Passing Loops operational practice

[colin penfold]

Good morning assembled brains!

 

I am wondering whether there was a standard procedure for the operation of passing loops on single lines. If it differs by time and location I would say post war GWR.

 

Are there set criteria for which direction the first train should arrive from, and which should leave first? Are there site conditions that would dictate (such as signal box position) or would it be based on the traffic? I am guessing priority traffic might be held for the minimum time, or that a train booked to stop would be held longer to facilitate one that wasn't.

 

I want to try and get this move right when I eventually get to operational stage with my embryonic layout.

 

Be grateful for any info.

[Armchair Modeller]

In the old days, there were quite severe restrictions on how far a facing point could be from the signal cabin. As a result, most passing loops would have had a signal cabin at each end. As distances were relaxed towards the end of the 19th century and beyond, opportunity was usually taken to eliminate one box, or build a new one and get rid of both old ones. If the loop included a level crossing it would make sense to keep the one at the level crossing, for example.

 

For a passing move, both trains would not be allowed to move into the loop at the same time. One would always be stopped at the home signal whilst the other was allowed to proceed into the loop.

 

Think yourself lucky yo are not modelling the Midland & Great Northern Joint, which regularly had 2 trains, both too long for the loops, passing each other. That takes a lot of explaining! A GWR country branch line, on the other hand, ought to be pretty straightforward.

[The Stationmaster]

1. Position of signalbox - basically a sort of 'just growed' thing as the Requirements for the minimum distance between a signalbox and facing points changed over the years plus local power operation of points (using a hand generator) had gained ground from the late 1930s/WWII onwards. SO - it should be reasonably conveniently sited for token etc exchange, adjacent to the level crossing if there is one. or adjacent or relatively near to the largest concentration of pointwork while bearing in mind the need for token exchange - which would most likely put at one end of a platform.

 

2. The timetable, will, or should, decide the relative importance and priority of trains for crossing purposes, particularly if it also includes an arrival time as well as departure. And the timetable will in theory at least decide which one should arrive first when trains are being crossed.

 

3. The Regulations make particular provision for acceptances and the working of fixed signals at crossing stations. The normal Clearing Point for acceptance is the loop Starting Signal - irrespective of its distance in advance of the Home Signal, i.e. there is not necessarily the normal 440 yards Clearing Point found in double line Absolute Block Regulations.

 

Because of what is effectively the relaxation of a safety margin the Home Signals have to be worked in a particular way to minimise the chance of signals being passed at danger or a collision occurring. Thus the following applied -

'When trains which have to cross each other are approaching a Token Station in opposite directions, the signals in both directions must be kept at "Danger" and when the train which has first to be allowed to draw forward has been brought to a stand, the home signal applicable to such train may be lowered to allow such train to draw forward to the station or to the starting signal, and after it has again come to a stand, and the Signalman has ascertained that the line on which the other train will arrive is clear, the necessary signals for that train may also be lowered.'

(Direct quote from GWR Block Regulations as reissued by BR c. 1950 but the wording is virtually the same as it was in the 1921 issue.)

 

So effectively what it means is that when two trains are approaching the Home Signals are kept at Danger until at least one of the trains has stopped at its Home Signal. If the second train to arrive at its Home Signal is timed to be the first to enter the station, crossing loop etc then if both trains arrive at about the same time the other train should be held - even if it got there slightly earlier (which was probably ignored in practice - the critical bit is keeping both Homes at danger until the first train has been stooped, allowed into the loop, and again stopped before the other Home Signal is cleared.)

 

Hope that helps - without confusing

[PaulRhB]

So effectively what it means is that when two trains are approaching the Home Signals are kept at Danger until at least one of the trains has stopped at its Home Signal. If the second train to arrive at its Home Signal is timed to be the first to enter the station, crossing loop etc then if both trains arrive at about the same time the other train should be held - even if it got there slightly earlier (which was probably ignored in practice - the critical bit is keeping both Homes at danger until the first train has been stopped, allowed into the loop, and again stopped before the other Home Signal is cleared.)

I'm with Mike and the only exception would be a loop equipped with catch points at both ends where the overlaps aren't over the points, not sure if this applied anywhere particular on the Western but it did on the Southern and is still in use at Marchwood. The catch points effectively make a long overlap which doesn't foul the single line at the far end so trains can arrive in both loops at the same time. This arrangement wasn't common because it cost more as you had 2, (or 4for bi-directional lines),extra mechanisims, it would only be used if it provided safety advantages like it does for the dangerous goods on the Fawley Branch.

