Crazy Transit Pitches

[F-Line to Dudley]

The I-93 northbound tunnel is under Atlantic Avenue all alongside the South Station tracks. It is diving downward at that point, eventually under the Silver Line turn around. You cannot get to the gray dot from the South Station tracks without going THROUGH I-93 northbound.

Yes. It's either this thread or the Green Line Reconfig thread that had multiple rounds of multi-page. . .

"No."
"Yeah, but. . ."
"No!"
"But what if. . ."
"NO! Why does building that at X times the cost matter so much?!?!"
"TECHNICALLY FEASIBLE IS THE BEST KIND OF FEASIBLE!"

. . .time-wasters that itemized every one of those blockers. Use the board search function this time to ID what those blockers are.


Our Big Dig engineering forefathers only left a few incredibly narrow trajectories through the maze of existing new tunnels for any new tunneling of any kind around SS.

1) Transitway. East-west from corner of Atlantic @ Essex to corner of Essex @ Surface. Loop on Atlantic remains as a very short stub (because highway tunnels absolutely positively prevent hooking direct into the loop from the south). Your choice on how you get to Chinatown Park in the first place, but this is the only viable insertion point into the Transitway.

2) NSRL lead tunnels. Centered under current commuter rail tracks, merging underneath current Cove Interlocking track split.

3) NSRL main tunnel leads, Option #1. Centered under Atlantic Ave./Dewey Sq. north of Cove. Non-preferred alternative because of the Federal Reserve Building.

4) NSRL main tunnel leads, Option #2. Centered under Dot. Ave. north of Pike vent building to Seaport Blvd.



That's it. Work with the map they gave us, because going off-script either runs straight into another tunnel wall or cancels out all other projects' viable alignments. I guarantee that this ground has been combed/scorched-over enough in these threads that there's no new eureka moment in feasibility to be had by throwing new darts at the wall on wacky new "because reasons" alignments through here.

 

[Scalziand]

The only way I see for getting from Fairmount to the Silver Line tunnel would require going under the existing platforms and bus terminal.

It would be incredibly disruptive to SS during construction, and would kill the NSRL allignment.

And EMUs wouldn't fit anyway.

Just thought I'd mention this because I haven't seen it as a possibility before.... but it's not a possibility.

 

[JumboBuc]

Or something like this:

I only brought this up in the first place because, like Scalziand, I had never heard it discussed before.

 

[F-Line to Dudley]

Or something like this:

I only brought this up in the first place because, like Scalziand, I had never heard it discussed before.

We have discussed it before. There's no injection point from anywhere on the loop because of converging floors/ceilings of the 93 ramps and the loop tunnel. The loop was never ever built for further extension via Atlantic Ave.


As for every cheat that ^^tries to find a way in in spite of this^^...forget it. You can't normalize the curve radius for an injection point like that without destroying half the Atlantic Ave.-facing side of the historically-protected SS building. Try 10 more alignments and the result will be exactly the same because of buildings, curves, or needing to heighten clearances in the tunnel. If they wanted to future-proof the Transitway for commuter rail vehicles in addition to any rapid transit mode...they would've baked that into the tunnel dimensions 15 years ago. They didn't. There are no force-fits that'll make it so.


The NSRL is significantly below the lowest levels of I-93, Silver, and Red. That's the only way it finds a north-south running seam through SS without fouling anything...and it takes a full mile's worth of descending grade in the NEC and Fairmount/Old Colony lead tunnels to get down that far.

 

[Charlie_mta]

Or something like this:

I only brought this up in the first place because, like Scalziand, I had never heard it discussed before.

Better radii for rail could be accomplished if the connector tunnel (purple) could swing into (and beneath) the future USPS redevelopment area:

This alignment might still be a bit tight for commuter rail. The NSRL would run underneath this tunnel.

 

[F-Line to Dudley]

Better radii for rail could be accomplished if the connector tunnel (purple) could swing into (and beneath) the future USPS redevelopment area:

This alignment might still be a bit tight for commuter rail. The NSRL would run underneath this tunnel.

