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Basic Signalling Information
#1
Hi,
I have combined some good literature which I downloaded from
www.railway-technical.com and thought it would be very useful for any one to understand the signalling.


Mangesh


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.doc   Signalling Practices.doc (Size: 560.5 KB / Downloads: 419)
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#2
Mangesh,

That was really helpful .. Thanks very much.

Regards





(06-03-2009, 05:16 AM)mangeshwakankar Wrote: Hi,
I have combined some good literature which I downloaded from
www.railway-technical.com and thought it would be very useful for any one to understand the signalling.


Mangesh
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#3
(06-03-2009, 04:10 PM)jimmyinin Wrote: Mangesh,
That was really helpful .. Thanks very much.
Regards
(06-03-2009, 05:16 AM)mangeshwakankar Wrote: Hi,
I have combined some good literature which I downloaded from
www.railway-technical.com and thought it would be very useful for any one to understand the signalling.
Mangesh

Yes I have had a quick read through and it seems pretty sound, but just a few comments to bear in mind when reading. I believe that it has been written mainly from a North American context and thus read from a UK perspective some things don't ring true. I am pointing this out in case it would be a source of confusion; don't get me wrong the article is extremely worth reading especially I think for Metro / TBS where there is otherwise a dearth of material.

Page 4: Interlocking. Control Tables were originally for the electrical controls which were included within electrical locks on the levers (primarily track circuits locking FPLs for points, Electrical Sequential locking) or indeed any electical controls within an electrically driven (motorised semaphore or colour light). Only later did technology move on to route relay interlockings and in this case obviously there is no mechanical lockingso all interlocking recorded on Control Tables. Technology is moving on again and where we depict those logical functions perfomed by the RBC within ETCS is still an "unresolved issue" but we'll probably end up making a special Control Table.

Page 6 Track Circuits- Block occupied. Description is wrong for UK context at least- the description is of a CONTROLLED signal, not a SEMI-AUTO. [The latter are basically auto signals but which are replaced to danger when points beyond them are released from the main signal box to be operated from a local Ground Frame]

page 6 Multi aspect signals. Don't be confused by the wording, on NR there is always a distant signal (or at least reflectorised board) regardless of speed. Technically there is a dispensation for very basic railways operated under the authority of a "Light Railway Order" - one of the limitiations is 25mph (40kph) maximum speed; I think it is only the heritage sector that has lines in this category now- and most of them have signalling including fixed distants anyway!

page 7 Four Aspect Signalling. This gives impression that this has now displaced 3 aspect signalling; NOT TRUE! 4 aspects are provided only where there is a need (high capacity) or desireable for other reasons (>100mph, positioning of consequtive signals to protect junctions etc.). Plenty of 3 aspect signalling, even on main lines. Also nowadays there is no presumption that trains may ignore the YY aspect if travel slowly enough!

Page 7. Nowadays the 200yard overlap is 180m; however particularly for higher speed lines 225m is the current default. In particular the advent of TPWS means that extent of provision of TPWS and the length of the overlap are considered together to achieve optimum arrangement.

Page 10. TPWS. Note that not all signals are fitted; primarily only those protecting junction conflicts. Many signals just have one pair of loops (TSS) just beyond the signal, others also have another pair of separated loops (OSS) whereas a few have a further OSS and /or a nearer OSS as well- the description is OK for a "typical" case but reads as if "every". A significant number of OSS associated with speed restrictions have indeed now been removed as counter productive.

Page 22. Moving Block. I am no expert on this but description seems to suggest that this predicated on "motorway driving" and the improbability of the first vehicle stopping dead. It is my understanding that in rail applications there is always full braking distance (at current speed) from a train and the one ahead- the value of moving block is it is to the rear of the train, not the extra length to the next train detection limit in rear of that train and thus "quantised". In fairness this does get implied later on.
Note that Transmission Based Signalling can just mean putting the "signal into the cab"; it does not necessarily imply using train to determine its own position instead of train detection.

Page 35. Description states it is referring to UK practice; presumably this is a metro example because it isn't quite what we'd expect on NR, although in truth not very different.

Page 37. Reference to signals C23/25 being approach locked is INCORRECT in the NR context; what is meant is APPROACH RELEASED- i.e. that the route may be set but the aspect would not clear until berth track occupied for time (train at or very nearly at a stand).

Page 45. A distant signal in mechanical signalling is ONLY permitted to clear if ALL the stop signals operated from that signalbox are already off! A distant arm at caution therefore warns the driver of the need to stop at ONE of them- where the distant can't be cleared the signaller should only pull off each signal as the train approaches it, so is "dropped down one-by-one" until the one that cannot be cleared.
PJW
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#4
Brilliant piece PJW, particularly the TPWS +/- explanation.
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#5
Hello Mangesh

Would you like some assistance in adding information to the site. There are many forms of AWS (the photo on your site shown the ramp has been hit by something!)?

Also, the TPWS arrangement shown could be bolstered by an OSS arrangement. There is plenty of blurb on this website on TPWS and AWS.

Jerry


(06-03-2009, 05:16 AM)mangeshwakankar Wrote: Hi,
I have combined some good literature which I downloaded from
www.railway-technical.com and thought it would be very useful for any one to understand the signalling.


Mangesh

Le coureur
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