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Nick

additional rails for what?

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Just curious. Besides the weight-bearing rails (whatever they're called) and the third rail, I see, in some but not all active locations, other rails bolted down at short intervals and electrically connected end-to-end, which suggests that they're not there just for storage. If storage was the only reason they're there, I doubt they'd need as many bolts to prevent lateral movement and they wouldn't need to be electrically wired. The additional rails usually look well-worn, not shiny. Sometimes, one is inches from a weight-bearing rail with nothing next to the other weight-bearing rail. Sometimes, there'll be two additional rails between the weight-bearing rails but with neither one so near a weight-bearing rail. Sometimes, the ends will be rounded leading to the top surface, suggesting something under a car gets tripped. An example is visible in

What are the additional rails for? What are they called?

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29 minutes ago, Nick said:

Just curious. Besides the weight-bearing rails (whatever they're called) and the third rail, I see, in some but not all active locations, other rails bolted down at short intervals and electrically connected end-to-end, which suggests that they're not there just for storage. If storage was the only reason they're there, I doubt they'd need as many bolts to prevent lateral movement and they wouldn't need to be electrically wired. The additional rails usually look well-worn, not shiny. Sometimes, one is inches from a weight-bearing rail with nothing next to the other weight-bearing rail. Sometimes, there'll be two additional rails between the weight-bearing rails but with neither one so near a weight-bearing rail. Sometimes, the ends will be rounded leading to the top surface, suggesting something under a car gets tripped. An example is visible in

Those are guard rails. The idea is that if a train derails on an elevated portion of a line, the guard rails will keep the wheels relatively near their normal path, preventing them from falling off the structure. 

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There are a lot of configurations though, which raises a lot of questions. I don't know if it would be possible to classify all of them and figure out what each configuration might be for.

A lot of the curves and switch area guard rails are obvious, but not for the straight sections which do not seem to have clear rules.

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13 hours ago, Nick said:

The additional rails usually look well-worn, not shiny. 

Actually, the reason running rails are shiny is BECAUSE they ARE well-worn. Rails are made of hot-rolled steel - not stainless steel - so the surface will not be shiny unless regularly polished. 

Regular train traffic effectively polishes the rails. 

For reference, look at this photo of a track segment on its way to be installed 

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12 hours ago, CenSin said:

There are a lot of configurations though, which raises a lot of questions. I don't know if it would be possible to classify all of them and figure out what each configuration might be for.

A lot of the curves and switch area guard rails are obvious, but not for the straight sections which do not seem to have clear rules.

There are specific rules for guard rails on curves based on radius. I remember reading a document outlining them at some point. 

For straight sections, they're usually installed in places where a derailment would be particularly bad. If I'm not mistaken, nearly all elevated segments have them, to prevent a train from leaving the viaduct and falling to the street in the event of a derailment. Underground, they may be in straight segments where a derailment could cause a train to enter the area of other tracks, or damage critical infrastructure. 

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@itmaybeokay, good point about the shine.

@RR503, interesting. I plan to keep my eyes open, since some elevated sections lack them and I wonder if those sections are less dangerous. Maybe it has to do with not crashing into the platform as hard rather than not falling to the street, especially since they'd only protect the street (@itmaybeokay) if the derailment is minor long enough for the rails to work.

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Interesting.

 

I'm used to the term "guard rail" being for something taller, meant to catch a fender, not a wheel, but the term here has an additional meaning.

 

On the elevated Brooklyn Q/B line at Sheepshead Bay, these rails don't go the whole length and part of where they don't go is part of a curve, which I assume would have a higher risk of derailment than would a straightaway, due to the train's momentum, so their ending short is a little surprising.

 

The Times Square shuttle has them on all three tracks, but not laid the same, and the shuttle at Grand Central does not have them. On the shuttle, there's one rail just far enough from one running rail to accommodate a wheel flange. I guess that could be for the same purpose, protection of infrastructure, but with a different design. The shuttle design seems to depend on holding the wheels with little lateral leeway but on one side only, the other running rail having no guard rail near it, but if the one guard rail is strong enough then two are not needed. I've also seen the narrow space elsewhere, I think on the East River bridge carrying the B, but only for a short length.

 

Many of the guard rails have a design that look like they're meant to catch something under the train, because they bend slightly inwardly near the ends and the ends are curved downward (and painted yellow). Whatever they should catch may be aligned to be outside of these guard rails. They don't put the down-curve ends on rails just being stored. I don't think that's necessarily for wheels except during a derailment, but maybe for a switch under a car, because sometimes there's a black metal box (perhaps electrical?) mounted between the running rails and the guard rails both terminate just before the box and resume just after it, and that would be a problem for wheels not in an emergency.

 

I think I've also seen rails, I guess guard rails, that were very thin on top, but not for long lengths. The same tracks before or after would have regular-thickness guard rails.


Thanks for answering my curiosity.

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