Urgent Safety Message from RAIB

[The Stationmaster]

21 hours ago, Edwin_m said:

I presume it is this one: extension://bfdogplmndidlpjfhoijckpakkdjkkil/pdf/viewer.html?file=https%3A%2F%2Fwww.railwaysarchive.co.uk%2Fdocuments%2FRAIB_Esher2005.pdf

 

Signaller realised that if he put the signals back against a particular train as required by the rules, it would be more at risk of being struck by another one that had passed signal at danger due to poor adhesion.  

 

Another one here: Rail https://www.railwaysarchive.co.uk/docsummary.php?docID=4795

 

Driver did the right thing in reversing the train off an embankment that was being undermined by flooding, without consulting Control first.  

 

Two hazards here: a multiplicity of signal aspects close together can be difficult to discern from a distance, and if the individual signals have red aspects then the driver has pass a red signal, which is considered to degrade its importance in other situations (though it's allowed for subsidiary aspects and could be got round by only having one aspect, lit only when no proceed aspect was displayed).  Problems of signal sighting may also be worse if multiple signal heads need to be easily viewable somewhere where space for them is limited.  

Another problem that arose with multiple head splitting signals was found on the LNER where at long distance the colours apparently combined to become white light.  The first thing theu used to get round the problem was using approach lit signals.  The next idea was to use cathode ray tubes to create 'junction indactors at various angles to thesignal head plus a vertical tube to indicate ''straight' (actually princlpal) route. This has some success but the idea was fairly quickly changed to using a row of small white lights  instead of tthe cathode ray tubes - which is where we are today.

 

I don't know what has changed about colour temperatures and shades of colour etc but the current splitting distants appear to have no problems with the colours combining to form something different at a distance.

 

But when I acted as an ISA on the secnid test of revised colours in the Ansaldo signal heads intended for the Manchester South scheme one disturbing thing that I noticed was that if the yellow light (which in any case still wasn't quite the correct colour) was seen through moving green leaves on lineside trees the signal appeared to be showing a green aspect - albeit not of the correct colour.

 

[Michael Hodgson]

9 minutes ago, The Stationmaster said:

 

I don't know what has changed about colour temperatures and shades of colour etc but the current splitting distants appear to have no problems with the colours combining to form something different at a distance.

 

I think it's because of the use of LEDs of particular wavelengths rather than translucent coloured glass lenses stuck in front of a white incandescent lamp.

[John M]

20 hours ago, eldomtom2 said:

The normal American way of route signalling uses this method, but as "searchlight" signals and other methods of reducing the size of a signal head were commonly used the space taken up could be reduced, though columns of "traffic light" signals are becoming a standard. Looking at the rulebook for Metra's Rock Island line, a surviving example of a solely route signalled railroad, the way in which the old system of multiple semaphore signals was preserved with colour lights is clear:

 

Although described as 'Metra Block and Interlocking Signals" the diagrams are a good example of American Speed Signalling practice and not dis-similar to the speed signalling used in New Zealand. 

 

Like the American Railroads, NZR adapted speed rather than block signalling for powered (CTC) double and single tracked lines to simplify the handling of (our relatively) heavy freight trains with 3 aspect colour light (automatic) signals spaced at regular intervals between signal interlockings.  

[The Stationmaster]

6 minutes ago, John M said:

 

Although described as 'Metra Block and Interlocking Signals" the diagrams are a good example of American Speed Signalling practice and not dis-similar to the speed signalling used in New Zealand. 

 

Like the American Railroads, NZR adapted speed rather than block signalling for powered (CTC) double and single tracked lines to simplify the handling of (our relatively) heavy freight trains with 3 aspect colour light (automatic) signals spaced at regular intervals between signal interlockings.  

Speed signalling still incorporates blocks.  As does any lineside signalling system - in order to achieve train separation.  Even the most sophisticated cab signalling systems still use block although some such systems use moving blocks instead of fixed blocks.  but in contrast to route signalling - which tells the Driver where their train will be going - speed signalling in its purest form tells teh Driver how fast the train is permitted to go.

 

Some signalling systems, especially in mainland Europe, tend to blur between these two extremes.  And even British route signalling incorporates some measures designed specifically to force Drivers to reduce speed - at some diverging junctions.  For example approach release from red will force a Driver to reduce speed.

[eldomtom2]

42 minutes ago, John M said:

Although described as 'Metra Block and Interlocking Signals" the diagrams are a good example of American Speed Signalling practice and not dis-similar to the speed signalling used in New Zealand.

Totally inaccurate I'm afraid - Metra's Rock Island is route signalling through and through. It conveys no information about how fast the train should take the junction - that is left up to the engineer's route knowledge. Compare with this example of speed signalling on Conrail, where there are multiple different aspects for diverging routes indicating how fast the junction should be taken:

[John M]

19 hours ago, eldomtom2 said:

Totally inaccurate I'm afraid - Metra's Rock Island is route signalling through and through. It conveys no information about how fast the train should take the junction - that is left up to the engineer's route knowledge. Compare with this example of speed signalling on Conrail, where there are multiple different aspects for diverging routes indicating how fast the junction should be taken:

 

 

I described the 'Metra Block and Interlocking Signals" the diagrams are a good example of American Speed Signalling practice because of the similarity of the signal diagrams and terminology to Speed Signalling systems used in North America and here in New Zealand. "Conrail Block and Interlocking Signals" diagrams appear more complex than METRA and local practice as it incorporates the Position Light Signals used on the ex-PR routes and intensive intercity and commuter traffic by American standards in the North East.

 

The Speed Signalling System used in New Zealand is simpler in nature than the Metra or Conrail systems, double headed signals are primarily used as controlled signals in interlockings, single head three aspect signals usually automatically operated at intermediate points between interlocking. In my experience advance caution signals are extremely rare in New Zealand.

 

The diagrams and descriptions are based on information on the nzrailphotos web page, there are some duplications in the descriptions and I have omitted the description and function of one of the signal aspects.

 

Locally a train taking a diverging route at a junction or loop would first have to pass signals displaying Caution Normal Speed and Caution/Clear Medium Speed before entering the loop/taking the diverging route. (Splitting Signals/Route Indicators are rate in New Zealand)

 

 

 I think the distinction between traditional Block and Speed Signalling has become blurred on this thread, Speed Signalling systems often include principals of block control to prevent two trains occupying the same section of running line or conflicting moves.

 

I think the distinction between British and International practice relates more to the British adaption of Route Signalling which is heavily dependent on an individual drivers route knowledge as they approach a junction and speed signalling which is less dependent on route knowledge.

 

Interestingly CIE considered the option of speed signalling and decided on route signalling when it began to convert its Dublin-Cork main line to power signalling during the 1970s. Many of the new "CTC" interlockings were placed at existing Block Posts with automatic signals at intermediate points to improve line capacity.  

[St. Simon]

Hi,

 

There is already a thread for discussing Speed Signalling here: 

 

https://www.rmweb.co.uk/topic/179337-route-signalling-vs-speed-signalling-an-oversimplification/

 

Shall we keep this thread to the incidents in hand?

 

Simon

[eldomtom2]

54 minutes ago, John M said:

I think the distinction between traditional Block and Speed Signalling has become blurred on this thread, Speed Signalling systems often include principals of block control to prevent two trains occupying the same section of running line or conflicting moves.

Speed signalling is block signalling. You are confusing speed signalling with time interval working.

[martin_wynne]

RAIB have just posted a video about the Spital Junction  incident:

 

 

Report released today:

 

 https://www.gov.uk/government/news/report-062023-train-overspeeding-at-spital-junction

 

Martin.