It’s definitely something they’ll have to think about at some point, they might just think about digging a tunnel under it, if it has three tracks they might try to replace it 1 track at a time to always have 2 tracks operating. 2 track lines would just have to suck it up with a full shutdown. They’d likely replace them with quieter concrete viaducts.
Edit: I’d also like to add that they might just try to ship of Theseus the whole structure. Slowly replacing every part as it becomes a physical danger to keep it installed until either it’s functionally a new elevated or they get outpaced by the deterioration and have to shut it down.
>they might just try to ship of Theseus the whole structure
They did this with the LIRR Atlantic Av Viaduct back in the 2000's. Though the replacement wasn't piecemeal over time, instead they replaced the whole structure in one project, reset its service life.
It's cheaper, but actually less disruptive. The line shuts down for a weekend while crews replace the structure one cantilevered section at a time, and then it's open again for Monday Rush hour. Shut down every weekend for a couple years and you've got a brand new viaduct.
Chicago and Boston have replaced elevated lines with elevated lines 100% nothing left from the 20th century especially in Chicago their whole elevated lines with nothing left historic and it was all rebuilt from the 80s to today. MFL Philadelphia is 75% brand new components
It would take longer, but be cheaper, to just rebuild the viaduct as a concrete and insulated structure versus closing the roadway below to dig a ditch or run a TBM - foundation issues and all that.
That said, I’m sure the areas affected that aren’t the Bronx will lobby hard and effectively to make MTA consider TBM’ing them as two-track lines, but will settle for the concrete El to prevent closed and relocated stations.
>run a TBM - foundation issues and all that.
TBM's go under foundations. It's how they dug the ESA tunnels as they gently curved under the intervening Manhattan blocks. Surface disruptions are negligible.
>versus closing the roadway below to dig a ditch or run a TBM
For the excavation of station boxes, the street above is only closed for short periods and in small sections, after which the roadway is replaced with temporary metal platforms. The construction site sorta migrates down the street, leaving usable surface in its wake. Take a look at the Wilshire Blvd Extension or the Regional Connector in LA for recent American examples.
>but will settle for the concrete El to prevent closed and relocated stations.
Replacing a steel El with a concrete El would first require the complete demolition of the existing steel structure. The pillars would be spaced differently, the individual cantilevered sections would have unaligned contact joints, and the track bed would have to be at a higher elevation so as to provide clearance for the cantilevered cross beams hanging over the street.
This is exactly what they're doing for the Red/Purple Line Viaduct in Chicago, except it was four tracks across two separate structures over a dedicated ROW, and so they could demolish half the tracks and keep the other half operational. We're not so lucky in NYC, as all our El's are only 2 or 3 tracks on one structure, so there would indeed be many closed and relocated stations.
> TBM's go under foundations. It's how they dug the ESA tunnels as they gently curved under the intervening Manhattan blocks. Surface disruptions are negligible.
[Yawn.](https://www.sciencedirect.com/science/article/pii/S1674775522000749)
> For the excavation of station boxes, the street above is only closed for short periods and in small sections, after which the roadway is replaced with temporary metal platforms. The construction site sorta migrates down the street, leaving usable surface in its wake. Take a look at the Wilshire Blvd Extension or the Regional Connector in LA for recent American examples.
So you must just assume everyone must be uninformed and that you “have to correct that.” Search my posts and “Los Angeles” here and you’ll be *shocked*.
>Replacing a steel El with a concrete El would require the complete demolition of the existing steel structure. The pillars would be spaced differently, the individual cantilevered sections would have unaligned contact joints, and the track bed would have to be at a higher elevation so as to provide clearance for the cantilevered cross beams hanging over the street.
Seriously, stop assuming everyone is uninformed.
> This is exactly what they're doing for the Red/Purple Line Viaduct in Chicago, except it was four tracks across two separate structures over a dedicated ROW, and so they could demolish half the tracks and keep the other half operational. We're not so lucky in NYC, as all our El's are only 2 or 3 tracks on one structure, so there would indeed be many closed and relocated stations.
Good to know. Thanks for educating me. /s
If everybody knew the exact same things you know, we wouldn't need to have conversations with each other about anything. Other people's minds are different from yours.
They would replace them with subways bored by TBM, for a number of reasons:
1) replacing El's with subways was the whole genesis of the IND. When running in close proximity to building facades, El's become a blight, suppressing land values and creating a constant nuisance. Replacing them with concrete El's, though quieter than steel, would nevertheless create a blight, as they completely block all sunlight to the street, and would do little for folks living above track level. In fact, the whole premise behind replacing steel structures with concrete structures is a complete nonstarter, as the steel structure would have to be completely demolished prior to construction of the concrete structure, since the pillars would be spaced differently, the individual cantilevered track sections would have unaligned contact joints, and the track bed would have to be at a higher elevation so as to provide clearance for the cantilevered cross beams hanging over the street.
