[sche]

Interesting article. I'd like to see an environmental audit of the various options. Sure megabores are cool. But do we end up expending twice as much energy and greenhouse gases from the concrete? Canadians have more or less abandoned small cars for big SUVs and trucks. Same trend.

I thought about this a bit. Based on some back of the napkin calculations and guesses, I feel like one 12m diameter megabore (e.g. Barcelona Line 9/10) would use a significantly greater amount of concrete than 6m diameter twin bores.

Walls:
The circumference of two 6m circles is exactly the same as the circumference of one 12m circle, so assuming the thickness of the walls is the same, the volume of concrete for the outer shell is pretty much identical (actually it is slightly more for the two 6m diameter bores due to the greater curvature). Maybe a bit more concrete would be used in the 12m bore if the walls have to be thicker.

Platform where tracks are laid:
In a double bore, a horizontal platform is typically built in the tunnel, and the space underneath is left empty. In a twin bore, they usually just pour concrete into the bottom of the tunnel to create a flat surface, filling the entire space underneath the tracks. Guessing a little, I'd think both of these would be similar amounts of concrete.

Stations, crossovers, tail tracks, pocket tracks, emergency exits, etc:
Here's the big one - since all of these pretty much fit inside the megabore but require additional outside structures for twin bores, I think it's reasonable to assume that twin bores would require more concrete for all of these structures.

Overall I can't imagine the amount of concrete is too different. If anyone has better information or actual numbers though, feel free to correct my guesstimates .

Besides, any transit (other than buses on deserted suburban bus routes) is far better in terms of GHGs than cars, so any transit is good in that sense.

 

[Allandale25]

On the agenda for the upcoming Executive Committee meeting:

"Provincial Priority Transit Expansion Projects - Subway Program Status Update Third Quarter 2020"

Agenda Item History - 2020.EX16.5

 

[CapitalSeven]

I thought about this a bit. Based on some back of the napkin calculations and guesses, I feel like one 12m diameter megabore (e.g. Barcelona Line 9/10) would use a significantly greater amount of concrete than 6m diameter twin bores.

Walls:
The circumference of two 6m circles is exactly the same as the circumference of one 12m circle, so assuming the thickness of the walls is the same, the volume of concrete for the outer shell is pretty much identical (actually it is slightly more for the two 6m diameter bores due to the greater curvature). Maybe a bit more concrete would be used in the 12m bore if the walls have to be thicker.

Platform where tracks are laid:
In a double bore, a horizontal platform is typically built in the tunnel, and the space underneath is left empty. In a twin bore, they usually just pour concrete into the bottom of the tunnel to create a flat surface, filling the entire space underneath the tracks. Guessing a little, I'd think both of these would be similar amounts of concrete.

Stations, crossovers, tail tracks, pocket tracks, emergency exits, etc:
Here's the big one - since all of these pretty much fit inside the megabore but require additional outside structures for twin bores, I think it's reasonable to assume that twin bores would require more concrete for all of these structures.

Overall I can't imagine the amount of concrete is too different. If anyone has better information or actual numbers though, feel free to correct my guesstimates .

Besides, any transit (other than buses on deserted suburban bus routes) is far better in terms of GHGs than cars, so any transit is good in that sense.

Thanks, I hadn't fully worked out the math. The point about the volume for the walls is true, as are most of the benefits you describe. However there are some other side effects. If I am correct, doubling the diameter quadruples surface area, so one 12 metre tunnel will require removing twice as much earth as two six metre tunnels - twice as much energy expended. And as the distance to the track level has to be further - both the height of the tunnel and the required overburden - more material and cost are required for the station. And it will take longer to get to the trains. I am not sure in the end there will be much cost saving.

The bigger issue from an environmental viewpoint is that nearly all the energy, material, and impact is a waste because the project depends on scrapping an existing line built with much less impact that could easily be renovated to carry all of the traffic for about 1/5 of the money.

 

[Rainforest]

Thanks, I hadn't fully worked out the math. The point about the volume for the walls is true, as are most of the benefits you describe. However there are some other side effects. If I am correct, doubling the diameter quadruples surface area, so one 12 metre tunnel will require removing twice as much earth as two six metre tunnels - twice as much energy expended. And as the distance to the track level has to be further - both the height of the tunnel and the required overburden - more material and cost are required for the station. And it will take longer to get to the trains. I am not sure in the end there will be much cost saving.

The bigger issue from an environmental viewpoint is that nearly all the energy, material, and impact is a waste because the project depends on scrapping an existing line built with much less impact that could easily be renovated to carry all of the traffic for about 1/5 of the money.

Even a small increase in daily transit ridership due to the more direct subway route will probably outweight the environmental impact of the underground construction.

Regarding the twin bore vs the wide 12-m single bore: indeed the wide bore might not be the wisest choice.

 

[Allandale25]

Review by Munro: https://stevemunro.ca/2020/09/25/drifting-timelines-on-metrolinx-projects-fall-2020-update/

Line 2 East Extension (Scarborough Subway)

This project is now shown with two portions: one for the tunnel, and the other for the stations, railway and systems.

There is no change in the tunnel portion of the project, but the remaining portion has reverted to the dates shown for the overall project in the Winter 2020 update.

Also, should this thread name be updated to say "Metrolinx" instead of "TTC"?

 

[Allandale25]

https://twitter.com/x/status/1317153461948088320

https://twitter.com/x/status/1317151624180228097

 

[Undead]

Given the delays with the Eglinton LRT and infrastructure delays in general, I'm not sure the LRT network would have been lickety split as some claim.

 

[salsa]

https://twitter.com/x/status/1317153461948088320

https://twitter.com/x/status/1317151624180228097

I guess it's time for another round of our favourite debate as to which transit plan was better for Scarborough!

 

[Coolstar]

I guess it's time for another round of our favourite debate as to which transit plan was better for Scarborough!

Looking forward to this one.

 

[Cobra]

I guess it's time for another round of our favourite debate as to which transit plan was better for Scarborough!

 

[Allandale25]

^ Is the point of posting that to show that Scarborough wasn't getting enough? Because that map doesn't show the full plan.

 

[H4F33Z]

I'm curious to know if building a temporary priority bus corridor on or paralleling Line 3 when Line 3 is no longer running. We gotta make a good alternative.

 

[OneCity]

https://twitter.com/x/status/1317153461948088320

https://twitter.com/x/status/1317151624180228097

Shocking....Another Downtown councilor and the usual Downtown political media operatives still trying to own the conversation of Scarborough transit

And then people seems surprised there is is such large and growing political apathy in this City come election time

Even when the Province steps in to prevent further damage, the long culture of entitlement and prejudice from some political outsiders in this City is far too strong. Atleast they can no longer impact on Scarboroughs major transit infrastructure

 

[OneCity]

^ Is the point of posting that to show that Scarborough wasn't getting enough? Because that map doesn't show the full plan.

View attachment 277067

Your map above is also misleading as the SMLRT was never funded

And as wonderful as the additional transfer on Sheppard and keeping the trasnfer on RT would be, Scarborough will be far better off now that planning has been removed from hyper polarized City. Unfortunate Scarborough even had to navigate thru massive outside political games to have these subways delayed this far

 

[Rainforest]

I'm curious to know if building a temporary priority bus corridor on or paralleling Line 3 when Line 3 is no longer running. We gotta make a good alternative.

This should be possible, if the Line 3 vehicles can no longer be fixed up.

But, probably better to refurbish the MK-1's again and keep them running till 2030. They are small for the demand, but still have more capacity than the buses. And, they ran faster than the buses because their corridor is better separated from the traffic, therefore they can make more round-trips per day.