Double Block Working

andrew jukes
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Double Block Working

Postby andrew jukes » Tue Jun 25, 2013 9:43 am

This is not really a modelling point as I can’t ever imagine implementing it but I am curious about how double block working actually worked. I understand it was used for the LNER streamliners and I am trying to picture what it would mean from a driver’s perspective.

As I understand it, double block working meant that a signalbox had to establish that the next box in advance had given ‘train out of section’ before being allowed to accept the special train from the box in rear. This would mean that the line from the box in rear’s starter to the starter of the box in advance was clear.

Having established this, the box can then clear the signals right through its block and accept the special. The special runs through the block unimpeded.

But the box in advance, having given ‘train out of section’, can clear its home signal but, if it’s been unable to obtain the necessary ‘train out of section’ from the next box in advance, its starter may still have to be at danger. Its distant will therefore be at caution.

The train crew, racing along with all the confidence given by double block working, will sight this distant at caution as their first indication that they need to stop. The available braking distance will be from the distant to the starter (assuming the home has indeed been cleared).

It seems to me (unless I’ve got something completely wrong) that double block working gives the illusion of miles of clear track ahead while in fact it only adds to the available braking distance the distance between the home signal and the starter……. and the distance between a home signal and its associated starter is sometimes not great.

Is this a correct understanding of double block working?

Andrew Jukes

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Noel
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Re: Double Block Working

Postby Noel » Tue Jun 25, 2013 12:08 pm

I'm no expert on this topic, Andrew, but my understanding is that if Box A offers the train to Box B, Box B then offers it to Box C as you describe. If Box C accepts then Box B gives 'line clear' as normal. If not, then Box B gives Box A a 'warning acceptance' and Box A clears its home and starter signals but leaves its distant 'on'. Box A's distant thus acts as an outer distant for Box B. If Box B has had a normal acceptance from Box C before the train arrives at Box B's distant then Box B will have cleared its distant and the driver will know that he can go back to normal speed. Otherwise he will know that he *may* have to stop at B's home signal or starter and will continue at reduced speed [i.e. the normal situation on passing a distant signal at danger].

I await further comments from those who know more than I do!

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Re: Double Block Working

Postby andrew jukes » Tue Jun 25, 2013 12:40 pm

I had wondered if it might work something like that but rejected it on the basis that it puts everyone in an ambiguous position. How can you have identical looking distant signals at caution which can have two different meanings with quite different implications for the speed through a block without creating serious risks?

Apart from having to trust the driver mentally to label each distant as an outer or inner depending on what had happened previously, it makes it harder to stop the train in an emergency. A signalman could revert all his signals and have the approaching train read his distant as an outer distant for the next block. Not good - but you may still be correct!

Andrew

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Re: Double Block Working

Postby andrew jukes » Tue Jun 25, 2013 1:07 pm

It seems to me the other key point is that offer and acceptance between boxes becomes a two stage process. The first stage is an enquiry, not really an offer - Is train out of section? The second stage is the proper offer. So in the example, B is enquiring of C, not making a proper offer.

If it's not done like this and every box's acceptance depends on the acceptance of the next box in advance, I see no way of avoiding clearing the while route before the first distant can be cleared!

Andrew

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Re: Double Block Working

Postby Noel » Tue Jun 25, 2013 3:53 pm

If you pass a distant at danger in ordinary block working, and then find all the homes/starters 'off', you would not [or should not] make any assumptions about the state of the next block. All you know is that you may need to proceed more cautiously to the next box until you find out, depending on the type of train and its loading, your brake power, the weather conditions, etc., etc. No ambiguity is involved in applying the same principle here, and the driver would be aware of the system, so that he would know that normally there was another distant between him and any stop signal. Emergencies are a different matter, but then they are in ordinary block working as well. Don't forget also that the sighting distance for the home and the starter on plain line is quite considerable.

I don't know the answer to your comment about having to prove the whole line is clear; it's a valid question certainly. My guess, and that is all it is, is that when A sent "train entering section" to B it was immediately passed on by B, and C then offered the train to D at that point. I'm not sure why you suppose that B's offer to C is not a 'proper' offer. In the absolute block system it cannot be anything else. Perhaps the semantics are getting in the way - formally the bell code means "Is line clear for" whatever the train is. Returning the bell code accepts the train and states that the section is clear at least to that box's (outer) home signal's clearing point and will remain so until the train has either passed or stopped. There are many reasons why the next section might not be clear, besides the previous train still being in section.

