Re: Yonge Express subway
Despite everything being done, I'm starting to think that an additional line up near Yonge is the only solution. Perhaps a quasi-express with less stations.
I've suggested before running a completely new line up Bay Street from Queens Quay with stations at Union, King, Queen, Dundas, College, Bloor, St. Clair, Eglinton. From Davenport to near Davisville they can actually run under Yonge, because Line 1 is further east. From Davisville you can run under Duplex. If you want to have some fun, you can swap the lines at Davisville with a Lionel-Groulx-like station, so the new line, takes over the "express" line under Yonge up to Richmond Hill, and the original line runs under Duplex further north.
Surely such a line would be infinitely cheaper (and have a lot less closures) than trying to double-track the current line! Ultimately something is going to be necessary if subway ridership continues to grow.
Believe it or not, just 4 days before this post I began sketching a map of Yonge Express subway with two same key elements: using Bay, and an swapping the lines at Davisville. Here is what I got:
https://imgur.com/a/i6dRSox
The southern terminus of the new express line is next to the new City Hall, under Bay just north of Queen. Two other stations in CBD are Dundas and College, in order to spread out the riders. Hopefully, those 3 stations don't need to be very deep.
It is tempting to extend the line further south, with a terminus at King, Wellington, or even south of Union. However, then we need to deal with the PATH tunnels and with the Queen Street's Relief Line.
The Bloor station of the new line will have to be deep, in order to get under Lower Bay. Thus, no stations between College and Bloor.
From Bloor, it runs express to Davisville. No station at St Clair, and that should help select the optimal underground route to reach Davisville.
Davisville becomes a major interchange between the "old" Line 1 and the new express subway. Being on surface, that station should be relatively easily expandable. Some space can be taken from the yard.
North of Davisville, the new line takes over the existing Yonge tunnel and runs to Steeles and RHC. The "old" Line 1 needs a separate tunnel that connects to Eglinton LRT, in order to evenly spread the workload between the two Yonge lines. It should be possible to build a new 1-km long tunnel under Duplex.