I spent a long time on New Year’s Eve playing around with a spreadsheet and thinking about the Bay Village Loop proposal. I’ve long been both enchanted and troubled by the idea, but really struggled to articulate my objections. I think I’ve managed to narrow it down at this point. This post was originally
much longer, but I think I can make the point more succinctly. (Maybe.)
Basically, my objection comes down to, “The Bay Village Loop solves the wrong problems,” which may be a little harsh – it might be fairer to say “The Bay Village Loop solves important problems, but still leaves key issues unresolved, and thus undercuts its own benefits.”
Background
The Big Idea™ of the Bay Village Loop, like its proposed counterparts at Brickbottom and BU Bridge (and sometimes Brookline Village and/or Chestnut Hill Ave), is to reimagine the junction from a diverging Y into a multidirectional “roundabout”-like junction that allows trains to travel “branch to branch” without taking up capacity on the main trunk; in the case of the Bay Village Loop, the Central Subway north of Boylston is the main trunk.
More practically, the Bay Village Loop offers a sort of “meet in the middle” compromise that would simultaneously solve the problems of how to connect the Central Subway to a Huntington Ave Subway (via Back Bay), a LRT branch to Nubian, an LRT connection to the Silver Line Transitway, and a transfer to the Orange Line at Tufts Medical Center.
Those first two in particular are vital: an LRT line to Nubian has been the clear and obvious replacement for the El for decades, and a Huntington-Back Bay subway is critical for eliminating the bottleneck at Copley’s flat junction, and for the consolidation of the E and D Lines (necessary to open capacity for other expansions). Both of these
probably should use the abandoned Tremont Street Subway, which already has a diverging flying junction to enable two branches.
These are serious needs, and the Bay Village Loop addresses them extremely elegantly. But it fails to address a more fundamental problem further north -- one that I see as threatening to the entire idea of a super-expanded Green Line.
Problem
Boylston to Park has a capacity of 40 trains per hour. (North of Park is a separate discussion, which we don’t need to deal with for this question.) Right now, those 40 trains are divided roughly evenly among four branches, to make for 6 minute peak headways (in theory, at least).
The definition of “rapid transit” is always situation-dependent, but in Boston, I would say that you need peak headways of 12 minutes or better (5 tph) to qualify as “rapid transit.” Certainly 15 minute headways would be outside the realm of “rapid transit”.
Now, on the face of it, this isn’t a problem – 40 trains per hour divided by 5 trains per hour per branch gives you 8 branches, which is roughly in the ballpark of what we usually talk about with the southern half of the LRT network:
- Harvard
- Boston College
- Cleveland Circle
- Riverside
- Needham
- Nubian
plus maybe
- Oak Square
- Brookline Village (if all Highland Service rerouted to Huntington)
- Seaport
But. That’s 12-minute headways as a
baseline. That’s not going to swing it on the branch to Nubian, where you definitely will need more than 5 trains per hour. (See discussion in addendum in following post.)
Robbing Peter to pay Paul
And this is where we hit my problem. As soon as you siphon a larger fraction of those 40 tph onto one branch, the others move, as a mathematical reality, out of the realm of rapid transit headways. If we assume 8 branches and 10 tph to Nubian, that alone forces every other branch to 14-minute peak headways.
And unfortunately, Nubian isn’t the only branch that would need an extra helping of those 40 tph.
The appeal of the multi-direction junction concept is to be able to bypass (literally and figuratively) those capacity limits by running extra trains on the branches that avoid the trunk. For example, the Bay Village Loop would allow extra trains on the Highland Branch to be routed instead over to the Seaport.
But there are at least
three branches that would not be able to be addressed this way: Nubian, Boston College, and Harvard. Boston College and Harvard have no access to the Kenmore Loop; Harvard can be supplemented by service via the Grand Junction, but the Harvard-Kenmore service is going to be vital, particularly as Kenmore will become the transfer point for southside BRT Urban Ring. Harvard and Boston College (to say nothing of Oak Square) has no way to receive supplemental service via Kenmore – it all has to come from that pipe at Park Street.
