Signals

THE SIGNAL BOX


Railway signalling discussion

Worcester Mechanical Boxes

Current and future British signalling (UK except Northern Ireland)

Re: Worcester Mechanical Boxes

Unread postby John Hinson » Tue Jul 28, 2015 4:28 pm

That is the typical arrangement with slotted signals.

John
Image
‹(•¿•)›
User avatar
John Hinson
Site Admin
Site Admin
 
Posts: 6780
Joined: Thu Nov 8, 2007 1:13 pm
Location: at my computer

Re: Worcester Mechanical Boxes

Unread postby Adrian the Rock » Wed Jul 29, 2015 10:11 pm

John Hinson wrote:That is the typical arrangement with slotted signals.
Indeed. But slotted signals in what is quite close to the traditional AB sense must be quite unusual on bi-directional TCB lines worked by mutual acceptance levers (/switches).

The question I was really asking was that, if TJ6 becomes slotted with SH2/3 then is there still also the need for SH to have a separate acceptance lever for this line? If so, what would it do that SH2/3 don't then already do?
User avatar
Adrian the Rock
Rest-day relief
Rest-day relief
 
Posts: 722
Joined: Thu Nov 8, 2007 8:03 pm
Location: Malvern, England

Re: Worcester Mechanical Boxes

Unread postby S2595/ » Thu Jul 30, 2015 6:21 am

After the alterations, it is my understanding that the overlap beyond the WSH home will be sufficient for a full line clear acceptance in all circumstances. But how will Tunnel Jcn distinguish whether Shrub Hill means to give the train the main aspect or the CO? If it is the latter signal, then he will need to check the train at his home signal first, otherwise another SPAD scenario is surely set up?
S2595/
Crossing box
Crossing box
 
Posts: 21
Joined: Mon Jun 7, 2010 2:16 pm

Re: Worcester Mechanical Boxes

Unread postby Mike Stone » Thu Jul 30, 2015 10:28 am

Surely the main aspect or the sub will clear dependent on whether the platform line/overlap is occupied or not.
Mike Stone
Mike Stone
Rest-day relief
Rest-day relief
 
Posts: 1119
Joined: Fri Nov 16, 2007 2:50 pm

Re: Worcester Mechanical Boxes

Unread postby S2595/ » Thu Jul 30, 2015 1:02 pm

My point is if the CO signal is used, it will not clear until the train has been brought almost to a stand at it. If all trains are accepted full line clear from WSH, how can Tunnel Jcn know whether they need to check the train at their home up to their slotted starter/WSH Home/CO in this circumstance?
S2595/
Crossing box
Crossing box
 
Posts: 21
Joined: Mon Jun 7, 2010 2:16 pm

Re: Worcester Mechanical Boxes

Unread postby John Hinson » Thu Jul 30, 2015 6:16 pm

S2595/ wrote:My point is if the CO signal is used, it will not clear until the train has been brought almost to a stand at it. If all trains are accepted full line clear from WSH, how can Tunnel Jcn know whether they need to check the train at their home up to their slotted starter/WSH Home/CO in this circumstance?

Shouldn't need to check the train if it has been accepted normally.

John
Image
‹(•¿•)›
User avatar
John Hinson
Site Admin
Site Admin
 
Posts: 6780
Joined: Thu Nov 8, 2007 1:13 pm
Location: at my computer

Re: Worcester Mechanical Boxes

Unread postby S2595/ » Thu Jul 30, 2015 7:28 pm

Heres the scenario I'm thinking of. I am the signalman at WTJ and have a train on line from Droitwich, offer it to WSH and it is accepted full line clear (always) Then I would pull the up home (a semaphore signal) and the slot lever which is my starter/WSH Home. The platform at WSH is occupied so that slotted signal isnt going to show yellow is it. Therefore will the driver not see yellow distant, green home (without being checked), red slotted starter/WSH home until the CO comes off. Isnt that wrong?!
S2595/
Crossing box
Crossing box
 
Posts: 21
Joined: Mon Jun 7, 2010 2:16 pm

Re: Worcester Mechanical Boxes

Unread postby John Hinson » Thu Jul 30, 2015 7:55 pm

I don't know the current or planned arrangements well enough but if Tunnel's home is colour-light it would show yellow as Shrub Hill's distant (or inner distant). If semaphore it should have a distant arm provided below it to serve the same purpose.

So if the train is refused by Shrub Hill (i.e. no clearing point), the old Rule 39 is applied by Tunnel to drop it to the starter, but if it has been accepted (i.e. there is an established clearing point) it runs direct to Shrub Hill's Home receiving a distant check before reaching it.

