Crazy Transit Pitches

[Charlie_mta]

Go back to page 73 of this thread; we talked a little about the geological challenges of tunneling.

http://written-in-stone-seen-throug...chitectural-geology-of-boston-roxbury_27.html

^This site has the bedrock maps of greater Boston. First map on the page copied below.

The pale tan coloring on the map shows all the glacial mush that's impossible to deep-bore tunnel under. The speckled tan area is slightly rockier debris field...not exactly solid, but bulky enough to support the integrity of Beacon Hill, Brookline Hills, Newton Highlands, etc. That little green toothpick threading from North Cambridge to the Middlesex Fels is a very dense, very hard volcanic dike. Black lines are geologic faults, which you can see cluster around the Charles, Muddy, and Neponset basins. For a reference point you can see they've added all the major water crossings: Longfellow, Mass Ave. bridge, Tobin, etc. Most of the mushiest mush goes 1/2 to 1 mile deep.

Everything we've dug in the tan mush is cut-and-cover, including the Big Dig. The only thing deeper than cut-and-cover ever dug in the speckled tan debris field are the cross-Harbor tunnels and the Charles-Park St. bore of the Red Line through Beacon Hill where the steepest side of the hill afforded soft-digging on a level trajectory without disruption above. And the only place where a TBM has carved out bedrock underneath developed property with no surface disruption is...that little few-blocks-wide toothpick of a volcanic dike from Porter-Davis.


There is nothing else. Tunneling inbound under Mass Ave. is a cut-and-cover job that not only stays in the mushiest of the mush as far south as Huntington, but also has to cross 4, if not 5, faultlines en route. Now consider the price tag NYC is swallowing for the 2nd Ave. Subway. Manhattan is one of the most solid slabs of coastline bedrock on the East Coast. Highly-compressed metamorphic rock with giant seams of marble running through midtown. It's easy to build some of the world's oldest and tallest skyscrapers on that little island for a reason.

If you take 2nd Ave. and re-project the costs to building through mush that requires more mitigation to abutting structures and mitigation to soil movement for all the faults it has to cross...price tag probably soars to half a Big Dig. More expensive than the SL Phase III that was too expensive to build, more expensive than the Urban Ring that was too expensive to build, and possibly as expensive or more than the N-S Link. With way more economic disruption because it's Mass Ave. that's going to be carved up in segments for a full decade. That's totally untenable. I think that would be totally untenable even if we went megaproject-mad and started tearing up streets for all the other officially-proposed downtown transit projects.



I know everybody wants this, but it's beyond the realm of physical possibility. No engineer with a straight face would sign off on a routing so self-defeating on required mitigation. This has nothing to do with political will or not thinking big enough...the very act of trying to construct it and fund all the mitigation required with that construction is patently insane. Its own transit Moby Dick-like pursuit. Civil engineering just doesn't work that way.

The Red Line from Harvard Sq to Davis Sq is a deep bore tunnel, and is in the tan area on the map.

 

[omaja]

If there's really no way to bore tunnels for a Mass Ave subway and the only options are to build an elevated structure or not build anything, don't you think the majority of people would say to go with the elevated?

 

[George_Apley]

Where the red line branches off Mass Ave on to Main St is right before MITs campus of buildings with large setbacks begin. A lot of the buildings between the split and MIT are short buildings likely to be demolished in favor of something taller soon. After MIT, the hypothetical subway could jut left and go underneath Charlesgate and the beginning of the Fens. Then bang a left after the MFA and go beneath Ruggles St, dive under Ruggles and follow Melnea Cass to Widett Circle, where it can reconnect with the Red Line at Andrew, forming a loop.\

How do you go under the Fens from Charlesgate to Louis Prang? Wouldn't that hugely fuck up the water shed?

 

[Matthew]

The Red Line to Davis goes through that strip of green on the map.

But more importantly, cutting headways on the busiest section of the Red Line, from Kendall to Andrew, is what's truly crazy about the proposal. Not going to happen.

 

[JeffDowntown]

The Red Line from Harvard Sq to Davis Sq is a deep bore tunnel, and is in the tan area on the map.

Also, please explain to Parsons Brinkerhoff that you cannot deep bore tunnel in Boston Blue Clay. They just completed the 2.5 mile, 17 ft. diameter deep bore North Dorchester Bay. CSO tunnel for the MWRA. The entire length is in the tan glacial fill material on the map.

