible, unencumbered operation that VIA is seeking.
It may not be cheap, but adding a third track alongside the CP might be preferable, since it would not conflict with other services and might be amenable to higher speeds than the Uxbridge route. The Uxbridge route might have looked preferable in the context of Peterboro GO and Stouffville GO intermingling, but RER at frequent headways wasn't on the table nor was hourly HFR.
- Paul