Position of colour lights for shunting facing points

[SZ]

I understand that ground position lights should be positioned at the toe of the relevant points but that for facing points off a running line there should be a subsidiary signal on a main aspect instead (to avoid passing a red ground position light at the facing point). How far in rear of the facing point can this main aspect be positioned? If the facing point is off a running loop I imagine this often results in having a main aspect positioned on the running loop solely for this purpose?

Edited September 27, 2020 by SZ

[ikcdab]

Assuming the track is fully track circuited, I guess there is no practical limitation. As soon as the train passes the signal, it occupies the track circuits and these hold the point locked. Clearly there is an operational distance, but the signal does not need to be right up by the toe of the point,  indeed to guard against the effects of a SPAD, there might be a few tens of yards. No doubt a real expert will give us the actual answer soon.

Ian

[Grovenor]

Many layouts have facing ground signals within the route, you don't have to have a main aspect at each one. Normally a main aspect will only clear if all such ground signals within the route are also clear so there is no passing of red lights.

See the station throat here for plenty of examples. Ahead of signals 64 and 65 for ezamples. You will have to click on the diagram several times to enlarge it.

Edited September 27, 2020 by Grovenor

[Dagworth]

47 minutes ago, SZ said:

I understand that ground position lights should be positioned at the toe of the relevant points but that for facing points off a running line there should be a subsidiary signal on a main aspect instead (to avoid passing a red ground position light at the facing point). How far in rear of the facing point can this main aspect be positioned? If the facing point is off a running loop I imagine this often results in having a main aspect positioned on the running loop solely for this purpose?

Can you give us a trackplan please? We can give a much more detailed answer if we can see what we are offering advice on.

 

Andi

[SZ]

5 minutes ago, Dagworth said:

Can you give us a trackplan please? We can give a much more detailed answer if we can see what we are offering advice on.

 

Andi

 

No particular trackplan, just trying to understand it in general terms, track circuit block, BR onwards.

[SZ]

11 hours ago, Grovenor said:

Many layouts have facing ground signals within the route, you don't have to have a main aspect at each one. Normally a main aspect will only clear if all such ground signals within the route are also clear so there is no passing of red lights.

See the station throat here for plenty of examples. Ahead of signals 64 and 65 for ezamples. You will have to click on the diagram several times to enlarge it.

 

Thanks but I can't see that diagram for some reason, so to clarify, a ground position light can be placed exactly at the toe of a facing point in a running line and no subsidiary signal is needed on the main aspect in rear of it? If it is cleared for running moves how would a driver know it has cleared correctly for a shunting move?

[The Stationmaster]

12 hours ago, SZ said:

I understand that ground position lights should be positioned at the toe of the relevant points but that for facing points off a running line there should be a subsidiary signal on a main aspect instead (to avoid passing a red ground position light at the facing point). How far in rear of the facing point can this main aspect be positioned? If the facing point is off a running loop I imagine this often results in having a main aspect positioned on the running loop solely for this purpose?

I'm not sure what the distance was originally on fast running lines  but it was pretty short.  it was increased to 880yds (half a mile) maximum distance between a running  (main aspect) signal and a facing point around the latter half of the 1970s (possibly by 1977 but I'm not certain of that date).

 

If it is reading from a running loop the distance will depend on ensuring there is an overlap between the signal in rear and the signal controlling the exit from the loop so the exit signal would be set back from the points to provide that overlap (dseveral u hundred yards in many situations although on a permissive running loop with restricted speed the overlap could be quite short.   Similarly in large station areas a speeds might well be restricted to allow provision of platform starting signals relatively v close to pointwork.

[The Stationmaster]

8 minutes ago, SZ said:

 

Thanks but I can't see that diagram for some reason, so to clarify, a ground position light can be placed exactly at the toe of a facing point in a running line and no subsidiary signal is needed on the main aspect in rear of it? If it is cleared for running moves how would a driver know it has cleared correctly for a shunting move?

Differentiate between the three classes of movement.

 

For a running movement the main aspect will clear after any intermediate ground position lights (GPLs) in the route have cleared and they will be held then by the route locking.

 

If it is a shunting move there are two options, viz -

a.  If the shunt movement starts from the main aspect signal it will have to have a position light subsidiary to control the shunt movement (it will be slightly different for what amounts to a calling  on movement for a passenger train because that will require the same route locking as a running movement so, again, all the intermediate GPLs have to be showing their 'off' aspect),

b. If the shunt movement starts from in rear of an intermediate GPL it will be signalled from GPL to GPL as a shunt

Edited September 28, 2020 by The Stationmaster

[Grovenor]

23 minutes ago, SZ said:

 

Thanks but I can't see that diagram for some reason, so to clarify, a ground position light can be placed exactly at the toe of a facing point in a running line and no subsidiary signal is needed on the main aspect in rear of it? If it is cleared for running moves how would a driver know it has cleared correctly for a shunting move?

Maybe you can find the diagram here, http://www.norgrove.me.uk/signalli.htm  click on them to enlarge. The one I linked to is Euston.

 

As the Stationmaster says, if the train is going on a shunt move then the main signal in rear will need a subsidiary for the shortened route up to the ground signal then will obey the ground signal. More commonly the main signal will have main and call on routes that require ground sigmals in route to be cleared Shunt moves using those ground signals for shunting will have arrived from the opposite direction by a route up to a limit of shunt. The scenario you envisage would be relatively rare,

 

Edited September 28, 2020 by Grovenor