Tunnel runs under the dense South Boston beachfront area from Pleasure Bay to Carson Beach.

Maybe the T doesn't know how to deep bore tunnel in Boston Blue Clay, other glacial fill, but competent tunneling contractors certainly do!

 

[JeffDowntown]

How do you go under the Fens from Charlesgate to Louis Prang? Wouldn't that hugely fuck up the water shed?

You mean like the way the red line goes effectively under the Fort Point Channel from South Station to Broadway? Engineers knew how to do it a century ago???

 

[JeffDowntown]

No...no...no. Go read up on the geology engineers have to contend with before making assumptions like that about "unimagination" or lack of political will.


Yes...you can theoretically deep bore. At what cost, and at how many complications? It's not easy-scoop clay of uniform composition. It's a glacial debris field of of terrain scraped off the western hills...loose rubble with boulders and soils deposited from umpteen different locations. Filled on top by a layer of mudflat silt and a whole lot of human landfill. And lined with faults because all this fill has points of instability that can shift over time as debris settles. There's absolutely nothing homogenous about the ground composition, and nothing "native" or permanent to Boston like bedrock is native. What you get on one 100 ft. stretch of tunneling can be completely different from what you get on the next hundred feet, and how you have to mitigate the tunnel and surroundings can be different every few feet. It's not predictable or mappable until you're actively digging. This added billions to the Big Dig cost and prevented seamless underground boring there.

If it costs $4B per mile to build a Mass Ave. subway--which is a distinct possibility--something is very wrong with the political will if it gets pushed that hell or high water. It's antithetical to civil engineering sanity to fight an uphill battle at any cost just to say you can. Engineering's supposed to mitigate challenges, not escalate. Choosing the most difficult possible path to build is irresponsible: fiscally, logistically, logically. It's a sign that something's dreadfully wrong with planning. One example of that run-amok would be the Tappan Zee Bridge being built over the single widest and hardest crossing point of the Hudson because of a stupid inter-agency political turf war. It will now cost $16B or higher to replace at that location. Attempting to do a deep-bore under Mass Ave. through the geological equivalent of vomit is Tappan Zee-crazy. So is the cheaper cut-and-covering with how much economic ruin it bring for the years if not decades that Mass Ave. businesses would be disrupted during such invasive construction.

Even the Big Dig played by the rules and chose path of least engineering resistance despite its enormous complexity and lifetime-long design compromises like the leaky slurry walls.


I'll say it again: civil engineering DOESN'T WORK THAT WAY. And trying to force it to work that way with the political equivalent of rabies so a 2D map of the city has pretty straight lines on it is not a virtuous thing: it's a serious brain illness. One that can't be substantiated with logic...only belief that things must be so because I say so, and if you don't agree you're the problem. The Tappan Zee Bridge was built from political spite, not factual arguments. So is the Mass Ave. subway if "unimaginative" pols are the prime argument for proceeding at mutually-assured financial destruction and construction so arduous we could build a completed Silver Line and N-S Link in less time with less disruption for less money.

A bit more on Deep Bore Tunneling (from Parson Brinkerhoff) in this impossible Boston Blue Clay and gravel fill: From a PB report in 2010:

"'The CSO runs 5 to 11 meters (17 to 35 feet) under Day Boulevard, the main road accessing the parkland along Carson Beach in South Boston. So as not to interrupt traffic, a cut-and-cover tunnel was ruled out in favor of a bored tunnel. Geotechical staff found that a TBM would have to tunnel through mostly clay as well as sand and gravel. “This was rather challenging—a TBM boring through different materials,” says Maybury. “Kudos go to our geotechnical team, who had accurately laid out profiles of the materials. This profile was instrumental in giving the contractor the necessary data to effectively plan his tunneling means and methods.”"

 

[JeffDowntown]

No...no...no. Go read up on the geology engineers have to contend with before making assumptions like that about "unimagination" or lack of political will.


