Green Line Reconfiguration

Brattle Loop said:
Best I can find is that the top of the OL tunnel was supposed to be no less than 1.5 feet below the bottom of the Mass Pike. The bridges over the Pike in that area all have more than 14 feet of clearance over the highway, so the tunnel has to be deeper than that 14'+1.5' at the very least, and there's not exactly a ton of running room between the Pike's trench and Marginal even if it's a grade there.
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But you have to add bridge depth as well (3-4 ft?) So, 18.5-19.5 ft minimum? How deep would a GL tunnel need to be? Can you get a floor and a roof in 5ft?
 
Brattle Loop said:
Best I can find is that the top of the OL tunnel was supposed to be no less than 1.5 feet below the bottom of the Mass Pike. The bridges over the Pike in that area all have more than 14 feet of clearance over the highway, so the tunnel has to be deeper than that 14'+1.5' at the very least, and there's not exactly a ton of running room between the Pike's trench and Marginal even if it's a grade there.
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I recall awile back seeing an early-1970's study archived on Google Books that looked at Washington St. light rail for El replacement, and managed to have its GL tunnel graft-on pass over the (then unused) 1967 OL South Cove tunnel at the corner of Oak/Marginal en route to a portal-up on Marginal on the Oak-Washington block. That would prove feasibility.
 
BTW...here's the 2004 PMT screencap for converting Silver Line Washington to light rail. . .
F-PMT.png


The MPO shanked it with a "low" priority rating because of the relatively low number of all-new transit riders, owing to the vast majority of the corridor already riding buses. But the on-mode increase of +34,300 daily riders was third amongst all expansion projects the PMT evaluated, behind only the Urban Ring and NSRL. And almost 2.5x the 13,783 daily boardings SL4/SL5 did in the last Blue Book. The lack of any behind-prepayment transfers downtown is a mega crippler of the current Silver Line, many times moreso than the current speed of trip. Shy of maybe getting one of both of the two northern UR quadrants roped in as Green Line appendages, this is pretty much the highest-leverage unbuilt rapid transit project on the books.
 
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So, does anyone know EXACTLY where in Norton Park the tunnel mouths were(are)? How many feet north of the southern edge of the park?
 
Tallguy said:
So, does anyone know EXACTLY where in Norton Park the tunnel mouths were(are)? How many feet north of the southern edge of the park?
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Northeast corner of the park, just off-footprint from Tremont St. Buried and fully intact basically underneath this little earthen mound of plantings. You can extrapolate by comparing Historic Aerials views from pre-1975 (the year it was capped) to today with the sliding compare view.
 
F-Line to Dudley said:
BTW...here's the 2004 PMT screencap for converting Silver Line Washington to light rail. . .
View attachment 22730

The MPO shanked it with a "low" priority rating because of the relatively low number of all-new transit riders, owing to the vast majority of the corridor already riding buses. But the on-mode increase of +34,300 daily riders was third amongst all expansion projects the PMT evaluated, behind only the Urban Ring and NSRL. And almost 2.5x the 13,783 daily boardings SL4/SL5 did in the last Blue Book. The lack of any behind-prepayment transfers downtown is a mega crippler of the current Silver Line, many times moreso than the current speed of trip. Shy of maybe getting one of both of the two northern UR quadrants roped in as Green Line appendages, this is pretty much the highest-leverage unbuilt rapid transit project on the books.
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So....I still cant believe that a street level 1.8 mile LRT path would cost $374M, or $200M per mile?
Even if it cost $100M to get over/under the pike, that's still $150M pm for the rest!
 
