In general, my rule of thumb when thinking about circumferential designs is that no journey will go more than 1/3rd of the way around. Once you go more than about 1/3rd of the way around a (perfect/idealized) circle, you are traveling a further distance than it would be to go directly to the center of the circle and then back out. So, in general the farthest I see a rider taking a circumferential service is about 1/3rd of the way around the circle. (More elaboration here.)
But… the Urban Ring corridor is not a perfect circle.
Here is a perfect circle, centered on Park St, that roughly hits key Urban Ring nodes, including Airport, Sullivan, and Nubian.
But that circle misses certain key nodes: it runs wide of Kendall, runs short of reaching Longwood, misses almost all of Southie, to say nothing of the Seaport, and literally does not even make it past the Mystic, leaving Chelsea untouched.
To stretch that circle to reach Chelsea, Sullivan, and Longwood, we get an oval (though, annoyingly, this particular oval I’ve drawn hits most of the nodes pretty well, but still only grazes LMA):
The actual Urban Ring corridor distorts this even further, with bulges out to the Logan Terminals, Everett, and probably Andrew, and tighter hewing inward to Kendall:
One of the consequences of this distortion is that not all segments of the Urban Ring Corridor are created equal. As I’ve mentioned, the Sullivan <> Airport segment has to diverge so much from the “perfect circle” that it (likely) would be just as fast to continue the Orange + Blue transfer at State.
On the other hand, the physical alignment of Sullivan <> Kendall <> LMA runs in nearly a straight line:
Meaning that a circumferential service from Sullivan/East Somerville to Longwood would potentially be competitive with the OSR radial journey via the Green Line.
The Chelsea segment underperforms for circumferential journeys, while the Kendall segment overperforms.
So, some specific routes:
| Terminus | via | Terminus | optional extension to |
|---|---|---|---|
| South Station | Seaport | Chelsea | Everett |
| Logan Terminals | Chelsea | Sullivan | Malden (branch) |
| Kendall | Sullivan | Chelsea | Downtown Chelsea or Revere |
| Sullivan | Kendall | Kenmore | LMA |
| Kendall | LMA | Ruggles | Nubian |
| Kenmore | LMA | Nubian | Dorchester |
| LMA | Nubian | JFK/UMass | |
| Nubian/Ruggles | [something] | Seaport | Logan Terminals |
| Revere | Tobin Bridge | Kendall | |
| Harvard | Allston | LMA |
A few notes:
- Red (e.g. JFK/UMass) <-> Green (e.g. Kenmore)
- This quadrant is always such a headache. Kenmore <> JFK/UMass seems a little long, so I might split into Kenmore <> Nubian (see note) and LMA <> JFK/UMass, but I think there are a lot of moving pieces here
- Blue (Airport) <-> Orange (e.g. Ruggles)
- I think this one is tricky. I’ve been sorely tempted by a limited stop Nubian <> Logan service designed for a maximally speedy connection to Logan and to the Seaport
- But just in terms of distance, Washington St LRT + Blue is actually a little shorter between Nubian and Airport station than a route via Logan and the TWT would be; the question will then be whether the Washington LRT would be fast enough to compete
- But… if we measure to Logan Airport itself as the destination, the calculus changes a lot — the distance becomes basically the same between the two, but the route via TWT would be a 1SR as opposed to the 3SR (Wash + Blue + shuttle) via downtown
- So, I would split this into SL3/SL1, plus a Ruggles/Nubian <> Seaport route, potentially with an extension through the TWT but with a question mark next to it
NOTE: if we stop thinking of them as “Urban Ring” routes, several of the routes I’ve laid out have some obvious potential extensions:
- SL3 could be extended to Everett or even into Malden, or have a separate Malden <> Logan Terminals with significant interlining between Chelsea and Airport
- A Kendall <> Chelsea route could extended along the 116 corridor into Revere. This route would be a bit long, and probably we could come up with a faster Revere <> Kendall alignment via the Tobin Bridge
- Alternatively, a Kendall <> Chelsea route could be rerouted into downtown Chelsea proper for its terminus, e.g. via Everett Ave
- A Kenmore <> Nubian route is already being proposed: the T28. Just as the Malden <> Logan or Kendall <> Revere routes I’ve suggested would actually be radial routes based out of Logan and Kendall, the T28 will become a radial route based out of Longwood, but like the others will also fill a circumferential gap for part of its route
(A lot of this is very similar to the initial proposal for Urban Ring Phase 1, though I’ve suggested some changes.)