Is my Trap point in the correct place?

[Dungrange]

The image below indicates part of the proposed station throat for my layout drawn in Templot.

 

When designing the layout, my assumption was that the tips of the switchblades on the trap point would be in line with (or fractionally in rear of) the tips of the switchblades on the adjacent crossover. However, now that I am looking to define fouling points and track circuit locations, I have come to the conclusion that the fouling point for the crossover is the tips of the switchblades, which would make the clearance point further to the left.

 

My question is therefore, should the trap point start to derail a train when it reaches the clearance point or the fouling point?  That is, is this trap point in the correct location, or do i need to move it to the left by around 5 metres?

[TheSignalEngineer]

The position is correct but depending on the rest of the layout in the area and the moves signalled for, a full crossing may be provided. 

As far as track circuit clearance at the traps is concerned the insulated joint would be at the end of the trap point stock rail, usually 5' 5" from the toe of the switches.

[martin_wynne]

My question is therefore, should the trap point start to derail a train when it reaches the clearance point or the fouling point?  That is, is this trap point in the correct location, or do i need to move it to the left by around 5 metres?

 

Hi David,

 

Looking at the plan, I think I would move it back a bit to be sure that a derailed vehicle would be clear of the crossover road. Or alternatively provide a full turnout as The SE suggested.

 

In any event, having two stretcher bars in line complicates the rodding runs, much easier if you stagger them by a couple of timbers. Not such a problem nowadays of course.

 

regards,

 

Martin.

[Dungrange]

Looking at the plan, I think I would move it back a bit to be sure that a derailed vehicle would be clear of the crossover road. Or alternatively provide a full turnout as The SE suggested.

 

In any event, having two stretcher bars in line complicates the rodding runs, much easier if you stagger them by a couple of timbers. Not such a problem nowadays of course.

 

The rodding at this location isn't a problem as the trap point would have been installed in a 1970s rationalisation using components from redundant bullhead turnouts in the goods yard and elsewhere.  As such, it would always have been point motor operated, but I may still move it back slightly, even although I wanted it as close to the crossover as possible. 

 

The position is correct but depending on the rest of the layout in the area and the moves signalled for, a full crossing may be provided. 

As far as track circuit clearance at the traps is concerned the insulated joint would be at the end of the trap point stock rail, usually 5' 5" from the toe of the switches.

 

The last part of your final sentence is the one that's generally confusing me.  Other guidance seems to state that the track circuit clearance point would always be at least 4.88 m from the fouling point, which would seem to be the tips of the switch blades of the crossover. However, if the trap point has a standard lead (ie 5' 5") then I don't have the necessary 4.88 m between the track circuit boundary and the fouling point with the trap point in the position shown. Therefore I think that I either have to increase the lead length of the trap point (to achieve 4.88 m between the stock rail join and the toe of the switches) or alternatively move the trap point to the left, such that the joints at the end of the trap point are 4.88 m from the tips of the switchblades on the adjacent crossover.   If that is the case, then I need to ensure that the two stretcher bars are offset by (4.88 m - 1.65 m = 3.23 m), which means moving the trap point by around 42 mm (in 4 mm scale).  The latter would address Martin's concerns about whether a derailed vehicle would be clear of the crossover.

[Dungrange]

The attached plan shows the proposed track circuits and signals placed around this particular trap point.  Dimensions are prototype dimensions.

 

Bottom left is a bi-directional single line used by passenger services.  Signal DG104 is the home signal (three aspect signal with theatre indicator and position light signal to control access to occupied platforms).  Signal DG108 is a fixed red signal at the end of a goods arrival loop.  The trap point therefore protects against an arriving freight train passing DG108 at red and colliding with a passenger movement either in or out of Platform 3 (top right).  The connection between the goods loop and platform 3 is required to allow a freight locomotive to run round.  

 

Ideally, I want to move the fixed red signal DG108 as close to the toe of the trap point under discussion as possible.  There is not enough space to fit a realistic overlap between DG108 and the crossover, which will therefore prohibit the simultaneous arrival of a freight train in the goods loop and a passenger movement in or out of Platform 3.  However, as I would like to be able to accept a freight train into the loop whilst platform 3 is occupied (ie track circuit PCB is occupied), the distance between DG108 and DG109 (the starter signal at Platform 3) should be the minimum overlap distance,  I think that this should be 200m (and I don't have the space), so will have to rely on selective compression.

 

Therefore, with a bit more information, would you still suggest that I replace the trap point with a full turnout.  If so, I think it will have to be a B6 since I already have a 1:6 pre-assembled V from C&L that I could add to the switch. 

 

The Chief Engineer has already decreed that the trap point currently shown in Platform 1 is to be removed, but I have yet to change the drawing in Templot. 