If these arrangements have not been accommodated, then it is indeed dangerous by design and becomes a . . . you've guessed it . . . "SPAD trap". I think it more likely that there will be planned changes to the signals in rear of the new signal which we are unaware of.

But perhaps you now understand my point about there being only one signal to slip up at rather than three with the new arrangements.

John
Image
‹(•¿•)›
User avatar
John Hinson
Site Admin
Site Admin
 
Posts: 6780
Joined: Thu Nov 8, 2007 1:13 pm
Location: at my computer

Re: Worcester Mechanical Boxes

Unread postby Adrian the Rock » Thu Jul 30, 2015 10:26 pm

Current layout and signalling shown here: http://www.roscalen.com/signals/Worcester/index.htm#Diagram (this doesn't pretend to be a proper signalbox-type diagram). TJ's up main home TJ5 has an outer SH fixed distant beneath it, and up starting TJ6 the SH inner fixed distant.

When restricted (fka warning) acceptance was limited to apply only if the clearing point is obstructed by either (a) a T3 posession or (b) temporary SLW arrangements, the equivalent of the old regulation was added to the local box instructions except that the bell code 2-2-2 is now used in place of the traditional 3-5-5. Cynics like me translate this code as "line clear to clearing point, not". :)

So if there is another train in P2 at SH and a permissive move is to be made, SH will accept the train from TJ using 2-2-2, and TJ will duly check the train at TJ5 before lowering this to allow it towards TJ5, where TJ will again check the train before pulling off. Finally, SH will in due course drop the caller SH3 below SH2.

As a result of past SPADs, there is a further special instruction that SH can only accept a train (by whatever method) from TJ if he is in a position to clear either SH2 (immediately) or caller SH3 (when the train closely approaches it).

So in the normal case where P2 is clear and SH can give a full line clear, he will also immediately clear SH2, and TJ can immediately pull TJ5, TJ6 and distant TJ1.

If TJ6 becomes slotted with SH2/3, then the fixed distant below TJ5 would become SH's only distant signal, meaning that every train would need to be prepared to stop at TJ6/SH2, and all drivers would need to be understand the significance of this change or it would become a SPAD trap. I have a notion that when this change was previously mentioned to me it was said that the TJ5/7/22 bracket was also going to be replaced by a C/L. This would be extremely logical as it could then show YY when TJ6/SH2 has also been cleared and obviously just Y otherwise, but I don't know for certain whether or not this is (still?) the plan.
User avatar
Adrian the Rock
Rest-day relief
Rest-day relief
 
Posts: 722
Joined: Thu Nov 8, 2007 8:03 pm
Location: Malvern, England

Re: Worcester Mechanical Boxes

Unread postby Fast Line Floyd » Fri Jul 31, 2015 7:54 am

S2595/ wrote:Heres the scenario I'm thinking of. I am the signalman at WTJ and have a train on line from Droitwich, offer it to WSH and it is accepted full line clear (always) Then I would pull the up home (a semaphore signal) and the slot lever which is my starter/WSH Home. The platform at WSH is occupied so that slotted signal isnt going to show yellow is it. Therefore will the driver not see yellow distant, green home (without being checked), red slotted starter/WSH home until the CO comes off. Isnt that wrong?!

Under semaphore signalling the WSH distants from tunnel junction are all fixed at caution therefore the replacement colourlight home signal at Tunnel Junction will only ever show red and yellow and will be approach released from red unless TJ6 has been cleared.
Graham
User avatar
Fast Line Floyd
Main line box
Main line box
 
Posts: 1624
Joined: Tue May 26, 2009 11:42 am
Location: Raunds

Re: Worcester Mechanical Boxes

Unread postby S&TEngineer » Fri Jul 31, 2015 2:10 pm

I am suprised that intermixing colourlight signals in a predominatly mechanical signalled area is thought a good idea. This can create further SPAD traps. Hope they did a thourough risk assessment......... :shock:
Regards,
S&TEngineer
-----------------------------------------------------
Out of this nettle, Danger, we pluck this flower, Safety.
Henry IV, Part 1, Act 2, Scene 3
User avatar
S&TEngineer
Moderator
Moderator
 
Posts: 1593
Joined: Fri Nov 9, 2007 8:17 pm
Location: Somewhere in the far South West

Re: Worcester Mechanical Boxes

Unread postby Fast Line Floyd » Fri Jul 31, 2015 3:40 pm

S&TEngineer wrote:I am suprised that intermixing colourlight signals in a predominatly mechanical signalled area is thought a good idea. This can create further SPAD traps. Hope they did a thourough risk assessment......... :shock:

