Interlaced or Trap Retarder?

[_Henry_]

Hi All,
I wonder if anyone has ever seen one of these on the UK network. I have heard they are used to slow or stop freight trains and work by the train being directed onto a pair of tracks which sit just outside the main tracks (hence the name 'interlaced). The extra pair of tracks gradually increase their gauge and this slows the train down.

They sound very interesting but I have never, never seen one before in the UK or anywhere else. I also have tried searching for them online but got nowhere.

 

[Railsigns]

Here's a photo of one at Newcraighall:

 

[peteb]

Are these the modern equivalent of catch points? Is the aim to stop a runaway, for example, and slow its speed to minimise the amount of train that actually derails?

 

[Railsigns]

Are these the modern equivalent of catch points? Is the aim to stop a runaway, for example, and slow its speed to minimise the amount of train that actually derails?

No; these are trap points. The requirement for catch points ended when the railway stopped running unfitted goods trains, so there's no modern equivalent of those.

 

[peteb]

No; these are trap points. The requirement for catch points ended when the railway stopped running unfitted goods trains, so there's no modern equivalent of those.

Ah ok thanks!

 

[Sheridan]

No; these are trap points. The requirement for catch points ended when the railway stopped running unfitted goods trains, so there's no modern equivalent of those.

I’ve seen a set of points on the up slow at Chester, coming in from Saltney Junction - these sit at the bottom of a rising gradient and would derail anything rolling back down and prevent it from reaching the main line. However, I assume that there are signalled shunt moves onto this line in the other direction, and probably a limit of shunt board somewhere along it, so if these are intended to derail anything that passes the limit of shunt board then presumably they’re technically trap points, although they would do the job of both catch and trap points?

 

[Taunton]

The (old) GWR had similar, about the same length, with a longitudinal open-top box around each rail filled with ballast to provide the retarding. Again, no derailment and, with effort, you could pull any vehicles in there back out again.

 

[John Webb]

The (old) GWR had similar, about the same length, with a longitudinal open-top box around each rail filled with ballast to provide the retarding. Again, no derailment and, with effort, you could pull any vehicles in there back out again.

Ballast or Sand? The few I've seen over the years seemed to be sand-filled and I've seen references in several books to 'Sand drags'.

 

[jamiearmley]

There used to be something similar at Bradley junction - (between Deighton and Heaton Lodge). There was a short length of track just after the junction towards Bradley Wood, which was surrounded by wooden boarding and filled with sand- albeit sand with grass, growing out of it, etc.
I did always wonder why it looked so different to the usually seen trap points which lead to nowhere - essentially 'derailers'.

 

[_Henry_]

Here's a photo of one at Newcraighall:

View attachment 160402

Thanks for sharing this - it looks very cool. But surely this is only suitable to stop a wagon or two and any full length train running backwards would just run straight over it and derail none the less?

Also, I read in Ellis's Railway Enclyopedia that it works because the check rails touch the wheel backs of the train which slows it down. But if this is the case, would it not damage every train that used it and they would not be able to enter service? I'm just confused, if it is damaging every train and only suitable for very slow moving trains / wagons anyway - what is the purpose of it? Wouldn't a sand drag be much better as it wouldn't damage the train?

 

[D7666]

Thanks for sharing this - it looks very cool. But surely this is only suitable to stop a wagon or two and any full length train running backwards would just run straight over it and derail none the less?

Also, I read in Ellis's Railway Enclyopedia that it works because the check rails touch the wheel backs of the train which slows it down. But if this is the case, would it not damage every train that used it and they would not be able to enter service? I'm just confused, if it is damaging every train and only suitable for very slow moving trains / wagons anyway - what is the purpose of it? Wouldn't a sand drag be much better as it wouldn't damage the train?

I read OP post as meaning wagon retarder not train trap/catch point, function to slow or stop train/vehicles, not derail it.

I am not sure but need to consider difference between UK English and US "English" here when googling; there are types of gauge widening or gauge narrowing static retarders elsewhere I have seen ref to on web but think it is north American practice***; there is a term for this type of retarder trap but not a term in UK use and I can't remember it. Static here means here is no gubbins to regulate speed or even an off/on setting, they are merely fixed kit. I do not think any are used in UK.

Digressing, and bringing back trap/catch points into it, LU use gauge widening traps but I think nowhere do these exist on main / NR lines ? These however work in an entirely different way and will derail the train running adversely into them, that is their purpose; some here may not consider the way these LU devices work to be gauge widening, nonetheless, that is their name - 'wide to gauge'.