Dungrange_Signals&TC.pdf

[TheSignalEngineer]

Thanks for posting the drawing. It raises a few more questions about what is outside that area and how the layout works.

 

1. What is the approximate time period and area when the layout is set?
2. Is the station a terminus or through station?
3. If a terminus I assume that all moves will be low speed.
4. What is the line at the top for?
5. What is the layout off the left of the plan?
6. How long has the layout been like this, was the main line ever double track, and what happens to the left?

 

A few thoughts to be going on with, although these may change depending on the questions above.

• As the line up to DG108 is a Goods Line with trapping protection an overlap is not necessary. I would be inclined to provide a full set of points with a short track and stop block or depending on te layout and gradients possibly even adding a sand drag. I can think of a prototype which used to exist at Wolverhampton in a similar but not identical situation

• DG 107 and DG109 should be parallel if it is a through station, but this is not so important if a terminus. Signal DG 107 is incorrectly positioned, it should be in PBC track circuit. Talking in old money as that is my era, the joint between PBC and PBD should be at least 16' back from the toe of the points in the adjacent line. DG107 should then be between 5' and 65' to the left of this joint. The joint between PCB and PCD should be at the 5' 5" joint of the points. 

• Signal DG104 should be a minimum of 60' from the joint at the toe of the first facing points. It can be less but it complicates the interlocking controls a little.

• Positioning of DG108 will depend on whether the Goods line is a one-berth loop or a longer through running line on the approach side.About 40 years ago I had a run-in with the Inspectorate over positioning Main and Goods signals apart as with DG104 and DG108. One he requested I managed to give a convincing explanation why it was not a risk but the other location I had to move the Goods signal back.

• With the track intervals as drawn it looks a tight fit to get signals DG104 and DG108 between the tracks, they would have to be mounted on a gantry. It is usual to have a wider spacing where there are more than two tracks but it can depend on the history of the line and the topography. For instance much of the 4-track section at the southern end of WCML would not be allowed, but it has been there so long that it is accepted. 

[Dungrange]

To answer each point in turn:

1. Scottish Region circa 2007, but signalling should relate to Scottish Regional practise circa 1970s when the station was rationalised and re-signalled.
2. The station was originally a through station when operated by the NBR / LNER / BR until the Beeching Era.  The line to the southwest was then closed and Dungrange became a terminus.  The goods yard closed around the same time.  The track layout was then rationalised and re-signalled with colour light signals replacing the previous semaphore signals.  The signal boxes would have been demolished and the points motorised.
3. Yes, all movements will be at low speed.  The turnout into Platform 1 is a B7 and the crossover is two B8s, so I suspect that I should have a 15 or maybe 20 mph speed limit at most.
4. The line at the top is an Engineer's siding.  This was once a goods arrival / departure loop that provided access to the goods yard, but the goods yard has largely become a car park, although Network Rail still have an access to the Engineer's siding.
5. In model form, to the left of the image is the fiddle yard.  In reality, it is a single track branch line with a goods loop that provides access to both the Engineer's siding and also a kick back to a private siding.
6. As above, I'm assuming that this was once double track, until circa 1970 when the line was singled.  What was previously the down mainline became the goods loop and what was previously the goods arrival / departure loop became an Engineer's siding.  I'm hoping that the attached diagrammatic layout may assist.  The broken black lines represent track that was lifted around 1970.  Of the track that remained after that date, blue represents passenger lines, red represents freight only lines and green is track under private ownership.  The track layout below the horizontal line is all that I am currently building and this horizontal line represents the left edge of the layout that I have drawn up in Templot.

It's good to hear that an overlap isn't required with trapping protection and I can provide a full set of points if required.  The trap point would in fact be the only new infrastructure in 1970 as the other point work would be unchanged from NBR / LNER days.  I had therefore assumed that the minimum required would be added during rationalisation and that it was installed using components recovered from elsewhere.

 

If DG107 and DG109 have to line up, then I'll move DG107 back.  Unfortunately, I'd like either Platform 2 or Platform 3 to be able to accommodate a Class 221 (five car Voyager set).  With DG109 as drawn, I don't think it will fit, which was the reason for moving DG107 forward - ie to accommodate a five cars set, I think I would need the leading axle to be around where I have marked the clearance point and therefore the signal would have to be placed accordingly (ie somewhere between the clearance point and the fouling point so that the driver could see it).  I had assumed that the track circuit boundaries between PBC and PBD and between PCB and PCD would align, but now that you've pointed it out, I can see why they don't have to.  This may therefore mean that DG109 can be mounted slightly further forward than DG107 and I could potentially make Platform 3 the only platform that can accommodate a five car unit.

