You are given as much money as you want to build a new bridge over the Charles River with a bike path, a pedestrian path, protected ROW for LRT (and maybe BRT) but no space for private automobiles.
The money is donated by a generous benefactor who also wants the bridge to be aesthetic and maybe even a destination unto itself, like a linear park. (Perhaps you even have a rapid transit stop mid-bridge.)
You do not have power of eminent domain, but you can use your endless supply of money to buy even the most expensive buildings and land. However, you are not immune to the court of public opinion: if you knock down a beloved building, your bridge better be absolutely amazing (i.e. "worth it"). You can also improve your public standing by addressing a transit gap or other infrastructure need.
A bit of a non-answer, but I would prefer widening or parallel spans for the Harvard, BU, and Anderson bridges. There's no transit gap (save for arguably Grand Junction LRT, which has a bridge available) worse than the chokepoints these bridges are for the 1, 47, CT, 66, and 86. Currently, there are no reliable north-south transit connections west of the Red Line, and no protected bike lanes over the Charles west of Mass Ave. Having even one of these bridges, much less all, have dedicated transit lanes (including approaches), protected bike lanes, and wider sidewalks would be transformative more than I think any single new span would be.
I would put it on Dartmouth Street, which would pretty much provide a direct BRT/LRT linkage between Back Bay and Kendal area. The Dartmouth ROW is extra wide so no eminent domain would be needed in Back Bay save one or two buildings on Beacon St. It would effectively direct the memorial drive greenway on the Cambridge into a loop with the Esplinade from where its cut off by the Longfellow Bridge.
I would put it on Dartmouth Street, which would pretty much provide a direct BRT/LRT linkage between Back Bay and Kendal area. The Dartmouth ROW is extra wide so no eminent domain would be needed in Back Bay save one or two buildings on Beacon St. It would effectively direct the memorial drive greenway on the Cambridge into a loop with the Esplinade from where its cut off by the Longfellow Bridge.
I think this is a great route for public transit, but there is a downside to putting a bridge there. The current Charles River Basin is used a lot for sailing, and a bridge down the middle would limit that. Local universities have their boat houses there and distant universities come here to compete. The Community Boathouse (which is awesome!) is open to the public, teaches people to sail, and does tons of work with local schools and kids orgs. People on the esplanade like watching the sailboats, and they've become kinda iconic (they are a part of the first two pictures that come up for "stock images boston"). For various safety reasons the sailboats can't go under the bridges, so a potential bridge at Dartmouth would separate various docks, limit where people can go, and limit how many people can be out on the water because it would be harder to spread out. For vastly better public transit, that could be worth it. But it would be a sad resource to lose.
The question was specifically about a new bridge. But for public transit, this could also just be a tunnel. The Charles isn't deep. Build some cofferdams and essentially cut and cover the river.
Create a new bridge connecting Charlestown to the North End, adding a new streetcar that connects various tourist destinations (Bunker Hill, USS Constitution, Quincy Market, BCEC) to transit more readily. Totally not the result of me trying to travel between the Seaport and Rowe's Wharf with a toddler in 20 degree weather this weekend.
If we were gearing the trolley to actual local usage, I would definitely send it fully down the Greenway instead, using the bus lane space on N Washington, and connecting to Haymarket. Really that's probably the better route overall, but there's definitely benefits to serving more of the North End than parts of Boston that already have ample transit.
View attachment 46827
Create a new bridge connecting Charlestown to the North End, adding a new streetcar that connects various tourist destinations (Bunker Hill, USS Constitution, Quincy Market, BCEC) to transit more readily. Totally not the result of me trying to travel between the Seaport and Rowe's Wharf with a toddler in 20 degree weather this weekend.
If we were gearing the trolley to actual local usage, I would definitely send it fully down the Greenway instead, using the bus lane space on N Washington, and connecting to Haymarket. Really that's probably the better route overall, but there's definitely benefits to serving more of the North End than parts of Boston that already have ample transit.
