I was thinking that most of an urban ring subway route could be done with cut/cover. There are only a few places I think that deep bore would be necessary one of which is under Harvard Station in Cambridge where apparently it is possible to deep bore. Now the rest could be cut/cover down Harvard Ave thru Allston and Brookline. It would be a huge pain in the ass, sure, but the pay off would be tremendous. The ease of mobility to Cambridge from just outside the downtown core would be insanely easier as well as less congestion in the downtown core itself. You all know that.
The point is that only a very limited amount of the project on the route would be deep bore. Basically I think just a connection between what is being cut/covered on either ends of Harvard Sq. would need to occur and if deep bore is possible there, the less disruption there would be to activities in the congested bustle of Harvard Sq.
I really think it could be done. As much as a temporary pain it would be to cut and cover these major thoroughfares, the payoff would help everyone that commutes on the T.
I see it possibly playing out as:
Cut and cover from Sullivan down Washington St. in Somerville
Continue cut/cover down Kirkland St. in Cambridge
Bore under Harvard Station continue under Charles River to N. Harvard St.
Cut/cover down N. Harvard St >> Cut cover down Franklin St. in Lower Allston
>>Cont. cut/cover down Harvard Ave thru Allston and Brookline....
...The rest could basically be cut/cover all the way to JFK/UMASS
The problem with Harvard is that if you undercut the station you have to nuke and rebuild the station. The whole thing is crammed around the contours of the Square, the abandoned Eliot tunnel, the bus tunnel, and all the pedestrian connections. It's a shitload of interfacing, load-bearing infrastructure of varying depth and wildly varying ages all converging in the same spot. With none of the bedrock Porter has, which means more reinforcement of above structures and even deeper depth than Porter if you go down and off- street grid. They did all the surgery that was possible from 1979-81 to remake the Red Line while keeping it, the buses, and the Square in operation during the disruption. There's no such option now if going lower requires tearing out the floor to underpin it, or burrowing 250 ft. below ground instead of 100 ft. like Porter and making transfer movements at such a busy station entirely elevator-dependent.
Trying to clean-room all of that gets to my point: how big a boulder pushed up how steep a hill before the effort becomes self-defeating? Taking Harvard Sq. out of commission for years isn't an option, and neither is building a station so deep that high-volume foot traffic between station levels is nearly impossible.
And this 66 subway? You're tunneling several miles down a motley collection of streets of varying widths. All packed as dense as possible with the densest residential in Allston and the densest commercial in Brookline. A water crossing. Uphill tunneling in Brookline. Sharp curves. Between construction, mitigation, and economic ruin from shutting down entire blocks of this corridor for years at a time...this is easily a $20B project. And worse, it will evict too many existing businesses and residents: the ones who simply won't survive the years their street grid is disrupted to uselessness, and the many more afterwards who get priced out before the area has even had a chance to recover from the disruption.
Who is this an economic benefit for? Not the people using the 66 or making a living off the 66. It's for the future people who'll replace them when they get squeezed out. That's not a neighborhood transportation improvement. It's urban renewal...renewed. Understand what unintended consequences that brought about the last time, and understand what failure to learn from history buys you. You can't just assume that such a project will be more careful and benign than bad old urban renewal. When the act of undertaking a project like this wreaks this level of long-duration disruption...displacement of the neighborhood becomes a 'feature', not a bug.
Please do consider this when drawing your fantasy transit maps. Transit equity is sacred enough that what you choose to build and how you choose to build it has to take into account disruption, and the corridor's resiliency against disruption. You can't just look at pretty lines on the map as a finished product. If it's going to take whole segments of Mass Ave. or the Allston and Brookline street grids offline segment by segment for close to 20 years, somebody is getting sacked with a whole lot of mobility loss that will not be repaid to them. It'll be repaid to the more fortunate who displace them. That's transit inequity. And the urban renewal tragedy all over again. Choosing the hardest possible path because it
must be so isn't learning from those mistakes.
Now...back to the Big Dig and why it was designed the way it was. The needs assessment for that project was to keep it entirely in the footprint of the elevated Artery so nobody else got displaced by the terrible mistake they made when the original Artery was built. The slurry wall cut-and-cover was explicitly designed to minimize disruption by jacking up the existing highway when the original underground supports had to be taken out, and preserving the street grid through the duration. The North End, street grid, and all highway circulation inside 128 could bend within tolerances but not break during the years of disruption, the area of disruption stayed self-contained, and the new highway got the simplest possible design for increased capacity without widening its footprint. Of all the things that went wrong during that project, construction mitigation wasn't one of them. The affected neighborhoods were less affected than some feared, and actually thrived during the project.
