from https://archboston.com/community/threads/crazy-transit-pitches.3664/page-261#post-448601
There are three version of this proposal.
One uses an elevated:
The others use a tunnel, either under Fitchburg St or within the bounds of MBTA property at Brickbottom Junction itself.
Lots of detail below.
Contents
Background
Prompted in part by the headache I described in the Green Line Reconfiguration thread, I’m spitballing a bit here.
When we’ve talked about putting LRT on the Grand Junction (the “Bronze Line” in this post), we usually have figured on connecting it to Sullivan via the Green Line Maintenance Facility (GLMF). This makes sense in a lot of ways, because the yard itself stretches close to halfway from Brickbottom Junction to Sullivan, so the thing’s practically already half built.
However, as I outlined in the Green Line Reconfiguration thread, that alignment creates headaches when trying to plot a northbound course from Cambridge through Brickbottom Junction to the GLMF. It’s somewhat feasible going southbound, but much harder going northbound, requiring either a massive viaduct crossing over the commuter rail maintenance facility, or a tunnel cutting through the heart of the junction.
What does that headache get you? To overstate the point somewhat, the GLMF alignment gets you a one-seat ride from Sullivan to Cambridgeport that manages to miss direct transfers with all three transit lines it crosses (Medford Branch, Union Branch, Red Line). The missed transfer to Red isn’t the end of the world, in part because Kendall is probably more of a destination for this service rather than a transfer node.
But missing the Green Line transfers stings. As close as I can figure, you maybe – maybe – can slot a Medford-Bronze transfer near the southwest corner of the GLMF yard, but that would involve shoving a one or possibly two platforms into the spaghetti there (possibly needing to put one of the platforms underground). Such a station would also have almost no walkshed, reducing ROI further on an already costly design.
The primary way we’ve figured on mitigating the missed transfer is by running a Central Subway <> Grand Junction Green Line service via Lechmere. This is workable, but inelegant. North Station <> Kendall is a useful OSR provided by this service, but by definition almost everything else would be faster via a Red Line transfer. And while northside Green Line capacity isn’t as constrained as southside, a Grand Junction branch still means that a hookaround service is taking capacity away from other more efficient radial services.
All of which is to say, a GLMF alignment for the Bronze Line isn’t as simple as it first appears, and also has significant drawbacks.
Elevated
Let’s take a step back and reset: what would the “ideal” route for a northeast Urban Ring be? Obviously you want to hit Sullivan, as well as Kendall. You also want to provide transfers to both branches of the Green Line. Lechmere would be one potential transfer point, but is relatively close to downtown – the other Urban Ring nodes tend to sit closer to 2-3 miles from downtown. The next transfer opportunities would then be at East Somerville and Union Square.
Could we do a Sullivan <> Union <> Kendall LRT route? Sullivan <> Union is at least a straight shot down Washington St, but going Union <> Kendall is much hairier.
But…
Let’s suppose for a minute that we add an infill on the Union Branch between McGrath Highway and Medford St. This would provide a Union-Bronze transfer point that is easier to access from Kendall (Grand Junction) than a transfer at Union would be. (Not to say it would be easy, just easier.) I’m gonna call this station “McGrath” for the moment.
So then we need to find a path that goes Sullivan <> East Somerville <> McGrath <> Kendall. And that… that might be doable.
Sullivan <> East Somerville is sorta straightforward. Washington St itself would require a subway or el, but New Washington St just to the south already has a freight rail track running along it, with potentially as few as two grade crossings and enough space between buildings to create a dedicated two-track surface ROW.
From the other direction, Kendall to McGrath Station should be relatively straightforward: tracks rise up from the Grand Junction ROW on to a viaduct that crosses over the Union Branch, putting an elevated platform perpendicular on the northern side of the Green Line above Somerville Ave Extension.
Getting from McGrath Station to East Somerville is hairier, but… well, there already is an elevated structure traversing most of that distance: McGrath Highway itself. If McGrath can be put on a road diet and dropped to surface level, and the elevated decking turned over to LRT, then you can have an el that isn’t any closer to houses/business than the current state.
Then you need to get between the McGrath Highway viaduct and the surface ROW on New Washington. This would require about 1000 feet of a greenfield elevated, either over Washington St proper, or over the adjacent lots (presumably purchased by the Commonwealth), with an elevated station above/above-and-north-of the current East Somerville station.
And… there you go. A Kendall <> Sullivan LRT line that provides transfers to both branches of the Green Line, and which serves actual neighborhoods instead of a no-man’s-land of maintenance facilities.