I have several ideas to the question @Riverside raised - and plan to write a more complete reply on that, maybe even a full article - but to quickly address a few points:
The question was specifically about a new bridge. But for public transit, this could also just be a tunnel. The Charles isn't deep. Build some cofferdams and essentially cut and cover the river.
Ironically, this section of Charles River (along MIT) is deeper than it is further upstream.
This is a map with incredibly detailed contours for most rivers in the basin: Charles, Chelsea, Mystic, etc. (Plus the entire harbor! Except Muddy River for some reason.) That's basically all you need for river depths.
Anyway, I did the following research before I found this map:
Charles River: This map summarizes it all east of Watertown. Pretty shallow for the most part (about 5 ft) except the lower basin near MIT, but even there it's only about 15 ft deep, save for some minor parts. (Confirmed by this article.) From Watertown to Waltham, it's less than 1 ft.
Chelsea River (Chelsea Creek): Between the McArdle Bridge and the Chelsea St bridge, it's about 35 ft deep. Apparently, that's also the depth at the end of the river.
Mystic River: From Boston Harbor to downstream of Alford St (Everett Broadway) is 35 ft. From there to just upstream of the bridge, it's about 20 ft. From there upwards (including the Eastern Route bridge), it gets much shallower to around 10 ft, and by the time you get to Medford, it's like 1-5 ft.
This map has a couple of "project depths" for the harbor and Charles, Chelsea and Mystic Rivers. This "project" may be some NOAA's construction or protection projects, and I assume it's a little bit deeper than the river depths but likely similar.
As for some tunnel depths, I found this "Transportation Tunnels in Greater Boston" article which seems super informative (not just limited to river crossings!!!). I also found that the Orange Line's Charles River crossing is an immersed tube tunnel that's 9.1m (29.9 ft) deep (not from that article), and the Silver Line's Fort Point Channel crossing is another immersed tube tunnel that's about 38 ft deep, as the first article stated. (It also mentioned the SL tunnel's turn under Russia Wharf was done with the Sequential Excavation Method, which is apparently cheaper than TBM and may be suitable for shorter tunnels, and that the South Boston section was C&C - despite the Seaport area being mostly on landfill.)
This monitoring station at Netherlands Rd (so southern edge of LMA) shows the river is usually about 7-8 ft deep:
I think this means that regardless of where you cross Muddy River in the LMA vicinity (from Fenway to Huntington), at most, an immersed tube tunnel will almost certainly be the way to go. This means the tunnel doesn't need to be very deep, and doesn't need to be TBM'ed.
For the Charles River tunnel itself, an immersed tube sounds sufficient - but at around 15 ft deep, I'm not sure if blatant cut-and-cover under the river with dams would be feasible.
The bigger problem is tunneling immediately adjacent to the river. This F-Line comment mentioned that any tunnel cutting through MIT needs to go through the "very low-density" subsurface landfill, which introduces both "manifold difficulties waterproofing a subway tunnel" and "problems anchoring it from slight lateral movement". In his words, the tunnel will almost need to be "designed like a cross-Harbor bore a la the Blue Line". He even hints at a Mass Ave subway (or any subway cutting through a similar length of MIT) having as much cost as NSRL.
And of course, south of the river is even more landfill across the entire Back Bay. While I have no information on the density of landfill in that area compared to MIT campus, tunneling there also sounds like trouble especially given the profile of residents in the neighborhood you're crossing under.
This might end up being a case where a deep-bored tunnel that goes deeper than all the landfill - and thus the river itself - may be an easier solution. But at that point, we're not talking about a cheap tunnel anymore, are we? (And I'm not sure if a TBM tunnel can even avoid all the issues that F-Line brought up.)
View attachment 46827
Create a new bridge connecting Charlestown to the North End, adding a new streetcar that connects various tourist destinations (Bunker Hill, USS Constitution, Quincy Market, BCEC) to transit more readily. Totally not the result of me trying to travel between the Seaport and Rowe's Wharf with a toddler in 20 degree weather this weekend.