• Signal DG104 can be 60' from the joint at the toe of the first facing points. In reality, this signal will actually lie in the fiddle yard, but I intend to make my own crude vastly over scale version just so that I know the correct road is set.  If in the future I extend the layout, I can address sighting then (ie both distance back from the facing point and also whether a gantry mounting is required to obtain adequate clearance).

I hadn't thought about having to align signals DG104 and DG108.  I want to move DG108 as close to the trap points as possible because I'd like to be able to have the locomotive that I'm pretending has pulled the freight train into the loop to be visible (even if the actual freight wagons don't leave the fiddle yard).  Therefore I was hoping to have DG104 'off stage' and DG108 'on stage' and clearly something like 120 feet apart.  Could this be justified based on either the length of freight trains or them having more momentum and therefore requiring a longer stopping distance from the outer home signal?

Dungrange_SteamEra.pdf

[TheSignalEngineer]

Thanks for the before/after layout drawings. It's making quite a bit more sense now. I'll have a proper look tomorrow so I can work out the likely scenario of how the job would have been planned and carried out.

[TheSignalEngineer]

I've been running through a scenario of the line having been reduced to freight only beyond Dungrange then closed in the pre-1968 era. Following that there was an attempt to close but turned down due to insufficient alternative public transport, and then line was rescued by the local council due to changes in the area, more houses, commuting to the big city, etc. Freight was closed and the layout rationalised at the time of the Surplus Capacity schemes in the period to 1973. The signal box or lever frame was declared to be beyond repair when some renewals were due so everything was made electric from a local temporary box. Traffic increased to the extent that a couple of workings of cross country services were started back from Dunrange during the morning peak with return services in the evening. The colour light signalling was later taken over during creeping expansion of the 'Big City' Signalling Centre.

 

Going through the layout, track first.

• Originally the Goods Loop would have been at standard 6' spacing from the Up Main and 10' from the siding. to fit in DG104 it would probably have been slued outwards, but only enough to get the signal inIt could still have been on the old alighnment when it gets to DG108.
• The trap in front of DG108 could be just a drop off as the speed is low, as long as the LH rail is shorter than the RH so the train falls towards the siding rather than the running line. It could have a full crossing, but the LH rail would still be shorter. As most of the work was done when we did it as cheap as possible I wouldn't bother with a short neck and stop block.
• I'm undecided as to the trap in Platform 1. If the line is used for stabling it may have been left in place.

 

A couple of observations/debate items regarding signals on-scene.

• At the time of the original works DG108 would probably have been a ground signal only, but may have been a fixed red aspect with a subsidiary aspect below it. That would allow the route up to it to be a main route rather than just a subsidiary signal. The signal would probably have been positioned about 6' back from the 5' 5" joint at the trap points.
• I seem to remember much of the ScR being mechanically signalled into the 1980s, so I would think that resignalling may have come a little later than you say. If so it would have been done to the BR principles current at the time. Reorganisations from the mid 1980s meant that many of these works came under BR HQ control and we had a lot of cross-working on standards between the different offices.

Edited July 24, 2017 by TheSignalEngineer

[Dungrange]

The scenario that you describe is broadly in line with my thinking.  However, in 2007 (the period modelled) a contract has just been let to remodel the station.  The crossover (still bullhead track) will be ripped up and moved further from the station, the old bay platform (platform 1) will be removed to permit platform 2 to be extended and a new platform is to be constructed between platform 3 and the former goods yard (in what is currently a car park).  This will allow the station to accommodate six car sets - I'm assuming that this is to increase capacity that is required on services elsewhere.  I'm not actually modelling this scenario, but it is the reason why there is going to be a large number of track workers on site, preparing for work to commence. 

 

I'm assuming that when the signalling was taken over by the 'Big City' Signalling Centre, that would be an opportunity to make some modifications to the signals.  In particular, DG108 could be changed from a ground signal only to a Fixed Red with ground signal below.  I've been advised that access to the loop would most likely be a shunt movement, if traffic on the branch was light (which it probably was in the 1970s / 80s under the scenario you've indicated) but given that the line is now reasonably busy (to the point where it may need to be re-doubled), access to the loop by a main route would be preferred.

 

With regards track spacing, I'm assuming that all tracks in the fiddle yard (I'm hoping this will be a traverser) will be equally spaced at 51 mm track centres (the peco streamline dimension).  However, through the crossover, the mainline and loop are 45 mm apart to represent the standard 6'.  Therefore the distance between the mainline and the loop is increasing as the line passes under the bridge (no imagination) that will form the current scenic break.  If I ever extend the layout, then I'll continue that increasing separation to accommodate signal DG104.  The spacing between the engineering siding and loop is intended to convey that this is a 10' dimension, although it is slightly less and tapers down to 51 mm  at the edge of the baseboard.  Unfortunately, I don't think I can increase this much further.

