I personally think that the current situation does not justify building a tunnel under Parc to replace the Mont-Royal tunnel which is now occupied. The fact is that right now, the only EXO line that terminates at Gare Centrale is the Mont-Saint-Hillaire line. I have a rather hard time justifying a new tunnel for a single line.
I think that several other things need to happen first. One of them would be to build more Exo branches as suggested on the map that I’ve published on the Vision - Métro de Montréal thread.
We also seriously need to increase the frequency of trains. If we are going to build a new tunnel, we definitely should make sure that we make good use of the capacity. Some of that capacity certainly could be used by a TGV in the Québec Montreal Toronto corridor.
The other issue that I see with those plans is the Victoria bridge. It is owned by CN and they dictate how many trains EXO can go through that bottleneck. That’s why I decided to provide on an alternate route on the map that I published on the Vision - Métro de Montréal thread.
The route that I propose uses the Outremont sub. It would necessitate a tunnel under Longueil and Hochelaga. The portals would be located right after Taschereau and station Préfontaine.
I question the notion that EXO trains necessarily have to stop at Gare Centrale. I think that it would be more beneficial to have a route that EXO owns and controls. I think that it is perfectly acceptable for the last few kilometers of a trip to be done on the metro. As the Outremont sub runs around the north of Mont-Royal, is intercepts all metro branches, meaning that transfers are possible.
Another major advantage of this route is that it would be simpler to build than a second Mont-Royal / Parc tunnel. The problem with a second Mont-Royal tunnel is that it would have to go through and under the fondations of skyscrapers in the downtown core. That makes the first kilometer extremely problematic. The route that I propose would be a deep tunnel which reduces risk and cost.