If we were gearing the trolley to actual local usage, I would definitely send it fully down the Greenway instead, using the bus lane space on N Washington, and connecting to Haymarket. Really that's probably the better route overall, but there's definitely benefits to serving more of the North End than parts of Boston that already have ample transit.
That's a very cool idea and draws many similarities to @Riverside's "Rose Line" tourist trolley, especially since the Charlestown section also passes through USS Constitution and Bunker Hill Monument.
However, why not move it closer to North Station / Washington St Bridge instead? That would give you better connectivity to rapid transit and regional rail.
Unfortunately, even that doesn't sound feasible: As we discussed last time, the maximum distance between two gondola towers (under normal circumstances) seems to be 1970 ft, while the Charles River basin near Kendall and Back Bay is about 2300 ft wide.
For the Charles River tunnel itself, an immersed tube sounds sufficient - but at around 15 ft deep, I'm not sure if blatant cut-and-cover under the river with dams would be feasible.
I'm not an engineer, so take all this with a grain of salt, but: yeah, building a cofferdam then cut-and-covering is probably feasible, and is the kind of thing done elsewhere. This is part of one of NSRL plans for building the new South Station partially under Fort Point Channel (page 79, about the cofferdams). This is also essentially how the new Canary Wharf Station on the Elizabeth Line in London was built. I can't immediately find any longer segments of rail lines or road tunnels built this way, so maybe there's some reason this doesn't scale well, but I'm not sure why that would be. (Actually, anyone know how the Red Line was built under Fort Point Channel?) You're right, an immersed tube tunnel would work here, for sure. I don't know how practically it would work to get the large tube segments into the basin, though. There isn't enough space to build things on shore in Boston or Cambridge. Bridges and dams constrain what can be brought in over water (but that might work, I couldn't say for sure). They're too big to go by road. There's a solution, I just don't know what it is.
The bigger problem is tunneling immediately adjacent to the river. This F-Line comment mentioned that any tunnel cutting through MIT needs to go through the "very low-density" subsurface landfill, which introduces both "manifold difficulties waterproofing a subway tunnel" and "problems anchoring it from slight lateral movement". In his words, the tunnel will almost need to be "designed like a cross-Harbor bore a la the Blue Line". He even hints at a Mass Ave subway (or any subway cutting through a similar length of MIT) having as much cost as NSRL.
And of course, south of the river is even more landfill across the entire Back Bay. While I have no information on the density of landfill in that area compared to MIT campus, tunneling there also sounds like trouble especially given the profile of residents in the neighborhood you're crossing under.
All our current subway lines already run though junky landfill. So did the Big Dig. So do whole neighborhoods and the city's tallest skyscrapers. I take F-Line's point that this makes a potential tunnel more expensive, but this isn't impossible. We've done it before. Besides, @Riverside 's question says money is no limit. And if that sounds like me copping out.... yeah, that's a bit of a cop out.
I'm not an engineer, so take all this with a grain of salt, but: yeah, building a cofferdam then cut-and-covering is probably feasible, and is the kind of thing done elsewhere. This is part of one of NSRL plans for building the new South Station partially under Fort Point Channel (page 79, about the cofferdams). This is also essentially how the new Canary Wharf Station on the Elizabeth Line in London was built. I can't immediately find any longer segments of rail lines or road tunnels built this way, so maybe there's some reason this doesn't scale well, but I'm not sure why that would be. (Actually, anyone know how the Red Line was built under Fort Point Channel?) You're right, an immersed tube tunnel would work here, for sure. I don't know how practically it would work to get the large tube segments into the basin, though. There isn't enough space to build things on shore in Boston or Cambridge. Bridges and dams constrain what can be brought in over water (but that might work, I couldn't say for sure). They're too big to go by road. There's a solution, I just don't know what it is.
