No alteration required - the SSI doesn't care where the input comes from, so long as it gets one!
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What is the purpose of a fixed distant?
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Greybeard33
Established Member
As explained to me on another forum, the interfaces required by the NR SSI include two Metrolink track circuits (to prove a tram has cleared the section) as well as the signal lamp proving. The Metrolink TMS is not allowed to simulate the inputs, because it is not to the integrity level required for a block signalling system.
edwin_m
Veteran Member
It would be more logical to change the last worked signal to a red/yellow and make the fixed signal a fixed red with a Metrolink signal underneath, as certainly used to exist on the signalling transitions at G-Mex and Victoria and probably still does somewhere near Brooklands.
The track circuit interfaces are clearly vital, and are proving what it says on the tin. The lamp proving of a signal not otherwise required by signalling principles, is itself effectively a simulation!
I fondly recall the concept of engineering judgement
Annetts key
Established Member
From a technically possible point of view, it is absolutely possible to provide ‘dummy’ inputs to the relevant Network Rail interface/boundary equipment cubicle. An SSI trackside functional module does not know or care if the inputs it receives are from real signalling equipment or are ‘dummy’ inputs.
For example, SSI signal interlocking does not need lamp proving when the signal has a route to a buffer stop...
I suspect the issue here is more of a contractual requirement between the two companies. If the contractual requirements specify directly or indirectly what the interface arrangements will be, then until and unless a new agreement is made, they will have to abide by the existing agreement.
The requirements of the ORR may also have to be considered
For example, SSI signal interlocking does not need lamp proving when the signal has a route to a buffer stop...
I suspect the issue here is more of a contractual requirement between the two companies. If the contractual requirements specify directly or indirectly what the interface arrangements will be, then until and unless a new agreement is made, they will have to abide by the existing agreement.
The requirements of the ORR may also have to be considered
That sounds much more plausible!
Greybeard33
Established Member
The northbound signalling transition is currently at Timperley station and is just marked by a metal plate, "Line of sight". No active signals of either type. The change will move the transition back by one block section - it will then be between stations.
I think @Annetts key has put their finger on the rationale.
Nottingham59
Established Member
The line north from Timperley is the old BR track, and as far as I can see the trams go just as fast on it as the Altrincham trains did before the line was converted to Metrolink.
Which rather begs the question (maybe for another thread) what other parts of the NR network could be run safely on a "Line of sight" basis, and not bother with signalling at all? Obviously you would have to use rolling stock with track brakes, and not mix them with freight trains - but the cost of these would be tiny compared to the costs and inflexibility of modern NR signalling.
There IS signalling on Metrolink, it's just limited to protecting junctions and single lines and interlocking with point operating mechanisms is provided just as it would be on heavy rail. What signalling exists is of the standard short-range 'symbolic' tramway type rather than long-range main line colour lights. Line-of-sight operation requires normally unidirectional operation with consistent rolling stock running at suitable speed limits, with excellent sighting and braking capability. Many rural heavy rail lines are single track at least in part and savings in numbers of physical signals would be fairly small in a light rail conversion. Where higher speeds and traffic levels are present, multiple tracks are involved and train size and traffic mix preclude tram style line of sight. Eventually, of course, cab signalling may result in the majority of conventional lineside signals being removed, but technical supervision of safe train spacing will continue to apply by other means.
If the scenario your referring to is at Kirkby it isn’t as clear cut as that.
Rainford to Kirkby is one train working with staff. Therefore only a train with the staff (it’s actually a token, just to confuse even more) can enter the single line and approach Kirkby. That’s why a fixed distant is used. It’s telling the driver to prepare to stop, in this case at the buffers. The platform isn’t permissive as there is only one staff so another train couldn’t leave rainford and head to Kirkby. There are exceptions to the rule e.g if the train failed at Kirkby another train could be sent forward to assist it. If the staff gets lost (it did happen about 20 years ago) a PILOTMAN can be used instead.
If the scenario you were referring to isn’t Kirkby then ignore all that l.
If a fixed distant is used, the protection for the train approaching the buffers is a stop signal in rear of the fixed distant - there will always be one!
The best way to understand the situation is to think of the buffers as a fixed stop signal - since it is fixed, its distant is fixed too. Just like distants in general there is braking distance between the distant and the stop - everything is consistent!
So using your nomenclature we have:
3) [stop] [fixed distant] (train) [buffers]
There needn't always be a fixed distant. If there is a suitable stop signal at braking distance from the buffers (typically because it also leads to other routes) it can act as the distant by clearing to a maximum single yellow. So:
4) [stop*] (train) [buffers]
* - max Y
[EDIT] I see that @Annetts key has replied similarly earlier
Nothing to do with Kirkby.
