class411
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Post by class411 on Nov 20, 2012 8:14:41 GMT
I've always wondered the exact purpose of these signs (I assume they are an updated version of the mechanical white circle with a black bar that moves from vertical to horizontal).
They seem to have something to do with departures but the often come on/change position before the scheduled time and the "Off" sign is often illuminated at my local station before a train has even arrived on the platform.
(I'm not sure if I've even seen these on the underground but BR certainly use them.)
Can anyone explain?
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mrfs42
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Post by mrfs42 on Nov 20, 2012 8:44:45 GMT
They are, in effect, a low speed version of a banner repeater. They are used when there is a compulsory stop, IIRC. However, it is a long time since I've read the SSPs. |
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Post by Harsig on Nov 20, 2012 8:49:40 GMT
They are merely an indication of the state of the signal at the end of the platform. The 'Off' indication is illuminated whenever that signal shows a proceed aspect. The 'Off' indication is provided for the benefit of staff involved in train dispatch who might otherwise not have a good view of the signal in an effort to avoid such staff giving the driver authority to proceed while the signal is still red. The underground generally uses two aspect (green / yellow) platform repeaters for the same purpose. However I believe you will find 'Off' repeaters on the Met line from Rickmansworth to Amersham. The reason they are used here is because the signalling in this area is multiple aspect and a green/yellow platform repeater would be inappropriate. For the same reason Fog Repeater Signals in this area use yellow/lunar white instead of the yellow/green indications found elsewhere on the underground.
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Post by Deleted on Nov 20, 2012 9:06:14 GMT
Moor Park NB/SB main also has (or had) them, certainly when I photographed them in 2007. The indications are 'on' and 'off'.
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rincew1nd
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Post by rincew1nd on Nov 20, 2012 19:40:06 GMT
The 'Off' indication is provided for the benefit of staff involved in train dispatch who might otherwise not have a good view of the signal in an effort to avoid such staff giving the driver authority to proceed while the signal is still red. AIUI, they were introduced for two reasons: - To help traffic staff, in that they could see the aspect of the signal, thus they would not give a Right Away only for the Driver to smugly turn around and say "Signal's still on mate".
- To prevent the "ding ding and away" phenomenon. I can remember at least one serious accident where the Guard gave the Right Away and the Driver set off through a red signal into the path of another. As such, Guards are required to check the signal aspect before giving the Right Away.
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Post by metrailway on Nov 20, 2012 21:19:46 GMT
I've always wondered the exact purpose of these signs (I assume they are an updated version of the mechanical white circle with a black bar that moves from vertical to horizontal). They seem to have something to do with departures but the often come on/change position before the scheduled time and the "Off" sign is often illuminated at my local station before a train has even arrived on the platform. (I'm not sure if I've even seen these on the underground but BR certainly use them.) Can anyone explain? I think the best description is in the Railway Group Standards S1 Rule Book which is applicable on the national network: If an Off indicator is provided at a platform, it will:
• show the word OFF when the signal to which it applies shows a proceed aspect
• allow a guard or person in charge of the platform to check the signal is clear before commencing the train despatch procedure
• show no indication when the signal to which it applies is at danger.
On a bi-directional platform line, the OFF indication may be accompanied by an UP or DN or other indication to show which route has been set.
On a platform line, the driver may, at certain locations, rely only upon the Off indicator showing the word OFF as an indication that the signal which it applies to is showing a proceed aspect. In these circumstances, the driver must not assume the line ahead is clear for the train as the signal may have been cleared for a train ahead.
Indicators may be provided at locations other than platforms to show the driver that the signal to which they apply is displaying a proceed aspect.As mentioned by others there are off indicators on the Met. They look a bit different to the ones you find on the 'mainline'. Metropolitan Line On/Off indicators at Rickmansworth:  Rickmansworth Underground station by bowroaduk, on Flickr Notably the indicators on the country end of the Met display 'On' when the station starter is at danger. This practise no longer occurs on the national network. |
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Post by norbitonflyer on Nov 21, 2012 7:12:44 GMT
I can remember at least one serious accident where the Guard gave the Right Away and the Driver set off through a red signal into the path of another. Paisley Gilmour Street (1979), and Bellgrove (1989), both on the Glasgow electric network, were two fatal examples. |
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class411
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Post by class411 on Nov 21, 2012 7:34:45 GMT
Thanks all for the responses.
They automatically answer a supplementary question I had about why our local station has them on one platform only.
The answer being, of course, that in only one direction can the train obstruct the relevant signal so that staff would be unable to see it.
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metman
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Post by metman on Dec 3, 2012 11:55:05 GMT
I always used to see them at Moor Park and assumed they were some form of platform repeater but never knew. Thanks  |
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rincew1nd
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Post by rincew1nd on Dec 3, 2012 19:50:43 GMT
I think it is platform 9 at Crewe (northbound main through) where there are about four of these indicators mounted sideways (ie facing the train). Under each is a sign marking to which signal each indicator applies, one of which has been locally annotated "Sleeper".
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Post by metrailway on Dec 4, 2012 1:18:22 GMT
For completeness, I think I should mention that in addition to Off indicators there are also Right Away indicators in use on the national network. They look similar to Off indicators and they let the driver to know that it is safe to proceed. The description in the Railway Group Standards S1 Rule Book states: Right-away indicators
Right-away indicators display the letters R or RA.
If this indicator is illuminated, it lets the driver know that:
• station duties are complete
• the train is secure
• it is safe to proceed as indicated by the signal aspect.
Most RA indicators are placed by the station starter like this one: www.railsigns.co.uk/pics/pic_clbws/pic_clbws.htmlThey are operated by platform staff by a plunger on the platform. It is mandatory for station staff to give a RA indication to DOO (Driver Only Operation) trains, if the platform is equipped with one. It is also mandatory to give a RA indication if a train has no driver - guard communication (bell/buzzer), if the platform is equipped with one. I'm not sure but I think RA indicators are interlocked with the signalling so that the indicator cannot be illuminated if the station starter is at danger. |
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