Umm Quite!
Graham
User avatar
Fast Line Floyd
Main line box
Main line box
 
Posts: 1624
Joined: Tue May 26, 2009 11:42 am
Location: Raunds

Re: Worcester Mechanical Boxes

Unread postby S2595/ » Fri Jul 31, 2015 6:34 pm

IF the up home at Tunnel Jcn is replaced by a colour light which is approach controlled when TJ6/WSH2/3 is at red then of course there is no problem. But from all the discussions over the years I've heard on this, no one ever mentioned TJ 5/7/22 being replaced. Relying on drivers to acknowledge the meaning of a fixed distant evidently does not work, given the number of times SH2 has been passed at danger.
S2595/
Crossing box
Crossing box
 
Posts: 21
Joined: Mon Jun 7, 2010 2:16 pm

Re: Worcester Mechanical Boxes

Unread postby John Hinson » Fri Jul 31, 2015 9:31 pm

S2595/ wrote:IF the up home at Tunnel Jcn is replaced by a colour light which is approach controlled when TJ6/WSH2/3 is at red then of course there is no problem. But from all the discussions over the years I've heard on this, no one ever mentioned TJ 5/7/22 being replaced. Relying on drivers to acknowledge the meaning of a fixed distant evidently does not work, given the number of times SH2 has been passed at danger.

There should be no need for approach control, that is over and above the requirements if there is an adequate overlap beyond Shrub Hill's Home. Approach control should only be applied when there is no overlap - i.e. the train has not been accepted. Admittedly It increased the number of signals to be observed to two - but this is a very confusing (to drivers) way to deal with the situation.

I would be very reluctant to blame the "number of times" the signal has been passed in error (wasn't it just twice?) on a single issue when we do not know the full story. At any rate what is the difference between a fixed distant under a home and a colour-light signal that only shows red and yellow? Neither shows the state of the next signal. The only thing that shows the state of the next signal to a driver is whether he sees a red changing to yellow or a yellow and I don't think that's in the Rule Book. If drivers start to expect this you have a . . . SPAD trap country-wide.

John
Image
‹(•¿•)›
User avatar
John Hinson
Site Admin
Site Admin
 
Posts: 6780
Joined: Thu Nov 8, 2007 1:13 pm
Location: at my computer

Re: Worcester Mechanical Boxes

Unread postby Adrian the Rock » Fri Jul 31, 2015 9:50 pm

Fast Line Floyd wrote:Under semaphore signalling the WSH distants from tunnel junction are all fixed at caution therefore the replacement colourlight home signal at Tunnel Junction will only ever show red and yellow and will be approach released from red unless TJ6 has been cleared.
I agree with John - do the new arrangements really need to be so constrained by the past?

To my mind, in cases where TJ5 and TJ6/SH2 can both be cleared to give a train a clear run into SH P2, and assuming both have been converted to C/Ls, it would be more logical on today's railway for TJ5 to display YY. An important comparison is with the Droitwich loop round to Foregate St. Currently, TJ7 has a lower-arm outer fixed distant for Henwick home HK22 (a short way in advance of the FS platform) and TJ8 a lower-arm inner fixed distant for same. Provided Henwick has accepted the train so TJ can pull off both of those, then it's even more logical for the TJ5/7/22-replacement to show YY (plus a position 4 PLJI) as it is still acting as HK's outer distant.

Restricting TJ5 to show at best single yellow for the main route to SH would then leave a situation in which up trains with a clear run round the loop to FS would see YY at TJ5/7/22 whereas those with a clear run into SH would see only Y, followed by a further Y at TJ6/SH2 - a less restrictive aspect for what is actually the higher-speed route. [The current line speed from TJ to SH is 25, whereas the loop is 25 across TJ but IIRC then reduces briefly to 15 over the double-to-single junction at Rainbow Hill before coming up to 40 for the stretch through FS and across the river.]

(There is also, IMHO, a fair case for allowing TJ6/SH2 to show a green aspect, if SH has pulled off right through, eg for a non-stopping freight train! The only risk I can see in that situation is of a driver forgetting what the speed limit through SH is.)
User avatar
Adrian the Rock
Rest-day relief
Rest-day relief
 
Posts: 722
Joined: Thu Nov 8, 2007 8:03 pm
Location: Malvern, England

PreviousNext

Return to Signalling - current

Who is online

Users browsing this forum: Yahoo [Bot] and 1 guest