Green Line Reconfiguration

[TheRatmeister]

Map for visual aid.

I'd update the comparison between routing options for the Seaport Connector to look something like this then:

	Full Pike Hugger (Pike+Lincoln St)	Essex St	Stuart/Kneeland
Total "Narrow street" new construction length	~1500' (Kneeland St to Essex St to Atlantic Ave)	~2900' (Tremont St to Atlantic Ave)	~1500' (Kneeland St to Essex St to Atlantic Ave)
Total other construction length	~2600' (Tremont to Lincoln under Marginal Rd/Hwy interchange) + ~2500' (Hynes to Back Bay, Huntington Ave subway to Tremont St portal not included in length)	~1300' (The wider part of Boylston St, Hassadah Way to Tremont St)	~5500' (Stuart/Kneeland Subway) + ~2500' (Hynes to Back Bay)
Total New Construction	~6,600'	~4,200'	~9,500
Total Length from South Station to Hynes	~10,100'	~9,300'	~9,700'
New Stations (Assuming Huntington-Tremont St connector)	2 stations, 1 expensive one	1 very expensive one	3 stations, at least 1 expensive one
Transfers	Same or cross platform to all other GL services, OL at Tufts with ~60-90s walking	OL at Chinatown with ~60-90s walking, other GL services at Boylston with 120-150s walking	OL at Back Bay with ~90-120s walking or at Chinatown with ~90-150s walking, GL at Back Bay with 60-90s walking.
Station Locations	Avoids downtown for the most part, Chinatown Gate is a mediocre alternative.	Basically as central as you can get	Slightly further than existing stations but overall okay
Service to Seaport from...	Kenmore and Huntington	Kenmore Only	Either Kenmore Only or Kemore+Huntington if a junction is built before Back Bay.
Big uncertainties	Tunnel under Prudential center Is there space for flying junctions or quad-track along shared Pike-Hugging section?	Essex St underpinnings Mid-block station viability	Tunnel under prudential center Dive under Tremont St and Washington St subways

Based on this I'm quite tempted to just strike Stuart/Kneeland entirely. It really just seems like the worse of both worlds (except for station placement, which is pretty good.) There's also the Prudential issue.

In terms of the 'Full Pike Hugger' alignment, the big scary thing for me is the tunnel under Prudential Center. The parking garage in particular seems like it may lie directly in the path of any tunnel there. If that's not an issue then we're back to discussing the merits of costs vs station locations vs transfer quality vs crowding etc etc.

 

[JeffDowntown]

View attachment 64953
Map for visual aid.

I'd update the comparison between routing options for the Seaport Connector to look something like this then:

Full Pike Hugger (Pike+Lincoln St)	Essex St	Stuart/Kneeland
Total "Narrow street" new construction length	~1500' (Kneeland St to Essex St to Atlantic Ave)	~2900' (Tremont St to Atlantic Ave)	~1500' (Kneeland St to Essex St to Atlantic Ave)
Total other construction length	~2600' (Tremont to Lincoln under Marginal Rd/Hwy interchange) + ~2500' (Hynes to Back Bay, Huntington Ave subway to Tremont St portal not included in length)	~1300' (The wider part of Boylston St, Hassadah Way to Tremont St)	~5500' (Stuart/Kneeland Subway) + ~2500' (Hynes to Back Bay)
Total New Construction	~6,600'	~4,200'	~9,500
Total Length from South Station to Hynes	~10,100'	~9,300'	~9,700'
New Stations (Assuming Huntington-Tremont St connector)	2 stations, 1 expensive one	1 very expensive one	3 stations, at least 1 expensive one
Transfers	Same or cross platform to all other GL services, OL at Tufts with ~60-90s walking	OL at Chinatown with ~60-90s walking, other GL services at Boylston with 120-150s walking	OL at Back Bay with ~90-120s walking or at Chinatown with ~90-150s walking, GL at Back Bay with 60-90s walking.
Station Locations	Avoids downtown for the most part, Chinatown Gate is a mediocre alternative.	Basically as central as you can get	Slightly further than existing stations but overall okay
Big uncertainties	Tunnel under Prudential center Is there space for flying junctions or quad-track along shared Pike-Hugging section?	Essex St underpinnings Mid-block station viability	Tunnel under prudential center Dive under Tremont St and Washington St subways

Based on this I'm quite tempted to just strike Stuart/Kneeland entirely. It really just seems like the worse of both worlds (except for station placement, which is pretty good.) There's also the Prudential issue.

