Crazy Transit Pitches

[F-Line to Dudley]

How far down would we have to go to do WMATA or even Copenhagen style tunnels?

Probably not comparable at all. Most of D.C. sits on hard rock outcrop at the heavily eroded shoreline base of the Appalacians. The only silt mush is in the immediate Potomac drainage area. The whole capital region is basically an ex-mountain range sticking into the Atlantic that was ground completely flat by the glaciers. Instead of a lumpy debris field like Boston where the glaciers just pushed a lot of refuse from higher elevations into the water...and then the humans did more of the same over a 250-year span.


The Big Dig didn't really make much use of traditional TBM's either. That was mostly hella deep cut-and-cover, some faux boring through ground around SS that was artificially cryogenically frozen to give it more hardness, and sunk precast tunnel sections for the Ted and the Pike tunnel under the Ft. Point Channel. To the extent that they'd be boring anything for the Link, it's more like a rotary dirt scoop to excavate the space under 93 and maybe more of that freeze-dried business around SS where things have to weave above/below other tunnels.

The last time anything resembling traditional bedrock boring happened was the Porter-Davis Red Line tunnel, which is the only reason it was possible to go so deep and travel inocuously under property lines. North Cambridge is a considerably higher-elevation pre-glacier rock outcrop. I don't think there's any place in Boston-proper comparable to that unless you were burrowing the Red Line from Mattapan Sq. under property lines to get onto the Fairmount ROW. The Neponset watershed around Mattapan-Milton-Hyde Park is where the hard granite deposits are.

Beyond that, just about everywhere has to be cut-and-cover and reinforcement of the mush for any underground structures including building pilings.



Some reading about Boston geology I found on 'th Google: http://written-in-stone-seen-throug...chitectural-geology-of-boston-roxbury_27.html.

I don't understand half the technical jargon, but the maps are instructive. You can see on the overhead map that little green toothpick...it's an ancient hard volcanic feature stuck in the middle of mud on all sides. That is precisely what they bored the Porter-Davis Red Line through. The basin in pale tan is all the tidewater mush...that's all of downtown, the Charles watershed, most of Cambridge and Somerville, Watertown, Everett, Chelsea, Eastie. All recent in origin. Then the speckled tan in Brookline, Roxbury, and Dorchester is somewhat rockier sediment (boulders and crap chucked in this direction off the Worcester Hills)...also recent glacial in origin, but more of a crushed pebble/boulder debris field than the tidewater mush. Then the dividing line at around Mattapan Sq between the glacial deposit and the hard-ass and very ancient volcanic and flattened-mountain rock in Dedham and Milton.

Then you can see on the cross-section map how the mush is pretty much like a lake sitting on top of firmer rock..."shoreline" bordered by the hard volcanic rock and that Porter-Davis toothpick sticking vertically upright. Then the black-and-white map showing the ages of it all, with the glacial mush all being very recent compared to the rest, the little volcanic dikes subdividing the mush in Cambridge and around Beacon Hill like a fence, and then the hard-ass Neponset granite being well over half a billion years old.

It pretty much confirms everything we know...the Central Business District is some soft, silty mush bordered by lots of lumpy mush. And it really doesn't get any better until you're at the city limits and the ring of inside-128 inner 'burbs.

 

[George_Apley]

Also working on the new google map maker. Its nice.

https://mapsengine.google.com/map/edit?mid=zDJ7PZTCibXk.kg-oClj1m5BQ

With my overlapping rail idea, here's my start on an OL and GL (both heavy rail). My goal is to have the 'inner' terminal for each line be someplace where there's some additional space nearby for logistical purposes. Regarding my heavy rail GL, I'm not really convinced Fenway is a good fit for that; Reservoir would be pretty damn good, but thats almost the entire length of the D line anyway. If the D line were all heavy rail, how far do people think we could extend it west? Through to Wellesley (ideal to catch the students)? Maybe even Natick/Framingham? Is there an ideal length for a heavy rail line?

Riverside is probably a good place to end it. The 128 Belt is "greater Boston" and about as far as rapid transit should go. Everything outside of that would be better served by Commuter Rail. For the communities just outside the belt, ramp up the bus services converging on the terminals.

