Yeah, we've discussed this before... it's definitely a big open question. This is again where the heavy metro/light metro distinction becomes pertinent -- do you need to make staging track space (and platform space, for that matter) for a single 112' T10, or for a double 225' T10? That will impact design and feasibility. (I think I did out the math one time and concluded that it could still be done even for doubles, but need to check that...)Surface? I suppose a Gold LRT surface terminal solves the problem of B's lack of access to the Kenmore loop, but if there's not room for some tail/pocket tracks there, that seems like it'd do...unpleasant...things to Gold's reliability (...like after Red Sox games...) unless you nuked half the cross roads for a reservation to the square. Not a reason to outright reject the idea, but it'd be one of the things I'd stick a pin in to scrutinize in any study as a potential danger spot.
There are a few potential mitigations. First, there is the extant pocket track at Blandford St, which would still be accessible. Second, in a world where a subway is built under Comm Ave, the space currently occupied by the portal and descending tracks could be covered and reallocated for a pocket track or two (depending on how much of the pavement we're willing to reclaim). Third, specifically for the Red Sox game example, an alternate service pattern that temporarily reroutes services into the subway could be established for high-volume crowding periods. (A lot of ways this could be played with, but since it will usually be outside of peak hours, there would be more flexibility.)
Someone (unfortunately, can't remember whom, it may have been @davem) pointed out that it could be possible to build a connection from the BU Bridge under the Mass Pike to hook into the subway under Beacon St, and thus access the Kenmore loop. That is more capital intensive, but could be an interesting alternative.
And finally... in an early-build version of Grand Junction LRT, it may be feasible for a few years to just run Grand Junction trains through Kenmore beyond to Copley & Park St. This doesn't have to be solved on Day 1.
Yes, Back Bay would need some sort of short-turn provision to make that service pattern work. I am not 100% certain how that would be done, so I designed this build-out so that the Back Bay short-turn would not be vital.Would a new Back Bay need any provision for short-turns? Wouldn't it be possible to configure Bay Village to allow cars coming from BBY to turn back there? (Even as a flat junction it wouldn't be the end of the world for an extra-helping service pattern.) That'd at least save on having to design-build an additional turnback, and in a more-constrained environment to boot.
For example, those short-turns could run to the Kenmore Loop instead (which could be a useful service pattern off-peak as well), and replace the Kenmore-Hyde Square branch (which is a fun idea but hardly vital).
Alternatively, those Back Bay short-turns could be rerouted to Seaport; in this build-out, the Transitway is full (ish) with Green to Park, Aqua to Huntington, and SL3 to Chelsea. But, SL3 can be rerouted to the service, freeing up capacity; and the Aqua to Boston College could instead be rerouted down the Highland Branch. So, Back Bay short-turns could be useful -- and I think would be worth looking at when designing that subway -- but aren't make or break.
Depending on how the Bay Village junction is constructed, short-turns could be done there; in @davem's original proposal, I believe the loopwork would enable that, but in my more recent proposal it would not be a viable turnback point. Given the complexity of the build at Bay Village, I'd rather offload the short-turn provision elsewhere.
In an ideal world, an LRT Back Bay station would be track-plat-track-plat-track: that would enable short-turn service, and also could be used for traffic regulation heading into Bay Village. But this is definitely not required if the footprint is constrained. Alternatively, I'm reasonably confident that space could be found for a pocket track somewhere between Back Bay and Bay Village.
(Finally... there will be about 400 feet of inactive double-track left connecting the Back Bay Subway with the Boylston Street Subway at Copley Jct. I'm not sure how useful this will be for short-turning at Back Bay, but it gives us an additional tool to play with.)
This is a valid critique. Ironically, Copley-North Station is most easily replaced by Back Bay-North Station via Orange/new Green. Hynes-Haymarket/North Station becomes a 2-seat journey, or a 1-seat-plus-walk, as do journeys from Arlington, and most journeys from Kenmore via Blue. (NSRL service from Lansdowne partially mitigates, but not fully.)As a transit nerd, I agree with you on this. As someone who spent the entirety of my high school career commuting from Copley to North Station on the Green Line, I'm extremely happy you weren't designing surface patterns at that time . (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.)
This is another place where my idealized Emerald/Green division of labor potentially should be modified to be more nuanced. Of the branches out of Kenmore, I'd feel most excited about running the branch from Harvard/West Station on through past Park St, mostly because I believe that branch's reliability will be the highest, between being a modern new-build and likely have little street-running and fewer stops. I'd likely run it to North Station.
How to "pay" for those extra trains? Probably the easiest way would be to "steal" 1-2 tph from each Green Line branch and have them short-turn at Park St, and run 5-6 tph of the Harvard Branch's 10tph super-extended to North Station. (This of course would make the map look significantly more complicated, but we can't have everything in life!)
Yes, you are totally right. I would only propose a Navy Line overlay (and yes, the rebranding is not accidental) when and if a robust LRT branch is in place/under construction. (I mean, I do think that the consolidated SL4/SL5 should be extended from South Station through downtown anyway, so in some ways this would just be a continuation of that service.) And we would need to have a strong success story (elsewhere) with true BRT to point to.Don't send anything BRT from Nubian to downtown, don't even whisper that you might send it anywhere that LRT could conceivably go. You'd just be asking for trouble. "Sorry, you have to take a bus to South Station/Seaport or reverse-transfer at Park? Boylston? because we don't want the hassle of building another leg of the Bay Village interchange at Marginal" is going to raise eleven different kinds of hell with the people who had the Elevated stolen and replaced with a crappy silver bus. I don't disagree with you with respect to the better flexibility of BRT, and I share the concern about the fact that Nubian's branching so close in magnifies its effect on Tremont capacity: I just think it's worth considering that accepting that outsize impact and potentially some service-pattern compromises might be the cost of business in avoiding some potentially-very-nasty political problems. We've all seen specific constituencies kill projects before because they weren't satisfied, let's tread carefully lest we lose more.
(Most of that's just a messaging issue, or at least manageable as one. BRT as a legitimate add-on to places otherwise unreachable from Nubian, fine. So much of a whiff of it as the way out of a harder LRT option, that's gonna be a problem. Even if the actual plan is good and realistic, its sales pitch has to be modified to account for a repeatedly-screwed-over neighborhood's understandable wariness.)
But I do think it's ultimately a messaging problem, and there are ways to frame it positively. In addition to an increase in OSRs, having dual layers of service would allow the Green Line to more properly replace the EL -- not as a local surface route, but as an express connection between Nubian and downtown.
And I should say -- Nubian-South Station BRT reduces the need for LRT infrastructure to support the same, but it doesn't necessarily eliminate it. And we can look at it systemically as well: redirecting some Nubian cars away from the Tremont Street Subway and instead to a Red Line connection at South Station would free up slots in the Central Subway, usable for any number of things discussed here. I am unconvinced that the cost-benefit calculation supports that particular solution, but it's something that can contribute overall.
Thanks again for the kind words and thoughtful feedback! I'm glad others find this as enjoyable as I do.