No. The problem isn't on that end. It's the loop end. You can't end-run around the highway ramp by playing games with curves. It's commuter rail. The curve you design for the EMU has to be in tolerance for the curve of any RR equipment. Them's the rules. So be prepared for anything that plays games with curves into the loop to take a wrecking ball to half the Atlantic Ave.-side historic South Station building.


Why are we still trying to force-fit commuter rail in here? The Transitway tunnel is already a 100% no-go on height. And the Congress St. curve may be no-go on radius too. If the builders wanted to leave the 1% possibility of putting commuter rail in there, they would've built it to commuter rail dimensions. They didn't...so it can't.

 

[Upstruk]

Better radii for rail could be accomplished if the connector tunnel (purple) could swing into (and beneath) the future USPS redevelopment area:

This alignment might still be a bit tight for commuter rail. The NSRL would run underneath this tunnel.

While this may not work for commuter rail I wonder if this alignment could be a light rail tunnel leading to Washington street (as a surface route to Dudley) and branching to the Tremont street subway underground

 

[F-Line to Dudley]

While this may not work for commuter rail I wonder if this alignment could be a light rail tunnel leading to Washington street (as a surface route to Dudley) and branching to the Tremont street subway underground

The only way to do that is down Essex St. to Chinatown Park. Not anywhere from the south.


I hate to sound like a broken record here, but how many times does that have to be said? It's the reality of how impossible it is to thread between the spaghetti tunnels there, not some sort of challenge to draw up even kookier routings that double-down on a southern trajectory because reasons.

 

[Charlie_mta]

While this may not work for commuter rail I wonder if this alignment could be a light rail tunnel leading to Washington street (as a surface route to Dudley) and branching to the Tremont street subway underground

Shown below is a viable (in my opinion) route for a Green Line branch tunnel, that would connect the Silver Line loop stub tunnel (next to SS) with the Huntington Ave Green Line tunnel. It would provide the desired Back Bay to SB Waterfront direct transit, as well as alleviate load on the Green Line Central Subway.

It would pass under the NB Central Artery tunnel, which shouldn't be a problem because the Central Artery tunnel is shallow depth at that point.

 

[F-Line to Dudley]

Shown below is a viable (in my opinion) route for a Green Line branch tunnel, that would connect the Silver Line loop stub tunnel (next to SS) with the Huntington Ave Green Line tunnel. It would provide the desired Back Bay to SB Waterfront direct transit, as well as alleviate load on the Green Line Central Subway.

It would pass under the NB Central Artery tunnel, which shouldn't be a problem because the Central Artery tunnel is shallow depth at that point.

No, it's a very big problem. For the thousandth time you cannot hook into the bus loop from a southerly trajectory at all. At all. There is zero room where one tunnel's roof and one tunnel's floor converge. And you cannot hook into the bus loop from a southerly trajectory that tries to cheat with side entry without a verboten demolition of the SW corner of the historically-protected SS building.

Do a thousand more map doodles through the 'exclusion' zone south of Essex and east of Surface and the answer is exactly the same.


Seriously...what is the point of this exercise? The pure thrill of masochism? Tripling-down for triple-dog-down's sake? Spending 3x as much in tunneling as the permissible alignments to slam head into same brick wall? These aren't Crazy pitches; they're parallel-universe pitches where the Big Dig was laid out in some different way than it was laid out. Work with the canvas we were given. South Bay ain't that canvas.

 

[Charlie_mta]

F-Line,

A detailed topo survey and mapping would be needed to verify, but as far as I can tell, there would be no demolition of the historic South Station needed for this route (see aerial below). The tunnel would curve away from Atlantic Ave immediately south of the old part of South Station. There is ample headroom above the NB Central Artery tunnel at this point to accommodate this new short piece of tunnel above it.

