Ultimately all of these recurring proposals for Track 61 DMU dinkies are just flailing-about desperation ploys to bring attention to the elephant in the room: that Silver Line Phase III was never finished. That's it...that's what's killing downtown mobility as the Seaport explodes. Except for southside commuter rail which can walk downstairs and an insignificant % of the bus system that can do the same, it is impossible to get there without taking a Red Line trip. And Red can no longer meet its default peak headways because of dwell decay downtown from all this overload. Park St. and Downtown Crossing are choking it to death, and this is going to keep getting steadily worse regardless of any short-term boosts like greater Orange frequencies with the new car fleet. Eventually congestion will worsen past a threshold where it starts tapering off economic growth in the CBD and Seaport because we simply can't move enough people around to those job centers...and it becomes a destabilizing effect on the whole region. This isn't an if, but a when. Long-term mobility attrition will choke off New Boston's economic pump and put the regional economy into a diminishing-returns era that's going to be rather unpleasant for those of us who've still got several more decades in the workforce.
The only way out is to pull riders off Park and DTX to spread the field. That means building the Red-Blue connector to zap a substantial number of double-transferees funneling through Park/DTX from the Blue Line...a build they can at least fast-track if there was a will in state gov't to finish the job. And the encore has to be creating that downtown direct via continuation of the Transitway so the Back Bay can get there without touching Red at all. The BRT plan up Essex St. did a complete belly-flop on feasibility from too many required structural underpinnings driving up cost (check out the stacked Chinatown station required under CT-Orange to make it fit under such narrow streets as Exhibit A of that engineering failure) and bus speeds so slow in a constrained tunnel space to move efficiently. So the reboot is going to take many years of redesign before shovels can go in-ground, and makes faster project starts like Red-Blue an outright prerequisite simply for the sake of buying time. And obviously since BRT impaled itself a sane reboot has overwhelming odds of needing to be light rail from Day 1 of the redesign to be feasible at all, with both modes overlapping between South Station Loop and Silver Line Way in the existing Transitway.
Say... -- Re-use of the abandoned Tremont tunnel. -- A Tufts Medical Ctr. intermediate station build diagonal across Eliot Norton Park, with (somewhat long) connecting walkway behind fare control to the Orange mezzanine on the next block. -- Continuation of the tunnel down nice wide Tremont St. to the traffic island on Marginal St., where the last pre-cancellation SL Phase III portal was supposed to do. Maybe even continue as a 4-tracker from Day 1 to keep all capacity options open for the old Tremont tracks. -- Bang a left onto Marginal, which is relatively easy tunneling being in the 1965 Pike urban renewal nuke zone. Slip under the Orange Line tunnel at the Oak St. intersection. This exact routing was studied in the early-1970's in a sweeping transit study as a possible "equal or better" re-use option for the Washington St. El to Dudley via Green Line once the SW Corridor realignment was built. So there is some official-study lineage to fall back on here. -- Split off a Washington St. Silver Line trolley replacement tunnel after the Orange pass-under that crosses the Pike diagonally, portals-up in the NEC pit by the former Boston Herald freight siding switch that's currently empty space occupied by a couple electrical boxes. Then climb the Herald St. retaining wall to the Washington/Herald traffic light for continuing to Dudley as a streetcar. Can possibly use 2 of the 4 Tremont + Tufts infill station tracks for splitting this branch off from the South Station connector. -- Continue the SS connector down Marginal. Find a least-painful way between Marginal and the tip of Chinatown Park where Essex St. meets Surface Rd. This is where most of the engineering uncertainty is going to be. -- The notch in the Transitway wall for Phase III to connect is under the corner of Essex & Atlantic under the front steps of 1 Financial Plaza, and the Big Dig cleanroomed the guts of Essex on the 2 blocks west of here for slipping Phase III around I-93 tunnels. This is the only viable insertion point, since the squeeze between tunnels and building foundations is just too implausibly tight for any due-south trajectory that comes up Atlantic instead.