F-Line to Dudley said:
The MPO shanked it with a "low" priority rating because of the relatively low number of all-new transit riders, owing to the vast majority of the corridor already riding buses.
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Hmm... the absolute ridership numbers might have been too optimistic but that the ridership is going to use public transit regardless of what is done is still accurate, no?
 
jklo said:
Hmm... the absolute ridership numbers might have been too optimistic but that the ridership is going to use public transit regardless of what is done is still accurate, no?
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Yes...they still ride local buses into Nubian at some point during their transit day to get somewhere/anywhere. But they're shut out from effective access to Downtown and easy transfers, so the mobility ends up cripplingly limited for Roxbury compared to what the El provided with its one-seat to Downtown. That's how you tally up a projected deficit of 2.5x Silver's current ridership through several decades worth of studies...in lost access to various linked trips around the system.

The El in its latter days was a little bit imperfect in that it had *too* few intermediate stops to adequately serve demand. Until 1938 it was complemented by a Green Line Dudley branch, and until 1956 an Egleston GL branch that took up the 43 bus's parallel route 2 blocks away on Tremont, so the 'tweener spots on the corridor were left a little exposed by the withdrawal of streetcars...but by that point they were already looking to tear it down. The Silver Line's stop roster is pretty close to the balancing point between too few and too many stops for adequately sucking up the corridor's demand. But it whiffs so badly on access to the prepayment transfers that it can't possibly fulfill any semblance of its mission statement.
 
F-Line to Dudley said:
Yes...they still ride local buses into Nubian at some point
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Into Nubian? I would think anyone taking a bus going by Nubian would just stay on and go to Orange. If you're saying that's the problem, I guess, Roxbury Crossing isn't that much further. Now there is a hole there for sure but I'm not sure those are riders of the SL today.
 
So would a all surface, dedicated lane(I’m thinking down Shawmut and up Washington) do the job?
 
Tallguy said:
So would a all surface, dedicated lane(I’m thinking down Shawmut and up Washington) do the job?
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Depends on how many appendages you envision for the reactivated Tremont tunnel. Remember, it's 4 tracks (OB-IB-OB-IB) to the old portal because of the flying junction in the old tunnel. So you have provisions for multiple grade-separated branches here guiding some of your construction decisions. Nubian can be one branch. A Transitway/Seaport hook-in through the South End in lieu of Silver Line Phase III's Essex St. dig-of-pain could be the other. A future relocation of the Huntington Ave. subway through Back Bay to here (eliminating the Copley Jct. chokepoint) is another and/or option. And also depends on if you want to do an Orange Line transfer station attached behind prepayment to Tufts. The Orange station is probably worth shooting for if any of the provisioned-for service patterns are likely to loop at Government Center some or most of the time, since then you'll be able to hit all line transfers.

In that case it may be better to drop a shallow subway station diagonally under Eliot Norton Park (nuking the uninhabited Church of All Nations building) with space provisions for two 225 ft. island platforms (whether both are active at the start or not), then continue the 4-track bore down wider Tremont St. to the corner with Marginal, where the extra road width under Tremont definitely allows you to keep all 4 tracks in-play. The traffic island at that corner is where the last-round Silver Line Phase III scoping portal was supposed to go (via a Charles St. S + Tremont tunnel trajectory), so there's definitely enough room to fit a 2-track portal amid the traffic pattern. 2 tracks could portal-up there for Washington, then notches in the tunnel wall could reserve futrue east and/or west tunneling provisions for the other 2 tracks. The only cost to the Nubian branch is that it's 1 block/1 light further back from Washington, but that's a small price to pay for being set for life on high-capacity branching.
 
F-Line to Dudley said:
Depends on how many appendages you envision for the reactivated Tremont tunnel. Remember, it's 4 tracks (OB-IB-OB-IB) to the old portal because of the flying junction in the old tunnel. So you have provisions for multiple grade-separated branches here guiding some of your construction decisions. Nubian can be one branch. A Transitway/Seaport hook-in through the South End in lieu of Silver Line Phase III's Essex St. dig-of-pain could be the other. A future relocation of the Huntington Ave. subway through Back Bay to here (eliminating the Copley Jct. chokepoint) is another and/or option. And also depends on if you want to do an Orange Line transfer station attached behind prepayment to Tufts. The Orange station is probably worth shooting for if any of the provisioned-for service patterns are likely to loop at Government Center some or most of the time, since then you'll be able to hit all line transfers.