As it heads south, this proposed Green Line route would be two levels down where it finally does cross under the one-level-down NB Central Artery tunnel. I think that's certainly do-able. In fact, any of the other currently proposed alignments connecting the Silver Line with the Green Line west of South Station would require a two-level down tunnel under the SB Central Artery. My proposal simply shifts this two-level down tunnel to cross under the NB Central Artery tunnel instead of the SB Central Artery tunnel.

Moving along my proposed alignment, where it crosses the SB Central Artery, the proposed tunnel would only be a one-level-down cut and cover because the SB Central Artery is basically at-grade at this location. It would not conflict with any of the other tunnels in the Mass Pike/Central Artery interchange.

Hopefully that explains it. The only potential hang-up I can see is where it crosses beneath part of the future USPS redevelopment, and where it crosses currently empty (soon to be developed) parcels south of Kneeland Street. These developments would obviously need to include the tunnel as part of their development.

 

[F-Line to Dudley]

F-Line,

A detailed topo survey and mapping would be needed to verify, but as far as I can tell, there would be no demolition of the historic South Station needed for this route (see aerial below). The tunnel would curve away from Atlantic Ave immediately south of the old part of South Station. There is ample headroom above the NB Central Artery tunnel at this point to accommodate this new short piece of tunnel above it.

No, there isn't. The loop's tunnel wall is load-bearing for the highway above. See below.

^^You can't punch through that double-thick wall surrounding the loop.^^ That extra thickness is what's holding up 93N at its single-widest underground point, where the ramp is in process of merging. Your only way in from the south or southeast is north of the double-wide wall, clipping the historic SS building. Verboten on historical impacts.

So for the 1001st time...THE LOOP IS NO-GO. It was never meant to offer any way in. It was never designed with wiggle room to get in. If they wanted to open up a possible trajectory from the south, the entire layout of the Big Dig tunnels would've had to been changed to offer that wiggle room. This configuration has no wiggle room. They knew this in 1995.

Make yet another time-waster render pushing this...the answer's exactly the same. It is not feasible without blowing up historic South Station, and blowing up historic South Station isn't feasible.

As it heads south, this proposed Green Line route would be two levels down where it finally does cross under the one-level-down NB Central Artery tunnel. I think that's certainly do-able. In fact, any of the other currently proposed alignments connecting the Silver Line with the Green Line west of South Station would require a two-level down tunnel under the SB Central Artery. My proposal simply shifts this two-level down tunnel to cross under the NB Central Artery tunnel instead of the SB Central Artery tunnel.

Moving along my proposed alignment, where it crosses the SB Central Artery, the proposed tunnel would only be a one-level-down cut and cover because the SB Central Artery is basically at-grade at this location. It would not conflict with any of the other tunnels in the Mass Pike/Central Artery interchange.

All of this is true...and completely, totally, utterly irrelevant. You can't get into the Transitway from a trajectory through South Bay. Can't. Draw another 500 renderings through the spaghetti ramps and there is still no injection point into the Transitway. South Bay doesn't matter.

Hopefully that explains it. The only potential hang-up I can see is where it crosses beneath part of the future USPS redevelopment, and where it crosses currently empty (soon to be developed) parcels south of Kneeland Street. These developments would obviously need to include the tunnel as part of their development.

See above. Not one single detail of this matters because the Transitway loop is no-go.

"Yeah, but. . ."
"Doesn't matter."
"How about. . ."
"Doesn't matter."
"I believe. . ."
"Believing doesn't make it real."



I'm not trying to sound pissy here, but this really is OCD run totally amok. The real engineers left us a real cleanroomed path in. It just isn't via South Bay. Focus on the feasibles, not quadrupling down on the ironclad impossibles.

 

[TallIsGood]

Ok - accepting that Essex is the only way into the transitway tunnel. Did they determine in evaluating SL Phase III that it was too difficult and costly to tunnel from Boylston under Essex to SS?

So the alternatives are how to get Green Line onto Essex into the transitway and not from south or southeast, correct?

