Great thoughts from everyone, appreciated as always. Let me try to tackle the various points raised...
1. Nubian subway: Which street to go under? Washington, Harrison, or Albany?
This question has downstream implications affecting demand
for a surface LRT/BRT route on Washington, even though Nubian subway and Washington service have different roles (the former primarily serving Nubian and possibly BUMC riders, the latter serving South End riders).
- A Nubian subway via Washington or Harrison will likely reduce the demand for local Washington service down to that of a regular bus route, due to significant walkshed overlaps.
- If Nubian subway is routed via Albany instead, Washington service may still merit LRT, as an Albany subway has no hope of serving South End.
- Albany subway's main advantage is lower cost, but how much lower is a question.
I agree that this is the #1 question. That said, I think it's possibly moot: I need to look at the SL numbers (and the Ruggles numbers, for that matter), but we know the number of boardings at Nubian is Very High™, and we know at least some fraction of that Nubian boardings ride all the way to downtown. I think it's possible that regardless
of the subway alignment, diverting Nubian <> Downtown riders away from the surface route will drop demand on the surface route sufficiently to make BRT a viable solution (though obviously there are still benefits for LRT in that scenario). But, need to look at the numbers.
The other thing to point out is that if an Albany subway actually runs on the I-93 alignment, it may be possible to construct a dedicated ROW at surface-level with only a handful of grade crossings; as far as I can tell, it's all parking lots under the highway on the northern half
, and the southern half has a number of small roads between the highway and the hospital/research buildings which could potentially be reclaimed for a dedicated ROW that runs all the way to Mass Ave & Melnea Cass. (At which point, yes, we probably need to build a short subway in order to achieve the reliability we want. Still, .75 miles (Mass <> Nubian) + .3 miles (Herald plus a portal under 93) = 1.05 miles, which is better than ~1.6 miles (via Washington).
3. If LRT: Tremont St subway, or some surface route?
As Riverside discussed above. This question is obviously irrelevant for BRT.
Neither here nor there but as @Charlie_mta
pointed out, strictly speaking we could
talk about BRT tunnels through downtown as well. And I mean, maybe we pull a Seattle, and build a bus tunnel under Congress St for these "Navy Line services" (SL4/5, T7, T111, etc), with an eye to eventually converting those BRT routes to light rail at a later date.
Does it make a difference if the service doesn't reach GC? I don't love the idea of any specific route not hitting all the transfers (though the B did it for most of the past decade), but assuming sufficient overall throughput of cars between Park and GC, is there room for more frequencies Park-south if they're turning at Park and not hitting that bottleneck tunnel? Curious if that affects the calculations at all.
I may have gotten confused. You're right with respect to the Tremont branch capacity, I think I was assuming the 30tph figure quoted was split between Tremont and Boylston-Kenmore, which was evidently a misreading. Did I miss where the Kenmore service has gone in this discussion?
I think Riverside is assuming 30 tph on Tremont St subway alone, i.e. Huntington and Nubian (subway), as shown here:
The implicit assumption is likely that all Kenmore trains terminate at Park.
Yes, sorry for the lack of clarity here -- I am indeed assuming that all Kenmore trains terminate at Park on the Inner Loop, which of course creates its own set of issues, but I figure that through-running to GC is a best
case scenario, so want to compare against that.
There's already a bus tunnel running right below the surface there. I would build a portal just to the north (and the south) and run the LRT line through the existing bus tunnel under Dewey Square.
You know, I was opening my mouth (proverbially) to object when I paused to think, and then reconsidered. A few points:
- The Transitway tunnel is deep enough down that I don't think it would be feasible to do a quick "dip" in order to cross Summer St
- Immediately below street level is the station lobby... mayyyyyybe you could completely rebuild the Atlantic & Summer intersection to include a transit-only underpass that uses that space but that seems unlikely
- But, your point made me look back again at the alignments between Tufts Medical Center and South Station
- I previously rejected the idea of sending a Washington streetcar into the Seaport subway because I was looking at an insertion point just east of Hudson & Harrison, which precludes a transfer to Orange
- But. If you instead run at street level up Washington St, with a transfer at Tufts Medical Center, and then turn east onto Kneeland, and utilize Kneeland's extra width to add a portal between Washington St and Harrison Ave, you could run a short subway under Kneeland to join a Back Bay-South Station subway around Kneeland & Albany
- The junction might be unpleasant and may need to be a flat junction; the math of the network means that Back Bay <> South Station LRT will be as frequent as Downtown <> Nubian (via subway) LRT, which will be between 10 and 15 tph in all likelihood (4 to 6 min); let's assume that Washington surface LRT will be no more than 10 tph; 10 tph merging to 10 tph is what the C and D lines did pre-pandemic, so maybe it would be doable?
- With your Orange Line connection assured, Washington streetcars could then continue to the Seaport
- You could also look to see if there's anywhere on Atlantic Ave north of South Station where you could add another portal, and have Washington streetcars split off from the Transitway and surface there to continue north. A quick eyeball doesn't suggest any great options for this, though
In a world where we are so lucky as to have both
a subway to Nubian and
leftover LRT tracks at surface level on Washington, I think I'd be okay sending Washington streetcars to the Seaport as long as there was a reasonable transfer available to the Orange Line.
If a portal on Kneeland really could be an option, then I think that would provide the needed flexibility to ensure that, even if Washington surface LRT is built first, it could still eventually be supplemented by a subway to Nubian -- trading a OSR to Park St/GC for one to South Station and the Seaport, which I think could be sellable.
EDIT: (because why wouldn't
I have more to say?) Overall though, my preference at this point is to build an LRT subway/dedicated ROW via the 93 alignment to provide frequent and fast express service to Nubian, and integrate a revived T49 into a "Navy Line" network incorporating the T7, the T111, possibly service to Logan, and possibly service to Everett. I know BRT on Washington St has a weighty, baggaged history, but I feel pretty strongly at this point the surface LRT doesn't meet the criterion of "equal or better" replacement for the El anyway.