I'm a little reticent to wade into this -- this particular corner of the Green Line Reconfiguration really just isn't that "fun" for me at this point, and I think it, more than perhaps any other component, will hinge on the outcomes of professional studies; I think there's a definite limit to what can be done here from a non-professional perspective.
But I also want to respond in kind to your substantial engagement with the topic!
So I'll see what I can do
To some of your specific points:
Alternatively, it might be possible (and simpler) to route both tracks to the far side of the viaduct (probably expanding the ROW a little bit). This would then leave the other track in place for easier yard access:
Stations: I agree that a station at Brickbottom Junction is pretty enticing from a network simplicity perspective. I think it would lose some points for (or would require increased cost to accommodate) pedestrian access from Inner Belt Road. (Access requiring either a pedestrian overpass or a tunnel.)
I'm also a little less optimistic about fitting in platforms along the viaduct; a 230' inbound platform would stretch from the merging switch all the way to where the tracks run right up against the edge of the ROW:
If the viaduct itself ends up requiring modifications to accommodate the new platforms, then that will also drive up your costs. Again, not fatal, but raises questions for me.
Inner Belt vs East Somerville: one item to call out about the value of an East Somerville Urban Ring station is that it would eventually enable transfers from the Lowell Line via a new infill. Combined with an infill at Sullivan, that would provide all northside Regional Rail lines with a single transfer to reach Kendall Square. (Fitchburg -> Porter -> Kendall, Lowell -> East Somerville -> Kendall, Eastern Route -> Sullivan -> Kendall.) I suspect that would actually result in substantial relief to the Green + Orange Lines at North Station. An Inner Belt station offers no transfer opportunity for Lowell.
McGrath vs East Somerville: if value-engineered to the bone, McGrath station could probably go (or be saved for a subsequent phase):
(Also, once the Union -> GLMF yard lead is built, you could also institute a Sullivan/beyond <> Union/beyond OSR, if you really wanted to.)
Interlining and incrementalism: the East Somerville option provides additional flexibility in the long term, enabling interlining without requiring it. I also think that the East Somerville option is worth consideration simply on the basis of being a way to enable a Lechmere <> Sullivan service, should that ever be desirable; the likeliest use case for that service (IMO) would be as part of an Everett radial branch of the Green Line. And while yes, I am not in favor of interlining the Green radial service and the Urban Ring service, rolling stock is inherantly impermanent, and it's pretty easy to imagine a future where both the radial and circumferential services use high-floor LRT. For a large infrastructure investment like this, those kinds of long-term concerns seem worth consideration.
And yeah, this comes back to my original point: no matter how you do it, this is going to be an expensive project. I think it's worth spending that money on a robust design, and ultimately I do think the McGrath/East Somerville option has more benefits on paper (which, yes, also will drive up the cost). But also, going back to my other original point, this is definitely an area that would need proper study to say anything concrete (no pun intended), so I'm definitely trying to keep an open mind.
But I also want to respond in kind to your substantial engagement with the topic!
This is an interesting idea, and is a good example of something that ultimately will just have to be vetted for feasibility from a professional perspective.You could build a cutting like this for the circumferential service. The station would be similar to your proposed McGrath station, built in a shallow cutting and then presumably covered over to deal with all the train yard noise. View attachment 58471
To some of your specific points:
I don't think it should? There should (barely) be enough room for a 82' curve to go around the building on the end of Fitchburg St:McGrath/East Somerville: Shorter tunnel, but it needs to go under buildings
Alternatively, it might be possible (and simpler) to route both tracks to the far side of the viaduct (probably expanding the ROW a little bit). This would then leave the other track in place for easier yard access:
Stations: I agree that a station at Brickbottom Junction is pretty enticing from a network simplicity perspective. I think it would lose some points for (or would require increased cost to accommodate) pedestrian access from Inner Belt Road. (Access requiring either a pedestrian overpass or a tunnel.)
I'm also a little less optimistic about fitting in platforms along the viaduct; a 230' inbound platform would stretch from the merging switch all the way to where the tracks run right up against the edge of the ROW:
If the viaduct itself ends up requiring modifications to accommodate the new platforms, then that will also drive up your costs. Again, not fatal, but raises questions for me.
Inner Belt vs East Somerville: one item to call out about the value of an East Somerville Urban Ring station is that it would eventually enable transfers from the Lowell Line via a new infill. Combined with an infill at Sullivan, that would provide all northside Regional Rail lines with a single transfer to reach Kendall Square. (Fitchburg -> Porter -> Kendall, Lowell -> East Somerville -> Kendall, Eastern Route -> Sullivan -> Kendall.) I suspect that would actually result in substantial relief to the Green + Orange Lines at North Station. An Inner Belt station offers no transfer opportunity for Lowell.
McGrath vs East Somerville: if value-engineered to the bone, McGrath station could probably go (or be saved for a subsequent phase):
- Riders from downtown can use Medford service and transfer at East Somerville (although most of them will probably have transfered at Park already and used Red to cross to Cambridge)
- Riders from an extended Union Branch can transfer at Porter instead
- Riders from Union Square proper should have a strong local bus service to reach Kendall (less than 1.5 miles away)
(Also, once the Union -> GLMF yard lead is built, you could also institute a Sullivan/beyond <> Union/beyond OSR, if you really wanted to.)
Interlining and incrementalism: the East Somerville option provides additional flexibility in the long term, enabling interlining without requiring it. I also think that the East Somerville option is worth consideration simply on the basis of being a way to enable a Lechmere <> Sullivan service, should that ever be desirable; the likeliest use case for that service (IMO) would be as part of an Everett radial branch of the Green Line. And while yes, I am not in favor of interlining the Green radial service and the Urban Ring service, rolling stock is inherantly impermanent, and it's pretty easy to imagine a future where both the radial and circumferential services use high-floor LRT. For a large infrastructure investment like this, those kinds of long-term concerns seem worth consideration.
And yeah, this comes back to my original point: no matter how you do it, this is going to be an expensive project. I think it's worth spending that money on a robust design, and ultimately I do think the McGrath/East Somerville option has more benefits on paper (which, yes, also will drive up the cost). But also, going back to my other original point, this is definitely an area that would need proper study to say anything concrete (no pun intended), so I'm definitely trying to keep an open mind.