[Sorry, got pulled away.]
F-Line -- I've been going backward through the backlog of posts, and I see now that some of my responses don't address your points about the Essex subway -- that's my bad, it wasn't my intention to ignore you. My point with bringing up the Essex subway isn't to advocate for that alignment per se, but to call attention to the idea of a new east-west outlet for Kenmore-originating trains, especially from Comm Ave where they can't be supplemented with short-turns. I'll happily concede that the Essex alignment is a firm no-go, but I'd raise that an alternative should be considered.
Re "
I'm not sure I agree on the 'Park St. can't support it' basis":
First off, ironically, this entire concept was kicked off
by the exchange you and I had back in December about Central Subway capacity. Rereading it now, I do see where some of the misunderstanding arose, but I do have to laugh.
I'm not indifferent to the possibility that the 40tph ceiling could be raised, but I still think it gets tight faster than you would expect. Like I said, I've spent a looooooooong time experimenting with these numbers in a spreadsheet, but I'll try to go through a brief illustrative example.
Comm Ave pre-covid gets a train every 6 minutes during rush hour, for 10 tph. 92% of ridership comes from stops east of Chestnut Hill Ave. (
@George_Apley this is why Chestnut Hill Ave helps a little, but not much.) 72% of ridership comes from BU West through Chiswick Road -- i.e. the stretch that would be uniquely served if a branch to Harvard and/or Grand Junction were layered in east of the BU Bridge. For the sake of argument, let's say you reduce those 10 tph to 8 tph, under the theory that it only needs 80% of the capacity if you have that supplemental service east of BU Bridge. I don't think you can justify dropping the service any lower than that. And there is nowhere else to feed that line, other than Park St.
Now let's talk about that branch between Harvard and Kenmore, which also can only be fed by Park St. The 66 pre-covid was scheduled for 9-min AM peak headways. Given the hopes for development in that area, plus the critical nodes this service would uniquely connect (Harvard and Kenmore), I think you at
least need to match that. We'll call that another 7 tph.
Now let's review Nubian. I
previously laid out my reasoning to argue that this branch needs 10 tph directly to Park. Maybe we could swing 9.
Just with these three, we are already eating up 8 + 7 + 9 = 24 trains into Park Street.
The peak headway standard on the T right now is 6 minutes or better. The exception is the Red Line branches, where it drops to about 8.5 minutes, or 7 tph. So let's use 7 tph as our average frequency for any other additional branches. (I know, I know, not all of the branches need to run to Park Street... I can go through them one by one, but enough of them would still need to that it's going to be a problem either way.)
Most of our proposals range from somewhere between 3 and 7 additional branches. At the extreme low end of that (wherein E and D are combined, and Riverside and Needham each get half frequencies, you keep Beacon through-running, and you add a branch to the Seaport), you'll already breaking the ceiling at 45 tph. If we go middle of the road and say 5 additional branches (for Harvard, Grand Junction, Comm Ave, Beacon, Riverside via Huntington, Needham via Fenway, Nubian, Seaport), and you're already at 56 tph -- i.e. almost half again what the station currently does.
(And, not for nothing, but with hopefully longer trains than what we currently have now.)
Maybe I'm just not fully appreciating how majorly the reduced dwell times can increase throughput. But in the scenario I just laid out, the majority of Comm Ave riders (comprising nearly a quarter of existing Green Line surface ridership)
still see degraded frequencies, and the Park St-South Station jog that is intended to reduce transfers gets served by -- at most -- one northside branch's worth of trains.
Am I saying that we
need to plan to send trains to all 8 of those destinations? No, of course not. What I'm saying is that the
bare minimum of what we talk about here with a Reconfig'd Green Line
already requires that ceiling to be raised, and any modest expansion of the network -- absent some sort of Kenmore-South Station connection -- would require capacity increases of 30% or more. This is what I mean when I say this becomes a real challenge very quickly, regardless of whatever the future holds, and regardless of whatever magic we can work by diverting trains out of the Central Subway.
I'm not saying it's impossible that "fewer transfers at Park" and "more Blue transfers at Kenmore" will do the trick, but I'm skeptical.
I'm not seeing where there's a looming crisis in all that causing ANY hesitation whatsoever in building the flexi junctions.
Ah, this is a good point: I 100% do not think that any of what I've laid out should cause any hesitation or delay in building the flexi junctions. (Nice term -- beats multi direction junction.) With the exception of the connection between Bay Village and South Station -- which is not integral to that build -- I think every single flexi junction we discuss here should barrel ahead full-speed. My point isn't that they are wrong to build -- my point is that I think they're insufficient.
And even if there were, absolutely no one is putting a gun to dispatch's heads to saturate each and every flexi junction with service levels to their outermost capacity limits. If on further review the comfiest ceiling is a little lower than breakneck-max...so be it. Maybe your South Huntington service to Hyde Sq. or Forest Hills rides the Copley Jct. alt route to Park Loop exactly like the old days while trunk Huntington service takes the South End thru-and-thru...neither interacting with each other on any track past the new level split abutting Prudential. For the ROI you're still exponentially expanding service levels and service routing flex as a Very Good Thing™, so glass-half-empty concessions like ^^getting extra-creative with track sharing keep-away^^ are part/parcel an outflow of the extra flex. We aren't hurling ourselves headlong into new-creation walls by embarking on this; we're actively avoiding such bottlenecks, even when actual traffic modeling games out on the more-pessimistic side than our best crayon-draw hopes.
This is fair, but, again, even in a modest 7-branch build (Harvard, Comm Ave, Beacon, Riverside via Huntington, Needham via Kenmore, Nubian, Seaport), each of those corridors pretty vitally needs thru-running to Park St/GC -- in some cases because you need a connection to Blue and in some cases because you can
only run those trains to Park (and ironically, those groups are nearly completely distinct). This isn't "all trains to everywhere", this is "basic fundamental service" in almost all cases. And, as I've laid out, the art of the short-turn only helps us in the places where we don't need it -- Beacon (low ridership), Brookline Village (short stretch), Huntington (already doubled if not tripled with D, E and Needham) -- but physically cannot help us where we do need it -- Harvard, Comm Ave (lack of Kenmore loop), Nubian (too close to downtown).
Is there a perfect solution? Probably not, and I'm definitely happy to focus on making sure that the perfect doesn't become the enemy of the good here. But I don't think this is a problem of obsessive completism.
Continued below.