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Re: Double Block Working

Postby JFS » Tue Jun 25, 2013 5:14 pm

This is one of those subjects where every case is different and is defined in the Local Instructions. But the basic principle is that, when double blocking, a train cannot be accepted from the box in rear until it has been accepted by the box in advance. The implication that the whole route has to be clear is limited by the requirements of the Local Instructions. Usually, this would define the limits for the working. In the descriptions above, one thing which is missing is the use of the "Train Approaching" bell signal - typically used to the box in advance, when the Entering Section has been received from the Box in Rear - this would instigate the train being offered forward before the Entering Section had been received.

To quote a specific example of Double Block working - at Exeter St David's, Up trains not booked to stop were Double Block worked. They used the Special Is Line Clear code 3-3-3, to distinguish them from other Class 1 Trains. City Basin Junction would Ask ILC to Exeter West who could accept them under normal Reg 4 conditions. West would offer to Middle who would NOT accept, but who would offer to East who would also not accept but would offer to Cowley Bridge. Cowley Bridge would accept under normal Reg 4. East would then Accept from Middle, who would then accept from West. Only at that point would West clear his signals as usual. Thus, a driver of an up non-stop, on seeing West's distant Clear, would know that the road was clear to Cowley Bridge. All a bit of a nonsense really given that there is a 35mph speed restriction over the Exe Bridge for Up Trains!!!

If you want to have a play with this, I have written a simulation of Exeter West which is available for Free Download here:-

http://www.blockpostsoftware.co.uk/downloads.php

The demo is fully working though limited to about 15 minutes - see also

http://www.youtube.com/watch?v=vxWWBOV- ... e=youtu.be

which shows that Exeter West has a few peculiarities - just like everywhere else - including 31 different Is Line Clear codes - nothing special for a large box.

Hope that helps,

Howard.

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Re: Double Block Working

Postby JFS » Tue Jun 25, 2013 6:46 pm

Andrew,

Just to help with your query regarding ambiguous distant indications - in the circumstances you envisage (the ECML I presume) the driver of the A4 going hell for leather at 105mph, spotting the adverse distant, would know that something was amiss - the line was kept clear miles in front of these trains - but would just apply a full service brake. The line MUST be clear to at least the next block post - otherwise the train could not have been accepted from the previous box. The signalman would keep all signals on, but, as the train approached the home, wheels, on fire, but nonetheless "under control" he would clear it and allow the train to approach the starter and again assuming the train to be by now "under control" (but probably still not able to stop!!) he would clear that and the train would now proceed with the expectation of adverse signals ahead. All this indicates just how costly (if not risky) it was to run trains at 100mph using systems only able to cope with 75mph. The impact on line capacity was very significant.

From a modelling point of view, all is clear - on layouts which portray 100mph running of steam trains, expect the signals to be "off" a good 15 minutes before you see a train!!!

Cheers,

Howard.

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Re: Double Block Working

Postby Natalie Graham » Tue Jun 25, 2013 9:44 pm

JFS wrote: on layouts which portray 100mph running of steam trains, expect the signals to be "off" a good 15 minutes before you see a train!!!


Not a chance. On most layouts there will have been a slow goods headed the opposite way down the single line not 30 seconds previously.

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Re: Double Block Working

Postby JFS » Tue Jun 25, 2013 9:59 pm

Natalie Graham wrote:
Not a chance. On most layouts there will have been a slow goods headed the opposite way down the single line not 30 seconds previously.


:D

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Re: Double Block Working

Postby andrew jukes » Wed Jun 26, 2013 12:18 am

Howard

You make it sound as though the ECML in 1937-39 could be emptied for the streamliners. Accepting that passenger train frequencies were far lower than today’s, there were three streamliners each way each weekday south of Doncaster averaging over 70mph and many more two track sections - and there were other trains which could clearly conflict with the streamliners. A quick look at the 1938 working timetable shows the down Coronation (4.00pm ex King’s Cross) in hot pursuit of the 3.25pm Scotch Goods. The 3.25 was due to pass Hatfield at 4.05, the Coronation at 4.19. Somewhere north of the Welwyn tunnels, the 3.25 must have been turned onto the down goods line because by Hitchen (where it paused at 4.28), the Coronation was on it (passing Hitchen at 4.30). It would appear that by the time the 3.25 had cleared the Welwyn bottleneck, it would if running to time be around 12minutes in front.