In that case it may be better to drop a shallow subway station diagonally under Eliot Norton Park (nuking the uninhabited Church of All Nations building) with space provisions for two 225 ft. island platforms (whether both are active at the start or not), then continue the 4-track bore down wider Tremont St. to the corner with Marginal, where the extra road width under Tremont definitely allows you to keep all 4 tracks in-play. The traffic island at that corner is where the last-round Silver Line Phase III scoping portal was supposed to go (via a Charles St. S + Tremont tunnel trajectory), so there's definitely enough room to fit a 2-track portal amid the traffic pattern. 2 tracks could portal-up there for Washington, then notches in the tunnel wall could reserve futrue east and/or west tunneling provisions for the other 2 tracks. The only cost to the Nubian branch is that it's 1 block/1 light further back from Washington, but that's a small price to pay for being set for life on high-capacity branching.
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Would the potential Huntington Ave. subway relocation be better as a Stuart Street subway or alongside the Mass Pike ROW like you described? I'd imagine any potential air rights development on Parcels 16, 17, or 18 could possibly complicate a tunnel alongside the Pike, but I can't say for sure.
 
themissinglink said:
Would the potential Huntington Ave. subway relocation be better as a Stuart Street subway or alongside the Mass Pike ROW like you described? I'd imagine any potential air rights development on Parcels 16, 17, or 18 could possibly complicate a tunnel alongside the Pike, but I can't say for sure.
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Stuart's awfully narrow to the west of Charles S...narrower than Marginal. So you're going to have an easier time spatially along the Pike, as well as having an easier time with utilities relocation in the 1960's urban renewal nuke zone. The hardest part is immediately at Back Bay station, but you're not at a loss for things you can cut-and-cover under away from building foundations.

I'd fully expect E relocation to be a further-future thing, when you need to free up Copley-west capacity for more thoroughly Urban Ring'ed service patterns. But if you're reactivating the Tremont tunnel first for something else it's a no-brainer to keep all 4 tracks in-play and notch the wall for a potential hook-in.
 
Brattle Loop said:
Best I can find is that the top of the OL tunnel was supposed to be no less than 1.5 feet below the bottom of the Mass Pike. The bridges over the Pike in that area all have more than 14 feet of clearance over the highway, so the tunnel has to be deeper than that 14'+1.5' at the very least, and there's not exactly a ton of running room between the Pike's trench and Marginal even if it's a grade there.
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Tallguy said:
But you have to add bridge depth as well (3-4 ft?) So, 18.5-19.5 ft minimum? How deep would a GL tunnel need to be? Can you get a floor and a roof in 5ft?
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Riverside said:
Did a quick skim, is it possible that you're thinking of this one, @F-Line to Dudley? https://archive.org/details/replacementtrans00cbtc/mode/2up
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F-Line to Dudley said:
One of the detail breakouts from that summary brochure, yes..."Tunnel option". I'm pretty sure the render did engage the Orange tunnel at that intersection, but it was many years ago that I skimmed it.
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I agree that the distance from pavement level of Mass Pike to pavement level of Marginal Street is likely 14' + 3' = 17', plus the aforementioned 1.5' between the Mass Pike and the tunnel. So, yes, probably 18' of underground to play with. According to this railroad.net thread, the running height of a Type 7 was just under 12'; someone cited signs on Huntington Ave claiming the catenary was 13.5' high (though I can't find any signs on StreetView today to that effect). This ArchBoston thread from 2008 has additional info about ruling heights on the Green Line, which is consistent with a running height just under 12'.

So... maybe you could fit a Green Line subway between Marginal Street's pavement and the Orange Line tunnel underneath?