Regarding the Red Line crossing under Fort Point Channel, the "Transportation Tunnels in Greater Boston" article - which I mentioned in the details in the last comment, and which is highly informative containing construction details of just about every tunnel - said this: (emphasis mine)
The tunnel under Fort Point Channel was driven using a 7.3 meter (24 foot) shield, hydraulic jacks and compressed air pressure (Cohill, 1916). The depth of the tunnel is approximately 6 meters (20 feet) below the bottom of the channel at an elevation -15.2 meters (-50 feet) BCB, according to the Boston Transit Commission report of 1916. Soil under the Fort Point Channel consists of fill and harbor mud overlying stiff blue marine clay and the hard sandy clay till (Cohill, 1916). The tunnel excavation was primarily through the clay.
So even though the rest of the Dorchester Tunnel (from Park St south) was done with cut-and-cover (which was also mentioned in the document), the river crossing was actually not, and it was done with an approach that's much more akin to TBMs.
All our current subway lines already run though junky landfill. So did the Big Dig. So do whole neighborhoods and the city's tallest skyscrapers. I take F-Line's point that this makes a potential tunnel more expensive, but this isn't impossible. We've done it before.
F-line himself addressed this distinction a couple comments after the one I quoted (in context of a mention of the Green Line as a C&C tunnel through landfill):
Well...you kind of bury the whole of the lede right then and there. A new Mass Ave. subway doesn't have any real usefulness unless it crosses the river...so it doesn't matter if 4 blocks from Main to Vassar is conventional cut-and-cover, you're going deep under the river and needing to waterproof for the inclines + anchor that sucker from small movement under tidal influence some distance back to your would-be MIT Campus Station before the river. And that's a mighty budget blowout.
The Green Line is a beyond-useless comparison. It doesn't cross Charles Basin. It doesn't cut across the ancestral tidal influence while it's not crossing Charles Basin. It doesn't go deep (the Muddy River undercut is not deep). It doesn't matter if the Back Bay fill is the same or different as it is in Cambridge; YOU AREN'T ATTEMPTING REMOTELY THE SAME THING.
Why do those extremely fundamental differences strike anyone as gerrymanderable out of a direct comparison? That makes no bloody sense.
View attachment 46827
Create a new bridge connecting Charlestown to the North End, adding a new streetcar that connects various tourist destinations (Bunker Hill, USS Constitution, Quincy Market, BCEC) to transit more readily. Totally not the result of me trying to travel between the Seaport and Rowe's Wharf with a toddler in 20 degree weather this weekend.
If we were gearing the trolley to actual local usage, I would definitely send it fully down the Greenway instead, using the bus lane space on N Washington, and connecting to Haymarket. Really that's probably the better route overall, but there's definitely benefits to serving more of the North End than parts of Boston that already have ample transit.
I think this actually makes a good bit of sense. These are 3 important areas that could use better transit but dont have a very good way of being added into the existing transit network. Also most other proposal takes 3 separate extensions to existing lines to reach all 3 places (seaport, north end, charlestown). This line gives access to all 3 neighborhoods at once with one line. I dont think a huge number of locals would be riding it end to end, but all 3 neighborhoods would be greatly served by the connection to south station. I think this is a pretty decent proposal for bringing all 3 neighborhoods into the transit network without overburdening the other lines with more branches, extensions, or reverse branching effects.
I've collaborated with world class architects to finally come up with a solution to our I90-shaped problem. I've managed to solve the transit needs of the area, preserve car traffic, as well as find a place to stick that ballpark that's taking up so much space that should be dedicated to labs and offices. If we put our heads together I'm sure we can get MassDOT to adopt this plan in no time.
I've collaborated with world class architects to finally come up with a solution to our I90-shaped problem. I've managed to solve the transit needs of the area, preserve car traffic, as well as find a place to stick that ballpark that's taking up so much space that should be dedicated to labs and offices. If we put our heads together I'm sure we can get MassDOT to adopt this plan in no time.
