I like that. Would it maintain the ability to branch through the Tremont St Tunnel towards Dudley?
Some here like F-line will talk about how impossible the Essex St tunnel is given all the uncertainties of what's below. I certainly am not informed enough to disagree about that, but I do think it's worth a study (one which already began with SL3 planning). I understand the loop down to the pike and back up Marginal is easier, although it will be quite indirect unless or until a Stuart St subway connects the Pike segment to Back Bay.
In a project reboot you definitely must study the Essex alignment to keep bases covered. Nothing is certain when it comes to EIS'ing under some of the oldest streets in the city; that was the whole lesson of SL Phase III. So even if
probabilities strongly favor a South End alignment, that doesn't mean there isn't quantifiable uncertainty with any of those possible paths that has potential to force you back to somewhat better-studied Essex. If you want it built at all there has to be an officially-studied fallback option, and Essex simply has the most quantity of previously collected information to lean on in the event of a fatal blocker on other considered alignments.
That's Alternatives evaluation 101 there. It's S.O.P. to let past studies inform future studies, even if the past study isn't a
probable build.
I just don't think from what we know in the aftermath of Phase III that it's going to end up any better-looking than a last-resort fallback for a project reboot. In fact, if last resorts force us to Essex/Boylston or bust there probably will never be a feasible Seaport-Downtown one-seat. Look at how much maximal risk territory Phase III tried to take on:
(Note: pink was the last-ditch preferred portal alignment before the plug got pulled)
Let's not even consider building impacts for now. Let's just name ONE engineering decision that posed the single largest viability risk to Phase III:
The required underpinning of very old existing subway stations and tunnels.
What did Phase III attempt to do:
-- Underpin the 1908 Orange tunnel and 1908 Chinatown station at their widest and most complex structural points.
-- Underpin 1897 Boylston station directly underneath the curve at the single most structurally-complex point where the station tracks were passing above/below each other, where a major pump room was located, and where the sealed Little Building entrance was located.
-- Underpin and abut an entire 750 ft. city block of 1897 Central Subway tunnel.
-- Spread the new tunnel out to its single widest point directly underpinning the spot where the Central Subway spreads out to its single widest point between stations: by placing the loop underneath the cavern where the Public Gardens incline, Boylston St. incline, and Park Square subway provision meet.
It attempted all of that at once.
Phase III only existed as a Supplemental Draft Environmental Impact Statement at the time of its cancellation. A long, long way from the Final EIS that would've preceded design-build. For 5 years before cancellation all the attention was tied up troubleshooting the fatal blockers between Boylston station and the South End portal. Projected costs sailed from $900M to $2.1B from all those project changes.
But the truly terrifying part was yet to come when--after locking down the final alignment--they would have to go back and re-study the whole shebang at a much more granular level for the FEIR report. That's where costs were going to double again from getting first truly detailed look at the revised west alignments, from itemizing the individual horrors under Essex and Chinatown station, for tallying up the building mitigation on Essex and Charles South, and from itemizing the individual horrors on underpinning the Green Line. The FTA pulled the plug on fed funding commitments before first crack at ballparking any of those numbers, and the state took the graceful way out while the "official" number was still sitting on $2.1B rather than even attempt the next recalculation with the blowback that would ensue. FEIR would've pushed it above $4B on base costs, and then the craptacular bid process would've dumped a GLX's 'corruption tax' on top. $6B+. And unbounded overruns beyond that mid-construction for the complications they didn't catch until mid-surgery. For a tunnel that probably was going to net worse headways than the existing Transitway because of the speed restrictions around the loop.
We are feeling the effects to this day of them choosing one of the intentionally hardest and riskiest builds, thanks to the stubborn insistance on it being mandatory BRT and mandatory linked to Washington St. It's not an abstract concept doodle; they tried to engineer it, and it failed. A project reboot has to attempt to learn some lessons from that. If there was only
one lesson you could choose as the most important, it's. . .
AVOID STRUCTURAL UNDERPINNING AS MUCH AS POSSIBLE.
Anything that doesn't structurally touch the 1897 Green and 1908 Orange tunnel + station structures is going to have an orders-of-magnitude better feasibility at orders-of-magnitude lower cost.
That means, for meaningful feasibility and cost improvement:
-- Don't lay a finger on Boylston or the Central Subway. Recycle, recycle, recycle old infrastructure. Like your civil engineering career depended on it.
-- The Orange transfer station needs to be completely structurally separate from the Orange level. Preferably total hands-off save for the concourse link-up from short distance away.
-- If any tunnels need to be underpinned, cross the
fewest number of tunnels at their
narrowest available points at the
most direct angles and choose the
newest infrastructure for the intersection points. That means the 1967 OL South Cove tunnel, not the 1908 Washington tunnel...and between-stations not at a station. That means doubleplusdon't touch the Central Subway if you can outright delete a tunnel underpin. That means stay the hell away from novel alignments through the South Bay spaghetti ramps. That means going as tangent as possible through the intersects.
It's pretty clear where following just that ONE golden rule is going to drag the gravity well for the revamped build: down the Tremont tunnel to Eliot Norton Park, and some kind of jog-around the South End. Which particular streets TBD. That's just how project scoring works. Draw up a table of routing possibilities and assign √+, √, √- scores on strictly the criteria that were fatal for SL III. Tally up the scores. This isn't an abstract thinking exercise; it's going to heavily favor the South End and relegate an Essex rehash to non-preferred last resorts . Sidelining any/all impacts to the 1897 and 1908 subway tunnels is simply that life-or-death when it comes to this happening someday, or happening never ever.
