Tunnel depth seems like a really big driver of costs...I know they've mentioned cut and cover a lot, but it looks like that was only going to be from Eau Claire to ~7th (and deep cut and cover by that point), with the rest being bored (
https://www.calgary.ca/green-line/construction/tunnel-and-underground-stations.html)
The boring seems to be based on three assumptions: gotta go deeper than the red line tunnel at 11th ave, gotta go deep under the future 8th avenue tunnel, and gotta be deep under the parking sprial/CP tracks. But what if we didn't have to go deep at all?
- run at grade along 11th Ave, but extend the underpasses on each Macleod Tr south by about 150 meters each (like how the 4th Street underpass also goes under 9th Ave). 1 lane would stay at grade to turn onto 11th Ave, but 2-3 lanes would become trenched, and can be sold as road improvements.
- shallow cut & cover* along 1 St SW (modifying existing underpass) - running at the same grade as the 8th Ave tunnel. Perhaps not ideal to have lines intersecting and it creates a critical failure point, but it's not impossible to do
* getting a little crazy here, but I've always thought 1st St SW would be an excellent pedestrian only street (ideally from 8th Ave to 17th)...what if you didn't even have to fully cover it (at least not to be load bearing for a roadway)? Probably makes things like HVAC and station access points cheaper/easier
- There are a handful of small storefronts on 1st that would be hugely impacted/compensated by this disruption (one of the benefits of 2nd St is there are essentially zero store fronts or critical building entrances...though I'd argue that also just means its an office wasteland). Based on cursory research this is still a way cheaper approach than boring (and dealing with those storefronts could probably have been more economical than expropriating a bunch of condos in the midst of a housing crisis...
I'm sure there are a bunch of drawbacks to this, but it gets you down to 1 underground station (7th Ave) and facilitates surface stations in beltline and north downtown, and opens the option to more easily run at grade over Centre St bridge.The vehicle lanes lost in this on 1st and 11th are pretty well used, but ultimately they are both redundant