Letter Combinations on Signals approaching Heuston

[Rob]

I was wondering what the Letters displayed on the signals approaching Heuston refer to?

I saw the letters  UM  displayed with the green signal on my walk there this morning.

I have seen in the past the Platform Number displayed but never the letters.

Sorry for poor quality of photo as it was far away and only getting bright.

[Robert Shrives]

Hi "UM" is up main route, routes to 299 signal - which then has a theatre display for 5 routes ( plats 4 - 8  256 signal you picture has 5 routes  available  so a few more to see yet !  I guess the only platform no it can  show is 10 as it "reads towards" other signals for the platforms but the diagram in the  IIRS journal I have shows it routes to down main. Up branch and middle road  last two are towards the tunnel.

The green suggests 299 signal protecting platform is showing a single yellow and a platform.  This will be a yellow as it is reading towards the buffer stop fixed red- effectively an unnumbered signal.

Robert   

[Rob]

That is really informative- never knew any of that.         Sounds very complicated though!

[DoctorPan]

On one of my first days as a PW designer, one of my senior colleagues was running through a design issue at a station on the project with me and the issues with the signalling requirements. He leaned into me and said "The Signalling guys are wizards at black magics". Stuff above proves his point!

[Robert Shrives]

So true, my S&T friends like to tell me but the concept of : one train in one section at one time. is beautifully simple. It is just the doing of it and ensuring should anything fail accidents are avoided that exercises the gods of complexity and record keeping !  Modern signalling allowing for improved braking and increased traffic volumes also means  giving drivers route information as well as speed/ braking advice. The increase in speeds on a fixed sized network also means drivers at more risk of simple  human errors so now signalling includes warning devices for drivers to manage and at best stop the train with full service or emergency braking at many signals that protect potential conflicts.

It is quite an overlay of subsystems - The graphic of Swiss cheese is often used to describe the still imperfect state and that if all the cheese holes line up then incidents occur. It has overtime grown and now many holes are down to the most imperfect beast - the human.   

The Stanley Hall series of books on railway safety are a good place to start. You can ask signalling engineers but of course they speak in tongues! and want to keep the naughty boys out of the grail!! 

Robert