TrainTrackJack
Member
Several fixed distants around the Worcester area - including two on the gantry at Shrub Hill, one on the Junction Bracket at Henwick and single ones at Wyldes Lane and on the post just outside Foregate going towards Shrub. As well as one with the home controlling the entry on to the Bi-Di north of Foregate for ex-Birmingham trains.
This website provides many a picture.
The purpose is that there is no need for working distant signals as train speeds are very low and thus it would be an unnecessary practice.
However a new working distant was installed at Henwick in 2017 along with a Home.
This website provides many a picture.
The purpose is that there is no need for working distant signals as train speeds are very low and thus it would be an unnecessary practice.
However a new working distant was installed at Henwick in 2017 along with a Home.
Snow1964
Established Member
This is where the usage becomes a bit fuzzy, the fixed distant can precede the fixed red (the light in front of the buffer stop), where the line beyond the distant has no other signals.
But it has been used where there is also a home signal between, an example might be if there was second platform or a siding. Of course that home signal could show a proceed to red at buffers, but as the speed is so low, the distant is fixed to save maintenance, but could have been active to show the status of the home signal.
In that case isn’t it just there because they always want you to slow down?
The OPS question was "What us the purpose of a fixed distant"
It's got to 76 posts now and ultimately for all the talk of how they are used and merits of locations the answer in truth as posted at the start of get debate is that fixed distant are cheaper to maintain and install. You need a distant as per signalling regulations, 2 options costly conventional with linkages, cables, wires, interlocking or, a static arm that needs a bulb changing once every few years and. WITH or a retroreflectice sign that needs a wash once every decade.
Yes you could fit in a few cases a conventionable loveable distant signal but for a minute here or there delay the installation and maintenence costs far outlay the benefit.
It's got to 76 posts now and ultimately for all the talk of how they are used and merits of locations the answer in truth as posted at the start of get debate is that fixed distant are cheaper to maintain and install. You need a distant as per signalling regulations, 2 options costly conventional with linkages, cables, wires, interlocking or, a static arm that needs a bulb changing once every few years and. WITH or a retroreflectice sign that needs a wash once every decade.
Yes you could fit in a few cases a conventionable loveable distant signal but for a minute here or there delay the installation and maintenence costs far outlay the benefit.
Annetts key
Established Member
The retro reflective type, are, I think, cleaned, inspected and the sighting checked at least annually.
Gloster
Established Member
I do like the idea of a loveable distant signal, especially as they are usually out on their own a long way from other signals. But what about the poor old stop signals?
thirdraildrive
Member
You'll find fixed distants between Sevenoaks and Ashford International as well, where there are SIMBIDS sections (Simplified Bi-directional Signalling).
You'll be signalled onto the adjacent line with a normal main aspect signal displaying a preliminary caution. Approaching the end of that SIMBIDs section there will be a fixed distant and then the exit signal. At this signal you will either be routed back onto the correct line or given a signal aspect that puts you into the next SIMBIDs section and the process repeats.
Sections are:
Sevenoaks - Tonbridge
Tonbridge - Paddock Wood
Paddock Wood - Headcorn
Headcorn - Ashford International.
Just a different example of when you will encounter a fixed distant. Not 100% sure why these sections exsist but I believe it may be due to the Eurostars using this line years a go and there needing to be a way to keep them on the move during disruption.
Kieran.
You'll be signalled onto the adjacent line with a normal main aspect signal displaying a preliminary caution. Approaching the end of that SIMBIDs section there will be a fixed distant and then the exit signal. At this signal you will either be routed back onto the correct line or given a signal aspect that puts you into the next SIMBIDs section and the process repeats.
Sections are:
Sevenoaks - Tonbridge
Tonbridge - Paddock Wood
Paddock Wood - Headcorn
Headcorn - Ashford International.
Just a different example of when you will encounter a fixed distant. Not 100% sure why these sections exsist but I believe it may be due to the Eurostars using this line years a go and there needing to be a way to keep them on the move during disruption.
Kieran.
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edwin_m
Veteran Member
SIMBIDS was installed on quite a few double track primary routes that were upgraded in the late 80s or early 90s. The East Coast Main Line north of Northallerton is another one. Not sure if they all had fixed distants, which probably meant approach control from red at the crossovers, or whether others had a less restrictive arrangement with worked distants.
thirdraildrive
Member
Very interesting to hear it was installed elseware too!
