Unholy diagram:
Comments:
Grand Junction
The eureka moment for me was realizing that there really are two corridors within the Grand Junction: a north-south corridor between Cambridge and Sullivan, and an east-west corridor between Downtown, Cambridge, and Allston. Hence why there are two services, both vaguely S-shaped, and layered on top of each other like this: >---<
So, services from Lechmere should head to Allston, and services from Sullivan should head to Kenmore.
Central Subway capacity
Soooooo this should in theory actually require not that much increase. The Green Lines stay on the outer tracks from Boylston through Park and beyond; Boylston-GC pre-pandemic saw 30 tph, so this could probably be doable. The Emerald Lines would stay on the inner tracks, which currently see 40 tph, until the interlockings between Boylston and Park; the question then becomes whether the Inner Loop can actually handle 30 tph shoveling through it.
That is where we'd probably need to lean on some additional "relief valves", including a reconstructed Outer Loop and potentially running some services through to loop at Government Center, or rerouting more Huntington Line services out to the Seaport -- the operational reality may be a bit less tidy than the idealized version discussed here.
Kenmore
I think you can swing a small LRT/BRT surface terminal, with a modestly expanded footprint. There's a lot of surface space at Kenmore Square that is given over to automobiles; building a true intermodal transfer center seems like a good reason to reclaim some of that space. If you truly cannot, then it's not the end of the world for the GO1 to terminate at West Station instead.
Riverside and Needham
Boy howdy was this an annoying part of this exercise. My self-imposed insistence in using 10 tph base headways worked pretty well everywhere else in the map, but makes a headache here. 20 tph east of Newton Highlands is excessive, and even 10 tph to both Riverside and Needham probably is a bit more than needed... Riverside probably could suffice with 7.5 tph, and Needham could probably do 6 tph. But 7.5 and 6 don't divide nicely into 10, so obviously (he said sarcastically and self-deprecatingly) I had to come up with a "better" solution.
What I landed on was a "base" frequency of 5 tph to each spur, with a layer-on service that increases the frequency using short-turning trains terminating at a new Back Bay Green Line station and/or at Kenmore. (Assuming the new Back Bay station could be built to accommodate short-turns.) On the map, I put the layer-on service at a full-on additional 5 tph on each spur, which may be a little excessive, but again is meant to explore the "maximum" possible.
Branch Pairings
I've felt for a while that the branches out of Kenmore should terminate in downtown, likely at Park but easily also at Government Center, and possibly at North Station. For the most part, they will be street-running, with surface transit stop spacing rather than rapid transit stop spacing. That's a different kind of transit than most of the rest of the network, and I think is best treated as its own thing.
Assuming we leave radial Chelsea service to BRT, that gives us three northern trunk-branches:
- Medford and points north
- Porter and points west (e.g. Watertown, Belmont, Waltham, Weston)
- Grand Junction & Allston (West Station)
And three southern trunk-branches:
- Huntington
- Nubian
- Seaport
(Porter, Grand Junction, Huntington, and Seaport can all be supplemented by services that bypass downtown -- the northern branches being fed from Sullivan, and having Huntington and Seaport feed each other on the south.)
Huntington basically has to pair with Medford, I would argue: running Huntington to Porter would mean likely running Newton to Waltham, which basically no one will ride end-to-end; running the Huntington to Grand Junction would encounter a similar problem, plus creates asymmetry with a much shorter northern leg than southern leg. Newton - Huntington - Medford pairs similar legs together and avoids doubling back on itself.
I would pair Nubian with Grand Junction. They are similar lengths, and both would have the most grade-crossings of this "Green Line subnetwork". Moreover, pairing them would allow both legs to short-turn at Government Center: if Washington St is seeing bunching, short-turn the next inbound Nubian train and do the same with the next inbound Grand Junction to balance things out.
That leaves Porter and Seaport, which actually works pretty well -- if you draw a straight line from the Seaport to Park St, and then keep going, you eventually end up... in Watertown and Waltham. So this pairing also maximizes direct crosstown trajectories.
Washington St
I believe that Washington St needs headways better than 6 minutes. Currently the SL4 and SL5 combine to offer irregular frequencies that average just under 5 minutes.
Pre-pandemic, these frequencies were closer to 4 minutes. As I’ve written about previously, Washington’s large appetite quickly has an outsized effect on capacity in the Tremont Street Subway, given that it branches off so close to the core.
Layering on LRT and BRT services allows for increased frequencies to downtown (and OSRs to a larger variety of locations downtown while still maintaining transfer access to most other core lines). This would also open the door to “express LRT, local BRT” service pairings to speed up connectivity between Nubian and Downtown.
In this particular build-out, I sent Washington St service north to downtown, with SL3 service running from Chelsea into the Transitway, and SL1 converted to Navy Line service running via Summer St and continuing into downtown. There’s a lot of opportunity for playing around here. Washington service could instead turn east down Summer St, or branch to serve both Seaport and Downtown. Airport service could be rerouted back into the Transitway, or could instead run via I-90 into the South Station Bus Terminal itself (an underrated idea, in my opinion).
Assuming a viable and robust BRT corridor between Washington Street and South Station could be built (and I believe it could), then the need for a southeast leg of a junction between the Nubian Branch and a Marginal Rd subway becomes less acute.
In Conclusion
For the most part, this is really just meant to be a thought-exercise illustration of what a full-build could look like. I do like the relative simplicity of this schema: Green has three branches north and three branches south, Emerald has basically the same shape as today’s Green Line, Gold has two branches, Aqua has two branches, and Navy has three northern branches and three southern branches. (The point about colors being too similar is well-taken, though.)
And again, to review, these are the infrastructure enhancements that enable this:
- D-E Connector to an extended Huntington Subway to Back Bay
- Creation of a three-way junction at Bay Village
- Bay Village to South Station subway, with conversion of Transitway to enable LRT
- Conversion of Grand Junction to LRT
- Creation of a multi-way junction at Brickbottom
- Creation of a three-way junction at BU Bridge
- Creation of an LRT branch from Kenmore to Harvard
- LRT/BRT transitway along the Eastern Route in Everett and Chelsea
- “Center City Link” BRT spine through downtown
- BRT infrastructure for Washington St, Everett, and Chelsea
None of those enhancements lock you into a single service pattern in perpetuity. All increase the flexibility of this system, meaning you can make something that looks like what I’ve done in this post, or something that looks quite different.
)
. (I know, I could have taken the Orange Line, and I did in fact in the mornings, but the noxious BBY fumes weren't worth the trouble when I actually had to wait there.)