This alignment is about 1.3 miles, as opposed to the GLMF alignment which is about 1.1 miles. However, the East Somerville alignment would serve more riders, provide better transfers, avoid costly modifications to Brickbottom Junction, avoid operational conflicts with the Green Line, and would do so primarily by using rights-of-way that are already devoted to transportation.
The problems I see:
- Putting McGrath Hwy on a road diet is hardly an original idea but obviously it’s also not a straightforward one, given that we’ve been talking about it for over 10 years
- And, it should be noted, replacing one elevated structure with another isn’t, you know, great
- Grade crossings on New Washington
- Not necessarily a huge problem now, but if/when that area is redeveloped that may change
- Imposing elevated near East Somerville
- See above; if McGrath finally is taken down, blocking out the sky again with another elevated structure is kinda a bummer
- On the other hand, depending on how the el and station are designed, it’s possible that this could provide station access to East Somerville significantly more directly than the current station’s placement
- Harder to build in stages – harder to use a Lechmere <> Grand Junction branch as a “minimum viable product” as Phase 1
- I think this is still doable, if you just plan to continue running a Lechmere <> Grand Junction branch and drop McGrath Station from the plans; you lose the Bronze <> Union transfer, but gain a Green <> Bronze transfer somewhere along the Grand Junction branch to the south
Fitchburg St Tunnel
This alignment uses a short tunnel under Fitchburg St to connect the Grand Junction line with the Medford Branch’s yard leads, from which a flying junction could then grab the New Washington St alignment described above.
The tangent part of the tunnel would only need to be 650′ (assuming you do an open cut southwest of McGrath Hwy to drop to -1), followed by a pair of ~250′ tunnels to connect to the yard leads to the north (with open cut descents), and about ~250′ of tunneling to the south to connect to the yard. I eyeball that at 650′ of double track, plus cumulatively about 1000′ of single tracks.
For a SWAG at costs, I’ll use my metric of “$1B per [double track] mile”, and arbitrarily assume that a single track tunnel is… I dunno, 75% the cost of a double-track tunnel? 650 feet = .12 miles, and 1000 feet = .19 miles, so
$1.00B x 0.12 miles = $120.0M
+ $0.75B x 0.19 miles = $142.5M
= $262.5M
(Comparing this to one of the elevated alts, eg via McGrath & Poplar, that’s about 1760 feet, about 30% of a mile, and assuming costs similar to subways, that would be $300M.)
The two things that terrify me about this version of the silly idea:
- The silliness that would be needed to maintain the yard connections
- Tunneling under Squires Bridge, particularly trying to thread a needle between the support pillars — I think there’s a path but…
Tunnel Within Brickbottom Junction
I went back to my design for a Kendall <> GLMF <> Sullivan alignment, and realized it may be possible to harmonize it with the concept for a Kendall <> East Somerville <> Sullivan alignment:
The western half of the junction remains as I proposed in February. The eastern half uses a similar topology, but a different alignment. For the westbound track, instead of using the GLMF -> Union yard lead, a new (tightly squeezed but I think still 82′) curve connects to the Medford yard leads. (See detail below.) The eastbound track still uses a tunnel, but instead curves around to also connect to the general vicinity of the Medford yard leads.
The key benefit of this harmonized design is that it enables a future via-East Somerville build, while still enabling initial partial builds to enable, e.g. Lechmere <> Grand Junction service as a Phase 1.
Is this tunnel any better than my previous design’s? Maybe. Certainly it’s less busy aboveground for much of it, so that could make it easier to build.
The hook-in with the yard leads would require non-trivial modification. By my reckoning, an 82′ curve that clears the property line would, unfortunately, align with the “wrong” track in the yard leads. We could tighten the curve somewhat, or try to purchase a small corner of the parcel in order to shift the entire curve to the west.
Here, I’ve proposed a slightly inelegant design where the revenue track switches from the “southbound” lead over to the northbound lead very briefly before doing a flat crossing again over the southbound lead as trains continue through the curve.
This unfortunately shifts the tunnel further northeast, and may require cutting under the viaduct, as I’ve tried to vaguely suggest here.
That all being said, this is a relatively large parcel, all owned by the T, so I think there’s room to play around here to find something that works.
Last but not least, this design is a little less friendly to a “McGrath” station, but it still is potentially doable — put the southbound Bronze Line platform in the subway, and the northbound Bronze Line platform at ground level. The parcel is enough that the track could be straightened for a 250′ tangent and still hook in to the necessary curves. (Sketch, not to scale, below.)
As discussed previously, ideally a second Bronze Line track could be added north of the westbound Union track to avoid the intermingling. But, again, that could be built in phases potentially. Likewise, a future build could expand the northbound tunnel to add a second track and abandon the cross-under at McGrath altogether to enable fully isolated running. But, like I said, that’s left open to the future.