For the sake of argument, let’s imagine that each of those three branches got 6 tph for 10-min headways. (I think this is too low anyway, but we’ll stay with it for the sake of argument.) That accounts for 18 of those 40 tph, leaving 22 tph to be divided up among Cleveland Circle, Brookline Village/Riverside/Needham (pick two of the three), and any other branches you try to add on (Oak Sq, South Huntington, Seaport, Grand Junction).
Let’s say you go with a “bare minimum” approach of six branches, each at 10-min headways (branches in italics have no supplement – strictly 10-min headways):
- A) Harvard via Boston University
- B) Boston College via Boston University
- C) Cleveland Circle via Kenmore
- D) Riverside via Kenmore
- E) Needham via Bay Village
- F) Nubian via Bay Village
At that point, you’re maxed out. You have 4 extra tph lying around to sprinkle on to a few branches – maybe you can lower those 10-min headways to 8-min – but that’s it.
If you want to add more branches, or improve frequencies on any particular branch, you will have to cut frequencies on other branches and move them out of rapid transit territory.
And remember: the bypass trick won’t work on branches to Harvard, Oak Square, Commonwealth, Nubian, or Grand Junction via Kenmore. So you’re again forced to choose between two bad options: prioritize those and require more forced transfers on other branches; or live with 12-15 minute peak headways.
Whither The Seaport?
And notice – through all of this, I haven’t even mentioned sending trains to the Seaport. Feeding the Seaport from the “Kenmore faucet” is workable, but feeding the Seaport from the “Park Street faucet” simply isn’t, unless you’re willing to sacrifice other branches.
Now, one positive of the Bay Village loop is that it would enable trains to run directly from Huntington to the Seaport – let’s call them the “Teal Line”, running alongside “Green Line” trains to Park Street.
There are many benefits. For one, it obviates the need for a “Track 61 shuttle”; it also sets you up for a rail replacement for Massport’s Logan Express shuttle bus service. It also provides a one-seat ride from South Station to Longwood – valuable for Fairmount and Old Colony riders. And it would increase frequencies within the Huntington Subway and optionally on any branches that feed into it.
However, there are substantial drawbacks to a Teal Line. Probably the most obvious is the lack of Blue Line transfer – and it’s a very large lack. Even with a Blue extension to Kenmore, it would require a connecting journey of three stops to reach Kenmore, Charles/MGH, Government Center or State from any of the possible Teal Line stations. Given the above problems with the “Park Street faucet,” you’re likely to see a minority of Green trains running to Park and Government Center from Huntington, so many trips will require that three-seat journey.
Likewise, riders on the Kenmore branches will also have a three-seat journey to the Seaport – whether via Kenmore-Brookline Village, Boylston-Bay Village, or Park-South Station (or a walk between Copley and Back Bay). For comparison, the current MBTA network requires three-seat journeys only for Blue-Red transfers and for Blue-Green transfers involving services that terminate at Park. Blue-to-Red and GLX and Green Line Transformation will eliminate virtually all of those, but the Bay Village loop will add more – and they will be significantly worse than the current one-stop jogs on the Green or Orange.
Revisiting the Essex Subway in the above light
Solving the “Park Street faucet” problem is – to me – the primary argument in favor of an Essex Street subway. Combined with a restoration of the abandoned Tremont Tunnels (and yes, potentially a Bay Village station to sew together Nubian and Huntington branches), an Essex Street subway would create an entirely new LRT core subway, enabling Downtown/Financial District to now be served by potentially 80 LRT trains per hour – which gives you more than enough capacity to do everything you could dream of.
An example of what this dual-subway network might look like:
To be clear – there are major challenges and obstacles to an Essex Subway, and it may be impossible. A Bay Village loop might be the best we can get. But solving the “Park Street faucet” problem is, to me, the fundamental question that underlies every proposed LRT expansion. An Essex Subway would solve that problem; the Bay Village loop would not.
See addenda in following post