Almost the same intervals apply between Hatfield and Hitchen with the West Riding Limited (7.10pm ex King’s X) and the 6.00pm Leeds braked goods.

Going back to my original question - what does double block working mean for the driver? - Noel’s description of the first distant at caution being treated as an instruction to reduce speed to normal express speeds (from say 90mph to say 60mph) by the sighting point of the next block’s distant sounds more sensible than your description of it requiring an immediate full service brake application - but it still leaves me uneasy. You write as though your description was definitely how it was done - is that right and if so where did you find the information?

Otherwise, more research needed. I shall have to find the instructions issued by the LNER for these trains if I’m to satisfy my curiosity.

The timekeeping and safety record of the streamliners was good, but the cost of achieving this performance must have been considerable. As always, high speed operation on a traditional railway is as much about finding ways of stopping before you hit something as it is about achieving the high speed.

Regards

Andrew

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Re: Double Block Working

Postby John Palmer » Wed Jun 26, 2013 1:09 am

Am I right in thinking that there's a radical difference between the two methods of working under consideration, viz. (1) acceptance only after 'Train Out' received for preceding train and (2) acceptance only after obtaining acceptance from the box in advance?

So far as I can see, the second of these methods does call for propagation of acceptances throughout a succession of boxes until the process is terminated by a conventional Reg.4 acceptance – as in Howard's example of Exeter non-stoppers.

Making acceptance of a double blocked train contingent upon receipt of 'Train Out' for the preceding train seems to involve an implication that the preceding train in question has passed the clearing point for the box in advance, since this is the normal pre-condition for the signaller at that box issuing the 'Train Out' bell signal and restoring his instrument to 'Line Blocked' in accordance with Reg.10. Unlike the second method, such a state of affairs will arise naturally during the ordinary course of working provided sufficient headway is available to the preceding train – therein lies the rub as double blocking effectively halves line capacity.

If such an implication has not arisen because the signaller has yet to receive 'Train Out' from the box in advance, neither he nor the driver of the 'double blocker' can make any assumptions about the whereabouts of the preceding train. What if it has failed, out of sight of the signaller, a few yards in advance of his section signal or even, conceivably, in rear of that signal? That suggests to me that a distant signal in the 'on' position conveys a message that is in no way ambiguous: 'You must be prepared to find the next stop signal to which this distant signal applies standing at danger and act accordingly. Even at Norton-on-Tees.'

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Re: Double Block Working

Postby JFS » Wed Jun 26, 2013 5:19 am

John,

Yes - these two situations are very different.

It was quite often the case that a train could not be accepted until the Out of Section had been received from the box in Advance - that would always be the requirement where boxes were closely spaced and the box in Advance lay within your own Clearing Point. Therefore, by definition, you do cannot have a clearing point until you have received OOS. Hence, this is therefore simply a normal Reg.4 Situation and thus is distinct from Double Block working. And it was very common in busy areas.

In the case of Double Block working, this is usually introduced to cover for the situation where the braking distance for the train is such that the distant signal itself does not give sufficient stopping distance - hence the driver cannot be expected to pull up at the next stop signal after encountering an adverse distant. Now that circumstance might arise for a variety of reasons - gradients, train classes with non-continuous brakes, trains running at higher than normal line speeds etc. As you rightly say, the MINIMUM inpact is to halve line capacity and often worse as double block working often meant quite long chains of boxes.

Just to quote a second example form Exeter West - Trains "off the Southern" could not be accepted from Exeter Central "B" until they had been accepted by Exeter Middle. The reason for this was that the gradient between the two boxes was 1:37 - hence no train could be expected to stop at Exeter West's Home Signal. Similarly, in the other direction, Exeter Central "B" would not accept a train from Exeter West until it had been accepted by Central "A" - but for the opposite reason - a train brought to a stand on the bank would not be able to restart (well not with a West Country on the front... :D )

Such operational aspects are often overlooked by modellers - and it all too often shows at exhibitions!

