At some point on the Internet, I’ve scoffed at the idea of extending the Blue Line across the Longfellow Bridge (somehow) and then run along Main Street to some superstation at Kendall (which there’s not room for) and then making a turn on the Grand Junction right-of-way (or something). I still do. You couldn’t reliably run the Blue Line and Red Line together on the Longfellow and they have separate loading gauges so would need different tracks at Kendall. To facilitate a Red-Blue Connector, it makes sense to stub-end the Blue Line at Charles Station and provide an easy answer to Kendall Square.
Or does it?
This would be a short and pointless blog post if the first paragraph was 100% true. Plus, I’ve written that blog post before. Twice.
One of the trickiest things about the Red-Blue Connector is shoehorning a good, useful terminal in to the space under Charles Circle. It’s not easy. You’d have to dig a wide tunnel, or long tail tracks, or dig out pocket tracks or tail tracks under a busy roadway and the supports for the Red Line. It would be somewhat difficult to build any sort of functional terminal: there’s just not the space. You could put something under Storrow Drive (technically Embankment Road) and Ebersol fields, which would result in a decent terminal, but you’d have to dig up and rebuild the fields, and you’d be digging adjacent to the river. It would provide for good operations; you could stack in several tracks for layover, storage and recovery, rather than using crossovers and/or the Bowdoin Loop.
So Ebersol would work for operations, but you’re still pushing more people in to the Red Line and the already-overburdened Kendall and Charles stations, and forcing every Kendall-bound Blue Line passenger to transfer (albeit an easier transfer than exists today). There’s another potential terminal. It’s bigger than Ebersol, would allow increased capacity across the Charles, the potential for further expansion and, oh, yeah, it’s already somewhere where a huge hole is going to be built in the near term.
I’m speaking of the Volpe site recently bought by MIT. Since they’re going to be digging a big hole, it would make sense to put something useful in it, not just more parking. It is an extra 3000 feet to tunnel from Charles Circle to Volpe, but it’s mostly in a shallow river and free from utility considerations (as far a I can tell). In theory, this should be relatively cheap tunneling: it could be done in a similar manner to the Ted Williams Tunnel: building tubes off-site, digging a trench, and sinking the tubes in to place, except downscaled by a significant factor: the width of two Blue Line trains is narrower than two highway lanes. The river is 12 to 15 feet deep just downstream of the Longfellow, so it would need to be excavated down about that much to accommodate current depths. The TWT required digging through muck and in to bedrock at times to accommodate a shipping lane clearance at low tide, but the Charles has no such river traffic. The disposal and mitigation of the sludge on the river bottom may be the trickiest part, although it would be beneficial to start cleaning up the muck on the bottom of the Charles River.
Then there’s the Broad Canal. This should be easy. It’s 15 feet deep, doesn’t need clearance for anything more than kayaks (although the waste heat from the power plant would have to be accounted for), and could be easily coffer-dammed, dug out, cleaned up, and filled in with several feet of water sheet above. To make up for any displaced water volume (hello, Waters of the United States), the canal above could be extended, Lechmere-style, to a water feature figuring in prominently in the new Volpe development.
What does this get you? A lot, actually. First of all, designing a subway loop terminal in Volpe’s basement would add minimal marginal cost to the development and would make it extremely transit-oriented, and add value to the project: there’d be no need to trek through the Marriott to Kendall Square to the Red Line for trips downtown. (Do you need a loop? Probably not, but if you can get MIT to dig the hole, you might as well put a good terminal down there, although if you wanted to run trains through to Binney and beyond in the future, you could build a simpler island platform with tail and storage tracks beyond.) This north/east side of Kendall is booming. In the past 10 years, several blocks have been rebuilt from gravel lots to job sites and residential developments: below is the same corner in 2011 and 2017, for instance. It would also bring transit a bit closer to the no-man’s-land in the mile between Kendall and Lechmere. With Volpe as the linchpin of several thousand more jobs and residents, expanding transit should be a priority in Kendall.
This plan would also give the Kendall area a direct connection to more of Downtown Boston, East Boston, the HYM Suffolk Downs site Boston is proposing for Amazon (but will be developed no matter where Amazon goes), and, most importantly, the airport (this could—maybe—provide the impetus to build a better connection to the airport from the Blue Line). It would provide more capacity across the Charles—although the north-of-Boston portion Red Line is most full from Central to Kendall—and more importantly would take some traffic out of the Kendall Station, which was never really designed for the number of people using it today.
Further down the road? The Volpe site hemmed in by Biogen to the west, but a right-of-way could be preserved over to Binney Street where a further extension could easily reach the Grand Junction. From there, much is possible. A line to Sullivan Square and Assembly via the Grand Junction. A line in the other direction linking Kendall to Allston, and then further west. Once GLX is complete, the Blue Line will be the only transit line which terminates in Downtown Boston, which is operationally inefficient. This would give it a terminal at both ends to improve operations.
I’m not sure how much this costs; I haven’t been able to find a good breakdown of the order-of-magnitude for the costs for the TWT. (I did speak to Fred Salvucci about it, and he said it was the cheapest and easiest part of the Big Dig to build, although that’s a pretty low bar.) I also can’t find information about the specific cost of the “Haymarket North Extension” tunnel costs, but that project seemed not to have broken the bank (as far as I can tell, the below-ground portion of that line did not use boring machines). Searching the Globe archives, the entire Haymarket North project cost $180 million at the time, equivalent to $750 million today. That number includes: the five miles of the line to Oak Grove, some tricky engineering building between buildings from Haymarket to the river, and the B&M holding up the state for $18 million ($95 million today) to build the line through Charlestown (This is more than half, considering 1970s inflation, of what the state would pay a couple years later to buy the entirety of the Boston and Maine lines in Massachusetts east of Fitchburg: $39.5 million, $170 million today). For this proposal, the state would only have to negotiate over a small portion of Broad Canal Way, and its owner—an REIT—would stand to benefit from better transit to the airport so might be willing to make the price right.
In any case, if Charles Station was built as a through station and not a terminal, it would reduce construction costs there (where they’re expensive) and improve operations. The station could even be built with side platforms to keep the width of the subway narrower. The Volpe terminal could be built basically for free if it was integrated in to the overall Volpe development. The question comes down to the cost of the underwater tunnel. If it’s reasonable—and it seems that it would be—this would make a lot of sense. What about transfers from further north on the Red Line? This would preserve the full functionality of the Red-Blue connector, except it would work even better. And if the North South Rail Link ever obviated the need for the Grand Junction to function as a freight corridor, the Blue Line could easily be extended west or north.