*** edit
thinking about it it might have been Brasil where I know of these from; BR does use quite an eclectic mix of US and European practices

 

[John Webb]

Thanks for sharing this - it looks very cool. But surely this is only suitable to stop a wagon or two and any full length train running backwards would just run straight over it and derail none the less?

Also, I read in Ellis's Railway Enclyopedia that it works because the check rails touch the wheel backs of the train which slows it down. But if this is the case, would it not damage every train that used it and they would not be able to enter service? I'm just confused, if it is damaging every train and only suitable for very slow moving trains / wagons anyway - what is the purpose of it? Wouldn't a sand drag be much better as it wouldn't damage the train?

Looking at a railway atlas I assume this is the 'Reversing Siding' south of the station, and is directly accessed from the left-hand track in the photo. Trains using it presumably then join the right-hand track, and the trap point is to protect trains on the right-hand line?

 

[mcmad]

I think that this is on the Dn Millerhill and it protects the line to the right is the Borders line to tweedbank. The line to the left is the up Millerhill which has a set of conventional traps behind the photographer.

 

[D7666]

No; these are trap points. The requirement for catch points ended when the railway stopped running unfitted goods trains, so there's no modern equivalent of those.

Must admit I was unaware of the difference here; I had always assumed catch and trap were interchangeable terms for the same things.

Thanks for the "learning byte"

 

[Tester]

Must admit I was unaware of the difference here; I had always assumed catch and trap were interchangeable terms for the same things.

Thanks for the "learning byte"

Not helped by the Australian usage of 'catch points' for what are clearly 'trap points'!

 

[Railsigns]

Digressing, and bringing back trap/catch points into it, LU use gauge widening traps but I think nowhere do these exist on main / NR lines ? These however work in an entirely different way and will derail the train running adversely into them, that is their purpose; some here may not consider the way these LU devices work to be gauge widening, nonetheless, that is their name - 'wide to gauge'.

Those do exist on NR lines, and there are two distinct varieties:
a) with both switches operating in unison but in opposing directions. These function solely as trap points, and they have a short run-off rail on the outside of the track on each side.
b) with each switch worked by a separate lever (or equivalent). These function as a normal set of points where trains can take either the left or right-hand route, but additionally will function as trap points when both switches are open and set to derail a train.

 

[GRALISTAIR]

The set of trap points on the Barton Loop north of Preston on the WCML has now been removed.

 

[M&NEJ]

The set of trap points on the Barton Loop north of Preston on the WCML has now been removed.

I always thought importance was given to flank protection, but I've seen numerous loops with just a home signal and a feed back into the main running line. What is the safety reasoning in such circumstances? Is it acceptable because the approach speed is supposed to be low?

 

[Tim_UK]

Those do exist on NR lines, and there are two distinct varieties:
a) with both switches operating in unison but in opposing directions. These function solely as trap points, and they have a short run-off rail on the outside of the track on each side.

There is a set in Sheffield filmed in a Don Coffey Video.

and then watch from 32:47

The video shows points with 2 arms facing you.

 

[D7666]

Those do exist on NR lines, and there are two distinct varieties:
a) with both switches operating in unison but in opposing directions. These function solely as trap points, and they have a short run-off rail on the outside of the track on each side.
b) with each switch worked by a separate lever (or equivalent). These function as a normal set of points where trains can take either the left or right-hand route, but additionally will function as trap points when both switches are open and set to derail a train.

TY. More learning bytes!

LU has b type; the are most often found at turnback sidings i.e. the exit from a siding between the two running roads is like that, both switches open to derail.

There is a set in Sheffield filmed in a Don Coffey Video.



and then watch from 32:47

The video shows points with 2 arms facing you.

yes I see;

but neither quite what I was thinking of LU - not the same configuration;

those two arms there go nowhere

the LU examples are in the form of an actual Y shaped set of points diverging on exit of a turnback siding with both the left and right 'arms' are tracks that lead to each of the running roads, but the switches move independently; when no route is set both are open to derail centrally, one is closed for entry from the running line, the other closed for exit. A quick google for an image not found one, yet.

 

[edwin_m]

I always thought importance was given to flank protection, but I've seen numerous loops with just a home signal and a feed back into the main running line. What is the safety reasoning in such circumstances? Is it acceptable because the approach speed is supposed to be low?

In general trap points are not preferred where the line that would be trapped is used by passenger trains. The risk of intentionally derailing a passenger train is presumably thought to outweigh that of preventing a collision. There may be exceptions in specific circumstances and these are likely to have extra measures such as the sand drags mentioned, so the train stops a bit less abruptly.