I've collaborated with world class architects to finally come up with a solution to our I90-shaped problem. I've managed to solve the transit needs of the area, preserve car traffic, as well as find a place to stick that ballpark that's taking up so much space that should be dedicated to labs and offices. If we put our heads together I'm sure we can get MassDOT to adopt this plan in no time.
If I were a god I’d design a streetscape that didn’t result in kids being killed by drivers, as you all might have seen on Congress and Sleeper St in Fort Point about that 4 year old girl the other day. Barring that, I’d eliminate parking on congress that previously destroyed sight lines and led to many people having close calls at this awful intersection. Thanks to the city or state for doing this, but the redesign is well overdue.
Putting here tentatively even though I think it's somewhat viable . . ..
So the NSRL isn't getting built for a long while, we need electrification first and all that,
So maybe (hopefully) in a better future where highways are less prioritized, the central artery can have every on and off ramp closed, and shrunk to 2 or 3 lanes either way so it only moves through traffic and leaves more space free beneath the linear parkway
This free space could be used to build my child: the perfect clean NSRL:
I checked and Im pretty sure there's room to have the tracks dip down 20-25 feet from the switchyard with minimal reconfiguration, the platforms would be a little sloped if they were in the exact same spot but since they'd be going under the station you could move them forward a bit so they're still flat
The rapid transit part of the station would obviously need to be rebuilt, it would be a bit tight but more importantly the NSRL tunnels wouldn't interfere with the red line or silver line tunnels (I checked) you could still have a single floor for navigating the station by building it above ground in front of the terminal building (probably just a glass dome)
This would also make a rapid transit-regional rail transfer very quick, instead of having to go down 120 feet
Putting here tentatively even though I think it's somewhat viable . . ..
So the NSRL isn't getting built for a long while, we need electrification first and all that,
So maybe (hopefully) in a better future where highways are less prioritized, the central artery can have every on and off ramp closed, and shrunk to 2 or 3 lanes either way so it only moves through traffic and leaves more space free beneath the linear parkway
This free space could be used to build my child: the perfect clean NSRL: View attachment 50228
I checked and Im pretty sure there's room to have the tracks dip down 20-25 feet from the switchyard with minimal reconfiguration, the platforms would be a little sloped if they were in the exact same spot but since they'd be going under the station you could move them forward a bit so they're still flat
The rapid transit part of the station would obviously need to be rebuilt, it would be a bit tight but more importantly the NSRL tunnels wouldn't interfere with the red line or silver line tunnels (I checked) you could still have a single floor for navigating the station by building it above ground in front of the terminal building (probably just a glass dome)
This would also make a rapid transit-regional rail transfer very quick, instead of having to go down 120 feet
This is an interesting idea! And welcome to the forum, it’s always good to hear fresh ideas on topics that have long been discussed on this board.
Having said that, I have a few thoughts.
1. It’s possible you’ve already considered this, but the central artery tunnel is too steep for FRA grade requirements and the current tunnel would be unable to achieve the necessary height clearance. The entire roadway foundation sits on a massive slab that redistributes the roadway and vehicle weights the soil below. The load bearing slurry walls at either side of the tunnel support the roof structure. It’s unclear to me if the roadway can be modified to fit trains but it likely cannot be. You may say, just excavate in the middle to open it up. Well, if you were to do that, you would need to re-support the roof that will remain above the roadway tunnels, which means building a pair of big walls, which would be immensely difficult if not impossible given the existing infrastructure of the tunnel and the necessity to keep it open throughout the whole project.
2. The second point is that the foundations beneath south station preclude any sort of tunneling. When they rebuilt the bus terminal in anticipation of the (now largely completed) south station tower they built very deep foundations beneath the existing platforms, between every pair of tracks. The original NSRL plan had utilized the same route as you’ve shown in your photo, but after the SS rebuild, it was determined to be infeasible. That’s why the most recent MassDOT NSRL study had an alignment along fort point channel, which will provide vertical and horizontal clearance from south station to the new underground station
This is an interesting idea! And welcome to the forum, it’s always good to hear fresh ideas on topics that have long been discussed on this board.
