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> The purpose of railway signalling, ... and tracks...
Bear 1923
post 17 Feb 2013, 11:07
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In the hope of gaining clarity I'm starting yet another topic.

It derives from here - http://www.modelrailforum.com/forums/index...mp;#entry295793 - but I think that we had tended to wander off a bit...

QUOTE (Richard Johnson @ 17 Feb 2013, 08:31) *
*** Correct. I am not asking at the moment, simply attempting to provide reference.

Bear - feel free to request deletion of this post if it distracts, but I think (hope) it is maybe in line with / reinforces your desires for your approach

One subject done properly or in detail is far clearer as a reference.

I would be happy for Bear to overview and explain the "why" of anything special or interesting at Settle as it was a good model subject as a smallish area centre / market town with good train variety and wide freight type handled but having thought about it, I really DO understand why Bear wants no distractions on each specific subject as if it happens, what is a case of "here is the specific circumstance and here is a specific answer and why" - something that gives a useful reference... becomes muddled when mixed with other examples, and nobody really learns anything useful.

So - by all means analyse Settle if its wanted but later - and as a separate subject..

On the subject of the Coldstream OS diagram.

Looking at your image there is FAR more to that station area yard approach than used in the diagram initially provided, apart from that XO near Alnwick.... at the RHS there is relevant added approach trackage and at least 2 loops and an XZO within the yard trackage which change the nature of non-passenger use and train handling and modify the need for wrong-line use.

I think it would have been far more sensible to first analyse the station COMPLETE, then look at how to condense it while not losing the operating potential and THEN signal it correctly. That approach would be far more sensible, more practical / useful and a more efficient use of knowledge and of time.

After all, apart from signalling, the big problem for modellers is that they need to understand how a train would interact using the trackage so they can make sensible decisions when they condense a prototype, otherwise they lose the wrong bits by focussing on sidings and the like first. The result is a boring layout to run on and loss of interest. (The main thing to do to make a layout satisfying is to keep operating potential, then make it a beleivable and interesting model of a railway - not to accumulate storage).

So - from my perspective, efficient and prototypically safe operation and signalling are the same subject from different perspectives. One can't exist without the other, so there is no point in Bear spending hours explaining WHY a signal is there to do what it does if the purpose and use of the tracks being signalled isn't equally understood at the same time.


QUOTE (Bear 1923 @ 17 Feb 2013, 09:53) *
ermm.gif Hmmm ermm.gif

There's no way I want to delete your comment Richard. smile.gif It gives me a very useful lead.

I have no problem suggesting and explaining the signals for a layout - at least - not one that has a track plan that would have been used by the real railway.

A couple of people who have PM'd me have discovered that if a layout isn't "realistic" in track plan then things get weird as far as signalling goes... and I can be really boring trying to get them to "correct" the layout. (That said - it's their layout to design as they want).

So - "Vanilla" wasn't such a bad layout to work on. It raised a few points/issues but it wasn't impossible.

Perhaps one thing it does do is make the point about OS maps and looking out for crossovers! tongue.gif

What track is there for...

In this context I think that we can come up with one definition...

Tracks are there to provide:-

    Routes for trains to run place to place on. (Running Lines).
    Seperate lines for opposite directions to tend to avoid head-on-collisions. (Except when cost against benefit prevents when there is only Single Line).
    Additional lines (over distance) to do two things. (Running Lines).
      provide enough lines for the traffic
      facilitate the operation of trains running at significantly different speeds

    Additional lines (for short distances) to get trains out of the way mainly for two reasons
      To stop at platforms for passengers - and sometimes mails/parcels/milk etc (platform loops and bays)
      To get in out of the way to either let following traffic pass or to wait for a specific location ahead to be ready to receive them (Refuges/Lay bys - almost always Freight or NPCS traffic).

    Additional lines for loading and unloading of freight. (Sidings and Yards). (It doesn't matter whether the traffic is one cow or thousands of tons of stone - they all amount to the same thing).
      This might have specific reception and Departure roads added for very large facilities

    Additional lines for servicing locos and stock. (MPD, Carriage sidings and service depots).
    Additional lines to facilitate shunting sidings and yards and MPD, Carriage sidings and service depots clear of the Running Lines. (Headshunts)
    Very occasionally (Usually at large stations) Pilot engine spurs.
    Additional parralel sidings usually quite long for storage of two kinds
      Mileage Sidings - to store stock not in use/waiting for use
      Full Load sidings (can't recall the correct name) - for things like coal that will be tipped into ships in a hurry so that the ship is in port as short a time as possible.

    Additional lines for all varieties of Engineering activity. ("Ballast Sidings" - but also Engineer's Crossovers at strategic locations).
    Run-round loops.
    "Cut offs" and Diversion Routes.

Have I missed anything obvious?

Apart from crossovers and run-round loops all of these tracks can be seen as solitary tracks in their own right... Except that they are awkward and want to join together and/or cross over each other. This most unreasonable desire is one of the reasons for signals and signalling. We can say that this is the "sideways" need.

The other main reason for signals and signalling is is the "lengthways" need. Trains/movements need to be kept from catching up with each other except when, where and how they are supposed to.

Which gives us a third reason - which is regulation of the traffic - so that it isn't a free-for-all and/or everything doesn't just queue up behind the slowest train.

More shortly...


QUOTE (Bear 1923 @ 17 Feb 2013, 10:16) *
There are two main requirements of railway signalling.

1. It must be safe and accurate.

2. It must be clear and unambiguous.

Safe and accurate.

Railway signals must achieve their purpose to be safe.
They must be:-
    Distinctive - standing out against any background.
    Where they can be seen clearly.
    Very simple and clear in meaning.
    Located where they will do the job they are meant to do.

Railway signals must achieve their purpose to be accurate
They must:-
    Only signal correct information - or "fail safe".
    Only be capable of signalling correct track conditions - so they are interlocked with the track (points etc).

Clear and unambiguous.

Railway signals must be clear.
They must:-
    Stand out in their surroundings (as unique from anything else).
    Give completely different indications for each message that they are to signal.
    Be uniform in design and application.

Railway signals must be unambiguous.
They must:-
    Be very easily read and understood.
    Give simple, clear messages.
    Be clear to the line to which they apply.
    Be clear to the postion to which they apply.
    Not conflict with any other signal.

I have managed to only have one "not" in the collection.

I suppose that the big question is going to be "How do they do all these things?"

Which I will try to get back to...


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