Jump to content
 

Placing signal at Red before loco has passed signal


Recommended Posts

  • RMweb Premium

Looking at the following video clip I assume the Green Signal is a clear road for the Deltic to depart Kings Cross? The Deltic starts to move and the signal is returned to Red before the loco has even passed the signal, surely this cant be right? 

 

http://www.rmweb.co.uk/community/index.php?/topic/70046-Bachmann-class-55-deltics/?p=1051115

 

Link to post
Share on other sites

  • RMweb Gold

I think the perspective from the camera position makes it hard to judge where the front of the loco is. In such a low-speed area, there is no reason to have long overlaps beyond the signal, and to do so would probably make operation much more lugubrious. The green signal indicates that the route is locked for a considerable distance. Occupation of the next track circuit doesn't affect that.

Link to post
Share on other sites

  • RMweb Gold

Looks like the cab may have been right under the signal to start with, even with permission to start in advance of the signal with how quick it goes red. Train was obviously right on the limit for the platform length. I'd hazard a guess they are set to replace as soon as the overlap is occupied because of sharing platforms or because of short overlaps to eliminate the chance of a second train in the platform reading it as a proceed as the first, especially if it was a light loco, departs.

Starting in advance of the signal is allowed as long as there's a clear procedure agreed between the crew and Signalbox.

Link to post
Share on other sites

  • RMweb Gold

Looking at the following video clip I assume the Green Signal is a clear road for the Deltic to depart Kings Cross? The Deltic starts to move and the signal is returned to Red before the loco has even passed the signal, surely this cant be right? 

 

http://www.rmweb.co.uk/community/index.php?/topic/70046-Bachmann-class-55-deltics/?p=1051115

Definitely looks a bit odd (could be telephoto effect of the lens?) as the signal is back at danger almost before the cab passes it.  But the whole lot is track locked and the layout is very tight to block joints only a short distance in advance of the signal are not entirely unexpected.

Link to post
Share on other sites

Aft'noon PT,

 

...nothing unusual in the signal returning to red once the loco cab had passed the signal in colour light areas.

 

There was variation between semaphore and colour light areas:

 

under semaphore one would expect the signalman to return a stop signal to danger once the train had passed (complete with tail lamp as it passed his box). There were some automatic (not signalman controlled) semaphore situations e.g. on the Southern ...an interesting question would be to ask when those signals returned to caution/danger.

 

in colour light areas overlaps, track circuits, clearances would determine the point at which a signal returned to its more restrictive aspect. 

 

Historically speaking, there were specific instructions for the train guard to consider re observing signals and bringing the train to a stand if he felt that a signal had been passed at danger.

 

Dave

Link to post
Share on other sites

  • RMweb Gold

I cant get the vid to play in the iphone but looking at the youtube still it appears to be a fairly recent video.....

 

Im not familiar with kings cross or the type of signalling there but could it be that the loco has passed over a track circuit paddle thingy/block joint just beyond the signal?

 

Funnily enough while travelling passenger to oxford over the last couple of weeks (on voyagers) i noticed some signals had already reverted to danger before we had full passed by which i found odd as i was normally sat in the 2nd coach

 

I did post a couple of pics in a thread earlier this year of the LED banner repeator at dorridge that had reverts to danger pretty much as the first carriage is along side it, in fact it has reverted back before the leading carriage has reached the associated signal!

 

EDIT: LNERGE's reply came in while i was typing, ref the block joint

Link to post
Share on other sites

  • RMweb Gold

Funnily enough while travelling passenger to oxford over the last couple of weeks (on voyagers) i noticed some signals had already reverted to danger before we had full passed by which i found odd as i was normally sat in the 2nd coach

 

 

On the other hand Jim there are some between Reading and Didcot where the first block joint in advance of the signal is the overlap joint so the entire train can be well past the signal before it goes back to red.  In fact there used to be several where a short train was out of sight round the corner before the signal went back to red.

Link to post
Share on other sites

On the other hand Jim there are some between Reading and Didcot where the first block joint in advance of the signal is the overlap joint so the entire train can be well past the signal before it goes back to red.  In fact there used to be several where a short train was out of sight round the corner before the signal went back to red.

I can remember colour signals where a 4 car was well past the signal before it dropped back.  To me it was more disconcerting to see a green light with a train in front.  Where locomotives were used to bring ECS (empty coaching stock) into platforms there were often instructions that the driver was to speak to the signalman before moving to the signal.  I'm sure someone can give examples.

Link to post
Share on other sites

That was/is the normal situation for automatic signals where the replacement joint is at the end of the overlap, 200 or 300 yards from the signal. At interlockings there are usually seperate track circuits for the overlap and replacement is done closer to the signal, commonly 25 yards from the signal but used to be up top 50 yards. Attached instruction was issued on the LM region when this change was made.

Most American railroads put the replacement joints right at the signal but IIRC one road put the replacement joint ahead of the signal specifically so the driver could see the signal drop back and would know that his train was protected in rear.

Keith

post-3169-0-75750900-1382291055_thumb.png

Link to post
Share on other sites

I'm guilty of not thinking about this enough in one of my designs in use on a heritage railway. We had to live with it until i drew up a modification to make the signals last wheel replace.