 

[Justin7]

^^You can't punch through that double-thick wall surrounding the loop.^^ That extra thickness is what's holding up 93N at its single-widest underground point, where the ramp is in process of merging.

Pretty sure you're wrong here.

 

[F-Line to Dudley]

Ok - accepting that Essex is the only way into the transitway tunnel. Did they determine in evaluating SL Phase III that it was too difficult and costly to tunnel from Boylston under Essex to SS?

So the alternatives are how to get Green Line onto Essex into the transitway and not from south or southeast, correct?

The runaway costs for SL were mainly tied up in. . .

• All the extra tunneling between Boylston and South End required to tie Phase III into the Washington St. surface line. And how many design revisions they had to do to that tunnel route southwest of Boylston when each of their earlier alternatives hit fatal blockers.

The end-to-end Dudley-Seaport route has little natural demand and was the thin veneer they used to justify doing BRT instead of rail. Cancellation of Phase III was their admission that this shotgun marriage of the routes wasn't going to work.
​

• Boylston Under station. The destruction underneath Boston Common and disruption of the burial grounds drove up the mitigation costs through the moon, and the tight loop they had to build to make the lower-level station work was such a speed-killer that it maimed headways through the entire Transitway. Think it's crowded now? Phase III would've made it a whole lot worse.

• Underpinning Chinatown station for Chinatown Under. Unfortunately the Orange Line and Chinatown station are positioned at the absolute narrowest block of Essex, so the abutter mitigation was obscene.

The whole stretch of Essex west of Surface Rd. + the last block of Boylston were very hard on building mitigation because of the narrowness of the street and extra width required for BRT, but it wasn't killer. The two new station levels, the superfluous extra tunneling to shiv in an acceptable South End portal alignment, and Boylston Loop under the Common were the fatal blows. The FTA, which the state was counting on to supply federal funding, slapped a "not recommended" rating on it because of all the problems, and the state had no means of covering the >$2B and rising cost.


Anything light rail would've cost substantially less, and anything light rail that tied into all or part of the existing Tremont St. tunnel and Boylston upper level would've cost half as much by eliminating Boylston Under and the thousands of extra tunneling feet to the South End portal.

It does mean that a straight Essex alignment into Boylston gets rendered impractical on LRT because of the interface with Boylston. You can't just punch through the wall and put an at-grade junction in the middle of the station; that would wreck Green Line traffic management. You can't easily slip under and do some convoluted loop onto the upper level without knocking down a couple buildings, or going around the block and building too much of the extra tunneling that sank the BRT project. You can't turn down Washington and go around the block because Orange is there and starts descending way deep between Chinatown and Tufts. And going lower-level to the place between Boylston and Arlington where the old Boylston portal/Public Gardens portal/Post Office Sq. subway provision meet points wrong direction for the downtown access where all the demand originates (it's very engineering-feasible, but it's going to score much more poorly on total utilization than a downtown-facing alignment and probably gets its rating dropped to a much lower priority level that won't get it funded in our lifetimes).


For all practical purposes you have to pick a different block to get between Chinatown Park and Boylston station. It doesn't necessarily have to be the Marginal Rd. alignment down by the Pike that we focus on most frequently.

• Could be nice, wide Kneeland. Although that requires some destruction of the old Tremont tunnel to punch in/out of it, and wouldn't have an Orange transfer because it crosses at the exact midpoint between Chinatown and Tufts (I guess you could snake a concourse to Tufts, but it would be longer than the Winter St. concourse between Park and DTX).

• Could be narrow Beach + Lagrange. Also requires some destruction of the old Tremont tunnel to punch into it, as well as some ugly sharp turns and more building mitigation. Nearer to Chinatown, but still a bit of a long concourse.

• Could be Oak St. Would hit Tufts more directly and recycle the entirety of the Tremont tunnel. But it's even narrower in parts than Beach/Lagrange with tightly-packed buildings, and requires the same building mitigation on the Hudson/Kneeland corner as the easier Marginal Rd. alignment.