My guess is that if you studies extension of RT to Wellesley you'd quickly discover that the community would much rather have their limited stop CR trip to BBY/SS over a slog on the Green Line. Especially if the Newton stops get Fairmounted off of the Worcester/Framingham schedule.

 

[Matthew]

Wow, wonderful geological link you found there. Looks like we'd have to go down at least a kilometer to get to proper bedrock.

Oh well.

P.S. I recall that the Red/Blue work done so far claims that they would have to use tunnel-boring for a segment, instead of cut-and-cover like we would expect. I remember because it surprised me to find that out.

 

[DominusNovus]

Riverside is probably a good place to end it. The 128 Belt is "greater Boston" and about as far as rapid transit should go. Everything outside of that would be better served by Commuter Rail. For the communities just outside the belt, ramp up the bus services converging on the terminals.

Generally agree. But my 'northern' green line wouldn't go down that far, without defeating the entire purpose of the overlap idea.

 

[F-Line to Dudley]

Wow, wonderful geological link you found there. Looks like we'd have to go down at least a kilometer to get to proper bedrock.

Oh well.

P.S. I recall that the Red/Blue work done so far claims that they would have to use tunnel-boring for a segment, instead of cut-and-cover like we would expect. I remember because it surprised me to find that out.

That's because there is a little bedrock at the base of Beacon Hill slicing Cambridge St. into the West End. It's one of those ancient volcanic dikes and faultlines shown on the map. I don't think it's a standard TBM per se so much as an underground rock cutter that saves them 2 extra years of fucking up Cambridge St. and everyone's ears around MGH with incessant jackhammering-on-steroids. It is going at cut-and-cover shallow depth with surface disruption above the tunnel footprint. It's just because Cambridge St. is so wide they can close the 2 center lanes and ban parking in the active construction segments to keep everything else including temp turn lanes moving mostly unimpeded. And all under-street utilities are well-documented recent origin from when the West End was wiped clean by urban renewal, so it's not the spaghetti mess the Big Dig had to clean up and Silver Line Phase III would've encountered in Chinatown.


The Red Line tunnel built deep under in 1912 was on the side of the hill away from the bedrock seam so they just human-scooped out clay to get to Park St. It just happened to be deep enough under the hill to be safely buffered from all the 18th century building foundations.

 

[DominusNovus]

Other than the commuter rail tracks that would only really allow DMU's, what would be a good route to extend the Blue line west or south out of the city?

 

[George_Apley]

Other than the commuter rail tracks that would only really allow DMU's, what would be a good route to extend the Blue line west or south out of the city?

Are you assuming it goes from Charles/MGH west under Storrow's footprint? Short of assuming the Riverside branch, there aren't a lot of options once it's in Kenmore Square, which is where I've had it terminate on my map. If you're ambitious about tunneling or elevating you could send through Allston into Watertown and from there to Waltham, but there are easier ways to get there from the north.

 

[F-Line to Dudley]

Other than the commuter rail tracks that would only really allow DMU's, what would be a good route to extend the Blue line west or south out of the city?

Blue was considered as one of the possibilities for GLX to West Medford in the initial studies, by boomeranging it down Embankment Rd. from Charles MGH. Red-Blue by happenstance has to have storage tracks past the wedge-shaped Charles island platform that fan out in both directions around Charles Circle. It's the only way to avoid the deep underground pilings anchoring the Longfellow and the elevated Red station. The northern tail track ends right at the intersection of Charles Circle and Embankment Rd. The southern track ends just shy of the Charles Circle-Charles St. intersection. Further extension is possible from either set of tail tracks, turning left or right under Storrow. The Blue-to-Medford build would've taken the right turn.

Ultimately Green proved easier to build, so it was eliminated from the design alternatives. And if HRT was desireable out there an Orange branch out of the Community College portal would've had better ridership than a Blue bending back on itself. You wouldn't get much thru ridership from 2 ends that both come in from the north.