Yes...you can theoretically deep bore. At what cost, and at how many complications? It's not easy-scoop clay of uniform composition. It's a glacial debris field of of terrain scraped off the western hills...loose rubble with boulders and soils deposited from umpteen different locations. Filled on top by a layer of mudflat silt and a whole lot of human landfill. And lined with faults because all this fill has points of instability that can shift over time as debris settles. There's absolutely nothing homogenous about the ground composition, and nothing "native" or permanent to Boston like bedrock is native. What you get on one 100 ft. stretch of tunneling can be completely different from what you get on the next hundred feet, and how you have to mitigate the tunnel and surroundings can be different every few feet. It's not predictable or mappable until you're actively digging. This added billions to the Big Dig cost and prevented seamless underground boring there.

If it costs $4B per mile to build a Mass Ave. subway--which is a distinct possibility--something is very wrong with the political will if it gets pushed that hell or high water. It's antithetical to civil engineering sanity to fight an uphill battle at any cost just to say you can. Engineering's supposed to mitigate challenges, not escalate. Choosing the most difficult possible path to build is irresponsible: fiscally, logistically, logically. It's a sign that something's dreadfully wrong with planning. One example of that run-amok would be the Tappan Zee Bridge being built over the single widest and hardest crossing point of the Hudson because of a stupid inter-agency political turf war. It will now cost $16B or higher to replace at that location. Attempting to do a deep-bore under Mass Ave. through the geological equivalent of vomit is Tappan Zee-crazy. So is the cheaper cut-and-covering with how much economic ruin it bring for the years if not decades that Mass Ave. businesses would be disrupted during such invasive construction.

Even the Big Dig played by the rules and chose path of least engineering resistance despite its enormous complexity and lifetime-long design compromises like the leaky slurry walls.


I'll say it again: civil engineering DOESN'T WORK THAT WAY. And trying to force it to work that way with the political equivalent of rabies so a 2D map of the city has pretty straight lines on it is not a virtuous thing: it's a serious brain illness. One that can't be substantiated with logic...only belief that things must be so because I say so, and if you don't agree you're the problem. The Tappan Zee Bridge was built from political spite, not factual arguments. So is the Mass Ave. subway if "unimaginative" pols are the prime argument for proceeding at mutually-assured financial destruction and construction so arduous we could build a completed Silver Line and N-S Link in less time with less disruption for less money.

One more detail about the North Dorchester Bay deep bore tunnel, the COST. (Yes, I know this is not a subway tunnel, but it also did not cost the bloated $4 billion per mile. Look at both the timeframe and the cost - because they did not have to disrupt all the surface utilities and streets!)

Completed (real) cost as of 2010, per MWRA public reporting:
http://www.mwra.state.ma.us/monthly/wac/presentations/2010/110410-ndb.pdf

North Dorchester Bay CSO Storage Tunnel
17-ft. finish diam.
2.1 miles long
19 MGal storage
Mined and lined
10,832 feet of
tunnel in 9 mos.,
incl. 1-month
suspension.
Contract cost:
$146.8M

 

[George_Apley]

You mean like the way the red line goes effectively under the Fort Point Channel from South Station to Broadway? Engineers knew how to do it a century ago???

Isn't the Red Line in a tube through the Channel?

 

[davem]

How do you go under the Fens from Charlesgate to Louis Prang? Wouldn't that hugely fuck up the water shed?

I mean, with all the pumps, gates and culverts the Fens is a prerty artificial waterway as it is. Besides, its not like it would run directly under the Muddy, but next to one of the roads along its edge. The Fens is a nice, wide reservation. I'm just looking for a way to build a cut and cover subway without killing Mass Ave. Running it through the Fens it could be only a foot or two under the surface, and not disturb anything more than a few trees.


As far as headways, who is saying this would cut downtown trips? That's insane. It would just be another branch. Depending if/where/how it connects back to the main line in the south, it could even loop back up to downtown, which would add trains. Also, I don't think you are taking into account how many people ride the green and orange lines east to transfer to red, especially from the back bay. This isn't just about the 1, but all the people going out of the way downtown just to go back out again, clogging up park st, etc.

 

[Matthew]

Basics of branching, dave: branching cuts frequency. Alewife to Andrew via Mass Ave would mean there are more trains running Alewife-Central than Central-Park.

 

[davem]

Basics of branching, dave: branching cuts frequency. Alewife to Andrew via Mass Ave would mean there are more trains running Alewife-Central than Central-Park.

