Re: Track 61 (Seaport - Back Bay DMU)
F-line, just curious, what's your take on the Essex Street surface link? Aside from a general aversion to street running, is there any impediment to the two portals and 1500 feet of track and wire?
1) Portaling anywhere on the block south of Boylston is pretty damn near impossible. Same tunneling nightmare under spaghetti utilities and around deep building foundations on a narrow street that doomed SL Phase III.
2) To get across the Boylston-Tremont intersection with historically-protected tunnels going 3 different directions, a historically-protected station, a mothballed and historically-protected second entrance into the Little Building, an underground electrical substation, and an underground pump room for keeping Back Bay groundwater out of the Green Line you have to go extremely deep. It can't just be a simple wye track at the curve and a T-shaped Boylston platform. This is the SL Plan...a second level way down, underpinning the start of the abandoned tunnel. To make it interface with the rest of the Green Line you'd have to take the incline into the depths and drop the floor many feet deeper, and lengthen the start of the incline further back towards Park St. Which will preclude ever using the abandoned tunnel again.
3) Since you're so deep it'll be impossible to get back up to a portal within 1 block before you have to cross under the Orange Line tunnel at the Washington intersection. Add +2 blocks, figure now Ave De Lafayette as your portal area...if you can fit it. Now you've built half of SL Phase III and between that and the station are at or north of $2B.
It's more circuitous but VASTLY easier to go the roundabout way through the South End recycling the existing tunnel. Build it exactly like you would a Washington St. portal: 1) Recycle the tunnel, plunking a Tufts Med Ctr. station under Eliot Norton Park at shallow depth under the grass in the ex- 'pit' portal with a long walkway connecting to the OL fare lobby; 2) Continue the tunnel +1 block under urban-renewal cleared land on the Shawmut-Marginal block, then +1 block diagonally under the Pike; 3) Portal in the NEC cut along the Herald St. wall on the space that used to be the Boston Herald's old freight siding, currently occupied by some
electrical boxes with room to squeeze two trolley tracks comfortably; 4) Graft the incline up the wall and add a traffic signal phase at the Washington-Herald intersection for the trolley.
All-in-one build, nicely consolidated and low-profile. Can easily be done at less cost than Red-Blue if they don't lose their gourds on designing the Tufts station, because there's no seams bedrock to blast through here or need to go deep and semi-complex with the station like Charles does to avoid the Longfellow piers.
Then...well, have to get creative. If you backtrack 1 block to Marginal you've got a straight shot to Curve St., Kneeland, and the SS bus station access road. But keep in mind you don't really have a portal option on the Marginal side of the Pike like you do on the Herald St. wall, so it probably is going to mean left-right for a block on Washington. Then changing the one-way direction of Marginal and Curve (which shouldn't be an issue, as they aren't load-bearing here).
(Looping up in the bus station wouldn't be a bad way to do it.)
Now, as for your portal into the Transitway...where is tricky because 93 is descending below ground right under Atlantic. But you do have that whole length of plaza along the bus terminal to go along. At some point 93 gets deep enough that you can probably dip under. The Transitway wall ends on the Atlantic-Summer intersection where the SL Phase III trajectory would've hit it coming off Essex. So 93 is most definitely deep enough by the SS headhouse for a shallow cut-and-cover incline in the plaza along the bus terminal to make the rest of the descent into the Transitway.
Not real expensive, but to avoid icky Kneeland and Atlantic you might be better off taking the right turn from Curve onto the bus terminal access road, then inclining off it down to the plaza when it makes the turn into the terminal-proper and up to the rooftop parking. That gets you off a hell of a lot of very congested public street-running.
Or...you could find a trickier way to go straight down Herald from Washington and find a way to weave through the ramp minefield at the Herald-Albany intersection, get onto the NEC near the wye, and just do a little flyover overpass of the wye like GLX is doing out of Lechmere to get over the Fitchburg. Herald is 3 lanes one-way here. But if you took the left lane + the NEC-facing sidewalk and plunked a jersey barrier there you probably have enough room for 2 grade separated tracks. Your guess is as good as mine how you find a path through
all this. You can do a pretty steep drop akin to the Science Park incline, but I have no clue where your entry point would be to get under all that.
I'm thinking the Herald-wall/Washington intersection uniportal...left, right...up the bus access road...down a bolt-on incline to the plaza...portal in the plaza along the bus terminal into shallow tunnel...deep descent on the Atlantic side of the train station...meet the Transitway by the headhouse is probably the cheapest, least invasive, most public street-avoiding, least ops-awkward, and most shared infrastructure-utilization way to do it. And then this will be your SL Phase III until they can fund the N-S Link in a future time and place...piggyback a trolley tunnel onto the NEC leads to bury it all as a real subway...and diverge off the back of that Link lead at around Kneeland to meet up at shallow depth with your plaza tunnel right where your portal used to be...and use the tunnel you already built for the rest of the descent into the Transitway.
However you do it, try to recycle-recycle-recycle and combined-build as much as possible, avoid the busiest streets at the SS/93 ramp nerve center, and don't try to replicate the path of SL Phase III because then you start counting costs in multi-billions.
Get some frickin' air rights buildings or a park over the Pike pit here and you might even be able to get more grade separation out to the bus access road by splitting the air rights parcels. Cross streets like Washington and Harrison on a signal phase, but not actually have to run on any of them until you're safely pulled off on the grassy knoll between Curve and the 93 ramp en route to the bus terminal access road. Make this thing drag some long overdue development kicking and screaming with it on top of the Pike canyon from Washington to the Boston Herald complex.