Having said that, I have a few thoughts.
1. It’s possible you’ve already considered this, but the central artery tunnel is too steep for FRA grade requirements and the current tunnel would be unable to achieve the necessary height clearance. The entire roadway foundation sits on a massive slab that redistributes the roadway and vehicle weights the soil below. The load bearing slurry walls at either side of the tunnel support the roof structure. It’s unclear to me if the roadway can be modified to fit trains but it likely cannot be. You may say, just excavate in the middle to open it up. Well, if you were to do that, you would need to re-support the roof that will remain above the roadway tunnels, which means building a pair of big walls, which would be immensely difficult if not impossible given the existing infrastructure of the tunnel and the necessity to keep it open throughout the whole project.
2. The second point is that the foundations beneath south station preclude any sort of tunneling. When they rebuilt the bus terminal in anticipation of the (now largely completed) south station tower they built very deep foundations beneath the existing platforms, between every pair of tracks. The original NSRL plan had utilized the same route as you’ve shown in your photo, but after the SS rebuild, it was determined to be infeasible. That’s why the most recent MassDOT NSRL study had an alignment along fort point channel, which will provide vertical and horizontal clearance from south station to the new underground station
Putting here tentatively even though I think it's somewhat viable . . ..
So the NSRL isn't getting built for a long while, we need electrification first and all that,
So maybe (hopefully) in a better future where highways are less prioritized, the central artery can have every on and off ramp closed, and shrunk to 2 or 3 lanes either way so it only moves through traffic and leaves more space free beneath the linear parkway
This free space could be used to build my child: the perfect clean NSRL: View attachment 50228
I checked and Im pretty sure there's room to have the tracks dip down 20-25 feet from the switchyard with minimal reconfiguration, the platforms would be a little sloped if they were in the exact same spot but since they'd be going under the station you could move them forward a bit so they're still flat
The rapid transit part of the station would obviously need to be rebuilt, it would be a bit tight but more importantly the NSRL tunnels wouldn't interfere with the red line or silver line tunnels (I checked) you could still have a single floor for navigating the station by building it above ground in front of the terminal building (probably just a glass dome)
This would also make a rapid transit-regional rail transfer very quick, instead of having to go down 120 feet
That's pretty cool. I've also thought a lot about repurposing the tunnels for trains, for the same reasons you mention, and just that the Big Dig engineering is fascinating. I don't think it's at all feasible, but it's fun to consider. Did you give any thought of what the trains would do north of your map? What a North or Central Station would look like? How to get get trains out of the tunnel on the north side of downtown?
In addition to @BosMaineiac 's notes, I think you have your depths wrong a bit for the tunnels around there. If I understand you, you're saying the NSRL would go over the Silver line tunnel at Atlantic Ave, but the Silver line tunnel is really shallow. Like, the roof of the tunnel is barely more than 15 feet underground there, which doesn't leave enough room for a new train tunnel to go over it. I could be wrong, though. Do you have some source you're looking at?
Yes, but this is still not easy. The two-track, no central station option studied in 2018 (Which means no OC or Fairmount trains can use the tunnel) still was estimated to cost $12 billion because of the complexity of the portals, the size of the stations, the depth of everything, and the obstacles you need to weave around while tunneling. Add 2 more tracks, a central station, and more portals for the OC/Fairmount lines and the cost nearly doubles. This is why I'm fairly pessimistic about NSRL in the long run, I just don't think it can provide $10 billion worth of benefits over electrification and regional-rail-ization alone. Plenty of cities run excellent suburban rail networks with stub end terminals, see the Translien lines in Paris, Londons bajillion terminal stations, or Milan's Commuter railways for examples.