Anyone aware if the design of new Harvard station precludes reopening the Eliot yard tracks? Turning either the new mass ave branch or the braintree branch at harvard would solve these issues (and it could later be extended to Allston). With the massive scope of this project, partially rebuilding harvard wouldn't be out of scope. Central would likely have to be rebuilt as a dual island station as well, if possible. Even with the existing configuration though, while there would be excess trains central-north, it doesn't mean they have to cut trips downtown. When it comes down to it the designers of the rl north extension really shot themselves in the foot not installing more frequent crossovers in general, and a pocket track after harvard. Having to run everything to alewife is a huge flaw.

And just to reiterate, a mass ave branch would siphon off a decent amount of existing RL traffic, which needs to be taken into account when weighing headways. So even if you do have to reduce the downtown headways by a train or two, the traffic might not even be there. I'm too lazy to find the numbers and am just doing this seat of pants, but it would be intresting to see just how many people are getting off the red line at park/dtx/south station and taking a train/bus east. That, plus the ridership of the 1 is the potential traffic for this branch. I have a feeling its a significant number.

 

[Matthew]

I'm not saying that it would necessarily reduce trips from current levels on the central section. But this design would end up putting the greatest number of trains per hour on the northern section of the Red Line, rather than having the greatest number of trains per hour be in the central section. I think that's a strange design for a rapid transit system, which usually focuses the greatest amount of service on the most central area.

Maybe census/job/source-destination data can justify it. But I think it should be a very thorough justification for what is a very expensive project that turns a rapid transit trunk inside-out in terms of service levels.

 

[c_combat]

What would converting the current D Line into a heavy rail line entail? I mean closing it down for an amount of time of course would be a thing. Would a heavy rail Green Line be cool?

 

[c_combat]

Converting GL stations downtown would be the most costly. Platform extension, track depth relative to the platform and such...

 

[davem]

I'm not saying that it would necessarily reduce trips from current levels on the central section. But this design would end up putting the greatest number of trains per hour on the northern section of the Red Line, rather than having the greatest number of trains per hour be in the central section. I think that's a strange design for a rapid transit system, which usually focuses the greatest amount of service on the most central area.

Maybe census/job/source-destination data can justify it. But I think it should be a very thorough justification for what is a very expensive project that turns a rapid transit trunk inside-out in terms of service levels.

I'm not really arguing with you, its just a "what the hell else do you do" situation. Not having a way to turn trains at Harvard that doesn't block up both tracks is a massive flaw, that is made worse when trying to figure out what do do with mass ave. The only solution I see is either to have wasted capasity to alewife, or rebuild harvard with turnbacks

 

[Matthew]

What do you do? Why, bus lanes on Mass Ave.

Maybe that's too "reasonable" for this thread.

Ok, crazy pitch: if somehow a deep bore were made to work, it probably would not be able to tie in with the existing subway anyhow. So it would be an independent system. Maybe use Copenhagen-style equipment. The yard would go somewhere down by Andrew/Widett/Newmarket. Or while we're thinking crazy, why not continue the ring over to City Point? Construction will probably require the taking of at least 1 parking space, causing a volcanic eruption in Southie, and voila: solid rock to bore through.

 

[davem]

What do you do? Why, bus lanes on Mass Ave.

Maybe that's too "reasonable" for this thread.

Ok, crazy pitch: if somehow a deep bore were made to work, it probably would not be able to tie in with the existing subway anyhow. So it would be an independent system. Maybe use Copenhagen-style equipment. The yard would go somewhere down by Andrew/Widett/Newmarket. Or while we're thinking crazy, why not continue the ring over to City Point? Construction will probably require the taking of at least 1 parking space, causing a volcanic eruption in Southie, and voila: solid rock to bore through.

^lol

Honestly, I feel like trying to fit and enforce dedicated bus lanes on mass ave would be almost as hard as building a subway. When they were building "west chester park" I have a feeling they never saw it being what it is today.

--also, I'm on the train to NY now, I really have nothing else going on but this site for another two hours.

 

[F-Line to Dudley]

The Red Line from Harvard Sq to Davis Sq is a deep bore tunnel, and is in the tan area on the map.