Marginal just ends up pricing out cheapest and having most overall farebox recovery with combination of. . .

• full re-use of the Tremont tunnel and no modifications required to Boylston
• fewest building mitigations because of the urban renewal zone around the Pike
• cheaper tunnel construction along the Pike and 93-to-Pike ramp because of the sideways access through the retaining wall, despite somewhat more total tunneling distance than the others.
• Fewer sharp turns, higher speeds, faster trip despite the extra tunneling distance
• Eliot Norton Park providing footprint for a linked Tufts station that avoids all need to underpin an Orange station (i.e. avoids one of the big blows that helped kill the SL alignment) and provides the *close enough* concourse access that the Kneeland and Beach/Lagrange alignments lack
• Easiest means of grafting on a tunnel split for conversion of Washington St. to light rail.
• Ability to infill an Ink Block station at the tennis courts on corner of Washington/Marginal
• Ability to provision for a multi-directional junction incorporating a future westbound subway to Back Bay station replacing Copley Jct., utilizing the 4-track flyovers in the Tremont tunnel and space under Eliot Norton Park for a 4-track station to handle the traffic loads. (Note: this probably means you use Tremont St. instead of Oak to reach Marginal since it's wide enough for 4 tracks without building mitigation, and the traffic island at Marginal is exactly the right size to put a multi-direction junction/wye underneath.

So for overall scoring purposes you get more √+ grades and fewest √- grades that way.


But it's not the only way to do it. You can play around with the whole street grid west and south of Essex @ Surface if there ends up some blocker to the Marginal alignment, or you simply want to try something different. The only thing that is 1000% impossible is through the South Bay spaghetti ramps, and anywhere north of Essex @ Surface where the Red Line tunnel under Summer and more highway ramps block every path. It must be Essex @ Surface, down the Big Dig-cleanroomed portion of Essex to Atlantic, and join the Transitway north of the loop under the front-entrance plaza of One Financial. That is the only way in. No others.

 

[F-Line to Dudley]

Pretty sure you're wrong here.

See for yourself: https://goo.gl/maps/DnhoTKaJLsD2. Dragging the little Street View guy to the exact point of entry in Charlie's render lands you precisely at the widest point of 93N and heaviest spot of load-bearing of the ceiling. This is the exact location of the double-wide spot in the Transitway loop's wall.

That thick wall lasts until the end of the ramp merge. Drag the Street View guy to the end of the ramp merge, and you're at or past the corner of the SS building.


It's no-go. It is 100% no-go.

 

[Upstruk]

Isn't the Transit way above 93 North? This is basically a two level tunnel where the floor of the transit way is the ceiling of 93 N below, correct? You can see from the linked street view that the ceiling of the 93 N tunnel appears to be the underside of the concrete structural slab. (This is different than the I-90 tunnel where the ceiling is suspended below the roof structure.)

If after the end of the existing transit way the roof of 93 N (floor of an extended transit way) changes construction to something that can not take the load of an extended transit way then yes the transit way tunnel can not be extended without great cost.

If that is not the case the transit way seems like it could ascend up the surface along with 93 N.

I do have a few questions regarding the Hudson St route. In Google Earth you can look at aerials back to 1995 for this area. In 2002 there is a view of the current Chinatown park which shows the former exit ramp from 93 south in the Dewey Sq tunnel. This ramp goes right up to the Danity Dot Building (now Radian). This is where the green line transit way tunnel would go. If this ramp was simply filled this seems like a very easy place to build the tunnel (however if the ramp was incorporated into the current 93 S tunnel, there is no place for a tunnel to Hudson Street). Also the Dewey Sq tunnel ventilation stack in the Chinatown Park is very close to the building with the Hot Pot Buffet at the Chinatown gate. Is there room here to slip a green line tunnel between 93 S, its ventilation stack and this building?

