What does a white shunt signal mean

Signals, Signalling and the Bluebell

This article (slightly modified from the one which appeared in the Winter 1998 edition of Bluebell News) is not intended as an in-depth highly-technical review of signalling practices, more a source of general information about this complex subject and how it affects the Bluebell Railway.

In the earliest days of railways, trains were not really regulated at all – they were despatched at intervals with a minimum time allowed between them. As railways grew and technology improved, both the number and speed of trains increased, leading to inevitable mishaps. To try to regulate things better, Railway Policemen were employed and they were literally a form of human signal, policing the traffic on their line and endeavouring to keep the trains a safe distance apart. (They were, naturally, nick-named “Bobbies”, a name which was subsequently inherited by Signalmen and is still in use to this day). The human knack for misunderstanding and error soon led to the development of a form of mechanical signalling controlled from a central point, the signalbox.

Much improved as this system was, there were still plenty of opportunities for error, leading to many well-documented accidents, so that eventually Parliament had to intervene and formally regulate the various railway companies to make them safer. There have been many, many different Acts of Parliament covering all topics of safety but probably the most important was the Regulation of Railways Act of 1889 which made compulsory: block working (making it impossible for more than one train to occupy any one “block” of track), interlocking (making it impossible to set a conflicting route, or signal a route other than the one set), the locking of facing points and the continuous train brake. This meant a lot of work for some of the railways, such as the Cambrian, which had (through their dire financial conditions) been unable to make much effort to improve the safety of their lines. The LB&SCR was one railway at the forefront of railway safety, having had the misfortune of some spectacular accidents early in its life!

Large railways developed their own systems whilst smaller ones would purchase “off the shelf” from companies such as McKenzie & Holland, Saxby & Farmer or Westinghouse. But, different as their appearance might be, the basic functions were all the same. By and large you can divide signals into three categories, running signals which control trains along their route, shunting signals which control movements over short distances and information signals. Here are described the various types you can see along the route of the Bluebell:-

1. Running Signals.
These are the most well-known, and easily recognised even by people with no interest in railways. They fall into two categories, the Stop signal and the Caution signal.

Fig.1 Stop Signals at the north of Horsted Keynes Station.

Stop signals are normally an arm with a red face and a white stripe on the front whilst the reverse is white with a black stripe. Fig.1 shows the Stop signals controlling the exit north from platforms 3 & 4 and 5 at Horsted Keynes, and the two First Advanced Starting signals by the bridge in the background. (Note the white-painted brickwork behind the signal arms, to help make them visible). Caution signals are usually “fish-tailed” and painted yellow with a black “>” stripe on the front and white with a black “

Fig.3 Left: The upper quadrant Inner Home signal controlling entrance to Horsted Keynes station from the south.
Photo: Chris Majer.

Fig.4 Right: The lower quadrant Advanced Starting signal at Sheffield Park that allows entry to the single line section.

Shunting signals

SIGNALS:

Shunting signals

Signals used for shunting purposes are distinct from stop signals as their function is different. They do not indicate that the line ahead is clear, but that movements may proceed as far as the line is clear.

On a signal post

Shunting signals can be in the form of a miniature semaphore arm, mounted on a signal post.

Lower quadrant	Somersault	Upper quadrant	Colour-light

Ground signals

Ground signals are mounted at ground level – you’d never have guessed! Many have the arm superimposed on a white or black disc to aid visibility. This type is generally called a disc signal, or in the case of the colour-light type, a position-light ground signal.

Their meaning is exactly the same as the miniature-arm signals above.

Lower quadrant	Upper quadrant	Colour-light

Yellow shunting signals

Shunting signals with yellow arms (with, sometimes, a black band) are usually found at the outlet of sidings where there is also a head-shunt.

Signals of this type should not be confused with Distant signals, as their purpose is quite different. The function is similar to that of the red arm shunting signal, with one additional feature. It may be passed when on for shunting movements along the headshunt. This saves frequent operation of the signal when shunting is taking place.

In well-lit locations, such as marshalling yards, a small yellow arm does not show well in artificial light and a black background is provided on discs to make the indication clearer.

Lower quadrant	Upper quadrant	Colour-light

Boring but true

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Signals

This page describes the representation of signals on the panel, their meaning and appearances as well as the control actions in relation with the signals. Fundemental information related to signals is available in the articles Basics and Routes. So if terms on this page are not explained, the explanation is likely to be in these articles.

