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Points on a bridge?


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Ok let me give you the scenario and I'd like your advice to see if it's exceptable.

 

 In planing a pre grouping Scottish  layout I've got a scene that I'm not sure would have been prototypical. A single line approaching a station with a passing loop and at the start the single line crosses over a stone arched river bridge. 

 

 I'm trying to use large radius points and third and forth radius curves but to do this I would need to have the points for the start of the station loop on the last third of the bridge its self would this be exceptable?

 

 The bridge would be 1 meter long so the point would be on the last third of the bridge.

 

 Your opinions please Steve

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It would be unusual, something the engineers would want to avoid mainly due to the extra cost.

 

But sometimes, due to a restricted site, it did happen. One example is the change from double track to single track at Midford on the SDJR.

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The main requirement was that the Point be within the maximum distance to the signal cabin,

Just north of Inverness the point blades were south of the bridge (Clachnaharry?) then the tracks were gauntleted (ie they diverged by only a foot or so) till the other side of the bridge when they split till normal distances. (once powered points came in, the point was changed to a normal one north of the bridge) an example of gaunlett track below...

 

I doubt there would normally be a point on a  bridge as it would have to be more than wide enough for double tracks, therefore costing more. The point would be one side with track double crossing, unless there were severe restrictions stopping that..

If you did have such a thing I would bet there would be extra check rails on the points..

 

Note a 1M bridge in OO being 250ft, or N being 500Ft would be a very substantial bridge to have something like the required  2.5 track widths to have a wide enough bridge for the points..

gaunt3[1].jpg

Edited by TheQ
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Hmm thanks chaps. I kind of figured this might be the case, I have verious options the top two having the set of points before the bridge but to an extent that just pushes the problem to the other side of the bridge the other option is to just make the bridge smaller which I certainly don't have a problem with so that's become the favoured option now.

Edited by Londontram
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Would offset Platforms Help?   as the straight on platform can be slightly closer to the point than the divergent track platform..

Edited by TheQ
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Not realy as that just creates problems at the other end of the platform where I was hoping to put the entrance to a small goods yard.

 It's a quart into a pint pot situation so the best answer really is to make the bridge and thus river smaller by about one third.

 

 I'm trying to give it an uncluttered feel plus as its early pre grouping there's going to be an awfull lot of 6 wheel stock that's not really happy on less than third radius curves.

 

 To be honest I'd rather loose a feature rather that try and compress everything to fit.

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5 hours ago, TheQ said:

Just north of Inverness the point blades were south of the bridge (Clachnaharry?) then the tracks were gauntleted (ie they diverged by only a foot or so)

gaunt3[1].jpg

"Gauntletting" is something I've neither seen nor heard of before, so I have to ask - what's the point of it?

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17 minutes ago, spikey said:

"Gauntletting" is something I've neither seen nor heard of before, so I have to ask - what's the point of it?

There are no moving parts so it is much cheaper to maintain. 

 

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My layout (very slowly developing layout) has a point on the bridge. It's prototypically accurate, and was put due to the very limited space on the prototype. In model form it's a real horror to motorise. I went down the route of the smallest possible motor that I could find, and that was expensive. Even then it only just fits under the trackbed and within the bridge construct. 

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3 hours ago, spikey said:

"Gauntletting" is something I've neither seen nor heard of before, so I have to ask - what's the point of it?

It was clearly explained by theQ in his post above when he posted the photo, it allows the points to be in reach of the signal box but the actual divergence to be the other end of a narrow bridge.

Regards

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A turnout on a bridge would be avoided if possible, but it wasn't always possible and when that was the case the operating needs overcame any objection cost wise.  A bridge under a formation with a turnout might be tapered towards one side to accommodate the turnout.  

 

Another situation might be that a railway is built to accommodate a double track but opened as a single track, in the expectation of increased traffic in the future.  Some of these railways for whatever reason never fulfilled this potential and remained as single track; by the 1870s or 80s enough experience had been gained in building railways for this to be a feature requested by hopeful branch line promoters.  In this situation a bridge would be built wide enough for a double track formation, along with cuttings, embankments, and tunnels, but only carrying a single track.  

 

Labour was cheap in those days and it didn't cost much more to build a double track formation than it did for a single track, but upgrading to double track at a later date, having to acquire land and deal with landowners and rights of way when you'd already done it once, often proved much more costly and delayed projects, so double track formations with single track laid on them were not uncommon.

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Probably not quite the same thing but the Royal Albert Bridge has a set of points on the end of the approach spans at Saltash where the single track on the bridge opens up to the double track.

 

i think I'm correct in saying that originally the points were off the bridge, within the station but were moved to accommodate longer trains in the station.  The last couple of approach spans had to be widened to take the points.

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Pontypridd Junction is (was) a full double junction, with facing points on the south side. Going north had FPL equipped trailing crossovers in both Merthyr & Rhondda directions. These points spanned over both formations. The down main had its home signals perched over the Rhondda river. You can still see the deflector sheets (corrugated steel sheet) which prevented injector overflow from the locomotives onto Mill Street.

 

Ian.

 

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Hi Londontram , have a look at the NB viaduct crossing the kelvin at maryhill. There still is a point on it, back in the day it was 4 tracks with several .  To be pedantic its not one viaduct but two next to each other with the top filled in . The north one is brick arched , the south stone , so it looks like a viaduct with a stone face on one side and a brick face on the other . 

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Hi,

 

There are a lot of points on viaducts in South London, so the national total is not insignificant, but for you it may partly come down to the wealth of the original railway company who built lines in the area you are basing your model on and the geography of the area (as has been said wouldn't put a point on a prototype bridge unless there was no other way round the problem).

 

Regards

 

Nick

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