Going west under Storrow to Kenmore in a rehash of the Riverbank Subway proposal from 100 years ago is probably the most viable one. If we ever reach the point where we want to tear down Storrow or bust it down to a leisurely undivided street through parkland there's almost going to have to be a 1:1 trade-in with transit. And in that case the Storrow EB roadbed pack makes an ideal re-use for a shallow subway tunnel, and the Storrow EB tunnel an excellent re-use candidate for rail and an Esplanade station at its widest point by the exit ramp. West of the tunnel the roadbed's in a cut below Back St. so you can pretty much build the tunnel in a half- above-ground box up to the level of Back St. and acting as the retaining wall for Back St. Similar to how the Red Line is in a surface-level box between Fields Corner and Ashmont...it's literally just an air rights cover-over there. It wouldn't have to support the weight of anything except grass on top, would be cheap construction (esp. around Mass Ave. where the cut gets deep), it would be waterproofed by virtue of being so shallow, and the Storrow WB roadbed can be used for your quiet 2-lane parkland drive. The only standard tunneling required is getting on-alignment to Kenmore from Charlesgate, and getting underneath the Kenmore Green level.

There aren't really any good eastbound destinations from Charles Circle with Blue-GLX studied out as a ridership loser with that bends-back-on-itself north-facing routing. Every other trajectory that way just bends back on the saturation-level transit coverage at North Station, which gets even more saturated when the N-S Link comes into the picture. Too much overkill to try circling Blue in that direction. Most of the ridership will have bailed by Charles.



WB under Storrow offers up more possibilities and a linear direction without that ridership-compromising bend-back. The D Line offers up an obvious trajectory. However, if the Needham Line is ever going to get a rapid transit replacement with the long-planned branch off the D the grade crossings are going to be LRT-suited and a bit expensive to all eliminate for HRT. Plus, if the Urban Ring Phase III rail tunnel through Brookline and Longwood is too expensive and too neighborhood-opposed to build, you need the D from the Fenway portal to Brookline Village to slingshot those UR trolleys through Kenmore Loop from a buried B tunnel to the D as a substitute. So it's not something you'd ever want to consider unless and until that Brookline UR tunnel is signed, sealed, delivered.

I also don't think it's going to be feasible to tunnel under the Worcester Line from there. You've got hard obstructions in the Yawkey station area with the crossing C/D portal tunnel and underground cables from the NStar substation on Beacon, and lots of leaky Charles Basin silt around Beacon Park. That rapid transit proposal that was on the 1945 expansion map pretty much died when the Pike took 2 of the 4 B&A tracks.


But, a Kenmore superstation is a big deal. It diverts huge number of riders off the Green Line Central Subway, and if the Urban Ring interfaces there it's going to become one of the most crucial transfer stations in the system with how many trains fan out in every direction (plus Yawkey DMU/EMU's a couple blocks away). As a terminal stop temporarily or permanently it's a very good anchor.

But you're not getting that far until we're ready as a city to let go of Storrow.

 

[George_Apley]

What was the proposed routing of the Brookline UR tunnel?

Cut and cover Harvard Ave would be WAY long weather you turn east at Longwood or keep going to Brookline Village. Crazy expenses to cut and cover all that, plus would only be accessed by UR from Harvard, which would be a dead end (a whole other issue to talk about possible northeast extensions for the UR from Harvard). But those are the only direct routes through Brookline. Tunneling under Longwood Ave once you get into the "Medical Area" would a lot more difficult to cut and cover without major disruptions to the functioning of the hospitals.

Joining the B until diving under Park Drive would presumably be a huge mess with the Muddy River right there, and goodness knows what else underground there. Plus you'd miss Brigham/Longwood Med in favor of MFA stop, or whatever subway stops take their place. Besides, that's not even in Brookline...

 

[George_Apley]

How to "complete" the ring someday as rail is a whole other animal. Doing Huntington Ave subway is great but you miss Dudley, Fairmount Corridor, and whatever Southie routing you'd do to get to Seaport and the transit-way.

This is the routing I came up with for a "someday when we have the money and drive to do it" plan, but I'm sure it has issues.

https://mapsengine.google.com/map/edit?mid=zlB7eZcVeXLk.kGguq6iTII0g

For one, it would have to be street running. I have it splitting from Huntington at Tremont, which would have to cut-and-cover to Malcolm X (pricey especially considering protecting the Church from tunneling effects), and street run to Dudley. Past Dudley Square? Street run on Dudley to say Cottage Street, meet Fairmount at Uphams Corner, street run to Edward Everett Sq, then turn North up Boston St to Andrew, then up Dorchester St to D St and head to Seaport that way? Probably too much street running on streets that are too narrow.

