The alignment of the Ontario line seems like it will largely be dictated by what we (the Ontario Government) want it to do/to be. A Dufferin subway is frankly a no-brainer; we have a smorgas board of alignment options for new downtown subways because we likely need more than just one. However, as a provincial project, there is an incentive for the
Ontario Line to serve a wide catchment area and act as a connector service rather than one that will primarily be generating its own ridership along the route. It will certainly do this, but not in the same way as, say, Line 1 or 2 which have local users and transfer riders. The reality is, there are some things which are true about the Ontario Line:
1. It will relieve Lines 1, 2 and 5 (transferring to line 1 primarily)
2. It will relieve Union station from some GO riders via Exhibition and East Harbour
3. It will partially relieve the 501 Queen streetcar
4. Relief of Bloor/Yonge and possibly Yonge/Eglinton
But this is it. The OL is more of a relief service than the Relief Line itself, with more connections and stations but less local connectivity and contiguity. That's all well and good, but it gives insight into the design logic of the Ontario Line. Fast forward to the 2051 plan and there is a clear intention to connect at Kipling somehow, then the airport, and circle around a loop and connect the simpler Northeast Don Mills segment. This makes it clear to me that the OL is going to primarily function as a relief line for the entire network, rightly or wrongly, by connecting at Kipling to divert the Mississagan volumes. With that in mind, the Humber bay alignment seems inevitable. It probably won't duplicate all of LSW, but the OL will be very functional and transfer-oriented. This has been made clear by the various design decisions on the line's route.
As mentioned before, the local contiguity of the alignment is inferior to the relief line, because it does not linearly follow Queen street. Well, this is where that functional component comes into play. Queen st itself merits a subway like Bloor, probably more so. We are not providing this with the OL. I am not going to repeat the arguments of old here, but it is hard to deny many stretches of Queen st will be more poorly serviced now than with the RL. This is fine, but it is a core detail of what differentiates the OL from the RL. The western bit of the RL would have taken Queen, and could have easily gone up Dufferin or Roncesvalles as a local service, like much of Line 2. The Ontario Line outright does not intend to service Queen on a local level however, that much is clear. The circuity of its alignment, the transfer points, and the relatively short section on Queen st itself makes it inefficient for local trips. It will probably generate enough ridership through transfers alone, so extending into a high-ridership corridor just doesn't make sense for the Ontario Government. If the TTC spearheaded the OL/RL, this would be a different story as different priorities would come into play.
Anyway, my point is we likely will not see the Ontario Line go up Dufferin. I do not think this project has regional implications, unlike what some posters have said. This is exactly why it is not going to travel up Dufferin; it will not have much relief potential, and will only hinder the intended function of the OL by bringing full trains to Exhibition and creating a circuitous route for Dufferin commuters or Line 2 transfers. This should not be confused with the
need for a Dufferin subway; in fact, I would be more than content with allowing the city/TTC to design and build a conventional long and heavy subway on the street. What is likely needed however is a completely different E/W tunnel for such a line. The OL will be at capacity eventually, and feeding a Dufferin branch into it would cause huge issues. I do think the OL has sufficient capacity for its current plans (even the planned extensions), but its capacity will be limited by its tight 90-sec headways in the future, unlike our traditional subways which can continue to be pushed to their limits with better signalling.
With the design logic of the OL in mind and the intended outcomes of its completed 'loop', I think its clear we will not see a Dufferin alignment
on the Ontario Line. Rather, we will likely see some pressure from the city and locals for a subway by the end of the decade, when much of our transit expansions will be complete. The OL will not relieve the inner city of capacity issues in the west, and GO may well make it worse with transfers at Dundas West. If I were the TTC, I would be drafting plans for a Dufferin subway right now. Keep it separate from the more regional plans, as that is for the OL. I would prefer to have the Dufferin subway go down Dundas or King, as the streetcars offer a good insight into where our transportation corridors ought to generally go. The King alignment should preferably intersect with the OL at Bathurst, but not through-run with it for any sections. Unlike the RL, I would not be opposed to a shorter Dufferin subway that only goes as far as Line 1 in the east, unless an infill GO station occurs at Cherry st or somewhere in that area. Crossing the Don is unnecessary, and I legitimately think that East Toronto/East York will be ok for transit for the next decade or two. The Dufferin subway should seek to serve Dufferin, and Dufferin only until we need to worry about a NW extension to perhaps Jane or Rexdale. As for the OL, sending it down LSW is the most financially feasible and does offer some good connectivity opportunities, probably on the cheap as well. Plus, lets not forget Doug is an Etobicoke resident. Why would he miss a chance to send
another project through it? The whole thing can be at-grade or elevated, while a Dufferin subway is most certainly going to be bored or C&C if we're lucky. The Government probably figures they can push off Dufferin transit by taking the lowest fruit first, sending OL far west and perhaps expanding the King st pilot to more lines to help push a Dufferin subway off for another few terms. Even though I am pessimistic about a Dufferin OL happening, I am still optimistic that Dufferin will see a subway. As we have seen here and worldwide, when transportation pressures become too much to handle, something gives and we build what is necessary, often with less regard for cost once it gets to those crucial levels. With that, we probably won't have to cross our fingers for long.
Below is my interpretation of a subdued subway plan for Downtown Toronto, one that is not overly predictive with far-off extensions for the Dufferin subway but rather one which takes its needs into account alongside the OL. I included a King alignment, Dundas alignment, and a fantasy with both (doing different things, of course). Feedback is appreciated!