If You Were God/Goddess | Transit & Infrastructure Sandbox

[ritchiew]

Yeah, it's been a while since I was reading about this, and I was trying to piece all this together from really incomplete snippets of data, but:

One issue I see past haymarket is the pinch between state st and the blue line tunnel roof. I’m not sure if the grade exceeds 3% but it’s pretty darn close. There’s also the vertical curve right at the pinch which could cause issues for trains.

Yes, it's close, but I am pretty sure it never goes above 3%. That's piecing together lots of partial diagrams, construction photos, and planning documents mentioning depths at certain points, so I have no one document to point you to. It seemed possible it never goes above 2.5%. But, I could never pin that down absolutely certainly, so I'd love if someone just knows that answer. And has a source.

The curve, though, you're right, that could be a problem. I have no idea the minimum allowed curve on a 2-3% incline. I don't know what that turning radius is, there. That might limit the speed there, or might be one of the many things that makes this plan fail.

I believe the photo in the linked post is of the Ted at one of the portals, which definitely has a large height clearance for trucks.

The CA/T, at least at the portals, has nothing between the girders and tunnel ceiling, as evidenced by past strikes by rigs:

Yeah, I should have been clearer. That picture is from I-90, not I-93, but I think all the new Big Dig tunnels were built like that. That was just the clearest picture of what's above the panels. Again, that was hard to confirm for the whole length the tunnels, so if anyone here has a secret stash of CA/T engineering documents (probably) I'd love to look!

As for the picture you posted, yes, some of the portals don't have that ventilation space immediately above, because the highway is too shallow to allow anything above it at that point. But the portals aren't usable for trains anyways. From Kneeland to South Station and from the Zakim to Haymarket, the new highways are 5% grade. That number is pretty clearly documented.

Well the overbuild does span the entire width of the platforms, so I imagine the deep foundations extend the entire width as well. There’s also a major difference between building the stations before building the foundations and going back and beefing them up as part of the underground train shed later.

That makes sense. I guess I was trying to get at a couple of other things, though. 1) When they built the bus station and tower, did they do any kind of provisioning to maybe make it easier to one day build tracks under South Station? and 2) Whether or not they did that, how expensive would it be to build those tracks? Doing that now isn't impossible, but I'm sure it's very expensive. How would that very expensive station compare to, for example, mining a new station 10-15 stories under Fort Point Channel?

 

[TheRatmeister]

Yeah, it's been a while since I was reading about this, and I was trying to piece all this together from really incomplete snippets of data, but:


Yes, it's close, but I am pretty sure it never goes above 3%. That's piecing together lots of partial diagrams, construction photos, and planning documents mentioning depths at certain points, so I have no one document to point you to. It seemed possible it never goes above 2.5%. But, I could never pin that down absolutely certainly, so I'd love if someone just knows that answer. And has a source.

The curve, though, you're right, that could be a problem. I have no idea the minimum allowed curve on a 2-3% incline. I don't know what that turning radius is, there. That might limit the speed there, or might be one of the many things that makes this plan fail.


Yeah, I should have been clearer. That picture is from I-90, not I-93, but I think all the new Big Dig tunnels were built like that. That was just the clearest picture of what's above the panels. Again, that was hard to confirm for the whole length the tunnels, so if anyone here has a secret stash of CA/T engineering documents (probably) I'd love to look!

As for the picture you posted, yes, some of the portals don't have that ventilation space immediately above, because the highway is too shallow to allow anything above it at that point. But the portals aren't usable for trains anyways. From Kneeland to South Station and from the Zakim to Haymarket, the new highways are 5% grade. That number is pretty clearly documented.


That makes sense. I guess I was trying to get at a couple of other things, though. 1) When they built the bus station and tower, did they do any kind of provisioning to maybe make it easier to one day build tracks under South Station? and 2) Whether or not they did that, how expensive would it be to build those tracks? Doing that now isn't impossible, but I'm sure it's very expensive. How would that very expensive station compare to, for example, mining a new station 10-15 stories under Fort Point Channel?

The choke point I would be much more concerned about is the Sumner/Callahan interchange. I believe 93S->Callahan has some pretty crazy swings in elevation that you'd need to navigate while also avoiding the Government Center exit and the Sumner ramps.

 

[ritchiew]

The choke point I would be much more concerned about is the Sumner/Callahan interchange. I believe 93S->Callahan has some pretty crazy swings in elevation that you'd need to navigate while also avoiding the Government Center exit and the Sumner ramps.

Yeah, that's roughly the problem section we're talking about: going from a high point as the highway goes over the Blue Line to a low point under the Callahan/Sumner ramps. That should be the steepest part of the CA/T between South Station and Haymarket, but I'm pretty sure it's still less than 3%. It would be a relative roller coaster ride for a train, but maybe, possibly within spec.

The clearest CA/T elevation diagrams I've seen actually come from past NSLR proposals. I wouldn't trust you could be measure grades too accurately from these, but they show roughly how things fit together, and they're neat.

Really what I want is like a 3d model of the tunnels under there. Add in all the ramps and subways, and it's a mess too complicated for me to keep in my head.