Is there a better route?

Maybe bypassing Dudley and sending the UR to Melnea Cass, then somehow to the Bypass Road? Truck shipping wouldn't be a fan of that in the least though...

Hence why busses will probably best serve as the Southern/Eastern legs of the UR.

 

[F-Line to Dudley]

What was the proposed routing of the Brookline UR tunnel?

Cut and cover Harvard Ave would be WAY long weather you turn east at Longwood or keep going to Brookline Village. Crazy expenses to cut and cover all that, plus would only be accessed by UR from Harvard, which would be a dead end (a whole other issue to talk about possible northeast extensions for the UR from Harvard). But those are the only direct routes through Brookline. Tunneling under Longwood Ave once you get into the "Medical Area" would a lot more difficult to cut and cover without major disruptions to the functioning of the hospitals.

Joining the B until diving under Park Drive would presumably be a huge mess with the Muddy River right there, and goodness knows what else underground there. Plus you'd miss Brigham/Longwood Med in favor of MFA stop, or whatever subway stops take their place. Besides, that's not even in Brookline...

It was the Park Drive plan more or less. 2 routings considered: http://web.archive.org/web/20031017...ojects_underway/pdf/urbanring/MISChapter3.pdf (p. 27).

-- Off the Grand Junction down Amory St. Brookline then on trajectory to Longwood station on the D then Ruggles. This is more or less the old Inner Belt expressway preferred routing, which was also rehashed as a tunnel dig under Brookline at the very end as a last-gasp attempt to get past the opposition. Given all the old Brookline money that would have the living shit ripped out of its quiet residential streets, the chances of this happening are nil-er than they were when the Inner Belt was soundly defeated.

-- Off the Grand Junction down Mountfort and Park Drive to Fenway Station with some sort of convoluted super-concourse connecting Yawkey, Kenmore, Fenway, and this half-Fenway/half-Yawkey stop under several city blocks. Then along the Fens to MFA (close enough to Longwood) and Ruggles. Yep...you're gonna dig next to the Muddy River and fuck with Olmstead's handiwork. This doesn't have a snowball's chance at passing an EIS.


So...there you go. Mid-ten figures construction where any considered routing is either Inner Belt Revolt II: Electric Buggaloo, or crushed to smithereens by the EPA and Historic Register approvals. And neither of them get all the way to Kenmore.



I think the only way this can happen is if they bury the B out to BU Bridge, do a flying junction underneath the BU Academy parking lot, pop a portal onto the grassy hillside no-man's land next the Bridge/Pike/Grand Junction for the UR route, and curve the B tunnel from under that hillside diagonally slicing under the Pike and back on alignment under Comm. Ave. at about that park next to the BU SFA building. Then portal-up at St. Paul St. Then at Kenmore reconfigure the loop track so it can go B-to-D instead of just C/D-to-C/D.


Advantages of this are:
1) It's dirt cheap and dirt easy to bury the B reservation. It's had trolleys on it without interruption since 1892 so there are no spaghetti utilities under the tracks and no street impacts.

2) It actually hits Kenmore-proper unlike the garbage that is the Fenway-and-a-long-walk $5B "direct" transfer or the billions-dollar Brookline dig to Longwood.

3) So long as they can configure the boomerang loop at Kenmore to not impede regular thru traffic there absolutely is the capacity in this B tunnel (which would presumably have subway stops at BU East and BU Bridge/Academy skipping every grade crossing and traffic light out to St. Paul). And on the under-capacity D ROW to handle the Fenway-Longwood-Brookline Vill. "boomerang" segment.

4) Whatever time penalty is incurred by the "boomerang" is balanced out by the increased ridership of hitting EVERY stop included on either the Inner Belt or Olmstead Evisceration alternatives...not just the either/or's. And the ability to do every alt-route option imaginable on the LRT system. And...you know...the fact that it costs $5B less to get the exact same thing at only a +5 minute schedule penalty.

5) This sort of makes a very effective case for the Blue-Riverbank-Kenmore extension as Storrow trade-in when Kenmore's a high-capacity center of the transit universe. All those folks who now take Blue to get to Kenmore are freed-up capacity for the zillions of LRT alt-routings.