 

All of the down colourlight signals in my Ely North Junction last wheel replace. One oddball i had to replicate was ENJ 40/CH14. ENJ 40 lever cleared the signal from red to yellow. Chettisham 14 cleared it from yellow to green. The latter function was first wheel controlled by Chettisham D track from green to yellow and last wheel replaced from yellow to red by ENJ G track

 

http://www.flickr.com/photos/pwayowen/10088608763/

 

http://www.flickr.com/photos/pwayowen/7657494206/

 

http://www.flickr.com/photos/nicholasy/5626872165/in/set-72157625458863993

Link to post
Share on other sites

There were some automatic (not signalman controlled) semaphore situations e.g. on the Southern ...an interesting question would be to ask when those signals returned to caution/danger.

We have motor operated distants which return to on as soon as the train hits the berth track circuit.

 

under semaphore one would expect the signalman to return a stop signal to danger once the train had passed (complete with tail lamp as it passed his box).

I was taught to replace signals once the train has passed to guard the rear of the train - this means that I will return the outer home to danger once the train has passed it (using the illuminated diagram for guidance) and I may not have seen the tail lamps. You can see the arrangement here, the outer home is just out of sight -

 

7955832590_2eb99219ea_b.jpg

158784 at Gilberdyke by JamesWells, on Flickr

 

The same would apply in a semaphore area where the signaller was dropping a train down to the section signal, signal to signal, while a train was in section, for example.

Link to post
Share on other sites

Looking at the following video clip I assume the Green Signal is a clear road for the Deltic to depart Kings Cross? The Deltic starts to move and the signal is returned to Red before the loco has even passed the signal, surely this cant be right? 

 

http://www.rmweb.co.uk/community/index.php?/topic/70046-Bachmann-class-55-deltics/?p=1051115

And no real hint here..

 

post-4034-0-70496400-1382296031_thumb.jpg

Link to post
Share on other sites

  • RMweb Premium

Thank you all for your inputs.

 

Whilst I can understand the short Track Circuit Sections, I would have thought that with SSI or modern equivalent, that a time delay could start when the front of the train (Loco in old money) reaches the next Track Circuit Section with sufficient time delay for at least the front of the train to clear the signal before returning to danger. 

Link to post
Share on other sites

Thank you all for your inputs.

 

Whilst I can understand the short Track Circuit Sections, I would have thought that with SSI or modern equivalent, that a time delay could start when the front of the train (Loco in old money) reaches the next Track Circuit Section with sufficient time delay for at least the front of the train to clear the signal before returning to danger. 

No time delay applies - the signalling system needs a definite indication that the train has passed the signal before it restores the signal to danger.  So the track circuit joint must be positioned beyond the signal if only by a very short distance.  Previous posts seem to have established that this is the case, and the apparent replacement before the cab passes the signal is an optical illusion. 

Link to post
Share on other sites

To go back to the original question, putting the signal at danger before the loco has passed, from memory as soon as the track circuit ahead of the loco is occupied, the previous signal controlling entry to that track circuit will return to danger automatically.

 

Some sections have a long overlap, some, like those at Kings Cross, have a very short or no overlap, so the signal will return to danger as soon as the leading wheels pass the insulated block joint. Simple.

 

At KX a light engine that has been released from a train "on the blocks" was allowed to follow the departing train as far as the platform signal and await clearance of that signal. If the loco did not follow the train, the driver would have to contact the signalman before the loco could move. (1974-1978 local instructions). Things may be a bit different now!

 

Sometimes the released loco would "offer assistance" to the departing train....

Link to post
Share on other sites

Why is 1S24 displayed at both plat 3 and 4?

I once had two 6B75's passing me - one on the up and one on the down! The Up train was about 300 minutes late! He was rerouted too - it was an interesting phone call with the next box...

 

"I've got 6B75 for you!"

"You sure? I've just sent that one to you"

"Yes! I've got another one for you!"

 

Of course could lead to confusion in certain circumstances...

Link to post
Share on other sites

To go back to the original question, putting the signal at danger before the loco has passed, from memory as soon as the track circuit ahead of the loco is occupied, the previous signal controlling entry to that track circuit will return to danger automatically.

 

Some sections have a long overlap, some, like those at Kings Cross, have a very short or no overlap, so the signal will return to danger as soon as the leading wheels pass the insulated block joint. Simple.

 

At KX a light engine that has been released from a train "on the blocks" was allowed to follow the departing train as far as the platform signal and await clearance of that signal. If the loco did not follow the train, the driver would have to contact the signalman before the loco could move. (1974-1978 local instructions). Things may be a bit different now!

 

Sometimes the released loco would "offer assistance" to the departing train....

I was on the 20:00 one evening (KX - Aberdeen MK1 sleepers) that received a considerable shove from the 31 that brought the empty stock in. It came with us and parted company in Gasworks tunnel. I'd never seen that before or since.

Link to post
Share on other sites

As others have pointed out it all depends on whether this is a first wheel or last wheel replacement. The signalled route would be locked in place by the occupation of the track circuit ahead of the signal so no chance of a conflicting move being signalled when the signal goes back.

 

In semaphore areas the signal should be replaced to danger once the train has passed it and any points ahead of the signal (replacing the signal early  could free up the lever(s) that control the points) or as any special instructions dictate.

 

If you want to see greens behind  a train, try the cross city line between Birmingham and Lichfield. Can be a bit disconcerting until you remember the next signal back is still at red.

This happens due to the signalling having one track circuit for both section and overlap (cheaper way to do it, less track circuits)  so the train has to run for 200yds before occupying the track circuit ahead, giving a definite indication to the interlocking that the train has passed the signal.

 

Andy

 

Just had a good look at the Kings Cross panel picture LNERGE posted above and the signals seem very close to the block joints (I know its not to scale, but there do not appear to be any overlaps installed) so the video probably makes it look worse than it is.

Link to post
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...