BurlOak
Senior Member
First, bridges are (relatively speaking) dirt cheap. If you want a rough number to go by, I'd say $100M/km.One of biggest issue of Sheppard West extension is crossing West Don Valley - require new bridge or deep tunnel dip under Don Valley West river. Now you're adding those sharp 90 degree subway turns at Sheppard & Bathurst along with Bathurst & Wilson will be difficult and really restrict where a subway station platform can actually be built to service those intersections.
Sheppard Subway Line 4 already has WYE subway turning tunnels onto Yonge Subway Line 1 - yes, eastbound train will actually have to reverse to service Sheppard-Yonge station!
Image looking north along Yonge at Sheppard:
View attachment 137818
So existing Sheppard Subway Line 4 would interline with Yonge Subway Line 1 between Sheppard-Yonge Station and Highway 401 where it heads west under Highway 401.
Now to cross the West Don Valley cheaply,.... use the "unoccupied" lower deck of Highway 401 Hoggs Hollow Bridge just west of Yonge Street,.... why does this sound familiar??? Oh, that Bloor Viaduct being built in 1918 with empty lower deck not being used until Bloor-Danforth line went in during 1960's!
View attachment 137819
https://en.wikipedia.org/wiki/Hogg's_Hollow_Bridge#/media/File:Hogg's_Hollow_Bridge_-_South.jpg
https://en.wikipedia.org/wiki/Hogg's_Hollow_Bridge#/media/File:Hogg's_Hollow_Bridge_-_South.jpg
http://www.uerev.com/index.php?pageid=galleryimage&itemid=1051
Warning: Getting MTO to agree to anything is next to impossible,... under our current Premier,... but hmmmm,... anyone hearing "subway, Subway, SubWay, SUBWAY!"
New subway tunnels bored under Highway 401 until it reaches Wilson Ave just east of Bathurst,.. now Bathurst & Wilson will have proper subway station with straight platform below intersection.
Portals I don't have as good of a feel for (you definitely need 1 on the East side, and likely another if it goes underground on the west as well). I would guess about $25M each.
Second, Hogg's Hollow bridge was not designed for the weight of a subway. Bloor viaduct (and Millwood Bridge) were. If you propose to run with cars filled with Hellium balloons, it may be able to work, but that leaves little space for passengers.