[The Stationmaster]

I'm with Mike and he only exception would be a loop equipped with catch points at both ends where the overlaps aren't over the points, not sure if this applied anywhere particular on the Western but it did on the Southern and is still in use at Marchwood. The catch points effectively make a long overlap which doesn't foul the single line at the far end so trains can arrive in both loops at the same time.

I was done on the Western Paul but I think mainly with WWII additions when loops were extended (e.g. DN &S line) although there were also places where one of the loops ran on to become a siding or yard access so in effect a Clearing Point could be created in one direction, but not the other!

 

However the Inspectorate began to take very strongly against having traps at the end of loops at one time (because of derailments - there seem to have been a lot on the DN&S as it happens) and I think in some respects this reflected what had already become the approach on some Regions. Our branch was singled in the early 1960s (with Acceptance Levers) and no traps were provided although they would have been quite feasible in one direction at the crossing station.

 

BTW just for a bit of amusement in later years there was also an interesting bell signal in use (informally of course) which went like this after a train had arrived at the terminus - 2-1-3-1-2 (and back to reading the 'paper)

[Joseph_Pestell]

When mentioning GWR (in particular but does apply to other lines), one needs to consider the signalling, trap points, etc. right from the start. Many stations with passing loops would be equipped with bi-directional running through the line that had the station building. So if no crossing move was due to take place, the train could let passengers off (and parcels could be taken off) at the most convenient location.

 

After that, considerations as above would be involved and any inclines on which there could be runaways might be considered too.

 

But most of all, I think it depended on where the signal box was. Regardless of the rules, the signalman would arrange things so that he had the least distance to walk (or cycle in some cases) with the token/tablet.

[beast66606]

When mentioning GWR (in particular but does apply to other lines), one needs to consider the signalling, trap points, etc. right from the start. Many stations with passing loops would be equipped with bi-directional running through the line that had the station building. So if no crossing move was due to take place, the train could let passengers off (and parcels could be taken off) at the most convenient location.

 

 

I don't think the term "many" should be used, "a few" would be more appropriate.

 

After that, considerations as above would be involved and any inclines on which there could be runaways might be considered too.

 

Short of providing run away protection, there's not a lot that could be done, there might be some local instructions, but we aren't talking specifics yet.

 

But most of all, I think it depended on where the signal box was. Regardless of the rules, the signalman would arrange things so that he had the least distance to walk (or cycle in some cases) with the token/tablet.

 

Cycling was a Scottish trick, where one signalman would man two boxes, I doubt if many (any?) GWR signalmen routinely cycled for token exchange, the exchange would take place at a given place, usually near to the box, the bobby would have little discretion over this.

[The Stationmaster]

When mentioning GWR (in particular but does apply to other lines), one needs to consider the signalling, trap points, etc. right from the start. Many stations with passing loops would be equipped with bi-directional running through the line that had the station building. So if no crossing move was due to take place, the train could let passengers off (and parcels could be taken off) at the most convenient location.

 

After that, considerations as above would be involved and any inclines on which there could be runaways might be considered too.

 

But most of all, I think it depended on where the signal box was. Regardless of the rules, the signalman would arrange things so that he had the least distance to walk (or cycle in some cases) with the token/tablet.

 

Most of all it depended on what the Regulations said as they were the key to working a crossing move safely (and there was a very good reason for them being framed in the way that they were written). The GWR did provide a number of places with bi-directional loops in the 1930s (e.g. on the West Somerset branch) but in earlier days the main reason for what were effectively bi-directional lines at crossing places was because one line was goods only and in effect was a loop as well as a crossing place and passenger rains were unable to cross there.

 

But all of this is drifting far away from the original question (and answer). Similarly special arrangements on inclines at crossing places were fairly uncommon. For instance Pentir Rhiw, which was situated on the well known 1 in 38 Seven Mile Bank on the Brecon & Merthyr had some very unusual Instructions (and track layout) because it lay on a long and very steep gradient - but those Instructions were still based on the standard arrangement I explained above.

[D6975]

Quote: Cycling was a Scottish trick, where one signalman would man two boxes, I doubt if many (any?) GWR signalmen routinely cycled for token exchange, the exchange would take place at a given place, usually near to the box, the bobby would have little discretion over this.

