If you look at the DRL study the TTC released last year it stated that no new yard would be needed for the DRL if it was build just st. Andrew to Pape. 4 storage tracks if the the East and West portions were built, and 7 storage tracks if the East line and the extension to Eglinton was built. The only time it would need an actual new yard would be if all 3 parts were constructed. This could easily be achievable under the powerlines in Flemingdon park.
Hmm interesting. I had always heard that a site in the Portlands was under consideration for the yard.
as for the stop, are you thinking something along these lines?
If so I find it quite counter-intuitive. The subway at the corner of Front and Yonge is very shallow. (the whole 1954 yonge line is) you would only really have about 150 meters to drop the needed 10-11 meters to build the station. That is about a 7% grade, something that subways simply can't handle. Not to mention the fact that it would be cutting right through the the foundation of the historic dominion public building. Then there is the fact that you would be building the stop underneath of 14 active rail tracks, instead of a closable king street.
This is more what I had in mind. You can see that the station box avoids the foundation of the Dominion building (although admittedly just barely). Based on the grades as well, I have the Yonge line passing overtop of the Spadina-Don Mills line. That may pose a problem coming east from the existing Union Station though. I admit that this would need a more detailed feasibility study than what I have the resources or the expertise to do, haha.
The new Union station would need to be a shallower station, that much is true. And as for digging under active rail lines, is that not exactly what they're doing now only a couple hundred metres away? If the new Union platform needs to be a Dundas-style station with the concourse underneath, then admittedly that's less than ideal, but it could still work, and would still be less expensive than a massive new station in the heart of the CBD.
In order to build the wye, Front from Bay to Church would need to be closed, as well as Yonge from the Esplanade to Wellington. This can potentially be mitigated by temporarily making Wellington a two-way street between Bay and Church.
And I don't really think King St is that closable, especially in the long term. Unlike Front (which is currently and will be closed for at least the next year), King has a busy streetcar route, and multiple parking garage access points on it. That is why if the separate line option is chosen, I very much favour Wellington.