 

[F-Line to Dudley]

Isn't the Transit way above 93 North? This is basically a two level tunnel where the floor of the transit way is the ceiling of 93 N below, correct? You can see from the linked street view that the ceiling of the 93 N tunnel appears to be the underside of the concrete structural slab. (This is different than the I-90 tunnel where the ceiling is suspended below the roof structure.)

If after the end of the existing transit way the roof of 93 N (floor of an extended transit way) changes construction to something that can not take the load of an extended transit way then yes the transit way tunnel can not be extended without great cost.

If that is not the case the transit way seems like it could ascend up the surface along with 93 N.

Thanks for pointing that out. I did get it that backwards. Doesn't change the infeasibility, however.


To clarify:

93 mainline is underneath the Transitway. End of the loop is where Transitway floor and 93 mainline's ceiling meet, corner of Summer and East St.

The onramp from the first divider peg out to the portal is on significantly steeper grade than the 93 mainline because its portal is much closer. So there's a 'hump' in the roof until that same East St. intersection spot where the divider wall ends. That accounts for the double-thick wall.


Now here's the math that serves up the same bad news as before.

Tunnel width:

• 10 ft. between track centerline and wall. (source: GLX design specs)
• 6 ft. thick walls (source: Mass Pike tunnel specs, http://www.concreteconstruction.net/Images/Concrete Boxes_tcm45-591056.pdf). Since this is same soil and depth, and the Pike walls are waterproofed where the leaky 93 walls are not, these walls will be same thickness to achieve same waterproofing.
• A center dividing wall between the tracks, since the tunnel will be supporting the commuter rail tracks/platforms above and the plaza in at the Atlantic Ave. entrance. Can be thinner than the side walls, but because of proximity of the nearest CR track to the Transitway hook-in I doubt it's any less than 3 ft. wide.

Tunnel width maths:

• (10 ft. centerline clearance x 2) = each track bore 20 ft. wide
• x (2 track bores) = 40 ft.
• + (6 ft. side walls x 2 = 12 ft.) = 52 ft.
• + (3 ft. center wall) = 55 ft.

Your tunnel is 55 ft. wide. Tangent track can get squeezed by 2 ft. on the centerline clearances per the design manual, but this is a curved tunnel so that's not in-play. 55 ft. or bust.


The loop is a double-loop--"inner" and "outer"--surrounded by a small center area arranged with support pegs and utility room. Inner loop is the minimum turn radius of a 60-footer, outer loop somewhat wider; loops are separated by pavement stripes. Only picture of it I was able to find, from Opening Day in 2004: https://sery2831.smugmug.com/Transit/Silver-Line-Opening/i-3pCHt8D/A.

Insertion point for the trolley tunnel has to stay clear of the loops if you have any intention of keeping SL1 (and any other present/future) bus service in the Transitway. Safe assumption that it's a dealbreaker if you're kicking the buses entirely out.

This creates a big problem. You can't ram the trolleys into the middle of the loop and follow the contours of the NE quadrant of the loop back onto the mainline (i.e. take a chunk out so it's a "two-thirds" loop / "one-third" mainline). The least-invasive means of construction ends up creating several incredibly dangerous safety issues for the transit vehicles:

• Bus drivers on the loop can't see to the right because of the curving wall. Outbound trolleys would be merging in at oblique angle mid-loop, with dividing wall ending too abruptly for a bus driver to see them. Extreme sideswipe risk.
• Bus drivers on the loop have obstructed view to the left because of the center supports + utilities and can't see the mainline ahead. Inbound trolleys would be crossing wrong-way across the NE quadrant of the very tight inner loop. Extreme head-on collision risk...and that's an instant bus driver fatality given the weight differential.
• You can't close off the inner loop and just leave the slightly less-dangerous outer loop because there has to be a place to stuff out-of-service buses and has to be a way around a bus disabled on the loop.
• Bus drivers slamming brakes on the loop to avoid a trolley they didn't see are at severe risk of jackknifing the 60-footers inside an enclosed/unventilated tunnel. Unacceptable risk for emergency personnel access and fire suppression.
• Can't install wayside traffic light signals mid-loop because of the obstructed sightlines and drivers paying attention to staying within their lane markers not the lights on the wall. A signal turning red at the last moment would be too easily missed, and the jackknife risk makes any sudden braking inherently dangerous.
• No potential for an auto-stop signal system in the Transitway like there is on Red/Orange/Blue and most likely will be installed in the future on Green. Impossible to co-mingle modes that way, so it's wayside signals + line-of-sight between the merging point and SL Way. Even if you could install collision avoidance on the trolleys alone, it makes no difference because the buses won't have it and they are the ones dealing with the most acute sightline dangers (see also: sudden involuntary brake application on bus rounding the loop = jackknife).

