Placing signal at Red before loco has passed signal

[RJS1977]

I seem to remember an article on signalling in RM about 20 years ago mentioned a situation at Llandudno (IIRC) where the front wheels of a Class 40, being in front of the cab windows, could set a starter signal back to danger before the driver had passed it!

[Edwin_m]

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.

Starting signals from dead ends don't have overlaps, since a train will never be approaching them at red (except in the limited case of loco release mentioned above). 

[Edwin_m]

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!

Not to do with whether the overlap is long, short or non-existent, more to do with whether there is a track circuit joint immediately after the signal.  Whether the next track circuit is part of an overlap or not, it will replace the signal to danger... unless the signal has "last wheel replacement" in which case the proceed aspect will remain until the whole train has passed it.  This is often seen where trains propel out of platforms, for example at Derby. 

 

Having the released engine following the train out was commonplace at major termini but forbidden a few years ago by which time loco release had pretty much ceased everywhere. 

[TheSignalEngineer]

The signal reversion effect was a particular problem when Type 1 diesels ran nose first. This was partly the reason for the 75 feet quoted in the instruction issued for the LMR by Eric Lofthouse. the alternative method adopted in places where the clearance point was very close to the signal was to replace 'Last Wheel or 2nd Track'. This meant that the route locking would be properly held as the train passed the signal with no risk of false release, and the signal would revert to red when the front of the train hit the second track circuit past the signal or in the case of a light engine when the rear bogie cleared the berth track circuit if the front bogie hadn't occupied the second track circuit past the signal.

[The Stationmaster]

 

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 -

 

 

 

I sincerely hope that you were taught more than that James .  A stop signal (except on a Permissive Line) should not be returned to danger until the whole of the train has passed it but if there are facing points in advance of the signal the signal should no be returned to danger until the train has passed them.  The only exception is that if a train comes to a stand with part of it still in rear of the signal the signal should be returned to danger  (what the SGI fails to make explicit is the situation regarding facing points when a train comes to a stand part way past the signal.

 

On a permissive line the signal should be replaced to danger as soon as the loco has passed it - for fairly obvious reasons of course.

 

And all of that has been in the Rules for more years than I can remember or care to research - it's just that in order to keep folk revising the Rules etc on their toes it has been moved around a bit over the years.

[phil-b259]

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. 

 

Why is there a need for that? surely the only requirement is that the signal retains a proceed aspect until the driving cab has passed it.

 

Under modern regs - while guards are required to check the signal is at a proceed before allowing the train to depart, IIRC they do not specifically have to observe the signal stays that way once the train begins to move. In fact modern guidance is more related to keeping a sharp lookout for passengers who may be caught in the doors or attempting to board the train as it departs.

 

Its also worth noting that were a signal to be replaced to red at the last minute TPWS would intervene a bring the train to a halt

 

You have also to remember that in track circuit block areas the train will remain protected by comprehensive track circuiting - there is no need to maintain signals at proceed to prevent accidental point operation etc.

 

The situation you observe with automatic signals only occurs because adding extra overlap track circuits has no benefit to anyone at all (again unlike in steam  days the requirement for guards to observe all signals is not present today) and all their installation would do is increase the signalling design, installation and maintenance costs

[James]

I sincerely hope that you were taught more than that James .  A stop signal (except on a Permissive Line) should not be returned to danger until the whole of the train has passed it but if there are facing points in advance of the signal the signal should no be returned to danger until the train has passed them.  The only exception is that if a train comes to a stand with part of it still in rear of the signal the signal should be returned to danger  (what the SGI fails to make explicit is the situation regarding facing points when a train comes to a stand part way past the signal.

They told us a few other bits too!

 

My bit applies quite well to Outer Homes - in many cases now any signals associated with facing points will also have back locking to prevent the signal being replaced and the points swung as the train approaches. There is also another point to add with regards replacing signals manually - you don't want to be doing with too much eagerness as it is possible to do it too soon and put it back in front of a train... That's not good!

[roythebus]

_{We had a guard at Rugby back in 1974, quite a keen chap, who used to regularly report drivers of goods trains for passing signals at danger; not realising that by the time his brake van went past the signal, it would have gone back to danger anyway!}

 

_{I don't see there would be any need for TWPS leaving a dead-end platform such as Kings Cross. As for pushing the night sleeper out of the platform, that' one of the heavy trains that needed a shove. the assisting loco would NOT have passed the starting signal.}

[Trainshed Terry]

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

Well spotted

[Edwin_m]

_{I don't see there would be any need for TWPS leaving a dead-end platform such as Kings Cross. As for pushing the night sleeper out of the platform, that' one of the heavy trains that needed a shove. the assisting loco would NOT have passed the starting signal.}

On the contrary, TPWS would be provided in this situation as there is a significant SPAD risk from "ding ding and away" or other causes such as driver reading across to the signal in the adjacent platform.  It would not stop the train going over the track circuit joint and probably stopping foul of points where other trains might be signalled, but it would be much less dangerous than the train carrying on into the tunnel as would probably happen otherwise. 

[The Stationmaster]

On the contrary, TPWS would be provided in this situation as there is a significant SPAD risk from "ding ding and away" or other causes such as driver reading across to the signal in the adjacent platform.  It would not stop the train going over the track circuit joint and probably stopping foul of points where other trains might be signalled, but it would be much less dangerous than the train carrying on into the tunnel as would probably happen otherwise. 

Agree, when we were SPAD risk assessing St Pancras we finished up at one stage with TPWS ramps all over the place on the drawings as Midland Mainline (as they then were) couldn't make up their mind about train length and, for example, among other things we were faced with a situation where a 170 unit starting from the stop blocks end of the platform could easily SPAD the platform starter because of the sheer amount of accelerative power it has.

[James]

_{I don't see there would be any need for TWPS leaving a dead-end platform such as Kings Cross.}

I think the only thing would be no need for the Over Speed Sensor in such cicrcumstances - it is a potential SPAD though. Guard gives the right away and the driver sets off out of habbit without checking the signal. 'Habitual behaviour', it was part of my last brief.

[LNERGE]

 

 

_{. As for pushing the night sleeper out of the platform, that' one of the heavy trains that needed a shove. the assisting loco would NOT have passed the starting signal.}

Perhaps should not have happened but it did.