Cheers,

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Re: Double Block Working

Postby Noel » Wed Jun 26, 2013 9:54 am

John, a signalman giving giving 'train out of section' to the previous box says nothing about what that signalman is going to do next. It does *not* say that his section is now clear and will remain so. He might open his level crossing gates, permit a shunting move to foul the main line within station limits for several minutes, let a freight out of the loop behind the train which has just passed or any one of a number of other things which would leave him temporarily unable to accept another train. All of these things are at his discretion and, with some exceptions [one of which is the situation that Howard mentions], do not require notification to the previous box. The only way to prove a section is clear is for the previous box to offer a train and have it accepted, and that acceptance is the only way of confirming that the section is clear and will remain so.

Exeter is somewhat of a red herring, I think, in that it deals with a static situation where the rules exist because of a particular set of operating hazards. In very simplistic terms, normal single block working involves a moving block containing a train, which is 'handed on' from one box to the next. The difference here is that instead of requiring two boxes to collaborate over the handing on, double block working requires three boxes to cooperate. The principles though have not changed.

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Re: Double Block Working

Postby LesGros » Wed Jun 26, 2013 11:35 am

andrew jukes wrote:
This is not really a modelling point as I can’t ever imagine implementing it but I am curious about how double block working actually worked. I understand it was used for the LNER streamliners and I am trying to picture what it would mean from a driver’s perspective.


Andrew,
This link may be of help; it describes absolute block and circumstances in which double block working is/was used.
http://memoriesofarailwayman.blogspot.c ... uble+block

cheerydoo
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Re: Double Block Working

Postby John Palmer » Wed Jun 26, 2013 12:46 pm

Les, you beat me to it in posting that link to the Memories of a Railwayman blog. Apart from the useful description of double block working the site's masthead includes a wonderful picture of Empire of India prior to departure from Kings Cross with the down 'Scotsman', with the bonus of one of the 1938 locker composites alongside.

Noel, I had not intended to suggest that the issue of the 'Train Out' signal in some way fettered the freedom of the signaller who issued it, but in practice some of the activities you mention do need to be communicated to, and authorised by, the signaller at the box in rear. Crossing gates are not, I think, regarded as an obstruction, but any movement that results in vehicles standing within the clearing point will involve a 'blocking back' signal to the box in rear, with the block instrument being placed at 'Train on Line'.

I think it's worth taking a look at Block Reg 4(e), the 1934 LNER version of which reads as follows:

"During fog or falling snow, except where instructions are issued to the contrary, if a Fogsignalman is not on duty at the Distant Signal, the Is Line Clear signal must not be accepted from the box in rear until the Train out of Section or the Obstruction removed signal has been received from the box in advance, and the block indicator worked from that signal box is in the normal position ; nor must the Blocking Back signal (4-2, 2-4 or 3-3) from the box in advance be acknowledged if permission has been given for a train to approach from the box in rear in accordance with this Regulation."

Any movement involving blocking back cannot be authorised until the blocking back signal has been acknowledged by the box in rear (Reg 13(b)), and when Reg 4(e) is in operation the signaller at that box is prohibited from issuing such an acknowledgment if he has already accepted a train from the box in rear of his own. This looks to me very much like double block working in action.

Andrew, am I right in thinking that the streamliners occupied timetable slots at times when other traffic is comparatively light? A 1600 departure of the Coronation and 1910 for the West Riding suggests this may be the case. I have a dim recollection of reading that the need to maintain a two block headway for the high speed trains more or less obliged the timetable compilers to fit them into periods when traffic was slack.

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Re: Double Block Working

Postby Noel » Wed Jun 26, 2013 3:02 pm

Thanks for the link to the MORM blog, Les. I read it with interest, but it has left me puzzled, I'm afraid. If taken at face value it does not answer Andrew's original query, since if C does not subsequently accept the offer of the streamliner from B the stopping distance becomes from B's distant to B's home, as B has already accepted the train from A after the 'out of section' from C. Admittedly this should not happen, as C will know what train is expected, but it still leaves the driver at risk of disciplinary action for a SPAD which is not his fault, which seems to me to be unacceptable for many reasons.