 

#

 

However, returning to my original question, if DG108 is 6' in rear of the track circuit join GLA / PCD and this join is in turn 5' 5" in rear of the tips of the switchblades of the trap point, does this not mean that it track section GLA is occupied, no passenger movements would be permitted across track circuit PBE?  That is, if GLA is occupied, it is not possible to prove that the locomotive held at DG108 is actually clear of the fouling point of the crossover because they are not 16' apart.  My understanding would be that the track circuit join GLA/ PCD would have to be at least 16' (ie 4.88 m) to the left of the switchblades of the crossover to allow a route to be set through track circuit PBE whilst GLA is occupied.

[TheSignalEngineer]

Think I may have to give you that one because of the curve. Will try to look closer this evening.

 

Meanwhile here's a fixed red put in at Kings Norton on the Saltley job in 1969.

 

They could be mounted on a short post as this one of there was enough space or direct onto a concrete block ang without a backboard if in a standard 6'. Note that this one is a two-aspect head with the bottom aspect blanked out and a PLGS with the red likewise.

 

[TheSignalEngineer]

Had another look and I am still with putting the insulated joint at the 5' 5" joint of the traps. To make a move from DG104 to platform 3 will need the traps normal. The geometry of the trap will be parallel to that of the connection from platform 2 line to platform 3 line, thus any vehicle of normal overhang will be clear.

The important thing is to maintain the passing clearance between a vehicle standing in the loop and a train passing it. This should be a minimum of 450mm clear between the bodywork in real life.

[Dungrange]

Okay - I think that the penny has finally dropped.  The trap points will normally be in the trap position (ie to derail a freight train).  Therefore, any arriving freight train that fails to stop at signal DG108 and crosses the track circuit boundary GLA / PCD (thus activating track circuit PCD) will not actually foul movements into and out of Platform 3 (assuming the closure rail of the trap point remains at least 11' 2" from the closure rail of the adjacent point at all times) because the geometry of the the two lines are parallel.

 

That is, if the trap point was extended to become a standard turnout accessing a platform 4, it would be permissible to have a train arriving at platform 4 and one departing platform 3 simultaneously because standard track centres are retained throughout.  Therefore it seems reasonable to accept that the same rules would apply in this situation.

 

I guess that the only question this raises is whether my track circuit PCD should be split between the trap point and the point that forms the rest of the crossover.  What I now need to understand is, if a freight train has passed DG108 at danger and has stopped on the trap point, movements in and out of platform 3 should clearly be prohibited (because track circuit PCD is occupied).  However, should movements in and out of platform 2 also be locked? To give a proceed aspect at signal DG107, it must be necessary to check the occupancy status of track circuit PCD to ensure that whatever occupies Platform 3 is clear of the fouling point, but this means that in relation to movements in and out of Platform 2, it is not possible to tell whether occupancy of track circuit PCD is a hazard (unit in Platform 3 in advance of the fouling point) or an unimportant occupancy (because a freight train has overrun DG108).  I'm therefore tempted to assume that the trap point needs its own track circuit.  If this is occupied, then movements in and out of Platform 3 are halted, but movements in and out of Platform 2 can still take place.  Is that correct?

 

It's interesting that you are undecided as to whether the trap point in the bay platform may have been retained.  My original thinking was that the bay platform would have been trapped in NBR / LNER days as empty coaching stock and possibly NPCS may have been stabled here.  Moving forward, I initially assumed that it would be retained in the rationalisation because it would cost money to remove it and I may use Platform 1 to stable a Tamper or MPV.  However, there would also have been a cost in retaining it, insofar as there would have been a requirement for another point motor and its inclusion within the electrical interlock alongside the ongoing operation and maintenance costs.  I'm not clear whether the balance of these costs would have been in favour of retention of removal.  However, I understand that today Network Rail would undertake a risk assessment that would effectively conclude that it wouldn't be required and therefore I have swayed towards its removal.  However, I'm assuming that railway vehicles have better brakes in the 21st century compared to what may still have existed in the 1970s and therefore the result of any risk assessment at that time may have been different.  I'm also assuming that there probably wasn't the same formal evaluation process in BR days and the choice as to whether to remove or retain such a trap point may have been made by the Engineer responsible for the job and may therefore vary from place to place.

 

Setting aside the probability of whether or not it was retained, the benefit of its removal is one less point motor, but against that I'm keen to include these sort of details (even if it is just retaining some of the old timbers when the trap was plain lined). 

Edited July 27, 2017 by Dungrange