There are a variety of signals on the panel. Almost always, signals are located on a track.

Contents

Main signal with a distant signal

This is a main signal with a distant signal. Notice the button with the red dot – this button operates the main signal. Buttons with red dots define Train Routes.

Shunt signal

The smaller signal with the gray button is a shunt signal. Gray buttons are used to set Shunt Routes.

Combined signal

When a tile contains both a main signal and shunt signal, the signal is said to be a combined signal. In this case, it has two buttons, a main signal button (red dot), and shunt signal button (grey). This is usually an exit signal.

Distant signal

A detached distant signal is shown at right. It provides a preview of what the next main signal aspect is showing.

Indications main signals

When a main signal is showing a “stop” aspect, the corresponding signal on the panel shows a red light.

When the signal is showing a “proceed” aspect, the signal on the panel shows a green light.

If a route is set and locked, the square white light becomes lit. This is the route lock indication for the signal, and simply means that the train route has been fully set from that signal.

Locking signals

Like switches, signals may be manually locked also. Locking and unlocking is done using the LsSpt (Switch Lock) and LsESpT (Switch Unlock) buttons.

To lock a signal, press the LsSpt button together with the signal button.

When a signal is locked, it is put to stop immediately.

Putting a signal to stop

To simply put a signal to stop, use the HaGT together with the signal button.

It does nothing more than change the signal aspect to “stop”.

Signal Panel Tiles

This section discusses the panel tiles representing signals, in the various forms they can be present in the simulation. Sometimes you will encounter slightly different representations, which however, should be covered as well with the information given here. The buttons and lights are each named clockwise starting in upper left corner. Indicators which are already described above will not be explained again.

Main signal with Distant signal

In general, main signals have the following indicators and buttons on the panel: ‘Auxillary signal activated’ indicator, ‘route set’ indicator, train route button, ‘Proceed’ indicator, ‘Stop’ indicator, signal locked indicator. (Exceptions below)

Single distant signals can show two green indicators (for aspect Vr 1 or Vr 2) or two yellow indicators (aspect Vr 0). A distant signal can be mounted on the main signal’s post.

Some of the main signals displayed on panel do not belong to your own dispatching area, but are controlled by the neighbouring signal box. for those signals you will only have ‘Proceed’ and ‘Stop’ indicators

Main signal and distant signal

Signal in Neighbouring dispatching area

Shunt signals

Shunt signals have a gray signal button, Stop indicator, Sh-1 indicator and a Signal Locked indicator. A shunt signal will also have a round Overlap route indicator (D-Weg melder) next to it, can be the end of a train route. If the shunt signal can be the begin of a train route, it will also have the square Route Locked indicator. The latter two options can also be combined, as in the image.

Sperrsignal mit Festlege- und D-Weg-Melder

Combined main- and shunt signals

There are also main signals, which can show the Shunt aspect Sh 1 beside the normal ‘Proceed’ aspects (Hp 1 and Hp 2). These kind of signals have both a grey-red Train route button and a grey Shunt route button. The signal in the image additionally has a Overlap Route indicator (underneath the Shunt Route button) as well as a Kennlichtmelder (between the Sh 1- and the Stop indicator).

Automatic Block Signals

Automatic block signals can be recognized by the fact that the foot of the signal’s symbol is connected to the track by a black line. Block signals in the central block have a ‘Route set’ indicator, which are not present for the automatic block signals. The two signals shown in the images both have a Subsidiary Signal indicator which is shown in the signal’s post.

Block signal in Zentralblock

Block signal in Selbstblock

Fleeting signals (Selbststellbetrieb)

There are three variants for fleeting signals: either with ‘D’ (automatic) and ‘O’ (controlled by dispatcher) indicators, ‘SB’ (Selbstbetrieb = fleeting) or an indicator with its signal number in a green Group-Button-Block on the panel.

Indicator in Group-Button-Block

Cover signals (Zugdeckungssignale)

Cover signal for one direction

Cover signal for two directions

Signal Zs 6

stand alone ‘Zs 6’-Signal

Halbregelabstandsankündigungssignal (Half-Distance-Rule Announcement Signal)

A signal with this somewhat strange designation is a main signal that can not show Stop (Hp 0). Therefor it does not have a signal button either. It only has a Proceed indicator and a Kennlicht indicator. The distant signal, which is located on the same mast, also has an additional indicator. This shows white light on the distant signal, which is to indicate the distant signal is just a repeater of at short braking distance from the next main signal.