In terms of the 'Full Pike Hugger' alignment, the big scary thing for me is the tunnel under Prudential Center. The parking garage in particular seems like it may lie directly in the path of any tunnel there. If that's not an issue then we're back to discussing the merits of costs vs station locations vs transfer quality vs crowding etc etc.

IIRC you have to approach the current Silver Line South Station tunnel and platform from the Essex Street alignment -- basically crossing the Dewey Square tunnel at Essex. You cannot come up on the east side of the old 93 tunnel, you have to come up on the west side -- basically a Hudson Street alignment, if coming around from Kneeland or Marginal Streets.

 

[Charlie_mta]

View attachment 64953
Map for visual aid.

I'd update the comparison between routing options for the Seaport Connector to look something like this then:

Full Pike Hugger (Pike+Lincoln St)	Essex St	Stuart/Kneeland
Total "Narrow street" new construction length	~1500' (Kneeland St to Essex St to Atlantic Ave)	~2900' (Tremont St to Atlantic Ave)	~1500' (Kneeland St to Essex St to Atlantic Ave)
Total other construction length	~2600' (Tremont to Lincoln under Marginal Rd/Hwy interchange) + ~2500' (Hynes to Back Bay, Huntington Ave subway to Tremont St portal not included in length)	~1300' (The wider part of Boylston St, Hassadah Way to Tremont St)	~5500' (Stuart/Kneeland Subway) + ~2500' (Hynes to Back Bay)
Total New Construction	~6,600'	~4,200'	~9,500
Total Length from South Station to Hynes	~10,100'	~9,300'	~9,700'
New Stations (Assuming Huntington-Tremont St connector)	2 stations, 1 expensive one	1 very expensive one	3 stations, at least 1 expensive one
Transfers	Same or cross platform to all other GL services, OL at Tufts with ~60-90s walking	OL at Chinatown with ~60-90s walking, other GL services at Boylston with 120-150s walking	OL at Back Bay with ~90-120s walking or at Chinatown with ~90-150s walking, GL at Back Bay with 60-90s walking.
Station Locations	Avoids downtown for the most part, Chinatown Gate is a mediocre alternative.	Basically as central as you can get	Slightly further than existing stations but overall okay
Big uncertainties	Tunnel under Prudential center Is there space for flying junctions or quad-track along shared Pike-Hugging section?	Essex St underpinnings Mid-block station viability	Tunnel under prudential center Dive under Tremont St and Washington St subways

Based on this I'm quite tempted to just strike Stuart/Kneeland entirely. It really just seems like the worse of both worlds (except for station placement, which is pretty good.) There's also the Prudential issue.

In terms of the 'Full Pike Hugger' alignment, the big scary thing for me is the tunnel under Prudential Center. The parking garage in particular seems like it may lie directly in the path of any tunnel there. If that's not an issue then we're back to discussing the merits of costs vs station locations vs transfer quality vs crowding etc etc.

I like the Lincoln/Esssex St alignment the best. I'm guessing the new GL tunnel could squeeze in between the CAT tunnel and the T-Mobile store at the junction of those two streets, even if you have to stack one track tunnel on top of the other, without needing to dip below the CAT tunnel, by shoring up the T-Mobile corner of the building.

 

[TheRatmeister]

IIRC you have to approach the current Silver Line South Station tunnel and platform from the Essex Street alignment -- basically crossing the Dewey Square tunnel at Essex. You cannot come up on the east side of the old 93 tunnel, you have to come up on the west side -- basically a Hudson Street alignment, if coming around from Kneeland or Marginal Streets.

Unless you're aware of something I'm not I don't think this is true. The 'hook' tunnel only goes through the tunnel for 93 NB, so as long as you're on Essex St before that you're golden. The SB CAT is only like 30 feet deep max, going under it is mostly trivial. The bigger concern is needing to climb like hell after crossing under the sewer located 30 ft under South St.

I'm guessing the new GL tunnel could squeeze in between the CAT tunnel and the T-Mobile store at the junction of those two streets, even if you have to stack one track tunnel on top of the other, without needing to dip below the CAT tunnel, by shoring up the T-Mobile corner of the building.

Because of the aforementioned sewer it's probably not worth the effort. You can't climb above -30ft until you've passed South St regardless, so the new tunnel would fit under the CAT without issue.

I like the Lincoln/Esssex St alignment the best.

Assuming the Prudential Tunnel isn't a problem, it's likely the cheapest. That said, the major compromise to station locations should definitely give pause. The cost difference would need to be decently large to justify that IMO.

 

[TheRatmeister]

Relevant page from the 2003 SL Phase III EIS