Exiting a depot onto the mainline (Signals?).

[phil-b259]

1 hour ago, John M Upton said:

Littlehampton Yard Carriage Sidings has a yellow ground shunt signal, two horizontal yellows and you are off up the unelectrified headshunt (until you run out of power), two diagonal whites and it into the station, platform 1 only as it is the furthest exit, the other has a conventional red/white shunt signal.

 

The whole area is being resignalled next year so I am not sure if it is being binned, it is the only one on our turf down here.

It will be binned.

 

As Simon mentioned up thread NR will not permit them to remain in resignalling schemes.

[St. Simon]

2 hours ago, John M Upton said:

Littlehampton Yard Carriage Sidings has a yellow ground shunt signal, two horizontal yellows and you are off up the unelectrified headshunt (until you run out of power), two diagonal whites and it into the station, platform 1 only as it is the furthest exit, the other has a conventional red/white shunt signal.

 

The whole area is being resignalled next year so I am not sure if it is being binned, it is the only one on our turf down here.

Hi,

 

Yep, LH38 will no longer be a Yellow Shunt.

 

Interestingly, Littlehampton is a case in point, there are two exits from the depot into the station, one (that I’ll call the south exit) that accesses only platform 1 and another (that I’ll call the north exit) that exits just before the station throat.
 

In a resignalling, the south exit would really only be a independent position lights would be used as it’s a bit too much for a main aspect (I can’t define ‘too much’ as it’s more of a professional judgement!), where as the north exit could easily be either a position light or a main aspect. 
 

A main aspect from the north exit would provide a marginal performance benefit as Littlehampton has permissive working into the platforms, so there would be a distinction as to how far the platform road was clear. Given the amount of traffic in / out of the depot, then that small difference could add up. However, it wouldn’t be that much of a difference as the exit is only a couple of hundred (if that) metres from the platforms, so a position light would be fine and of course there might be clearance problems for a main aspect. 
 

As it happens the resignalling will keep the north exit as a position light, but there are lots of lots reasons for it which I can’t go into.

 

I should know, I designed the scheme and that was exactly the discussion I had with myself and ops :)

 

Simon

Edited November 20, 2022 by St. Simon

[John M Upton]

Having just put the 313 to bed for the night, there in the middle distance is our famous yellow shunt signal!

 

[St. Simon]

1 minute ago, John M Upton said:

Having just put the 313 to bed for the night, there in the middle distance is our famous yellow shunt signal!

 

It’s even a LED ‘Yellow-Yellow’ shunt, even rarer, there must only be a dozen left or something!

 

Simon

[TheSignalEngineer]

On 16/11/2022 at 16:55, phil-b259 said:

Also, these signals were ALWAYS fitted with filament lamps - NOT LEDS so a 'warm white' LED should be utilised when portraying them in model form.

Warm white would be incorrect for most types as the glass of the white aspects was pale blue, which gave what is known as a Lunar White aspect when placed in front of a paraffin flame or incandescent electric lamp. It is sometimes combined with a white coated element known as Flashed Opal glass which is an opaque white colour in daylight. This is the glass that was used in oil or tungsten lit stencil indicators.

This demonstrates the difference between a Lunar White aspect in the ground signal and a stencil indicator with just a flashed opal front. This was taken in 1972.

On 16/11/2022 at 15:50, St. Simon said:

The choice between main and independent position light is down to whether operations can live with the train going at very slow speed from a position light to the next main aspect. If yes, position light, if not then main aspect. That can be based on a number of factors, distance to next main aspect, sighting of next main aspect, platforms etc etc.

 

However, the principle in days gone by was position lights always unless you really really needed a main aspect.

Certainly was almost all position lights when I was a lad. That gradually changed on the LMR when I was in the drawing office 1970s/1980s. We slowly migrated to using a main aspect for moves straight to the running line in the normal direction of travel. The initial criteria we used was the distance to the next signal. If for instance the next signal was in sight when the whole of the train had crossed the points and was on the main line then a position light was adequate. If the train could get to the place where it was out clear and permitted to accelerate then a main 3 aspect signal would usually be provided. There were a few instances where a 4 aspect signal was necessary.

[phil-b259]

1 hour ago, TheSignalEngineer said:

Warm white would be incorrect for most types as the glass of the white aspects was pale blue, which gave what is known as a Lunar White aspect when placed in front of a paraffin flame or incandescent electric lamp.

That is a very good point which I had overlooked - though the ‘blue’ tint was in itself quite subtitle and not as harsh on the eye as the ‘bright white’ effect a pure white LED gives.

 

I wonder if a very light blue paint layer/ Wash (replicating the slight blue-ish tint) across a warm white LED would do the trick….

[Dagworth]

3 hours ago, TheSignalEngineer said:

which gave what is known as a Lunar White

Is that the origin of junction indicators being known as Lunars on the Southern region?

 

Andi

[TheSignalEngineer]

6 hours ago, Dagworth said:

Is that the origin of junction indicators being known as Lunars on the Southern region?

 

Andi

Correct

[TheSignalEngineer]

6 hours ago, Dagworth said:

Is that the origin of junction indicators being known as Lunars on the Southern region?

 

Andi

Slightly OT but Lunar had a different meaning on many USA railroads. It was commonly used as a restricted aspect. Red and Lunar together is usually proceed with caution to next signal being prepared to stop short of any obstruction. Very similar to Red and Cats Eyes for Calling On in the UK. 

[Nick C]

On 16/11/2022 at 19:13, phil-b259 said:

 

True - if you had a situation where the signal heads were simply changed from mechanical / semaphore to colour lights (or an extra colour light added into the mix as part of a minor layout change) but Absolute block was retained.

 

However for decades such a 'mix'n match' has not been permitted to be newly created - and thats why we have seen NR actually building new semaphores where Br might have just put up a colour light.

 

I know of at least two locations on preserved lines with a mix of colour light and semaphore controlled by the same box, including one that's not yet commissioned - but in both cases the colour lights are capable of showing a yellow aspect (thus avoiding the need to 'caution' the driver if the next signal is at danger)

[Michael Hodgson]

I believe the policy of like for like on renewals is Network Rail policy rather than a safety directive, so preserved lines can choose to use a combination of types, as long as they're safe. 

 

Both colour lights and semaphores are historically correct, so they comply with objectives of saving/using historical equipment.

Mixtures of the two are also historically correct - it was quite common to replace a semaphore distant with a colour light, that removed many of the heaviest lever pulls and replacing oil lamps with more powerful colour lights often improved visibility, particularly important with distant signals on lines where speeds are rather more than the 25 mph most preserved lines must observe.

 

Replacing a home signal with colour light but leaving the preceding stop or distant as semaphore would sometimes be unwise because of the increased risk of "reading through".

[Michael Hodgson]

On 16/11/2022 at 19:13, phil-b259 said:

 

True - if you had a situation where the signal heads were simply changed from mechanical / semaphore to colour lights (or an extra colour light added into the mix as part of a minor layout change) but Absolute block was retained.

 

Semaphore doesn't necessarily imply absolute block.  You do get boxes which are all semaphore but work Track Circuit Block (or of course Permissive Block etc); you can also have all colour light boxes still working AB.  You would have to remain on AB to ensure the train arrives complete, unless either the line is fully track circuited or more recently if there are axle counters.