What is the purpose of these rails in the centre of the track?

[bradleyd]

I've seen these middle rails on a few train tracks around the place, but I've never been able to figure out their purpose.

Is anybody able to explain?

 

[Mcr Warrior]

Look like they may be guard rails or check rails.

If so, the general idea is to mitigate against derailments on curving trackwork, noting that the photo is of a location that ends up at the buffer stops.

 

[bradleyd]

Thank you very much for that, had never considered that as a reason, but it makes sense

 

[a_c_skinner]

Where is the picture?

 

[sharpinf]

Where is the picture?

Not OP but looks like platform 1 at Pontypridd to me

 

[edwin_m]

They are not check rails. A check rail is very close to one of the running rails, either on the inside of a tight curve or at switches and crossings. The back of the wheel touching the check rail prevents the opposite wheel climbing over the rail on a curve, or going through the gap at a crossing.

They could possibly be guard rails, as these are positioned further from the running rails. They are generally provided on bridges without solid parapets, where if the train derailed for any reason it would risk going over the edge. If the train dropped off the rails it's likely that the guard rails would prevent it from deviating sideways far enough to topple of the bridge. There doesn't have to be a particular increase in likelihood of derailment for guard rails to be fitted - it's all about the increased consequences if a derailment happens. I guess a tight curve on a bridge could have both check and guard rails, but I can't think of anywhere that does.

However, in that photo it looks like a train derailing to the right would just plough into an area of ballast, and one derailing to the left would scrape the platform before it got far enough over for the wheels to contact the guard rail. In either case the train would be going quite slowly as it's heading towards or away from a buffer stop, so it would stop in a short distance. Therefore I don't think they are guard rails. I recall somewhere (St Ives branch?) where they are installed to strengthen the track because the formation is prone to subsidence - could these be the same?

 

[swt_passenger]

They are not check rails. A check rail is very close to one of the running rails, either on the inside of a tight curve or at switches and crossings. The back of the wheel touching the check rail prevents the opposite wheel climbing over the rail on a curve, or going through the gap at a crossing.

They could possibly be guard rails, as these are positioned further from the running rails. They are generally provided on bridges without solid parapets, where if the train derailed for any reason it would risk going over the edge. If the train dropped off the rails it's likely that the guard rails would prevent it from deviating sideways far enough to topple of the bridge. There doesn't have to be a particular increase in likelihood of derailment for guard rails to be fitted - it's all about the increased consequences if a derailment happens. I guess a tight curve on a bridge could have both check and guard rails, but I can't think of anywhere that does.

However, in that photo it looks like a train derailing to the right would just plough into an area of ballast, and one derailing to the left would scrape the platform before it got far enough over for the wheels to contact the guard rail. In either case the train would be going quite slowly as it's heading towards or away from a buffer stop, so it would stop in a short distance. Therefore I don't think they are guard rails. I recall somewhere (St Ives branch?) where they are installed to strengthen the track because the formation is prone to subsidence - could these be the same?

The area of ballast leads to a significant vertical drop to street level, and there’s a solid looking bridge parapet in the background as well. Although there‘s a set of buffers not far beyond the bridge, would a bridge like that on plain track usually get guard rails?

 

[edwin_m]

The area of ballast leads to a significant vertical drop to street level, and there’s a solid looking bridge parapet in the background as well. Although there‘s a set of buffers not far beyond the bridge, would a bridge like that on plain track usually get guard rails?

The area of ballast probably held a run-round loop or siding at one time - plenty of width to stop a slow-moving train and it isn't even the outside of the curve. Bear in mind that with no guard rails, the opposite running rail would do the same job if the train deviated by a bit less than the track gauge. The guard rails only make a difference if that amount of deviation would tip the train over the edge, or I suppose if a serious break in the running rail nearer to the edge not only caused a derailment but also prevented the rail from curbing the sideways movement.

For me to answer the second question I'd have to have a better view of the structure, and I'd have to be a structural engineer.

 

[John Webb]

Not OP but looks like platform 1 at Pontypridd to me

This photo seems to confirm the location:
Platform 1, Pontypridd railway station

© Copyright Jaggery and licensed for reuse under this Creative Commons Licence.
(Click on the photo to go to the larger original on the Geograph website.)
Mapping of the area shows two road bridges run under the station a little distance apart, so I deduce these are guard rails to restrict movement of a derailed train as it crosses these bridges, although I would have thought approaching the end of this bay platform would have been at low speed and derailments very unlikely!

 

[AM9]

Aren't additional rails sometimes laid like that in the four foot to stiffen track on poor ground or over weak bridges?

 

[75A]

Aren't additional rails sometimes laid like that in the four foot to stiffen track on poor ground?

Indeed they are.

 

[swt_passenger]

Aren't additional rails sometimes laid like that in the four foot to stiffen track on poor ground or over weak bridges?

Yes, @edwin_m had mentioned this being done recently on the St Ives branch.

 

[bradleyd]

Not OP but looks like platform 1 at Pontypridd to me

It most definitely is. Taken on my way to work this afternoon

This photo seems to confirm the location:
Platform 1, Pontypridd railway station

© Copyright Jaggery and licensed for reuse under this Creative Commons Licence.
(Click on the photo to go to the larger original on the Geograph website.)
Mapping of the area shows two road bridges run under the station a little distance apart, so I deduce these are guard rails to restrict movement of a derailed train as it crosses these bridges, although I would have thought approaching the end of this bay platform would have been at low speed and derailments very unlikely!

There's one bridge (taff street/high street) running up to the graig, but there is a very slight gap when you walk under it and look up (I don't know if that means it's two separate bridges, then the next one going up valley is the one ove the A4058 roundabout, also where the Rhondda line and Merthyr line split. Going down valley, the next bridge is the foot underbridge halfway down Broadway and then it's over it's a road bridge going over before reaching treforest station. The rails are positioned over the bridge to the graig tho, so the guard rail bit really makes sense

This photo seems to confirm the location:
Platform 1, Pontypridd railway station

© Copyright Jaggery and licensed for reuse under this Creative Commons Licence.
(Click on the photo to go to the larger original on the Geograph website.)
Mapping of the area shows two road bridges run under the station a little distance apart, so I deduce these are guard rails to restrict movement of a derailed train as it crosses these bridges, although I would have thought approaching the end of this bay platform would have been at low speed and derailments very unlikely!

There's one bridge (taff street/high street) running up to the graig, but there is a very slight gap when you walk under it and look up (I don't know if that means it's two separate bridges, then the next one going up valley is the one ove the A4058 roundabout, also where the Rhondda line and Merthyr line split. Going down valley, the next bridge is the foot underbridge halfway down Broadway and then it's over it's a road bridge going over before reaching treforest station. The rails are positioned over the bridge to the graig tho, so the guard rail bit really makes sense.

In my photo, you can see the ramparts (if that what they are called) of the graig bridge, just behind the bushes to the right of the track

The area of ballast probably held a run-round loop or siding at one time - plenty of width to stop a slow-moving train and it isn't even the outside of the curve. Bear in mind that with no guard rails, the opposite running rail would do the same job if the train deviated by a bit less than the track gauge. The guard rails only make a difference if that amount of deviation would tip the train over the edge, or I suppose if a serious break in the running rail nearer to the edge not only caused a derailment but also prevented the rail from curbing the sideways movement.

For me to answer the second question I'd have to have a better view of the structure, and I'd have to be a structural engineer.

From what I am (very slightly aware of) of the history of pontypridd station, I think the track used to lead along further, and I think there possibly may also have been another track further left, and then it was cut back, and that bit of the graig bridge removed