Double block working on the ECML

[corneliuslundie]

In LNER days at least double block working was required for trains running at 90 mph or more at least on certain stretches.

My question is: did this apply to the whole route, only to the ex_GNR section or to more limited sections?

Jonathan

[The Stationmaster]

The only bit of non GNR I know anything about was part of the route between Selby and York and double blocking for the fastest trains there was a a much later - long after the war.  However possibly it had been used Pre-War and was subsequently dropped once train speeds were restricted post-war?  

[D9020 Nimbus]

I've read in the past that "double-blocking" was used for the Silver Jubilee and Coronation pre-war. I'd assume on all the "fast" stretches probably as far north as Newcastle.

[Michael Hodgson]

The justification for double block for high speed would be that you didn't really trust the train's brakes to stop at the Home Signal on seeing the Distant on, and so the overlap beyond it was critical.  If the Distant was far enough away, you shouldn't need double block, but given an insufficient spacing, double block mitigates the risk of collision in the event of any SPAD of  the Home Signal. 

 

The 1/4 mile overlap required beyond the home signal for acceptance had only been only 400 yards on the NER, and the outer homes were only 400 yards from the inner where applicable.  So at least in theory I could see a stronger case for double blocking there before they were brought into line with the rest of the country, however that could have been mitigated by better protection by the distant signals.

 

However at Grouping I believe the LNER inherited no fewer than four different sets of criteria governing the circumstances for giving Train out of Section, Blocking Back etc.  Some of these would have resulted in bigger overlaps in practice than others, albeit a cost of longer headways.

 

I am sure I have read that Mallard's famous high speed run was under double block, GN section of course.  Inadequacy of the GN's original distant spacing tends to be confirmed by the addition to some Starting signals of colour light lenses, resulting in a hybrid semaphore/colour light in the form of a semaphore stop signal combined with a YY/G colour light acting as outer distant for the box in advance.  A sort of poor man's resignalling using 4-aspect, it gave the fastest trains a chance to slow down enough to have braking distance when it reached the existing distant signal.

[kevinlms]

A couple of questions on double blocking.

 

How did a loco driver know if double blocking was being correctly applied? In other words did the signals show something different than a standard distant being clear meant that the next block was clear. He needed to know if two blocks were clear.

 

Did the relevant signal boxes have to send a modified bell code to the next signal box, to ensure that double blocking was required for the next train?

[beast66606]

4 hours ago, kevinlms said:

A couple of questions on double blocking.

 

How did a loco driver know if double blocking was being correctly applied? In other words did the signals show something different than a standard distant being clear meant that the next block was clear. He needed to know if two blocks were clear.

 

Did the relevant signal boxes have to send a modified bell code to the next signal box, to ensure that double blocking was required for the next train?

 

The drivers would just see the signals as normal, and take appropriate steps on sighting adverse ones.

 

I suspect the signal box notices / timetables / local instructions (eg all class 1 trains to be double blocked, class 2 and below offer on section) would cover which trains were to be double blocked

[Michael Hodgson]

No, the driver didn't know the double block working was in use, he didn't need to know and was still expected to obey signals.  Double block was the signalman's responsibility, and he was just giving the special train extra margin in case a driver couldn't stop in time.  Box instructions were often issued, for example for the APT runs on WCML.  It wouldn't necessarily apply to all boxes.  Instructions issued to signalmen would typically specify which trains they were required for.  

 

The classic use of double block was for Royal Trains, and booklets of standing instructions were issued on various dates to stationmasters, signalmen and others specifying a number of other details, such as closing level crossings well beforehand, not running another train on a parallel line where Joe Public could be gawping in!

 

No speical bell code was used in general.  However the Royals would be 4-4-4, and special bell codes were also used for the APT high speed runs.

[meil]

I had assumed that double blocking simply meant offering the train on when offered to you rather than waiting for the TES?

[LNERGE]

Distant indicator working was introduced also. This was to allow higher speeds.

[kevinlms]

3 hours ago, beast66606 said:

 

The drivers would just see the signals as normal, and take appropriate steps on sighting adverse ones.

 

I suspect the signal box notices / timetables / local instructions (eg all class 1 trains to be double blocked, class 2 and below offer on section) would cover which trains were to be double blocked

Yes, I 100% understand that any driver would ALWAYS drive to the signals. Unless told otherwise, by being stopped and advised, but that isn't applicable to high speed trains.

 

I still don't really see the purpose, if he was unaware of wherever or not it was being carried out properly.

 

So just a bit of breathing space, which would do little except stop him from getting done for a SPAD.

 

 

[The Stationmaster]

3 hours ago, meil said:

I had assumed that double blocking simply meant offering the train on when offered to you rather than waiting for the TES?

Exactly so.  In normal Absolute Block Working (assuming short sections aren't involved) a train is offered forward on receoit of TES and when it is accepted by the 'box in advance the Signalman can clear his own signals.

 

In double-block working the train is normally offered immediately on receipt of the 'Is Line Clear?" bell signal and that is not acknowledged until the 'box in advance has accepted that train.

In other words two successive block sections have to be clear and with the block set to 'Train Accepted'.  Double blocking could often extend over a succession of sections and no doubt the 'Train Approaching' bell signal (or a special bell signal) would also have to be used to avoid 'Line Clear?' being asked too far ahead.

 

The system served two purposes - firstly it would be a means of taking care of sub-standard braking distances for maximum line speed - that is its primary safety role.  But it also had a traffic regulating role in that it could ensure a delay free path over an extended stretch of railway.

 

As a matter of pedantry double block working was NOT used for Royal Trains.  The 1957 issue of the 'Grove' Instructions (which I have checked) simply required in the case of 'normal' length block sections that the 'Train Out of Section' had been received for the section in advance before a 'box could accept a Grove/Deepdene train.  i.e the block in advance was not required to be standing at 'Line Clear'  Thus in some circumstances the Clearing Point at the 'box in advance might well be fouled, even if only for a very short time, when the 'box in rear of it was permitted to accept a train running under 'Grove conditions.  I have also checked all the earlier issues and exactly the same Instruction applied in both the 1949 (as amended to 1951) issue of the Instructions and in the original 1942 issue (which was the inception of such Instructions).  what I have this far been unable to check is the 1950 booklet although I might have a copy somewhere but I doubt things were substantially different in 1950 from the two earlier Instructions and the (last) 1957 reissue.  

 

The Grove etc Instructions were discontinued completely completely during the 1960s (I have the date somewhere) and normal block working henceforth applied, except where Special instructions were issued in resect of a Royal Train.   When I was dealing with such trains on the WR. albeit in the 1980s, we never issued and such Signalling Instructions in respect of the occasional Royal Trains which we had on the Region.  And although we had plenty of Special Trains - i.e. conveying lesser members of the Royal Family than the Monarch - we never issued Special Signalling instructions for any one of them.

 

The situation in earlier years, especially prior to the Grouping, was of course very different. 

 

 

Edited May 29, 2021 by The Stationmaster

[Andrea506]

I remember reading about when the prototype Deltic was being tested on the ECML they tried doing a full service brake application on passing a Distant signal at over 90mph, the train hadn't stopped before reaching the Home signal, hence the need for double block working and also one reason for the change to air brakes rather than vacuum.

Edited May 29, 2021 by Andrea506