In the case of loops it’s quite difficult to imagine how an overrun of the exit signal could lead to collision (with no trap). A long freight approaching that signal has just cleared the points at the loop entry so the overtaking train will only just have been signalled and is unlikely to be approaching yet. Any overrun of the exit signal will replace the signal in front of the overtaking train. Loops without traps will have an overlap at the exit signal instead, giving more distance for an overrunning looped train to stop. If it doesn’t, there is more time for the overtaking train either to pass through or to stop.

Yards and sidings are a bit different. They have risks of shunting going wrong or of stabled stock running away. These are non-passenger tracks and as far as I’m aware are always trapped. Instead of a dedicated trap point, the exit to the main line may be a crossover with both ends worked together so any runaways just remain within the yard.

 

[Gloster]

Recollection, which admittedly dates from many years ago, is that ‘interlaced’ is when two lines share a profile (envelope?) only slightly larger than that for one train. The lines, usually double, come together, but although there is a common crossing where they meet there are no points: trains from one line use a different pair of rails to those used by trains on the other. At the end of the section of interlacing the lines separate out through a common crossing to double again. You therefore have four rails running alongside each other on a formation only slightly larger than one needed for a single line. I think that the Boyne Bridge at Drogheda used to be like this and there is also the bridge at Tornio on the Finland/Sweden border, although the latter has two gauges.

 

[edwin_m]

Recollection, which admittedly dates from many years ago, is that ‘interlaced’ is when two lines share a profile (envelope?) only slightly larger than that for one train. The lines, usually double, come together, but although there is a common crossing where they meet there are no points: trains from one line use a different pair of rails to those used by trains on the other. At the end of the section of interlacing the lines separate out through a common crossing to double again. You therefore have four rails running alongside each other on a formation only slightly larger than one needed for a single line. I think that the Boyne Bridge at Drogheda used to be like this and there is also the bridge at Tornio on the Finland/Sweden border, although the latter has two gauges.

Ccorrect. Known as gauntlet track in the States. The Selby swing bridge used to have the four tracks through the station converging to two interlaced pairs so the moveable switches were on the same side as the signal box.

In the UK I can only think of current use on tramways - Croydon and Nottingham both have some, in one case to get through a narrow spot in an otherwise double track cutting, and in others to avoid putting switches in the middle of a road.

 

[Mr. SW]

the LU examples are in the form of an actual Y shaped set of points diverging on exit of a turnback siding with both the left and right 'arms' are tracks that lead to each of the running roads, but the switches move independently; when no route is set both are open to derail centrally, one is closed for entry from the running line, the other closed for exit. A quick google for an image not found one, yet.

This may answer your question: Centre siding trap at Rayners Lane

Detail from video:

(about 4:45)

"What is a rusty rail move and why do we do it? Piccadilly Line"/Dale Charman Travels

 

[D7666]

This may answer your question: Centre siding trap at Rayners Lane
View attachment 160528

That is the thing.

Thanks.

Yep, I knew what I was talking about, just couldn't quickly find an image.

What I really meant in my question about main line is examples of this configuration. When I asked, I was not thinking in terms of a double trap that goes nowhere (per the Sheffield video upthread) when open or one route when closed, but this configuration of a real switch with independent blades between two actual routes where no route set acts as a central trap. Are there any on main line like this ?


The OP question has now been totally lost !

 

[Railsigns]

What I really meant in my question about main line is examples of this configuration. When I asked, I was not thinking in terms of a double trap that goes nowhere (per the Sheffield video upthread) when open or one route when close, but this configuration of a real switch with independent blades between two actual routes where no route set acts as a central trap. Are there any on main line like this ?

Yes, at Stranraer Harbour.

 

[D7666]

Yes, at Stranraer Harbour.

What kept you ?????



Thanks for the answer !

Must be fairly uncommon though ?

 

[MadMac]

Those do exist on NR lines, and there are two distinct varieties:
a) with both switches operating in unison but in opposing directions. These function solely as trap points, and they have a short run-off rail on the outside of the track on each side.
b) with each switch worked by a separate lever (or equivalent). These function as a normal set of points where trains can take either the left or right-hand route, but additionally will function as trap points when both switches are open and set to derail a train.

Is there still a wide to gauge trap at Perth? On a related note, is the sand drag at Hamilton Central still there?

 

[Railsigns]

Is there still a wide to gauge trap at Perth? On a related note, is the sand drag at Hamilton Central still there?

There are no wide-to-gauge trap points left at Perth (but there's one at Waverley, on No. 16 Mid Road). The sand drag's still there at Hamilton Central.

 

[TSG]

Exit from Woking platform 3 (bay between up and down fast lines) has a wide to gauge trap I think.