All on the SE line have fixed distants, otherwise we would have to be signalled over onto the SIMBIDS section with a single yellow aspect and then with the 70mph limit would be a high risk of overspeed approaching the exit signal and/or a SPAD on the exit signal.
This area was resignalled to Ashford IECC in the early 90s. Having SIMBIDs enables single line working during engineering work, disruption etc.
Apart from the northern ECML, SIMBIDs is also found in places including Didcot-Bath Spa and parts of the Brighton Main Line. Generally it's an 80s/90s thing, and more modern installations have tended to have 'full' signalling where bidirectional running is incorporated.
thirdraildrive
Member
Thanks for the info.
Always just assumed it may be to do with the Eurostar but now I know otherwise!
They only teach us how it works, not how it came to be, very annoying
Kieran.
bramling
Veteran Member
LU has a timing section on the last (or in a few cases last-but-one) stop signal, which has a similar effect. Unlike national rail, LU stop signals do not have to be preceded by a yellow aspect, therefore it fits in with LU signalling principles to not need any repeating aspect for the red stop lamps at the buffer stops.
Needless to say there have been exceptions. Shoreditch I don’t think had any arrangement on the last stop signal, perhaps because it had a decent length overrun so the train stops were deemed sufficient. Then there was the fixed yellow lamp on the approach to Ongar, and the rather strange signal which still exists approaching Chesham.
Annetts key
Established Member
SIMBIDs was provided and intended to be used so that one line could be closed for engineering works (T3), while keeping one line open for a reduced train service without needing pilot working or ticket working.
It would also be available to use in case of a train failure, track (P.Way) fault or signalling failure.
Before SIMBIDs, some double lines already had full bi-directional signalling.
In 1987 to 1989, BR Western Region installed and commissioned SIMBIDs between North Somerset Junction (Bristol T.M.) and Thingly Junction (near Chippingham). 40 MPH crossovers were provided just west of Bath Spa and extra crossovers were provided at Bathampton Junction. The exit signals for each reversible section all had colour light distant signals at service braking distance. Plus the longer sections were provided with intermediate section signals and each has it’s own colour light distant signal (so that more trains could run). Three aspect heads were used for most of the exit signals, with two aspect heads being used for most of the others. No AWS was provided, and there was a no suppression of the AWS of the normal direction signals.
There were plans and indeed, some points and signals were provided, but not all were commissioned for SIMBIDs between Pilning (where the signalling controlled by Newport already had some bidirectional signalling) and Stoke Gifford, between Stoke Gifford and the existing full bidirectional signalling at Chipping Sodbury.
There were plans (but no actual work) for Bristol T.M. to Taunton.
When TVSC took control from Bristol Panel, the SIMBIDs section between North Somerset Junction and Thingly Junction was upgraded to have normal AWS arrangements.
And since then, full bidirectional signalling has been provided on some lines between Pilning and Stoke Gifford. Plus between Filton Abbey Wood and Stoke Gifford.
At no point were fixed distant boards provided.
I remember when I first started at LT and having some familiarity with the mainline system found their's a little confusing at first.
For a start there is no requirement for a red to be preceded by a yellow as long as there is sufficient braking distance from where the driver first sees the red. As a result 'fog repeater' signals are provided for when visibility is reduced. Secondly, what looks like a 4-aspect signal is usually two signals (nominally home and distant) placed on the same post. Depending on the aspect of the next home signal, the driver may see either one red, green and yellow, or green and green though he/she won't see two yellows. Nor will he/she see one yellow or one green at such a signal.
(NB: I left LT almost 20 years ago so this may have changed since then)
Steptoe
Member
There are some interesting replies on this thread but I don't believe anyone has mentioned that a common requirement for fixed distants is on the approach to train crew operated level crossings where the stop board is obviously always at red. There are several still in in existence on the Mid-Norfolk Railway remaining from the days when it was operated by BR as a long freight siding and as, very occasionally nowadays, a gate may not be manned, they still fulfill their role.
Annetts key
Established Member
On the Western, normally a black St. George's cross on a white background sign is provided on approach to a train crew manually operated crossing (TMO) or on the approach to an AOCL (Automatic Open Crossing Locally monitored). Here there will also be a sign with a St. Andrew's cross above the crossing speed restriction figure.
But distant boards are used on the approach of stop boards not associated with level crossings.
But distant boards are used on the approach of stop boards not associated with level crossings.
Dstock7080
Established Member
now changed in that fog repeaters are permanently switched on for SPAD mitigation and no requirement to install them, hence several area where green stop signals are followed by red with no repeater.
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