Nope. It's shallow cut-and-cover tunneling for the first half-mile out of Harvard. There's a regular below-street emergency exit at the corner of Chauncey St. that puffs out a loud blast of subway air with each passing train as you're waiting for the walk signal to cross the street to the new Lesley U. building. And you can solidly feel the rumble beneath your feet as far north as the Shepard/Wendell intersection, further if you've got keen senses. Remaining distance to just shy of Porter Exchange Mall is the transition zone from shallow to deep, but at such a gradual descent that most of the construction was still done as ever-deepening hole in the road until they were almost at Porter. That bedrock seam starts at roughly the same latitude as the northern tip of Fresh Pond. They weren't TBM'ing through real surface-supporting terra firma until past Linnaean St.

This is the widest portion of Mass Ave. in town--75' curb-to-curb--and in 1980 was mostly a drab stretch of 1-2 story storefronts with occasional 4-5 story brick apartments. Road's only 60' wide from Main St. to the River and 55'-58' wide on the Boston side, and has 6-story or greater abutting structures on nearly all of that stretch. It'll also require it's own transition zone deep dig on both sides to get under the Charles, so that's a very deep gash in the road in the places where the construction causes maximum disruption and where the soil is at its siltiest. See where this starts getting entangled in itself?

Also, please explain to Parsons Brinkerhoff that you cannot deep bore tunnel in Boston Blue Clay. They just completed the 2.5 mile, 17 ft. diameter deep bore North Dorchester Bay. CSO tunnel for the MWRA. The entire length is in the tan glacial fill material on the map.

Water tunnel ≠ double-bore transit tunnel. Not in size. Not in weight distribution. Not in utilities carried. But why don't you go explain to Parsons Brinkerhoff why all tunnels are exactly the same. I'm sure they'll say, "D'oh! Why didn't we build the Big Dig that way?!?"

Maybe the T doesn't know how to deep bore tunnel in Boston Blue Clay, other glacial fill, but competent tunneling contractors certainly do!

Right. Because every public piece of civil engineering is designed and built totally in-house by nuthin' but state employees wearing mining hats. And nobody like Parsons Brinkerhoff with actual engineering expertise and experience subcontracting gets allowed to touch it. Because that's how state gov't really works!

Nope, bud. You're on the same nonsensical spleen-venting ¡UNIMAGININATIVE POLS! rant you were on last page. Calm down for a sec and think how the real world works before trying to pass this off as your argument.

 

[F-Line to Dudley]

Anyone aware if the design of new Harvard station precludes reopening the Eliot yard tracks? Turning either the new mass ave branch or the braintree branch at harvard would solve these issues (and it could later be extended to Allston). With the massive scope of this project, partially rebuilding harvard wouldn't be out of scope. Central would likely have to be rebuilt as a dual island station as well, if possible. Even with the existing configuration though, while there would be excess trains central-north, it doesn't mean they have to cut trips downtown. When it comes down to it the designers of the rl north extension really shot themselves in the foot not installing more frequent crossovers in general, and a pocket track after harvard. Having to run everything to alewife is a huge flaw.

And just to reiterate, a mass ave branch would siphon off a decent amount of existing RL traffic, which needs to be taken into account when weighing headways. So even if you do have to reduce the downtown headways by a train or two, the traffic might not even be there. I'm too lazy to find the numbers and am just doing this seat of pants, but it would be intresting to see just how many people are getting off the red line at park/dtx/south station and taking a train/bus east. That, plus the ridership of the 1 is the potential traffic for this branch. I have a feeling its a significant number.

Tracks were switched from the Eliot side to the Alewife extension in a single weekend, so technically no train movements are prevented from a split that way. But the lack of space to tie a whole parallel set of 6-car Red Line platforms into the station renders it totally moot. You'd have to blow up buildings in the Square to finagle that, and construct egresses into the station from a tunnel that was never designed for that. Plus the curve is truly a wretched place to put a junction. It's a bad enough crawl into the new station to have a tight pinch. It would get even slower as a derailment prevention necessity (much moreso on the Alewife side, but the Eliot side would be sluggish too) if you threw down a switch right at the start of that curve from hell.