Half-Distance-Rule Announcement Signal

Meaning of the indications

Stop indicator

The red ‘Stop’ indicator is lit, when the signal is showing the ‘Stop’ aspect. If no other indicator (i.e. auxillary signal) is lit, no train is allowed to pass the signal. The ‘Stop’ indicator will flash in the event of a signal fault or defect (see below).

Proceed indicator

The green ‘Proceed’ indicator is lit, when the signals is shwoing a ‘Proceed’ aspect. A train movement can take place. Whether signal aspect Hp 1 or Hp 2 is shown, can not be seen on the panel, but this is also irrelevant for the dispatcher and irrelevant. Any additional signals at the main signal’s post (eg Zs 2, Zs 3, Zs 6) are not shown on the panel. The interlocking circuits however make sure that the signal can only show the Proceed’ aspect once all the additional signals are activated and function correctly. Therefore, it is assumed that everything is fine when the ‘route set’ indicator lits.

A flashing ‘Proceed’ indicator is shown in the event of a signal fault or defect (see below).

Sh 1-Indicator

The Sh 1 indicator, a diagonal white bar, is lit when the signal is showing the Sh 1 aspect. A shunt movement may then take place from this signal. Main signals will keep showing the Stop aspect, menaing that a train movement from here is not allowed.

Kennlicht-indicator

You will see a yellow ‘Kennlichtmelder’ in case a signal can show the so-called ‘Kennlicht’. ‘Kennlicht’ means that the signal along the track has no meaning, as if it is not even existing. It is the normal aspect being shown for cover signals. Additionall, Kennlicht is used for the so-called Half-Distance Rule (Halbregelabstand) as well as for long-/short entrance/exit train routes. More information on when and where ‘Kennlicht’ is applied can be found in the article Dispatching in Köln.

Distant signal indications

A distant signal you will see either two yellow (Vr 0, expect Stop) or two green lights(Vr 1 or Vr 2, expect Proceed aspect) indicator lights. Distant signals which, depending on the situation (i.e. not permanent), are used as a distant signal repeater or are located at short braking distance from the corresponding main signal, also have a yellow indicator that lights accordingly. Distant signals, which are attached to the mast of a main signal remain dark if this main signal shows the Stop ascpect; this also applies to the indicators on the panel.

Route Locked indicator

The square Route Locked indicator lights white, wenn a train route starting from the signal has been set and locked. Its lighting is one of the necessary conditions to get a main signal showing the Proceed aspect. As soon as the indicator lights up, a set route can only be revoked using the Revoke Train Route Button (FHT).

Overlap route indicator (D-Weg-Melder)

Exit signals and other main signals (sometimes even shunt signals) in the station have a Overlap route indicator (D-Weg Melder). This indicator is round and lights up when a route is set towards such a signal. It indicates that the Overlap route behind the signal has been set and fixed. As soon as the train route towards the signal has been completely dissolved, the indicator will start blinking for a certain time. After that, the overlap route will be released automatically. See also: Revoke Shunt Route Button (FRT) and Revoke Overlap Shunt Route Button (DRGT).

Subsidiary signal indicator (Ersatzsignalmelder)

The Subsidiary signal indicator is shown as a yellow triangle, surrounded with a black circle. It will be lit steady when auxillary aspect Zs 1 or Zs 7 is shown(see Show Subsidiary Signal Button), and will be flashing in case auxillary aspect Zs 6 is shown (see Show Subsidiary Signal to Wrong Line Group Button).

Signal locked indicator (Sperrmelder)

At the foot of each signal, being part of your own control area, there is a round, yellow ‘signal locked’ indicator. It will be lit when the signal has been locked (using the Lock Signal Button or Block Disable Button, and therefor can not be set to ‘Proceed’.

