Massachusetts Avenue Subway

It is common knowledge that Boston was once the center of the universe. The Boston Elevated Railway Company ran with this reasoning when they built the subway network that is now known as the MBTA. It reasoned that all should be grateful for the honor of passing through the bowels of city, no matter where their destinations lie. Trying to get from the South End to Cambridge? You'll transfer downtown, and you'll like it, too.

Sadly, by the time the MBTA took over the system, Boston had lost its claim as the center of the universe, on account of the Intergalactic Council's relocation to Bethlehem, PA. Deprived of its crown, people began to notice the subway's highly radial design made trips between outer neighborhoods and nearby towns needlessly long.

Of course, somebody at the MBTA did notice this, and proposed the Urban Ring Project. By 2010, this had devolved into a tangle of BRT services, which maybe could be upgraded to rail if the Transit Gods were pleased with the ridership. Naturally, nearly all of this was cancelled in the following decade.

But what if we were blessed by the Transit Gods, given unlimited power to build whatever, without fear of our newborn transit expansion being strangled in the crib by its own price tag?

The Idea

Massachusetts Avenue is long and wide, as many subway-hosting streets are. It travels parallel to the city center, connecting Cambridge to Back Bay, the South End, and Dorchester, all of which are densely populated and currently unconnected without a downtown transfer. Some popular locales, like MIT's main campus, Boston Medical Center, and UMass Boston, have no direct subway access at all!

In my endless love for the Madrid Metro's Line 6, which travels deep under circumferential thoroughfares like Mass Ave, I am proposing that the MBTA should plagiarize that system wholesale. Line 6, a circular route, serves a similar purpose to the MBTA's #1 bus, but with far greater speed, reliability, and capacity than a bus could ever hope to achieve.

This subway line, which I am calling the Aqua Line for no particular reason, would begin at Central Square and end at the main UMass Boston campus. It would require modifications to the following existing stations:

• Central Square (Red Line): track connection and free transfer, including between Red Line platforms
• Hynes Convention Center (Green Line B/C/D): free transfer
• Symphony (Green Line E & Orange Line): connection between the current Massachusetts and Symphony stations; free transfer, including between Green Line platforms
• Boston Medical Center (Silver Line SL4/SL5): provisions for a future underground Silver Line connection; indoor connections to the hospital; free transfer
• Newmarket (Fairmount Line): provisions for upgrade to rapid transit; free transfer
• Columbia (Red Line): renamed from JFK/UMass due to the new station closer to UMass; track connection with Red Line; free transfer

Besides these transfers, the line would also need to tunnel under the Charles River, Storrow Drive, I-90, the Worcester Line, the Southwest Corridor, and I-93. Given the sheer number of below-grade obstacles, this line should be dug deep with a tunnel bore, as the Madrid Metro's Line 6 was. All stations would need to be somewhat large, to allow for high volumes of people rushing through them, and would feature at least one exit on each side of the platform.

The exception to this plan is when the line enters UMass Boston, where the ground is mostly landfill and only a few feet above sea level. For future-proofing against sea level rise, it seems best to put this final segment on a viaduct, with skybridge connections between the terminal station and university buildings.

Over the course of its route through Boston, the Aqua Line would pass through perennially underserved areas, most notably the South End and northern Dorchester. By bringing subway access to Boston Medical Center, it would make it much easier for low-income people to access the largest safety net hospital in New England.

Why is it Implausible?

Without a doubt, subway construction costs will be very high. I mostly ignored this in my last post, but it is the primary limiting factor here. At a total length of 5.3 miles, not accounting for track connections, new rail yard construction, and the difference in cost between deep-bore tunnels and elevated tracks, a ballpark estimate cost for this project would be $5.3 billion. I have based this price on the LA Metro's Purple Line Extension, which reportedly costs roughly $1 billion per mile.

I am using LA's Purple Line Extension as a comparable project because it is also a heavy rail subway line dug with tunnel bores. However, if we use the Second Avenue Subway in New York City as a comparison point, the cost gets even grimmer. Some have reported it costing $2.5 billion per mile, which would make our new Aqua Line cost $13.3 billion, and that's not even accounting for the added complexity from all of the crossings and underwater tunnel. The Transit Gods will not be pleased with this.

Frustratingly, according to the same source, the Paris Metro's Line 14 cost $450 million per mile, while crossing many other subway lines and cutting through the heart of Paris. At this price, the Aqua Line would cost $2.4 billion in total, not much more than the MBTA's ongoing $2.3 billion Green Line extension, and less per mile than that new light rail route! Nevertheless, prices like that have rarely been seen in the US in recent years, so construction costs like that might as well be a fantasy.

Of course, price is not the only obstacle to a large subway project like this. Though the bulk of the subway would have to be constructed by tunnel bores, the stations would likely need to be excavated by cut-and-cover, if we use the Purple Line Extension as a model. This has the potential to produce a lot of surface disruption. Fortunately, Mass Ave is a wide street, so traffic would only need to be reduced in places, rather than be cut off altogether. If the MBTA can buy property next to the street to dig the stations from, as LA appears to be doing, it might be able to avoid roadblocks altogether, though this could also drive up costs.

Like many things in life, a project like this is a balancing act. Appease the Transit Gods with your low expenses, and you might anger the residents who refuse to pay their high tithes. Appease the residents with minimal disruption, and you might incur the wrath of the Gods with your blasphemously high budget. Unfortunately, that brings us to our third obstacle, money management. The MBTA has an abysmal track record with this, most famously showcased by the Big Dig, and most recently by the Green Line Extension. It seems unlikely to me that the budget of a new subway line in Boston would escape incredible cost overruns, even if the initial projected price is reasonable. They may even cop out altogether and sacrifice most of its utility to save money.

Come to think of it, this sounds a lot like what already happened with the Silver Line. Once promised as an equivalent or better rail line to the Orange Line route it replaced, it was delivered as paint on asphalt.

Introducing the Aqua Line: a revolutionary new bus lane for Massachusetts Avenue!