Incidentally, the person who posted the entry in question, Robert Webb, whose relationship to the railwayman of the blog is unclear [son perhaps?] has not been a railwayman according to the biographical note on the blog. He has missed the point somewhat with the story about 'District Inspector's block'. George had previously been a Goods Inspector, and the punchline to the story was "In a few days he went back to his goods." Clearly authority was not amused [the previous train had been less than 100 yards ahead when he gave the green light to the next one and visibility is obstructed by an overbridge on a curve] and sent him back where he wasn't a danger to the travelling public and other railway staff.

John, just for clarity for other readers, and no reflection on your comments intended, I would just point out that I was referring to activities which did not foul the clearing point and you are referring to one of the exceptions I mentioned, i.e. activities which do foul the clearing point, and which would therefore prevent that signalman accepting another train on that line. Whether the fog working you refer to is true double block working or solely a precaution against drivers overruning signals I don't know. Either way, it is interesting that it was apparently not in force at Gidea Park in 1947 - perhaps because the line was equipped with Sykes Lock and Block? I wonder what the rules were if the ECML was suffering fron fog when a streamliner was running?

Public level crossing gates were definitely an obstruction if across the track, though, were normally protected by fixed signals and had to be open before accepting a train, if within the fouling point of the outermost home signal, even if the train was not going that far. At Grange Court Junction [BR(WR)] there were two crossings on the up line after passing the box, operated remotely from ground frames, and both equipped with distant signals, resulting in the presence of three distant signals within the section [one crossing had both inner and outer distants], mounted under the inner home, starter and advanced starter. The last also had a slot to allow it to act as the stop signal for the first crossing; the second crossing had no fixed stop signal. Presumably the red gate target was regarded as the stop signal.

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Re: Double Block Working

Postby andrew jukes » Thu Jun 27, 2013 6:23 pm

When I started this thread, I said I couldn’t imagine ever implementing double block working - but what I might hope to do is play out the consequences of it. I am modelling Welwyn North in 1938/9 and, if the signalling is ever installed and I have the trains to do it, I will be able to play out something on the following lines.

I am the signalman at Welwyn North. It is 4.10pm on a Wednesday in August 1938 and I have accepted the down Scotch Goods which should have a clear run through to Hitchen where it stops for water and inspection. It’s running to time and all seems in order as I watch it approach at around 70mph across the viaduct. Then I spot something - smoke from a van halfway back in the train. As it gets nearer, it becomes obvious it’s a hot box well on the way to disintegration. Thinks - were WGC asleep, why did they not see it? - as I throw my down distant to caution then the starter to danger. But the V2 is already into Welwyn South tunnel and as the guards van speeds by the guard seems more interested in the scenery than the signals (which I expect he had already checked...).

(This is where my ignorance of bell codes becomes obvious) Next I alert Woolmer Green box - obviously too late to turn the Scotch Goods onto the slow at Woolmer Green - but there seems a good chance Knebworth will get it stopped so the van can be inspected and (probably) the train proceed dead slow to the yard at Hitchen to cut out the van.

My problem now is the down Coronation running on time at 90mph which WGC want me to accept. Woolmer Green has given the Scotch Goods out of section but Knebworth probably won’t be able to for some time. The aim is clear - the Coronation must be slowed, possibly stopped, and either put on the slow at Woolmer Green and back on the main south of Stevenage or crawl along behind the Scotch Goods until it is turned on to the slow line north of Stevenage.

I obviously have to keep my distant at caution, but what do I do with my stop signals?
If I keep them at danger, do I clear them as the Coronation nears them (as Howard suggests)?
If I clear them, can I count on the Coronation reducing speed and approaching the Woolmer Green splitting distants at normal line speed, so ensuring the incident ends safely?

(Now I’m the driver of the Coronation) On time departure from the Cross, Empire of India running well and my fireman seems to be coping with shifting a ton of coal an hour. We race through WGC at 90mph and then (expletive deleted) the Welwyn North distant is at caution!
Do I do all I can to stop as quickly as possible (easy enough on a model but I will be deep into the Welwyn tunnels before coming to a stand in real life) or do I assume this is rather like a double yellow and slow to an appropriate speed for the next (Woolmer Green) caution?

From our discussion, I don’t think the answers are clear. (No doubt though there will be lots to correct in my description of traditional train operation!)