@F-Line to Dudley, looking at the pamphlet again, it doesn't really help us out here -- their tunnel option rises to street-level between Tremont and Shawmut, and has risen to street-level by the time it reaches Shawmut (approximately where it would cross the Orange Line tunnel). Any ideas what your thinking was at the time, F-Line?

So the question is whether a Green Line subway under Marginal should go over or under the Orange Line.

I went spelunking waaaaay upthread, skimmed the first 23 pages before giving up. @davem argued for a shallow tunnel just below street-grade, over the Orange Line. F-Line later argued in favor of going under the Orange Line tunnel, though I'm not clear why.

As it happens, I've actually been sketching out diagrams for most of these alternatives for the last couple of months. I'll try to post those later this week.

One reason to dive under the Orange Line is if you want your Nubian Branch's portal to be south of the Mass Pike; if so, you'll need to dive under the Mass Pike anyway, so it might be better to reach "Level -3" (where Orange is Level -2 and Mass Pike pavement is Level -1) further to the east. This would also allow for a gentler curve under the Pike to Washington St.
 
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I have been in multiple cities which have side platform light rails running in the street on the side (i.e. Charlotte uptown) and everything operates fine. At first I pictured something like this as median only but I think side of road works great.
 
Riverside said:
I agree that the distance from pavement level of Mass Pike to pavement level of Marginal Street is likely 14' + 3' = 17', plus the aforementioned 1.5' between the Mass Pike and the tunnel. So, yes, probably 18' of underground to play with. According to this railroad.net thread, the running height of a Type 7 was just under 12'; someone cited signs on Huntington Ave claiming the catenary was 13.5' high (though I can't find any signs on StreetView today to that effect). This ArchBoston thread from 2008 has additional info about ruling heights on the Green Line, which is consistent with a running height just under 12'.

So... maybe you could fit a Green Line subway between Marginal Street's pavement and the Orange Line tunnel underneath?

@F-Line to Dudley, looking at the pamphlet again, it doesn't really help us out here -- their tunnel option rises to street-level between Tremont and Shawmut, and has risen to street-level by the time it reaches Shawmut (approximately where it would cross the Orange Line tunnel). Any ideas what your thinking was at the time, F-Line?

So the question is whether a Green Line subway under Marginal should go over or under the Orange Line.

I went spelunking waaaaay upthread, skimmed the first 23 pages before giving up. @davem argued for a shallow tunnel just below street-grade, over the Orange Line. F-Line later argued in favor of going under the Orange Line tunnel, though I'm not clear why.

As it happens, I've actually been sketching out diagrams for most of these alternatives for the last couple of months. I'll try to post those later this week.

One reason to dive under the Orange Line is if you want your Nubian Branch's portal to be south of the Mass Pike; if so, you'll need to dive under the Mass Pike anyway, so it might be better to reach "Level -3" (where Orange is Level -2 and Mass Pike pavement is Level -1) further to the east. This would also allow for a gentler curve under the Pike to Washington St.
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Somewhere up thread F-Line outlines a portal location for the Nubian direction that is available in the Mass Pike/NEC cut between Tremont and Washington, that can feed you up to Washington Street. I think it is the zone along Marginal just before and after Shawmut, where the NEC pulls away from the Marginal Street wall.
 
JeffDowntown said:
Somewhere up thread F-Line outlines a portal location for the Nubian direction that is available in the Mass Pike/NEC cut between Tremont and Washington, that can feed you up to Washington Street. I think it is the zone along Marginal just before and after Shawmut, where the NEC pulls away from the Marginal Street wall.
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Maybe I'm misunderstanding, but I think this doesn't answer my question. For the purpose of this discussion, I'm looking for an alignment that allows the Green Line to remain underground north of the Pike, cross the Pike underground to the south, and also enable an underground subway east along Marginal toward South Station. I don't want a portal north of the Pike, and I think that is what you're describing? My apologies if I'm misunderstanding.
 
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