^There's no give with these kinds of safety considerations.^ It won't be approved for build if the lowest-profile insertion point makes the loop unsafe for buses.


Therefore, you have to insert after the loop has almost completely straightened and there's adequate sight distance for bus drivers coming off the loop to see if they've got a green or red signal where the trolley tracks merge. The notch in the wall for Phase III up Essex is roughly at this spot (depicted in the Blue Book, p. 46 as the "Bellmouth" on the Transitway wire schematic map), if you want a very rough indication of what those sightlines need to be. You also have to insert after the tunnel has narrowed enough that you can end the dividing wall between the loop and the trolley tunnel and have one cavern for the rest of the merge, because--recall--you're supporting the plaza and commuter rail entrance upstairs and are a lot closer to the surface than 93N.

To get a sense of where this insertion point has to be, see the tunnel diagram a few posts up. Tilt your head at the loop so the mainline towards SS is pointing at the 12:00 position. Your insertion point for the trolley tunnel is probably no lower than the 2:00 position. That corresponds on the surface with the curb across the street from the Essex Hotel front door, along the taxi stand parking row.


At that spot you have a less-than 50 ft. radius between the SW cornerstone of the historic South Station building and that 2:00 spot on the loop, so you've run out of room before that 55 ft. wide trolley tunnel can thin out and shed its inbound-side and center walls for the merge into the Transitway cavern. It's close, but not close enough to build to-spec while avoiding catastrophic building impacts. Even if that radius estimate is on the low end and you do wind up with a very snug-fitting merge of your your 55 ft. wide trolley tunnel, you are not going to be able to dig up to the last inch of the SS cornerstone. It's a 120-year old granite foundation. Several feet of buffering is mandatory (no less than 5, but probably more like 10) if you don't want to crack the SS foundation and walls like the Copley station elevator shaft cracked Old South Church from a distance of 15 ft. away. Several feet of buffering gets you right back where you started: below the minimum allowed tunnel width for making the merge at the soonest possible safe spot for mixing trolleys and buses.

It's no-go. Unless you kick out the buses so you can cannibalize the loop. But kicking out SL1 lowers the value enough that it will never get approved for build, so it's still no-go.



So...to recap, I got my vertical levels flip-flopped there. But the exact point on the map where you run out of room to insert the tunnel ends up same as before (now verified by calculator). It can't be done without grave impacts to the SS building, or safety impacts that won't be allowed for co-mingled buses.


If you want to call it "So you're saying there's a 1/1000th of a chance it'll work?"...yeah, sure, knock yourself out. It doesn't make it any less insane to keep quadrupling-down on the 0.001% for sake of proving...something?...when this is a transit project the Seaport must ultimately have in order to sustain its growth. The existence of a Silver Line Phase III equivalent isn't a Crazy Transit Pitch; it's an officially proposed unfunded mandate. Nobody tries to fulfill a public works mandate on a scratch ticket odds of engineering feasibility at twice the price. They left us Essex St. Don't waste time endlessly debating functional impossibles; bloody use it and get the Seaport its transit mandate.

