While it's beyond the scope of this redevelopment exercise, I wonder if the city has looked at options for developing over the tracks south of the Beltline bridge that face onto Mt Pleasant Cemetery? Given the width of the right of way there, they could cut Yonge Street down to 2 lanes and shift it to the east up against the cemetery. This would free up space for some small format retail and building entrances to enliven this segment of Yonge while allowing towers and midrise above.. Tower separation (to the west) would only be a problem at the south end. Servicing could be provided by the new N/S service and access road.
To further ease development, they could eliminate much of the grade change in this area on Yonge and bring it in line with the subway tracks. It would create an elevation drop off down to the cemetery, but access to the cemetery here is blocked by a fence under the current conditions. You could actually start this leveling out of Yonge at Merton as it wouldn't effect the existing building at the southeast corner of Merton and Yonge (it would actually improve its relationship to the street). You would need to raise the Beltline bridge though.
I raised some question about that myself just above:
https://www.toronto.ca/city-government/planning-development/planning-studies-initiatives/next-stop-davisville/ An in-person meeting happening tonight!
urbantoronto.ca
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That said, the City would not likely consider raising the grade of Yonge here, in part because:
1) There is major infrastructure under Yonge which would then be much deeper when you need to access it. Raising the sewer in particular is not feasible, because Toronto's sewers all drain by gravity, no pumps.
2) This would mean cutting down literally well over 100 mature trees
3) It would position Yonge above the cemetery in some areas and that not only has shadowing implications, but drainage ones as well.
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Also, you couldn't place retail here, because the TTC mainline tracks aren't moving, and raising Yonge to the point where the retail was over said tracks would be enormous there's be a huge wall at the edge of Mt. Pleasant.
None of that, however, precludes building over the southern section, it simply wouldn't address Yonge really.
I assume some of the complexities I noted in my post, along w/shadowing the cemetery and potential ROI figured into not looking at that area more closely (but don't know)