The only thing that tunnel could feasibly be used for--and we don't even know this for sure--is an LRT stub terminal off the Urban Ring from Allston. You might be able to coherently fit a 4-car LRV platform with a track grade crossing to a hole punched in the wall to the fare lobby within the space of the 3-track portion of the tunnel. You almost certainly can't do that with 6-car RL trains or fitting a grade-separated egress that doesn't have to disruptively bust outside the existing tunnel structure. But...caveat...we don't even know if that much is possible. Plan B on a cross-Charles LRT line may well have to be putting rails back in the bus tunnel pavement and going back to the 1950's when streetcars, TT's, and diesel buses all co-mingled in the same space.



Branching anywhere to the north just doesn't work the way the RL is set up. Be it a Main St. split to the south, a Harvard split, or an Alewife split to Waltham or Lexington. Cabot Yard only points south from JFK, so there's a very big problem of how you're going to supply enough northbound vehicles when all revenue service through downtown still has to be tethered off the small storage yards at Braintree and Ashmont and the Ashmont + Braintree schedules running the full length north. Any way you slice it there's a capacity cap here that starts harming the works when it has to feed equivalent headways on all northern branches. It's physically impossible to turn the spigot out of Cabot to the north to bootstrap it. JFK isn't configured to reverse direction into downtown service or pull a short-turn out of service something like 1 out of every 3 rush-hour trains that it would take to adequately supply these branches.

That starts creating imbalances. So if, for example, you had branches forking off Harvard trans-Allston or Alewife to Lexington and Waltham. Each branch can have its own storage yard (for Waltham it can even be at Alewife-proper, but pointed in the wrong direction for Lexington to use). So there's no shortage of how many southbound vehicles you can send. But northbound can't keep up because they have to run the full 26 miles from Braintree or 20+ from Ashmont and JFK turns can't non-disruptively make up the difference.

Or...say there's the Mass Ave. subway. The only place that can have a yard is in South Bay outside the subway. Possibly even looping around from Cabot. You can feed that one as full as you want. But it puts the single biggest-ridership chunk of the entire MBTA system--Andrew thru Kendall--in a bind. Harvard curve is still a limiter to capacity to the north. The T estimates today that CBTC signaling can establish best-case 2-3 minute headways throughout the JFK-Alewife stretch. Maybe a little worse, but still a healthy improvement over today. Harvard curve is still going to be the ruling bottleneck for the max possible service density on legacy infrastructure. Therefore feeding Central and Harvard with another fork out of downtown can't really increase service density beyond the best-case they envision with a CBTC installation (which...remember...could happen as early as decade's end if they chose to fund it, and could still fall below that 2-minute best-case when actual engineering is done). What has to pay the price to support this: Kendall-Andrew and the 4 (w/Red-Blue) consecutive transfer stops. Maybe 5 consecutive if Broadway gets an Urban Ring routing. Either both subway flanks have to load-balance to the Cambridge merge at something a little worse than today's headways on each, or making Mass Ave. have useful headways means it has to get 100% of the extra headways above today and downtown gets capped at status quo forever. Keep in mind downtown does not stop growing. Orange and Blue feeding the DTX and Charles transfers become capable of the same 2-3 minute headways under CBTC. So "status quo" Red gets a ton more transfers dumped onto it by the headways-on-steroids Blue and Orange will get. Plus a completed Seaport-Back Bay connection and ever-expanding southside commuter + intercity rail keep shoving more load onto SS.

Maybe the Mass Ave. subway blunts the crush of 50-year RL growth considerably and establishes an ultimate equilibrium, but you are still looking at growth towardss more total RL riders at the downtown stops than today. And the Red Line there becomes structurally incapable of tapping the necessary headways to track with this 50-year downtown growth because all that service density got diverted out to Cambridge. Welcome to more-harm-than-good territory. Saving the Red Line in Cambridge ends up breaking the Red Line downtown.

Given the billions that bypass alone costs, the only way around this is spending billions more nuking the downtown RL for a different configuration entirely and tackling the same godawful engineering issues in even greater density. And like another couple billion to nuke Harvard station in its entirety--including the bus tunnel--for an even lower-level rebuild that can pass underneath Harvard Yard on a gentler curve that lifts the capacity cap. Rebuilding the entire works once more with god knows what else in mitigation.



Do you guys see where nihilistic pursuit of pretty lines on a map starts exponentially harming itself the harder that boulder gets pushed uphill out of spite for the size of the boulder?