6) They can do this MUCH sooner. As soon as the Grand Junction becomes available and the RR connection can get relocated somewhere...N-S Link or outside of town. The only new concrete required is that easy buried B tunnel and the slight reconfiguring of Kenmore. The rest is all existing infrastructure and existing routes. So...for example, the UR could make use of D-to-E connecting surface trackage out of Brookline Village and alternate through the Central Subway and down the E to complete its Lechmere-BU-Lechmere circuit on an initial built.

Or...turn down S. Huntington to a restored Arborway Line to connect with JP. That wouldn't be the final route once they find a way to hit Roxbury and Dudley, but that is an effective spur circulator. Plus, it's not like this thing could ever be built in a monolith the way the segments are going to have to be spread out over multiple decades. So choose the segments that can be bootstrapped onto a previously wholly functioning circulator...like the Green Line. BRT is going to suck ass with only short dedicated segments then decades on end of clogged city streets while waiting for the rest of the build that may never come. This at least works as a rapid transit trunkline in its own right from Day 1 for similar money, and if they can never complete the south half of the network...it also works as a permanent finish if things never progress beyond that.


If they ever pick up the planning on this again they better hope all the ex- I-695 planners who worked on the first study have retired and that somebody with real experience with interconnected LRT can point out the duh-obvious things they missed with those ludicrous routings.

 

[Fred R]

This thread has proposals for extending the Blue Line westward from its hoped-for terminus at Charles and for extending the Huntington Avenue subway to Brookline Village and diverting the Green D line to Huntington. Why not combine the two goals? Extend the Blue Line under Embankment Road and Arlington Street, turn westward under Stuart Street and Huntington Avenue and thence out to Riverside.

Based on distance, the amount of tunnelling would be less than the proposed Riverbank subway and would avoid having to construct a "super station" at Kenmore. The remnant of the D line could run from Kenmore to Brookline Village or even be extended on South Huntington to Heath Street to replace that portion of the E line.

 

[George_Apley]

This thread has proposals for extending the Blue Line westward from its hoped-for terminus at Charles and for extending the Huntington Avenue subway to Brookline Village and diverting the Green D line to Huntington. Why not combine the two goals? Extend the Blue Line under Embankment Road and Arlington Street, turn westward under Stuart Street and Huntington Avenue and thence out to Riverside.

Based on distance, the amount of tunnelling would be less than the proposed Riverbank subway and would avoid having to construct a "super station" at Kenmore. The remnant of the D line could run from Kenmore to Brookline Village or even be extended on South Huntington to Heath Street to replace that portion of the E line.

The same problem that's always encountered. Tunneling through Back Bay fill... We're not going to tunnel down Arlington Street or Stuart Street. The tunneling problems aren't based on distance, but the corridor it's taking. It's easier to do more tunneling down riverbank in the Storrow footprint than it is to mess around under Back Bay streets. Think about all the troubles that the Copley Station elevator project ran into. Time and cost overruns, largely due to the negative effects it was having on buildings around the project. Imagine that but along a dozen blocks of Back Bay.

It would also cut off the best/cheapest routing of the Urban Ring, which would need both the Riverside and Huntington lines intact as Green to work properly.

 

[DominusNovus]

Did anyone ever come up with any ideas on places to put the blue line going south?

 

[George_Apley]

Here are Van's old proposals for Blue on his FutureMBTA site. All of them are quite crazy I assure you, except for the Red/Blue and the Riverbank->Riverside/Needham. But enjoy!

 

[Equilibria]

Did anyone ever come up with any ideas on places to put the blue line going south?

The best place for it to go is to Allston or Watertown underneath the B reservation and Brighton Ave. Failing that, might we do what the gentleman said earlier and combine this with the D/Huntington idea, but in a different way? Bury it under the existing D out to Longwood and Brookline Village, providing HRT access to Longwood? Is that too much of the "ripping out Olmstead's landscaping" problem from earlier?

You could even tunnel under the D to the park section, then use the parallel roads (Colchester and Chapel) like you'd use the Pike access roads with that scheme. The urban ring trolleys can use the surface track, the Blue can make a turn under Longwood Ave. for a couple more stations, maybe at Brookline Ave. and the terminal/transfer with D at the current site of LMA on the E.