Fleeting (Selbststellbetrieb)

There are several variants of indicators to show whether a signal has fleeting enabled (SB) or not:

Operating Signals

Signals should normally not be operated individually. They are operated automatically when setting routes. Nevertheless, if necessary, there are some things you can do with signals:

Anomalies and defects with signals

Anomalies and defects with signals may endanger the railway operations. Therefore, there are some technical measures in place to ensure that an irregularity will not affect the safety:

A distinction between anomalies (requires no operational measures: signal can still be operated, such as defective Red light bulb, but «Ersatzrot» lights, or a Zs display partially defective, but still recognizable) and defects (operational measures required, such as signal completely dark). Signs at the signal’s mast show the driver, what he has to do in case of a defective signal. On the meaning of the different signs on the mast, please refer to the Signalbook DB website.

On the panel anomalies and defects with signals become apparent by a blinking or extinguished Stop- or Proceed indicator, or that the signal is no longer working properly (eg no Proceed aspect, although all conditions are met). In case of a malfunctioning signal a red alarm indication in the red Group Button block will start flashing, and a horn will sound. The horn can be silenced with the Buzzer interruption button (HuT). The alarm indicator will keep blinking, until all anomalies and defects with signals are resolved.

The following measures can be taken in case of for anomalies and defects:

Anomalies with fleeting signals (Selbststellbetrieb)

Fleeting signal can also have anomalies or defects. In that case an (annoying) buzzer will sound and the signal’s Fleeting enabled indicator (SB) will flash. This can happen when:

The first thing to try, is to set the route manually. If that does not work, then switch of the fleeting and try again later. Does this not work either, then the only remaining options is lock a route manually and applying the subsidiary signal or a issueing a written order.

Important: do not forget to enable fleeting again after resolving the anomalies!

What do the white dumb-bell signals indicate?

From ICAO Annex 2:

4.2.3.1 A horizontal white dumb-bell (Figure A1-4) when displayed in a signal area indicates that aircraft are required to land, take off and taxi on runways and taxiways only.

4.2.3.2 The same horizontal white dumb-bell as in 4.2.3.1 but with a black bar placed perpendicular to the shaft across each circular portion of the dumb-bell (Figure A1-5) when displayed in a signal area indicates that aircraft are required to land and take off on runways only, but other manoeuvres need not be confined to runways and taxiways.

Please try to elaborate on the text from Annex 2, and give examples of practical use of these two signals.

2 Answers 2

I keep thinking of some of the big fly ins (like Air Venture in Oshkosh) where pilots are allowed to park on the grass.

During the fly in they might use that second symbol (dumbbell with stripes) to let people know it’s okay to park on the grass, but you still need to take off, land, and taxi on official taxiways and runways (as defined by the event rules). Thus significantly increasing capacity during the event.

But during other weeks that same airport probably doesn’t want anyone taxing onto, or parking on, the grass. So they would display the first symbol (dumbbell with no stripes) to remind everyone that the exception is gone, and the rules have changed back to what you would normally expect at most airports. Thus people would be aware they need to stay off the grass and use official tie down areas for parking.

In essence, I think the first symbol exists mostly because of the second one. At airports where there are occasionally exceptions along the lines of those described above, they may also want a symbol to help pilots know when the exceptions are not in effect.

These symbols are intended for old-fashioned «airfields» which just have a large grass area instead of a runway. This used to be the norm before the increasing weight of aircraft in the Second World War. The whole surface of such a site is suitable for the movement of aircraft, so you don’t need to be on a particular runway or taxiway: you can just take-off and land in the wind direction.

This was the norm when the ICAO rules were drawn up, so the case of only being allowed to operate on a particular surface was the exception then, not the rule. The runway-only aerodromes probably wouldn’t have their grass in good condition, so it would be dangerous to land on grass: you might put your undercarriage in a rabbit hole. Back then, when most aircraft didn’t have radio, you would have needed a signal at the unusual runway-only aerodromes so that visiting pilots wouldn’t assume it was OK to land where they liked. The signal would more likely be a permanent fixture at these aerodromes, rather than something flown at particular times.

Nowadays, the only situation where this is common is in glider flying. At a popular glider site, there might be a hard runway provided for the tow airplane or for winch launches, but gliders can land anywhere on the aerodrome. Or there might be a marked (hard or grass) runway for take-off and landing, but no taxiways at all: you just vacate onto the grass. As Jay Carr points out, a fly-in or a gliding competition would be an example of when a particular aerodrome might change from one to the other, but that might go either way. The same aerodrome where normally everyone lands on grass might be worried about the condition of the grass at a high-traffic event (and about the safety implications of a variable landing direction), so they might have people stick to the runway for that one event.