I think curving the connector tunnel up Marginal through Hudson St. along the 93/Pike ramps would probably work. There's a new tower going up on the ramps side, but it's set back far enough from the sidewalk to not cause abutting foundation problems. The only truly delicate parts are crossing Kneeland St. and threading oh-so-carefully for about 250 feet on that block of tightly-packed Chinatown restaurants before pulling off into the park and changing elevation on a curve for the slip-around of 93 South onto Essex. Could even situate an intermediate subway stop on this routing at Ink Block on the Washington-Harrison block of Marginal, under the tennis courts, to serve that huge new neighborhoodlet going up across the block. Or...you could do some other routing contained anywhere in a square footprint bounded by Essex to the north, Marginal to the south, Tremont to the west, and Hudson/ramps to the east. None of them particularly appealing on cut-and-cover and building mitigation, but many different variations to study out.
It can be done, and it serves all the project goals. You will get a one-seat through all the Green Line transfer stops straight through to North Station that can be paired at robust headways with the Medford Branch, thus saving the world from having to overload the Red Line and substantially taming dwells at BOTH Green and Red @ the Park St. stairs. You can match the Union Branch with Washington St. It would take advantage of the part of the Central Subway best equipped to absorb a big service increase, via the Boylston outer tracks and Haymarket-north. You only have to be super-delicate with traffic flow at the Park-GC pinch, but that can be mitigated by revisiting the canceled 2010 plan for constructing thru-service crossovers on the inbound inner Park track so past-GC trains can be waved ahead of GC-turning trains. And you would get a flanking Orange transfer 1 stop down from Boylston @ that Tufts/Eliot Norton Park station, clearing out a lot of downtown Orange congestion as well as a lot of GL congestion to Copley with that one-stop Green + one-stop Orange transfer hop to Back Bay station. You get trolleys looping at Silver Line Way...maybe continuing on to swallow SL2 to design center, and maybe reanimating the old City Point branch if we can get over our fear of street-running. SL1 to the Airport would continue as a bus, and there'd be 4 consecutive stops to hop on/off the platform between bus and trolley. But this is it...the be-all/end-all. This is the killshot build that solves the congestion problems and keeps the New Boston economy's growth cap unbounded through mid- and late-century. Now how bad do we want it?
Not gonna lie: it's a scary-expensive $1-2B megaproject (IF managed correctly), where only those first 3-4 blocks + Tufts intermediate + Washington St. portal split constitute anything resembling "easy" construction free of potential nasty surprises. The best you can say is that the light rail reboot via the Tremont tunnel won't be as suicidal as the BRT tunnel up Essex with nuthin' but building and historic property mitigations and multiple levels of structural underpinning. But it'll still be flirting with death on overall difficulty, and easily take >decade to engineer before one shovel (other than maybe front-loading that Washington St. split) can be turned. Any which routing you choose the mitigation in spots qualifies as "brutal". That Hudson St. routing I posited ^^above^^ bases its logic on picking a semi-logical route with fewest overall count of tough building mitigations. It doesn't mean it'll actually prove feasible on degree of difficulty of mitigations. No potential routing is a sure-thing in that dept.
But we don't have 20 more years to dicker about doing this before that mobility chokehold starts to cut off the oxygen supply to the economy. The re-study and engineering Alternatives that address all the fatal flaws in the first SL III attempt have to kick off much, much sooner than that. We know for sure that these Track 61 flights-of-fancy don't even begin to address the problem...so, let's get going on the planning front? And we know for sure what the consequences for not doing it will eventually be, and that they're economically worse and longer-lasting than the short-term terror of taking on a really big build.
Interesting F-Line. not a bad idea. Unfortunately I feel that it would be a very tough sell in the current environment.
One thing I feel should be fixed if they put rails in the tunnel is extending the tunnel under D street or at least time the lights better. I have to assume there was a very logical reason to do it as they did.