I've always thought that the problem with tunneling in Brookline is that you can't get to Longwood without hitting expensive houses, but this would accomplish that fine. Could you tunnel through Longwood without any issues in the hospitals?

 

[F-Line to Dudley]

The best place for it to go is to Allston or Watertown underneath the B reservation and Brighton Ave. Failing that, might we do what the gentleman said earlier and combine this with the D/Huntington idea, but in a different way? Bury it under the existing D out to Longwood and Brookline Village, providing HRT access to Longwood? Is that too much of the "ripping out Olmstead's landscaping" problem from earlier?

You could even tunnel under the D to the park section, then use the parallel roads (Colchester and Chapel) like you'd use the Pike access roads with that scheme. The urban ring trolleys can use the surface track, the Blue can make a turn under Longwood Ave. for a couple more stations, maybe at Brookline Ave. and the terminal/transfer with D at the current site of LMA on the E.

I've always thought that the problem with tunneling in Brookline is that you can't get to Longwood without hitting expensive houses, but this would accomplish that fine. Could you tunnel through Longwood without any issues in the hospitals?

It's the same problem. Tunneling in the mush is too hard. If you deck under the D from Kenmore you run into the same groundwater and Muddy River overflow issues responsible for the great subway flood of '96 (and several similar events in previous decades). The EIS'ing would be extremely difficult. The waterproofing would be extremely difficult and require a huge number of high-capacity pumps capable of handling a groundwater breach from an overtopped Muddy. And it would be much more expensive than it looks. Plus, there's the matter of your trajectory from Kenmore with the existing C/D tunnel and the underground electrical trunklines from the NStar substation requiring a deep bore and underpinning through very soft soil...similar issues to trying to underpin the Central Subway downtown with a lower level.

My guess is it's impossible. And the only way the ROW can be shared is by 4-tracking it, which gets into major "fucking with Olmstead" territory with how close the ROW runs to the path system. The only reason it runs so close today is that Boston & Albany RR entered a public-private partnership with the city to finance the building of the Emerald Necklace and its associated swamp-draining and Muddy-rechanneling. The then-commuter rail ROW and the park were designed and built in tandem, with the Riverside Line being B&A's payoff for supplying the environmental engineering and labor to Boston and Brookline for reconfiguring the Muddy basin. It was a unitary build, which leaves no give for expansion. Especially since it all required draining a marsh to do it on top of spongy marsh soil.


Burying the B is real easy because of the limited impacts of going under the reservation footprint and the 'dry' cut-and-cover job. So is the E reservation. Brigham Circle to Brookline Village is more painful for street-level disruption, but short distance with nothing compared to the building pilings or human landfill further downtown. Recycling the bottom hard pack of the Storrow roadbed for a box tunnel is easy and free from groundwater breach because of its extremely shallow depth. Underpinning Kenmore with a lower-level station is...involved, but straightforward from an engineering standpoint given that stations have more spread-out load bearing than tunnels and the lower level coming from Charlesgate would intersect only an angled portion of the Green level.

But the D is a whole different story with the ex-swampland groundwater. Whether you build a tunnel or widen on the surface you probably need to dig up the shore of the Muddy (and, consequently, the entire path) toreinforce it with a channel wall under the dirt to keep the marshy seep away from the ROW, and probably need to re-engineer the entire drainage into the Charles Basin with a lot bigger volume of water being channeled downstream to offset the lack of ground absorption. Plus all the ROW flood controls if there's a tunnel, or total reconfiguring of the path and vegetation if there's a widened surface ROW. It would be very extremely invasive and be more or less a teardown/rebuild of the Necklace in the places it abuts the tracks closest. I can't ever see a final design passing an EIS or passing the historical impacts portion. It's the same blocker that dooms the Urban Ring Fenway routing.


The cross-Brookline UR routing may claim buildings on the corner of Amory and Comm Ave., the Beacon apartment complex spanning the Amory-Kent block, and the corner of Kent and Longwood where the tunnel has some sharp curves to stay on the not-real-contiguous street grid. So not many buildings of consequence that may have to come down. But it does render the old-money homes on Amory and Kent virtually inaccessible from the street for years on end while there's a giant hole in the ground, destroys all of the old trees lining the sidewalk the whole length, destroys front yards, destroys the edges of Knyvet Sq. Park and Amory Woods Sanctuary at the places where Amory curves and the tunnel has to follow, and has some deep building pilings to hold back on not-real-wide Longwood that are probably going to drive the cost way up. Way too many abutting structures the whole length, way too many potential impacts to old masonry foundations (i.e. Copley elevator syndrome), and the old tree-lined streets will never ever be the same after they're put back together.