 

[TheRatmeister]

Yeah, that's roughly the problem section we're talking about: going from a high point as the highway goes over the Blue Line to a low point under the Callahan/Sumner ramps. That should be the steepest part of the CA/T between South Station and Haymarket, but I'm pretty sure it's still less than 3%. It would be a relative roller coaster ride for a train, but maybe, possibly within spec.

The clearest CA/T elevation diagrams I've seen actually come from past NSLR proposals. I wouldn't trust you could be measure grades too accurately from these, but they show roughly how things fit together, and they're neat.

Really what I want is like a 3d model of the tunnels under there. Add in all the ramps and subways, and it's a mess too complicated for me to keep in my head.

View attachment 50275

View attachment 50276

My concern is not necessarily that the grade over the CAT is too steep, it's that this area is to some degree infringed upon by all the ramps, and that makes weaving a tunnel through said ramps without exceeding a 3% grade impossible. You'd for sure need to go under the Callahan tunnel ramps, but I can't tell if there's enough room to also go under the Sumner Tunnel ramps. It seems like there is, but if not that's an immediate dealbreaker, you'd need at least a 4% grade to do an under-over.

The other big concern is North Station. I don't think you can get 800, let alone 1050, straight feet with a <1% grade until about Community College OL station, and a central station might also be off the table. A transfer station here isn't a bad idea in an Urban Ring world, but it's also not a substitute for North Station, and would almost certainly lead to massive overcrowding on the OL and at South Station.

 

[ritchiew]

My concern is not necessarily that the grade over the CAT is too steep, it's that this area is to some degree infringed upon by all the ramps, and that makes weaving a tunnel through said ramps without exceeding a 3% grade impossible. You'd for sure need to go under the Callahan tunnel ramps, but I can't tell if there's enough room to also go under the Sumner Tunnel ramps. It seems like there is, but if not that's an immediate dealbreaker, you'd need at least a 4% grade to do an under-over.

I'm not sure I follow. To be clear, this was all based on a god-mode proposal to repurpose the CAT tunnels for trains as much as possible. So the trains would be in the current tunnels, following whatever grade they are. I was saying that's maybe remotely possible between South Station and Haymarket.

 

[TheRatmeister]

I'm not sure I follow. To be clear, this was all based on a god-mode proposal to repurpose the CAT tunnels for trains as much as possible. So the trains would be in the current tunnels, following whatever grade they are. I was saying that's maybe remotely possible between South Station and Haymarket.

Ah that makes sense, I thought we were talking about effectively bolting a rail layer on top of the existing CAT.

 

[F-Line to Dudley]

Really what I want is like a 3d model of the tunnels under there. Add in all the ramps and subways, and it's a mess too complicated for me to keep in my head.

The 2019 reassessment had some 3D renders of the stations. . .

 

[Charlie_mta]

Weird question — the north station incline to science park is actually four tracks wide towards the bottom. There’s two tracks that appear to dip under but just end at a wall. Are those storage tracks or are they actually a provision for service points east?

My wish is that the two tracks would continue on to a new portal next to Sorrow Drive between Leverett Circle and Longfellow Bridge, then continue on the surface to Charlesgate alongside a road-dieted Storrow Drive in which the current 6 traffic lanes are reduced down to 4 lanes, with the two (former) lanes made into a GL extension to Kenmore Sq.

 

[Longfellow]

Posting this while stuck on the 69 bus in bumper to bumper traffic. Urban ring is provided for reference. Has this ever been proposed? I feel like if Cambridge were much denser this would be the perfect Manhattan-esque pair of spine routes (along with Red) for the city. You’d probably have to cut and cover a subway.

 

[TheRatmeister]

View attachment 50339
Posting this while stuck on the 69 bus in bumper to bumper traffic. Urban ring is provided for reference. Has this ever been proposed? I feel like if Cambridge were much denser this would be the perfect Manhattan-esque pair of spine routes (along with Red) for the city. You’d probably have to cut and cover a subway.

Like this?

 

[Longfellow]

View attachment 50340
Like this?

That would do it. I suppose sometimes the crowding of the lines kind of fools me

 

[Tallguy]

Yeah, that's roughly the problem section we're talking about: going from a high point as the highway goes over the Blue Line to a low point under the Callahan/Sumner ramps. That should be the steepest part of the CA/T between South Station and Haymarket, but I'm pretty sure it's still less than 3%. It would be a relative roller coaster ride for a train, but maybe, possibly within spec.

The clearest CA/T elevation diagrams I've seen actually come from past NSLR proposals. I wouldn't trust you could be measure grades too accurately from these, but they show roughly how things fit together, and they're neat.

Really what I want is like a 3d model of the tunnels under there. Add in all the ramps and subways, and it's a mess too complicated for me to keep in my head.

View attachment 50275

View attachment 50276

Is there a similar
diagram for the Pearl/Congress route?

 

[ritchiew]

Is there a similar
diagram for the Pearl/Congress route?

None that I've ever come across, no. Sorry