 

I remember this being done at Nairn ( IIRC) as late as around 1989/90. It was when the IS-AB service was a mix of 37s and 47s with the occasional 156/8.

[dvdlcs]

Hello.

 

This may have been described above, but I'm not too sure as I'm not a signalling engineer.

 

The rail network that I am most familiar with (not in the UK) has a system called "simultaneous meet" for passing loops on a single track.

 

This means that where two trains are approaching a loop from opposite directions, the facing point for the train to be looped can be set for the loop while the facing point for the train that remains on the main is set for the main line. Both trains are heading towards red signals at the opposite ends of the loop section as the points they protect are set in the direction for the other train.

 

The idea is that the train with priority (on the main) is delayed as little as possible (or not at all) by being able to proceed up to the far end of the passing loop before a red signal is encountered.

 

I'm not sure if all of the loops have catch/trap points beyond the red signals, some certainly do.

 

 

David.

[Phatbob]

Fascinating stuff chaps.

I think the key point for operation of a passing loop on ones model is that generally speaking, due to way in which tokens are exchanged with the signaller and the block instruments "cleared" by the signaller, the trains end up running "first in, last out".

So my advice to Mr Penfold would be to operate his passing loop in that manner.

No doubt there will now be plenty of postings about exceptions to this, but as I say, I'm offering up a general guidence here, not in anyway a hard and fast rule.

HTH,

Bob.

[The Stationmaster]

Fascinating stuff chaps.

I think the key point for operation of a passing loop on ones model is that generally speaking, due to way in which tokens are exchanged with the signaller and the block instruments "cleared" by the signaller, the trains end up running "first in, last out".

So my advice to Mr Penfold would be to operate his passing loop in that manner.

No doubt there will now be plenty of postings about exceptions to this, but as I say, I'm offering up a general guidence here, not in anyway a hard and fast rule.

HTH,

Bob.

That was almost certainly the case at many places Bob but, as I said above, the critical point is the operation of the Home Signals and that is probably the most noticeable thing on a model (it definitely made a noticeable difference on one well known layout on the exhibition circuit).

 

As far as 'first in last out' is concerned the key point for many Signalmen (unless there were Auxiliary Token Instruments) was avoiding a long walk. The best way round that was to ensure that the train on which the loco would finish up furthest from the signalbox was the second one in as that - with a bit of smart work - would allow it to exchange tokens as it passed the signalbox. But notwithstanding that the Home Signals should be worked in accordance with the Regulations to ensure maximum safety.

[Eggesford box]

In relation to previous posts here is a photograph of an auxiliary token instrument. As Mike has said they would be provided at the end of a loop remote from the signalbox.Sometimes, as in this case they could be provided at other locations where the position of the box made it awkward for the signalman to change tokens himself. Obviously, they where under the control of the signalmen.

 

At a crossing loop not provided with trap points the interlocking in the lever frame would prevent both home signals being cleared at the same time.

 

As Mike has pointed out, the signalman, wherever possible, would cross trains in such a fashion as to save himself as much walking as possible (and the trains would get away quicker) but as you have guessed there where exceptions! I can remember being at Moreton in Marsh once, admittedly, at that time a double to single track location but the principle is the same. The box is at the London end of the station but the signalman let the engine and stock from Paddington into the station first instead of holding it outside for a couple of minutes. Once the service from the Worcester direction had arrived and the signalman had collected the token and put it through the instrument he then had to walk the length of the train to give to the driver of the engine and stock the token. It turned out that the well heeled clientele from Moreton in Marsh had complained about having to wait outside 'their' station instead of being allowed to run straight in.

[Xerces Fobe2]

Here is a passing lop with a diffrence?

 

 

XF

[The Lurker]

Think yourself lucky yo are not modelling the Midland & Great Northern Joint, which regularly had 2 trains, both too long for the loops, passing each other. That takes a lot of explaining!

Could you point me to an explanation of this please?

 

I once saw this set as a question on a children's tv programme in the early 70's, and have been wondering how it worked ever since ...!

[The Stationmaster]

Could you point me to an explanation of this please?

 

I once saw this set as a question on a children's tv programme in the early 70's, and have been wondering how it worked ever since ...!

There used to be a website with an animated GIF in its heading which showed how to do it - does anyone recall the name of teh sire because I definitely can't?