Incidentally, if I were the LNER’s Chief Operating Officer, if the agreed method of operating involved telling my drivers to run to time (involving speeds perhaps 30mph faster that the signalling was laid out for) but to aim to stop at the first stop signal after any distant at caution, I would be campaigning relentlessly for the installation of additional (outer) distants to restore braking margins.

Regards

Andrew

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Re: Double Block Working

Postby grovenor-2685 » Thu Jun 27, 2013 8:12 pm

Its clear from the above that there are at least 3 reasons for double block working that would have different regs to go with them.
A. local problems with close spaced boxes where the distant would be slotted and need two or more blocks clear to clear the distant.
B. fog and falling snow where the aim is to protect against driver error in the adverse conditions
C. High speed services above normal line speed.
Each of these would have its own set of regulations, and somebody somewhere must know what the LNER regs were for the streamliners, it might pay to put this question on RMweb.
IMHO C. was an inherently risky enterprise that would be highly unlikely to get through a hazard analysis under present day change control processes as it relied on lots of staff obeying regulations different from the norm with a serious hazard attached to a mistake. And surely the whole point was that the driver could count on two distants at caution before finding an obstruction such as a train ahead or points not set. If the stop signals between these two distants were on it would re-inforce the message but it would not be possible to blame the driver for the resulting SPAD.

A. above I would expect to be covered in local instructions, B. as already mentioned is regulation 4(e) in the 1960 regs. C. I would be interested to see.
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Re: Double Block Working

Postby Noel » Fri Jun 28, 2013 10:48 am

Nobody has commented on the third paragraph of my last post, but further consideration has left me thinking I got it wrong and that I should have said in the first sentence

"John, just for clarity for other readers, and no reflection on your comments intended, I would just point out that I was referring to activities which foul the clearing point temporarily, and prevent the signalman accepting another train, and you are referring to one of the exceptions I mentioned."

My apologies, and I hope I have made more sense this time.

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Re: Double Block Working

Postby andrew jukes » Fri Jun 28, 2013 1:09 pm

Keith’s right, C is the case I’m interested in and it would be good to see the instructions given at the time for the streamliners.

Thinking about it some more, under double block for the streamliners I would expect the first distant at caution to be followed by clear home and starter and the driver’s instructions to be to bring the train down to normal line speed by the sighting point of the second block’s distant. This would be the ‘normal’ controlled way of running.

If there were an emergency (‘obstruction danger’ from Woolmer Green for example, or maybe a luggage trolly on the four foot at Welwyn North) then the Welwyn North home(s) and starter would be set to danger and the driver would know that the first caution followed by the home at danger was reason to stop as fast as possible. A SPAD in such circumstances would not be an offence.

This is pretty much what Keith said, perhaps more precisely defined (and also what Noel said right at the beginning!).

Regards

Andrew

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Re: Double Block Working

Postby John Palmer » Fri Jun 28, 2013 1:55 pm

I have posted an enquiry about instructions for working the high speed trains on the LNER forum and hope that this will bear fruit.

Noel, thanks, your correction makes better sense of your original post. The terms of Block Reg. 13 suggest to me that there are not many circumstances in which the signaller at the box in rear doesn't receive notification that the clearing point of the box in advance has been fouled after 'Train Out' has been given for the last train. The notable exception is a movement that does not have to stand within the clearing point, the word 'stand' actually being italicised for emphasis in the LNER regulations. Theoretically that would seem to mean that a movement can be signalled out onto the running line via a trailing connection only a few yards in advance of the home signal without need of a blocking back signal, provided such movement keeps going!

In Andrew's scenario, I fancy the Welwyn North signaller might well be exercised by events at Castlecary some nine months earlier. He has put back his signals in the face of the 3.40 goods but it has proceeded, apparently oblivious, into the tunnel. What if its crew has, like that of the Dundee express at Castlecary, apprehended his actions and brought their train to a stand somewhere in section – almost certainly within the tunnels? He now needs to establish what has become of it, but whatever steps he takes to do so he is bound, under the double block arrangement, to refuse WGC's offer of the 'Coronation' pending receipt of 'Train Out' from Woolmer Green, so the streamliner's crew are going to be checked by WGC’s distant rather than that at Welwyn North.

