"Permissive" shunt signals

I recall (from my single visit some 3 years ago) there was one from the unused platform line at Chessington onto the line beyond which I understand from a bit of googling was once some sort of yard.

EDIT: Ah I've just seen the pic on Wiki from 2008 which looks like a normal red GPL. I must be mixing it up with elsewhere.

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I'm struggling to find an example of a yellow shunt as they're not that common]

There's one in Thingley Yard, visible as you pass in the Up direction. At least it was there last time I went past a few weeks ago.

SN201 is still a yellow shunt, and is set to remain so until Thingley is resignalled in the new year.

Sorry, I meant "in a sim". SN120 was the example I linked to earlier, but the sim shows it as a red shunt.

" said:

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I'm struggling to find an example of a yellow shunt as they're not that common]

There's one in Thingley Yard, visible as you pass in the Up direction. At least it was there last time I went past a few weeks ago.

SN201 is still a yellow shunt, and is set to remain so until Thingley is resignalled in the new year.

Sorry, I meant "in a sim". SN120 was the example I linked to earlier, but the sim shows it as a red shunt.

An error seemingly introduced in the conversion to the loader, it was correctly shown as yellow in scrolly. I would've said it was yellow in Simsig until looking just now! Also applies to SN232 and SN271.

Sorry, I meant "in a sim".

Easiest of all on a frame: simply omit a bar and a couple of dogs. But there aren't that many of them going in at the moment so it's a bit academic. And with the loss of wagonload traffic and the move to fixed-formation trains, there's less shunting generally than there used to be, hence less need for any signalling in & out of headshunts (and, as Clive says, just a line of code - perhaps pretty standard so it goes in as a template to fill in the numbers? - in any case).

The really big change is attitudinal - a move away from local arrangements operated using the knowledge and skill of the staff to complete signalling of everything (including numbering stop blocks in the signalling system and proving the red lights) so there's a complete signal sequence to put down on paper for every move going. Along with that is the change to methods of communication, with phonetic alphabets and suchlike. I'm sure there are benefits - maybe one day we will even authorise unsignalled wrong-road moves through sections by radio (on the rare occasions there's anything to gain by doing so). But I still find it quite peculiar at meets to hear people referring to 'two alpha so-and-so' rather than 'the up parly'.

" said:

Easiest of all on a frame: simply omit a bar and a couple of dogs. But there aren't that many of them going in at the moment so it's a bit academic. And with the loss of wagonload traffic and the move to fixed-formation trains, there's less shunting generally than there used to be, hence less need for any signalling in & out of headshunts (and, as Clive says, just a line of code - perhaps pretty standard so it goes in as a template to fill in the numbers? - in any case).

The really big change is attitudinal - a move away from local arrangements operated using the knowledge and skill of the staff to complete signalling of everything (including numbering stop blocks in the signalling system and proving the red lights) so there's a complete signal sequence to put down on paper for every move going. Along with that is the change to methods of communication, with phonetic alphabets and suchlike. I'm sure there are benefits - maybe one day we will even authorise unsignalled wrong-road moves through sections by radio (on the rare occasions there's anything to gain by doing so). But I still find it quite peculiar at meets to hear people referring to 'two alpha so-and-so' rather than 'the up parly'.

My comment was directed at the reason something like OLO was never set up in the first place and yellow shunt signal system was implemented.

In North America the alternative to a drill signal is to have a non-interlocked hand throw switch to the siding or to place the signal on the connection between the siding and the main track, leaving the siding points outside of interlocking limits.

clive said:

This system requires extra interlocking circuitry. The yellow shunt was something that could be installed very simply and cheaply, even in mechanical interlockings. As attitudes have changed, and as interlocking circuits change from "lots of extra relays" to "one line of code", the balance has swung from yellow shunt to OLO.

It seems fairly simple to set up on a mechanical frame.

At Yeovil Junction, there is/were two shunt discs on adjacent sidings, one red, one yellow.

Barnetby Down sidings has a yellow mechanical shunt signal to exit the reception sidings in the up direction. I believe it BE35 (don't have the sim or sim data to hand so I am guessing...if its not BE35 its BE "thirty something").

Did look for a piccy but all I found was piccys of pretty much every Barnetby signal EXCEPT that one, of course!! (sure now I've said that someone will now find it.

What you're forgetting is that on a mechanical frame a yellow shunt is implemented in exactly the same way as a normal shunt signal. To have a second shunt signal and OLO, you need to have an extra lever, signal and wire run. Hence the cost savings in using a single yellow shunt signal.

Clive, I hope that this is not an impermanent question. Where were you when you posted your message today?

Barry
Sydney Australia

" said:

This system requires extra interlocking circuitry. The yellow shunt was something that could be installed very simply and cheaply, even in mechanical interlockings. As attitudes have changed, and as interlocking circuits change from "lots of extra relays" to "one line of code", the balance has swung from yellow shunt to OLO.

It seems fairly simple to set up on a mechanical frame.

I find it quite amusing that a lot of extra wiring or data that needs to be provided in electrical or computerised interlockings was actually provided for free in a mechanical installation. For example, if lever 1 locks lever 2, then lever 2 must lock lever 1 unless something clever is done - as a solid bit of metal will conversely lock in either direction (although there are some very clever ways around this - but swinging tappets and Stowells locks are the topic of a whole new post) - whereas signal 1 will not always automatically conversely lock signal 2 in relay or SSI unless specifically designed to do so. So, as a mechanical designer, it was often the case that by the time you have designed half of the locking, the other half had already been done for you.

" said:

I'm struggling to find an example of a yellow shunt as they're not that common]

There's one in Thingley Yard, visible as you pass in the Up direction. At least it was there last time I went past a few weeks ago.