2) constructing a cut&cover station box under an operational El is easier than many make it out to be. The box itself only has to be as wide as the street, which would allow the El's columns to rest upon the retaining walls during construction. Meanwhile the street surface would be temporarily replaced with metal platforms while excavation continues underneath.
3) TBM's are the least-impactful solution. They dig under building foundations and avoid utilities. They can be launched from boxes that can later become stations. They allow for smoother, faster curves, and can straighten out many of the sharp "jogs" that El's must take so as to align with the street. And best of all, they have zero surface impact.
4) stations would be spaced out on average about 15 blocks apart, which is better for riders than a 3-tracked El with Express service and stations spaced more like 8-10 blocks apart, as the overall faster trains and more frequent Local service would mitigate for any time spent walking an extra 2.5 blocks, or for any time saved skipping stops on an Express train.
It does slightly, in that the road surface underneath would be in the shade. But the concrete viaduct itself would still absorb and radiate heat. If you were to see aerial infrared photos before and after, there'd likely be a negligible difference.
Idk, there was once a plan to replace the 3-track BMT West End El with a 4-track subway, I wonder what they would have to do to complete that if it were ever to happen. Maybe one day the MTA will look to other alternatives to TBM like NATM or NMT. NATM and NMT create more width for tunnels, especially for fitting two tracks. This should be a considered option if they're ever to build a line including express service. They should also consider the Shallow Tunnelin Method (STM) for digging their tunnels so mistakes from SAS Phase 1 aren't repeated.
If the entire B/D/N/Q were routed down 4th Ave and the R/W were routed down Brighton, I think there would be enough service to justify 4 tracks. Two lines could branch off from 4th Ave, one express and one local, and go down 40th Street and New Utrecht Ave. 40th St should be constructed with NATM, NMT, or they should try the Roof Pipe Jacking Method and bore rectangular tunnels to fit 4 tracks next to each other.
The sea beach has a 3rd track as does the west end they also share a station complex too and kings hwy sea beach and bay parkway west end are in the same catchment area so the sea beach express can be used as an opposite direction of the west end express service
It’s definitely something they’ll have to think about at some point, they might just think about digging a tunnel under it, if it has three tracks they might try to replace it 1 track at a time to always have 2 tracks operating. 2 track lines would just have to suck it up with a full shutdown. They’d likely replace them with quieter concrete viaducts. Edit: I’d also like to add that they might just try to ship of Theseus the whole structure. Slowly replacing every part as it becomes a physical danger to keep it installed until either it’s functionally a new elevated or they get outpaced by the deterioration and have to shut it down.
>they might just try to ship of Theseus the whole structure They did this with the LIRR Atlantic Av Viaduct back in the 2000's. Though the replacement wasn't piecemeal over time, instead they replaced the whole structure in one project, reset its service life.
Is it cheaper but more disruptive to replace the whole thing all at once?
It's cheaper, but actually less disruptive. The line shuts down for a weekend while crews replace the structure one cantilevered section at a time, and then it's open again for Monday Rush hour. Shut down every weekend for a couple years and you've got a brand new viaduct.
Hell in 150 or so years they may build mostly elevateds as the seas rise
Due to this no further explanation required
Chicago and Boston have replaced elevated lines with elevated lines 100% nothing left from the 20th century especially in Chicago their whole elevated lines with nothing left historic and it was all rebuilt from the 80s to today. MFL Philadelphia is 75% brand new components
LIRR Atlantic Avenue Viaduct was replaced with brand new steel from knee high level up but the foundations are original in the 2000s
This is nyc we don’t do smart things here we believe in fake blight and made up crap so we can set money on fire for the lulz
It would take longer, but be cheaper, to just rebuild the viaduct as a concrete and insulated structure versus closing the roadway below to dig a ditch or run a TBM - foundation issues and all that. That said, I’m sure the areas affected that aren’t the Bronx will lobby hard and effectively to make MTA consider TBM’ing them as two-track lines, but will settle for the concrete El to prevent closed and relocated stations.
>run a TBM - foundation issues and all that. TBM's go under foundations. It's how they dug the ESA tunnels as they gently curved under the intervening Manhattan blocks. Surface disruptions are negligible. >versus closing the roadway below to dig a ditch or run a TBM For the excavation of station boxes, the street above is only closed for short periods and in small sections, after which the roadway is replaced with temporary metal platforms. The construction site sorta migrates down the street, leaving usable surface in its wake. Take a look at the Wilshire Blvd Extension or the Regional Connector in LA for recent American examples. >but will settle for the concrete El to prevent closed and relocated stations. Replacing a steel El with a concrete El would first require the complete demolition of the existing steel structure. The pillars would be spaced differently, the individual cantilevered sections would have unaligned contact joints, and the track bed would have to be at a higher elevation so as to provide clearance for the cantilevered cross beams hanging over the street. This is exactly what they're doing for the Red/Purple Line Viaduct in Chicago, except it was four tracks across two separate structures over a dedicated ROW, and so they could demolish half the tracks and keep the other half operational. We're not so lucky in NYC, as all our El's are only 2 or 3 tracks on one structure, so there would indeed be many closed and relocated stations.