Plus this tunnel has some sharp curves so you have to wonder what the resulting speeds are going to be. It's a godawful mess. Pretty much anything is a godawful mess except for the minimum-impact Kenmore loop "boomerang" and bootstrapping on as much existing Green Line infrastructure as possible. I'm not even sure tunneling will EVER be possible south of Brookline Village. Even if you cheaply and effectively eliminate the cross-Brookline/Fenway boondoggle with the "boomerang", look at what you have to contend with trying to tunnel across Mission Hill and Highland Park to get on-alignment with Dudley Sq. Egad. You may have to make do with north-half LRT loop between Brookline Village and Lechmere on a super multi-trunk routing Green Line, and a south-half Silver Line loop from Brookline Village (probably with a Kenmore end-run down Brookline Ave.) to the Transitway. Or a streetcar route from BV to Dudley. And that's it...no contiguous grade separation all the way around.

But this wouldn't be a bad thing to save the money and bother of near-impossible engineering and community buy-in because the number of people who need a one-seat all the way around the horn from Roxbury to Chelsea is microscopic...and would be faster transferring downtown instead of taking the scenic route around the Ring. It's a mid-distance, high-capacity circulator for fast/efficient transfers, not a linear line through the CBD. They can do that in two halves and make the south half work on the surface. Melnea Cass would have a nice, efficient reservation to make the east-of-Dudley leg a good ride, so if there has to be a choke point it might as well be the modest distance Melnea Cass-Dudley-Longwood/BV/Kenmore stretch mitigated with as much signal priority and limited stops as the roads will bear. It's not the ideal...but every permutation of the ideal is impossible, so what are you going to do?

 

[Shepard]

Here's a surface route that could work if you got all the various agencies to agree:
Montfort

Park Drive - Fenway surface connection

Fenway - eat most of the street for a dedicated reservation and make Park Drive across the fens two-way traffic to compensate - Longwood Area stop at Louis Pasteur

Louis Prang across Huntington by the MFA to Ruggles St streetcar - surface connections adjacent to both MFA and Ruggles Station

Reservation along Melnea Cass or Malcom X to Dudley following a short jog along Tremont.

And beyond.

 

[George_Apley]

Okay. Assuming the northern portion of the UR is built according to the Kenmore-Brookline Village "boomerang", the B is buried at least to St. Paul, the E is buried to Brigham and connected as a subway to the D, how horrifically impossible would a cut-cover from Brigham Circle to Roxbury Crossing under Tremont be? The building pilings would be an issue. The Mission Church obviously. Possibly draining issues being at a ridge on the slop of the Hill. Would it hugely more painful than the jog from Brigham to Brookline Village? It would be a ~3,000 ft tunnel with a portal somewhere at the western end of Malcolm X Blvd, which seems wide enough to hold a reservation if you're not afraid to cut a lane... from there you can street run to Dudley, join a Washington St streetcar line one stop to Melnea Cass and then split over that way.

The sub-Tremont tunnel would be this; Brigham-RoxX:

Ignore the streetcar line to the south and east out of Dudley...

 

[Shepard]

Here's a surface route that could work if you got all the various agencies to agree:
Montfort

Park Drive - Fenway surface connection

Fenway - eat most of the street for a dedicated reservation and make Park Drive across the fens two-way traffic to compensate - Longwood Area stop at Louis Pasteur

Louis Prang across Huntington by the MFA to Ruggles St streetcar - surface connections adjacent to both MFA and Ruggles Station

Reservation along Melnea Cass or Malcom X to Dudley following a short jog along Tremont.

And beyond.

I'm realizing this was pretty unclear. Here's the map: https://mapsengine.google.com/map/edit?mid=zyf9IzSqHCJE.kBY724_3vyb8

I don't think there's anything crazy about this - a workable mixture of streetcar and dedicated reservation.