Green Line Extension to Medford & Union Sq

Supports for entrance from the Lowell Street bridge.

They used a hi-rail flatbed tractor trailer to bring the elevator frames down the ROW from Gilman. It was an interesting set of overnights this past weekend.
 
vanshnookenraggen said:
Those are some tall beams. Those can't be for a sound wall that high, can they?
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Tall beams on the centerline are Overhead Contact System (OCS)

They are overbuilt to be capable of supporting future Electrification of the Lowell line which must be higher to be able to clear clearance route freight under a 25kv wire

Sometimes the OCS support is from the side sound wall, With, say, every fifth H beam poking up to support OCS and the OCS beams are also considerably taller than the wall in that case.
 
Arlington said:
Tall beams on the centerline are Overhead Contact System (OCS)

They are overbuilt to be capable of supporting future Electrification of the Lowell line which must be higher to be able to clear clearance route freight under a 25kv wire

Sometimes the OCS support is from the side sound wall, With, say, every fifth H beam poking up to support OCS and the OCS beams are also considerably taller than the wall in that case.
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good to know.
I've noticed that these beams are taller than the bridge at cross street and right beside it. So if they were to electrify the Lowell line would they have to raise the bridge (again)?
 
Ruairi said:
good to know.
I've noticed that these beams are taller than the bridge at cross street and right beside it. So if they were to electrify the Lowell line would they have to raise the bridge (again)?
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In the open the overhead is at a fixed height for fullish extension of a pantograph, and is allowed to squeeze down at underpasses. Lowell Line electrification will require considerable number of mods (some bridge raisings, lots of trackbed undercuts) because it's a protected Plate F freight clearance route cleared for 17 ft. tall cars. Under 25 kV electrification it requires +2.5 ft. of safe wire clearance over an unshielded car roof, so the eventual electrification there will have to have 19.5 ft. clearance.
 
F-Line to Dudley said:
In the open the overhead is at a fixed height for fullish extension of a pantograph, and is allowed to squeeze down at underpasses. Lowell Line electrification will require considerable number of mods (some bridge raisings, lots of trackbed undercuts) because it's a protected Plate F freight clearance route cleared for 17 ft. tall cars. Under 25 kV electrification it requires +2.5 ft. of safe wire clearance over an unshielded car roof, so the eventual electrification there will have to have 19.5 ft. clearance.
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so you're telling me they have the foresight to put in big poles because the line might be electrified but when they re built the bridge 5 years ago they didn't have the same foresight?
 
Ruairi said:
so you're telling me they have the foresight to put in big poles because the line might be electrified but when they re built the bridge 5 years ago they didn't have the same foresight?
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No. The catenary out in the open is *higher* than the bare minimum, because it's less stress on a pantograph to run at full-extension vs. straining the springs at near-max compression. Go anywhere on the NEC and you can see this kind of contrasting cat layout in the open vs. at the squeeze-down at foot of a bridge.

Lowell will need work, but it's way more often going to be trackbed undercuts than additional bridge touches.
 
Unlike a highway overpass, it shouldn't be quite so loud underneath. Could be a nice place for some food trucks!
 
Why didn't they build a steel-framed elevated in the model of the previous one, considering what a massive graffiti magnet the concrete will be? Personally, I love the look of graffiti on concrete, but I know the MBTA doesn't.
 
Hubman said:
Why didn't they build a steel-framed elevated in the model of the previous one, considering what a massive graffiti magnet the concrete will be? Personally, I love the look of graffiti on concrete, but I know the MBTA doesn't.
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1. value engineering
2. steel's become quite expensive (relative to previous costs).
 
Hubman said:
Why didn't they build a steel-framed elevated in the model of the previous one, considering what a massive graffiti magnet the concrete will be? Personally, I love the look of graffiti on concrete, but I know the MBTA doesn't.
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I don't know if the MBTA considered this point, but concrete viaducts are, in general, far quieter compared to steel-based ones because they rattle much less as the train rolls by.
 
Segmental concrete box girders, like those used on the Big Dig, require specialized equipment to assemble. Steel erection is the cheapest and fastest method, which satisfies the Governor’s need to VE the project.
 
RandomWalk said:
Segmental concrete box girders, like those used on the Big Dig, require specialized equipment to assemble. Steel erection is the cheapest and fastest method, which satisfies the Governor’s need to VE the project.
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Funny how they can do the gold-plated deluxe version on a highway project (the Big Dig) but not on a transit project. Priorities?
 
Question: Will they put some screening up under the beams to keep the pigeons from getting up there & crapping all over the place? if not, they'll mess up everything, along with that beautifully clean ground just laid!!! :(
 
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Charlie_mta said:
Funny how they can do the gold-plated deluxe version on a highway project (the Big Dig) but not on a transit project. Priorities?
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I mean, those decisions were made decades apart... Also, RandomWalk's point was that concrete (as used here) is more expensive, I think.
 
Equilibria said:
I mean, those decisions were made decades apart... Also, RandomWalk's point was that concrete (as used here) is more expensive, I think.
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I could be misinterpreting what Random and Charlie are trying to say, but I think what is meant is: the concrete box girder structures used for some of the big-dig era elevated roadways are the potentially better/quieter but more costly approach. However, that's not what's used here. These are steel girders on top of concrete supports. The big dig era structures have customized hollow box-beams made out of concrete that carry the roadways.

Here's an example from the big dig:
goo.gl

Google Maps

Find local businesses, view maps and get driving directions in Google Maps.
goo.gl goo.gl
 
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The Big Dig also used custom built railings along the tunnel access walkways that ended up decapitating a motorcyclist, which were not only more dangerous but also more expensive than standard railings.
 
Yes. The Big Dig concrete viaducts are more likely to be quieter than a similar steel viaduct. However, it needed a casting yard in Western Mass to produce all the segments for the project and the specialized gantry to assemble them. That would cost more money and take more time than the steel construction that is used on the GLX.
 
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