In these circumstances the 2-1 from Woolmer Green will probably come as an enormous relief, but what Andrew hasn't told us is what other signals he has exchanged with Woolmer Green. I would expect him at least to have sent 'Stop and Examine' to Woolmer Green, and if possible he would also inform Woolmer Green of the hot box that prompted such a signal, in accordance with Reg. 17(a). Woolmer Green's actions are dictated by the same regulation:

"The Signalman in advance must immediately exhibit his signals to stop any train coming from or going towards the signal box from which the signal was received."

Since Woolmer Green lies more than 1.5 miles beyond Welwyn North, there is a good prospect of the 3.40 being brought to a stand at its home signal, with the signaller then having the option of turning it into the Down Slow. In any case, receipt of 'Train Out' from Woolmer Green entitles Welwyn North to accept WGC's offer of the Coronation under the double blocking arrangement and to offer it forwards to Woolmer Green – in other words, the acceptance problem has now become one with which the next block post will have to deal!

<edit> Andrew, I respectfully disagree that it is permissible for the first distant to be at caution but the stop signals to which it applies being cleared. If Welwyn North refuses the streamliner under double blocking because Woolmer Green has yet to give 'Train Out' for the preceding train, then WGC has no authority to clear its section signal. </edit>

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Re: Double Block Working

Postby andrew jukes » Fri Jun 28, 2013 2:56 pm

Thank you John for posting the enquiry.

There is something missing here. I think.

If it's ever possible to bring the Coronation to a properly controlled stop, using the distants of two successive blocks to reduce its speed to normal, It must be possible for the box in advance to distinguish between giving a proper double block acceptance (for which it will already have 'out of section' from the next box in advance) and giving a normal single block acceptance.

A normal single block acceptance from Woolmer Green would (under double block working) require Welwyn North to keep its distant at caution. This would make controlled braking from the Welwyn North distant (followed by clear home(s) and starter at Welwyn North) then the Woolmer Green distant also at caution and finally a drama-free stop at the Woolmer Green home at danger.

Regards

Andrew

andrew jukes
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Re: Double Block Working

Postby andrew jukes » Sat Jun 29, 2013 9:15 am

A better way of thinking about type C (Keith’s definition) double block working may be that what it’s trying to do is shift control of every distant signal to the box one in advance.

Thus, with an A - B - C sequence of boxes/blocks, box B needs block A’s distant only to be cleared when box B is able to clear all the stop signals in block B. Similarly, box B needs to have effectively ceded control of its distant to box C.

Easy enough to say and in principle easy to do - but a nightmare to do through bell codes and to be sure everybody involved is working from the same script.

Regards

Andrew

williambarter
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Re: Double Block Working

Postby williambarter » Sat Jun 29, 2013 9:25 am

Just a thought - are we actually sure that the double-block working was safety-related, to allow high speeds? After all, with the right load other trains and locos could have reached the same speeds and probably did from time to time. Or was it simply to reduce the risk of one of these prestige trains being stopped? Didn't double block working also apply to Royal trains, presumably for that reason?

William

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Noel
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Re: Double Block Working

Postby Noel » Sat Jun 29, 2013 10:50 am

William, I think you may be unduly influenced by current conditions. In 1939, the best speed fom Kings Cross to Newcastle was 68.7 mph overall. The average express passenger service speed for the same trip was 55.3 mph. On the GWR for the same year the average express passenger speed from Paddington to the main centres was under 50 mph in virtually all cases. The only real exception was Bristol, where the average was 54.6 mph and the best 67.6mph. That would have been the Bristolian. With the exception of the LNER streamliners, a smaller number of trains on the SR and LMS, and the Bristolian, even normal express passenger train speeds were pretty slow by modern standards, which is why the streamliners stood out. It took the loss of freight traffic, some major engineering work to remove speed restrictions, and the advent of HSTs to make any significant change to this. Even the Deltics only lifted the average a little, partly owing to the number of serious speed restrictions to which the ECML was still subject even in the 1960s. There would have been little reason for other trains to approach streamliner speeds in normal service.

The figures are from G F Fiennes again, in 'I tried to run a railway'.

Delays to prestige trains such as streamliners were not well received, certainly, but I would think the main issue was safety. An accident to a streamliner would have been *very* bad PR given the way they were promoted. So far as I know double block for Royal trains is also safety, not because of the high speed risk, but because no-one wanted to take any chances with the life of the monarch.

Noel
Noel


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