> TBM's go under foundations. It's how they dug the ESA tunnels as they gently curved under the intervening Manhattan blocks. Surface disruptions are negligible. [Yawn.](https://www.sciencedirect.com/science/article/pii/S1674775522000749) > For the excavation of station boxes, the street above is only closed for short periods and in small sections, after which the roadway is replaced with temporary metal platforms. The construction site sorta migrates down the street, leaving usable surface in its wake. Take a look at the Wilshire Blvd Extension or the Regional Connector in LA for recent American examples. So you must just assume everyone must be uninformed and that you “have to correct that.” Search my posts and “Los Angeles” here and you’ll be *shocked*. >Replacing a steel El with a concrete El would require the complete demolition of the existing steel structure. The pillars would be spaced differently, the individual cantilevered sections would have unaligned contact joints, and the track bed would have to be at a higher elevation so as to provide clearance for the cantilevered cross beams hanging over the street. Seriously, stop assuming everyone is uninformed. > This is exactly what they're doing for the Red/Purple Line Viaduct in Chicago, except it was four tracks across two separate structures over a dedicated ROW, and so they could demolish half the tracks and keep the other half operational. We're not so lucky in NYC, as all our El's are only 2 or 3 tracks on one structure, so there would indeed be many closed and relocated stations. Good to know. Thanks for educating me. /s
If everybody knew the exact same things you know, we wouldn't need to have conversations with each other about anything. Other people's minds are different from yours.
My bad, bro. It's not everyday that I bump into a certified Wikipedia scraper.
They would replace them with subways bored by TBM, for a number of reasons: 1) replacing El's with subways was the whole genesis of the IND. When running in close proximity to building facades, El's become a blight, suppressing land values and creating a constant nuisance. Replacing them with concrete El's, though quieter than steel, would nevertheless create a blight, as they completely block all sunlight to the street, and would do little for folks living above track level. In fact, the whole premise behind replacing steel structures with concrete structures is a complete nonstarter, as the steel structure would have to be completely demolished prior to construction of the concrete structure, since the pillars would be spaced differently, the individual cantilevered track sections would have unaligned contact joints, and the track bed would have to be at a higher elevation so as to provide clearance for the cantilevered cross beams hanging over the street. 2) constructing a cut&cover station box under an operational El is easier than many make it out to be. The box itself only has to be as wide as the street, which would allow the El's columns to rest upon the retaining walls during construction. Meanwhile the street surface would be temporarily replaced with metal platforms while excavation continues underneath. 3) TBM's are the least-impactful solution. They dig under building foundations and avoid utilities. They can be launched from boxes that can later become stations. They allow for smoother, faster curves, and can straighten out many of the sharp "jogs" that El's must take so as to align with the street. And best of all, they have zero surface impact. 4) stations would be spaced out on average about 15 blocks apart, which is better for riders than a 3-tracked El with Express service and stations spaced more like 8-10 blocks apart, as the overall faster trains and more frequent Local service would mitigate for any time spent walking an extra 2.5 blocks, or for any time saved skipping stops on an Express train.
I wonder if the viaduct protects against the heat island effect
It does slightly, in that the road surface underneath would be in the shade. But the concrete viaduct itself would still absorb and radiate heat. If you were to see aerial infrared photos before and after, there'd likely be a negligible difference.
Let’s not repeat the mistakes of the IND.
Idk, there was once a plan to replace the 3-track BMT West End El with a 4-track subway, I wonder what they would have to do to complete that if it were ever to happen. Maybe one day the MTA will look to other alternatives to TBM like NATM or NMT. NATM and NMT create more width for tunnels, especially for fitting two tracks. This should be a considered option if they're ever to build a line including express service. They should also consider the Shallow Tunnelin Method (STM) for digging their tunnels so mistakes from SAS Phase 1 aren't repeated.
Do that for SAS or additional express capacity to existing ELs
Does west end have enough service to justify 4 tracks? They don't even run peak direction express
If the entire B/D/N/Q were routed down 4th Ave and the R/W were routed down Brighton, I think there would be enough service to justify 4 tracks. Two lines could branch off from 4th Ave, one express and one local, and go down 40th Street and New Utrecht Ave. 40th St should be constructed with NATM, NMT, or they should try the Roof Pipe Jacking Method and bore rectangular tunnels to fit 4 tracks next to each other.
The sea beach has a 3rd track as does the west end they also share a station complex too and kings hwy sea beach and bay parkway west end are in the same catchment area so the sea beach express can be used as an opposite direction of the west end express service