The same was true when Harvard Sq. got torn up for the new Red Line alignment. They kept all the transit operating at full capacity with full mitigation--2 stations load-spreading the capacity, and fully undisrupted bus service. They chose the design that was not 'perfect' for ops with that sharp curve, but which had the shortest-duration construction through the Square and most mitigation options for keeping businesses afloat. They were done cutting up the street through Cambridge Common in under 2 years. They would not have been if they chose a more
elegant routing that severed the Red Line or bus tunnel during construction, required tearing up part of Harvard Yard, or required years longer drilling of shafts through the Square and undercutting buildings for a deeper station. They didn't do it with the expectation that all the weaker native businesses would probably be on their way out as direct result of the disruption (over-gentrification came way way later and mostly at the hands of Harvard itself). It was done with the explicit intention that they'd be unscathed during construction and thrive...not be displaced...after it.
The same shapes other transit projects. The Transitway got bundled in with the Big Dig and Ted with a routing through Seaport moonscape. The N-S Link could've been bundled into the same package, but instead is pre-provisioned to have no disruption to anything in the main tunnel, to burrow under rail yards and 5-track ROW's in Pike and Leverett ramps no-man's land elsewhere, and to handle its trickiest stretch at SS by straddling Dot Ave. and the Channel at a spot where all the other tunnels were pre-prepped to have another tunnel threaded between while remaining in service. Every other proposed rapid transit extension of the postwar era--GLX, Blue to Wonderland and beyond, Braintree branch, the D line, relocated Orange Line, Red from Davis station--bootstrap onto RR ROW's. So do the unbuilt ones: entire north half of the Urban Ring, further Orange extensions in both directions, Red-Lexington, Blue to North Shore, Green to Needham.
The ONLY ones that involve invasive tunneling are the shortest possible gap-fillers: Orange from Chinatown to Back Bay to get on alignment (done 20 years before it actually opened while the neighborhood was in the act of being urban renewal-wiped), Red from Harvard to Davis on the path of least destruction, North Station superstation, Red-Blue on only a few blocks of supersize Cambridge St. Ditto some of the unbuilt unofficial proposals we frequently talk about: recycling the Tremont tunnel and Pike canyon to connect Back Bay and Green with the Seaport, recycling the B reservation footprint to BU Bridge to link Urban Ring LRT to the Green Line, burying the E reservation and limiting the street-level disruption to 1/2 mile between Brigham Circle and Brookline Village, reserving a path through remade Beacon Park and Harvard's Allston land to bring an Urban Ring spur to Harvard Sq. (maybe first in mixed traffic from the bridge to the bus tunnel, then in a new Charles crossing), taking advantage of the rock-solid Milton-Mattapan granite and lack of tall buildings to deep-bore a future Ashmont Branch extension under the 2000 ft. between Mattapan Sq. and the Fairmount ROW to reach Hyde Park, trading in Storrow for a shallow semi-surface Riverbank subway extension of the Blue Line from Charles. And so on.
What are the common themes here? They're all carefully risk-managed on the disruption, stick as closely as possible to pre-cleared space and previously available ROW's, and do as little invasive tunneling as humanly possible to get from Point A to Point B and meet all the key points of the needs assessment. They use the most minimalist engineering as feasible to get the job done, even when that's less perfect as what's engineering
possible with enough might. They do not force displacement or temporarily acute economic hardship on their surroundings as a construction necessity.
The ones that don't get built are the shakiest on disruption. Silver Line Phase III's disruption to Chinatown and the Common, plus its required mitigation, proved killer. Ditto the cross-Brookline tunnel envisioned for the Urban Ring...too much unnecessary destruction when a more roundabout LRT routing via a B Line subway, Kenmore, and the D recycles existing infrastructure. In each case, however, the engineering assessments said that was the most risk-managed way to build BRT tunnels through urban density. But that's more an indictment of the needs needs assessment mandating the BRT mode than it is intentionally choosing a harder engineering job for mapmaking perfection.
So do you see where the 66 and Mass Ave. subways fall on the side of this divide? The sheer complexity and disruptiveness of the builds IS a flaw of the process that identified those builds as the only way to fill a need on those corridors. Have other lower-impact projects been gamed out well enough to see how much they can indirectly help these corridors? Does the 66 even have to travel its current route, or would reshaping its ridership onto Urban Ring LRT relieve enough end-to-end load to make it a better bus for each individual segment? Have we even begun to exhaust Mass Ave. improvements to the 1 and 77, and how much would an Urban Ring through MIT, a Dudley streetcar, an Arlington Ctr. Red Line extension, and a Porter Sq. Green Line extension divert those loads? Have we even answered these questions fully, or are we just looking for the prettiest 2D lines on a map?
