Bay Platform - Trap Point

[Ray H]

I'm looking at (yet another) layout option, hoping this one will get built!

 

I'd like to be able to "squeeze" two coaches and a loco into the (BLT) bay platform. I can do this within the space available but would like to be as prototypical as possible.

 

There is just space for a (working) single blade switch to divert anything starting up against the starting signal but what I believe is a more conventional trap point/sand drag combination won't fit.

 

Were (controlled as opposed to sprung) single blade switches ever used on sections of track where passenger trains operated over them in a facing direction?

 

How close could any form of trap point be positioned to the running line that they're designed to protect such that the use thereof would not foul said running line?

 

I seem to recall seeing a two bladed switch that was slightly longer than a single bladed catch point somewhere (and it may have been on a model). What I can't remember is whether it was acting as a trap or catch point.

 

 

[The Stationmaster]

From what I can recall only two blade traps were used on passenger lines but that is based almost entirely on Western examples (but it was what the Requirements demanded).  However if it is a bay there is no need for a sand drag as they don't seem to have been universally applied - it depends very much on the circumstances and site constraints.

 

As far as function is concerned a trap point should be designed to keep what it derails away from the line it is protecting but you could find traps with two blades but no crossing - in other words the wheel that was derailed into the four foot remained there when it hit the opposite side rail, unless it rode over it; so basically no longer than a single blade trap.  Also the Requirements said ' trap point or similar suitable acceptable appliance' in the case of passenger bays leading to main lines and some Companies did have alternatives - for instance where it didn't have room for a trap the GWR used a 3 shot detonator placer instead (not that there were many of them in total on the entire GWR network).

[Ray H]

Thanks Mike.

 

I suppose a lot depends on how far anything deflected is expected to travel from a standing start. I wonder how far one would expect a loco starting from close to the toe of the trap to be able to travel based on the speed it could attain before derailing and how much further would one starting from three coach lengths back go?

 

Presumably the faster they could be going, the more likely they have of getting closer to the running line even if wheels on one side stayed in the four foot.

 

I bet someone would comment if I included a short two bladed trap without common crossing and sand drag. I wonder if there'd be less comment if I didn't put the trap in at all?

 

. . . where it didn't have room for a trap the GWR used a 3 shot detonator placer instead . . .

 

I wonder if anyone makes a working model of one of those? Presumably it would need to be a sound fitted DCC device!

[The Stationmaster]

Thanks Mike.

 

I suppose a lot depends on how far anything deflected is expected to travel from a standing start. I wonder how far one would expect a loco starting from close to the toe of the trap to be able to travel based on the speed it could attain before derailing and how much further would one starting from three coach lengths back go?

 

Presumably the faster they could be going, the more likely they have of getting closer to the running line even if wheels on one side stayed in the four foot.

 

I bet someone would comment if I included a short two bladed trap without common crossing and sand drag. I wonder if there'd be less comment if I didn't put the trap in at all?

 

 

I wonder if anyone makes a working model of one of those? Presumably it would need to be a sound fitted DCC device!

I doubt anyone makes a model of one, let alone with sound(great idea) but Brian Daniels kindly posted a pic of one on this thread -

http://www.rmweb.co.uk/community/index.php?/topic/21496-detonator-placers/

 

And I bet someone would comment about it if you modelled one without a crossing - time to search out prototype pics perhaps (I'm fairly sure that I haven't got any, sorry)

[Norm81]

There's a picture of one without a crossing here http://www.rmweb.co.uk/community/index.php?/topic/41633-wymondham-and-spooner-row-and-an-x-rated-crossing/page-2, 12th and 34th pictures down I think.

[Gwiwer]

Do you need a trap point at all?

 

Not every BLT with a bay platform had one if that platform were fully signalled to passenger standards and was used (or was intended to be used) by class 1 or class 2 (i.e. passenger) trains.

 

Other options - which might not be as easy to model but may have been found in a restricted space - would be a derailing block or a detonator placer.  Those would have been worked from the signalbox and interlocked with the starting signal (and any subsidiary arm or shunt dolly which may be present) such that the device was always across the rail until the controlling signal was cleared.

[Ray H]

Sprinters1981 link showed what I had in mind save that my guess from the two images is that they aren't on a passenger line.

 

Mike's link to a detonator placer reminded me that there was one at Silvertown if I remember correctly, I think it was there to protect the junction linking to the PLA which was not normally used for passenger trains - I never managed to go "over the top", something that would only be done when the tunnel on the line to Custom House flooded and, I presume, a train was trapped at North Woolwich. I was a Booking Clerk there for about a year about 1965 and never actually remember anything being routed via the PLA although their railway was still open. I think by then the only practical access was via Thames Wharf.

 

Rick, I can understand where you're coming from. Presumably as terminal platforms at somewhere like Euston don't have trap points, why would they be necessary at a much smaller terminus with just two platforms one of which has no run round facility and is shorter than the other but is no less just a terminal platform like the other. That could be a good excuse reason for not providing one!

[The Stationmaster]

The official 'Requirement' was as follows (1950 edition but in force well before then)

 

'Facing trap points, with sand drag where practicable, may also be necessary on passenger lines in the absence of other acceptable arrangements:-

 

(a) At crossing loops on single lines, if the Stop signal at the entrance to the loop is not at an adequate distance from the fouling point at its exit or where the line is worked on any non token method.

(b ) At the exit from passenger loops and from bay and loop platform, to protect traffic on the through lines.

(c ) Approaching swing or other movable bridges.

 

It will be noted that the wording says 'may' and not 'is' meaning that there was an element of flexibility but it depended very much on circumstance and site details and - using modern terminology - the perceived level of risk.  I've just done a quick check on Reading to Paddington and apart from the passenger platform lines at Paddington there was only one bay or loop platform in that entire distance which wasn't trapped (the west end middle bay at Slough), all the others were trapped in some way or another either with a trap point or leading to a siding.

 

If you take a small terminus then - just like a large one - the platform lines would have approximately equal status and normally wouldn't be trapped against each other (with the possible exception of those often used as sidings).  But of course at such places there were no through lines - so traps clearly weren't needed to comply with the requirements.

 

Incidentally the use of wheel stop blocks on passenger lines was, I'm fairly sure, regarded as dangerous as there was no guarantee about which way something would go when derailed.

[RailWest]

The original question referred to a BLT bay platform, so I would have thought that no trap would be necessary, in line with Mike's comments about lack of through lines.

 

What period/company are we talking about?

[Ray H]

Chris/Mike

 

We're talking about a 1950s/60s Midland Region scenario.

 

I obviously hadn't recognised the relevance of "through line" so with two similar terminal platforms I don't appear to need to worry about trap points on the exit from one (or both). That suits me.

 

Thanks for your responses.