For this comment only, I'm limiting the scope to
northern half of Urban Ring - keep in mind, that's like 50% of the whole route.
And then there's the Grand Junction. Everyone always likes to dream about rapid transit over it, but what would that look like? Obviously the line would need to be double tracked and grade-seperated, most likely in the form of trenching it given that it passes under/through some buildings, and new stations would need to be built underground in a way that avoids demolishing a bunch of buildings on the surface, likely somewhat deep. By the time we're this far, why are we even using the Grand Junction in the first place? Why burden the construction of the project by forcing it along a route that frankly isn't even that good when we're basically building 80% of a bored tunnel subway anyways?
The two bolded parts are not equivalent. A double-tracked and completely grade-separated ROW can run service just as effectively regardless of whether it's at the surface, in a subway (C&C or TBM), or in an elevated structure like
these.
And the first bolded part is not exactly obvious. If you can afford, say, 1-2 grade crossings in a way that hugely reduces the cost, then as long as you're still running light rail, those 1-2 grade crossings don't significantly reduce your reliability. That basically describes Grand Junction. Main St is a constraint as you have buildings above and Red Line below, but to the north, you can start rising into a viaduct or descending into a tunnel or trench, however you wish.
Grand Junction is the most popular choice not just because it's already there, but because it connects Kendall, one of the biggest employment centers outside of the downtown core. Looking at how many people dream of BLX to Kendall only reinforces this idea. And it also nicely brings you to Sullivan, a major transit hub that's at the doorsteps of Kendall and begging for a one-seat ride.
I'm by no means married to Grand Junction (which is why I made the Binney & Gilmore proposal in the first place). But
for the purpose of bringing Urban Ring to Kendall, I honestly think an almost-grade-separated surface light rail line with a single grade crossing at Main St offers the best service-cost tradeoff, by far.
I know you're asking... Why Kendall?
Is it really the ideal urban ring route? Going a bit further out, more following the 66 route, could allow for areas like Allston to be included.
Most Urban Ring proposals that use Grand Junction - both crayons and the official Urban Ring study - do have a spur from Harvard that goes
south to meet the ring, most frequently via West Station. That can take care of Allston with simple changes.
Yes, Harvard is another major transit hub and commercial destination. And yes, going from Sullivan to Harvard doesn't require as much engineering headache as crossing under the Red Line in the flood-prone area that's Kendall. But Harvard-Sullivan is still not trivial either, and a comparison needs to be made between tunneling through the entire Sullivan-Harvard-(somewhere near BU and Allston) and likely much cheaper ways of Sullivan-Kendall-BU Bridge with a single grade crossing.
I'm not saying "Kendall good, Harvard bad", but unless you're dead set on total grade separation, the benefits that Harvard brings need to be bigger than Kendall to justify the cost. I don't know the answer myself, but the studies that F-Line mentioned above seem to imply that's not the case.
This map that Riverside mentioned also shows that while they're both notable employment centers outside of downtown, Kendall seems to provide more jobs:
Bottom line is, Kendall vs Harvard is a question that needs detailed analyses, and neither should be discounted completely.
Lots of the urban ring would be challenging from a flood perspective, especially the portion near the airport. But as I said, I think a tunnel across the river makes more sense anyways, and it seems that avoids most of the immediate problems.
The problem isn't tunneling under the river, it's tunneling under the old Red Line tunnel in a flood-prone area that Kendall is.
Even for the river crossing itself, while I'm not opposed to a tunnel under the Charles, there is already existing rail infrastructure across the river: the BU bridge.
I'll just be blunt here, I think that's a stupid assumption. Orbital light rail often suffers from its own success, with the inherently limited capacity of tram-like vehicles hamstringing rapid transit service. Look no further than the GL today to see why that's a problem. Not to mention that grade separation will be necessary, across the entire route, for headways to be short, consistent, and generally well suited for the service provided. That's the hard part of building any transit, and the only reason why light-rail should be considered in this context (IMO) is to allow for at-grade street/median running and local service, neither of which suit a subway line and would severely constrain any conversion attempts in the future. If we're already building a new right-of-way, let's run a metro or light-metro on it.
You might be misinterpreting what I implied by Urban Ring being light rail. I was saying most people imagine it will use light rail vehicles akin to GL Type 10s. I was
not saying most people want Urban Ring to be a glorified streetcar route running in street medians like the B, C and E branches are.
I think there's a general consensus that Urban Ring, at least in its "final" form, should have as much grade separation as possible. But I think it's reasonable to start off with light rail vehicles running on a
mostly "heavy metro" route, if there are a handful places where grade separations may not be achievable yet (e.g. Main St in Kendall). Especially when you factor in the operational flexibility with the Green Line (and a potential future Huntington Ave subway as part of a reconfigured GL system), as F-Line mentioned above. And if we're designing Urban Ring from scratch without being limited to Green Line's platform lengths, you can increase capacity by running longer train sets where possible.
Given the current political climate for transit, it's probably better to have something up and running first (as long as they do provide good grade separation initially even if not perfect). In the event that Urban Ring does become
that much of a success (which I certainly hope!) that it's worth converting to heavy rail at the cost of separating from the Green Line system, then we can figure out the last few pieces of grade separations (which do include viaducts like the ones I proposed).
(While that means we may end up having to revisit grade separation through Kendall again, if the cost will be there regardless, I think it will be much more feasible to leave the problem for the future, rather than having to figure it out on day 1 and potentially killing the project. And I mean,
some people did propose an El on Vassar St.)
I'll conclude by saying this: I
want to see more heavy rail systems not just in Boston, but across the US. I really do. But the trend of brand new transit lines across the nation generally lean more towards light rail than heavy rail.