I do have a few questions regarding the Hudson St route. In Google Earth you can look at aerials back to 1995 for this area. In 2002 there is a view of the current Chinatown park which shows the former exit ramp from 93 south in the Dewey Sq tunnel. This ramp goes right up to the Danity Dot Building (now Radian). This is where the green line transit way tunnel would go. If this ramp was simply filled this seems like a very easy place to build the tunnel (however if the ramp was incorporated into the current 93 S tunnel, there is no place for a tunnel to Hudson Street). Also the Dewey Sq tunnel ventilation stack in the Chinatown Park is very close to the building with the Hot Pot Buffet at the Chinatown gate. Is there room here to slip a green line tunnel between 93 S, its ventilation stack and this building?

It was infilled. They deleted that ramp, cannibalized the northbound side of Surface to make it a SB-only one-way, and put a new onramp on the old NB side. The infilled offramp was on what's now the parking row and bike lane on that block of Surface. If you go back to that grainy shot on Historic Aerials you'll notice the Surface SB travel lanes are in the same exact position but it entirely lacks a shoulder.

At the narrowest point of the park directly in front of the Radian you have 60 ft. of width to work with for the tunnel. However...unlike the Transitway approach that comes underneath the CR tracks, has to support the weight of commuter trains...and merges too soon into the Transitway to shed its center wall and narrow...this trolley tunnel has more room after underpinning 93S to shed its center wall and shrink in width as a single bore. That means (per GLX specs). . .

(10 ft. of inbound track centerline clearance to wall)
+ (10 ft. of outbound track centerline clearance to wall)
+ (13 ft. of between-tracks centerline clearance)
= 33 ft.

A 7 ft. reduction in width eaten up by the centerline clearances, minus another 3 for deleting the center wall. Therefore, if the walls stay 6 ft. thick, you have a 45 ft. wide tunnel instead of 55 ft. and 15 ft. of buffer space in front of the Radian. There's no risk to the Radian's new-construction concrete + rebar foundation from that distance like there would be to South Station's century-old granite foundation from a lesser distance.

Equal 15 ft. slack space for slipping between the Hot Pot Buffet building and the tunnel vents, so that's likewise a non-issue.


And as for Hudson St...because the tunnel is tangent and not curved, you can shrink those 10 ft. centerline clearances to the minimum allowable 8 ft. (source: GLX specs) and lop another 4 feet off the tunnel width to net a 41 ft. wide tunnel for a short stretch. That gets you through the extreme-narrowest portion of Hudson between the Golden Leaf building and the Wings Kitchen building (tight...careful mitigation required...but no worse than what SL III was going to have to mitigate on whole blocks worth of upper Essex). All points on Hudson south of Kneeland it's >50 ft. thanks to the plaza in front of One Greenway, and then you're home free in Pike urban renewal land.



Don't get me wrong; this is an expensive-ass project with building mitigations on any potential route. $1B-2B range when inevitable (but hopefully sub-GLX) bloat gets baked in. It's just not the $3B-4B that Silver Line Phase III was surging towards and assuredly going to top by the time design-bid and all that contractor bloat hit its final estimate. But figure that SL Phase III projected +20,000 new daily Silver Line riders and +4500 all-new transit riders in its headway-crippled incarnation shackled to the Dudley route through speed-killing Boylston Loop. As a much faster Green Line branch hitting all the downtown transfers, all heavy rail lines (SL III didn't go near Blue), and both North and South Stations the projected ridership is a whole lot higher and capital cost per rider craters to pretty reasonable level. Compared to the GLX sticker shock, $1-2B is about the going rate for an all-tunnel project with 1 all-new transfer subway station (Tufts), 1 all-new infill subway station (Ink Block) and 3x the projected ridership.

 

[Upstruk]

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Thanks for the research and analysis. Above is the image I referred to of the former ramp adjacent to the Radian.

 

[Deetroyt]

F-line, would the new Tufts transfer station allow riders from Dudley (or anywhere on Washington st.) to change to a Seaport destination green line train? Or would they need to go to Boylston Station to switch ?