From Wikipedia, the free encyclopedia

The application of railway signals on a rail layout is determined by various factors, principally the location of points of potential conflict, as well as the speed and frequency of trains and the movements they require to make.

Non-provision of signals

Before discussing the application of signals, it is useful to highlight some situations where signals are not required:

Purpose of signals

Signals exist primarily to pass instructions and information to drivers of passing trains. The driver interprets the signal’s indication and acts accordingly. The most important indication is ‘danger’, which means ‘stop’. Not every signal is equipped with a ‘danger’ aspect.

Protection of conflict points

Signals are provided where required to protect items of infrastructure where conflict may arise, including:

A signal cannot display a ‘proceed’ aspect unless the infrastructure item(s) that it protects are in the correct position for the passage of a train or, in the case of flat junctions and gauntlet track, no other signal is cleared for a conflicting move. This is enforced by interlocking.

Protection of following trains

Running lines (as distinct from sidings) are divided into sections. Under normal circumstances, only one train may occupy any section at a time. A signal is provided at the start of every section, which may only display a ‘proceed’ aspect when the section ahead is completely empty, at least as far as the next signal.

The length of the sections, and hence the distance between signals, determines the railway’s capacity. A railway with short sections can accommodate more traffic than one with long sections.

Signalling a layout

The provision of signals is dependent on the intended use of the layout and the movements that are expected to take place. It is not necessary to provide a signal for every conceivable movement that the layout physically permits. If, during perturbed working, a movement has to be made in a direction for which no signal is provided, this can be done under special instruction. The same applies during signal failure.

Signal categories

Main signal

A main signal controls a train movement along a running line main line. A ‘proceed’ aspect on a main signal indicates that the line is clear at least as far as the next signal, giving the driver confidence to run at speed. Trains running long distances, especially passenger trains, will usually travel throughout under the authority of a succession of main signals.

Shunting signal

A shunting signal controls low speed movements where provision of a main signal is not appropriate, such as moves into sidings. Clearance of a shunting signal does not necessarily imply that the line ahead is clear of vehicles. Shunting signals are often mounted at ground level and are smaller than main signals, reflecting their status.

Stop signal

A stop signal is one that is equipped to show a ‘danger’ aspect, which commands an approaching train to stop. Its function is to prevent conflict with other trains and to indicate that moveable infrastructure features are in the correct position. Depending on the manner in which they are used, and the nomenclature favoured by the railway administration concerned, stop signals may be further categorised as ‘home signals’ or ‘starting signals’, for example. Some stop signals are in the form of a fixed signal, generally a white board with a red solid circle. There is usually a panel underneath with instructions to the driver as to what circumstances he may pass the signal. Examples of such signals were used on lines signaled by the radio electronic token block system.

Distant signal

A distant signal is one that cannot display a ‘danger’ aspect. However, it is able to display a ‘caution’ aspect, which gives the driver advance warning that the stop signal ahead may be displaying ‘danger’. The distant signal is installed at roughly full braking distance on approach to the stop signal to which it applies, taking into account the gradient, the permitted speed, and the braking performance of trains. On sighting a ‘caution’ aspect, the driver must prepare to stop at the signal ahead. If the distant signal shows a ‘clear’ aspect, the train may maintain full speed. A single signal may be equipped to function both as a stop signal and a distant signal. Some distant signals are in the form of a ‘fixed distant’. That is: they only ever display a ‘caution’ aspect and never a ‘clear’ one. Such signals are usually in the form of a standard distant arm fixed in the horizontal position to the signal post. An alternate form is a picture of a horizontal distant arm painted onto a white board.

Permissive signal

The ‘danger’ aspect of a permissive stop signal means «stop and proceed». Drivers are permitted to pass the signal at ‘danger’ under their own authority, in accordance with the rules, after first coming to a stand.

Subsidiary signal

A subsidiary signal permits movements onto a portion of track that is already occupied. These are commonly used at terminal stations to permit two or more trains to enter a single platform.

Junction signalling

The driver of a train approaching a diverging junction needs to know which route the train will take, so that its speed can be regulated accordingly. A diverging route might have a significantly lower permissible speed than the main route, and if the route taken was not the one expected, it could result in derailment.

There are two methods of junction signalling. Signalling in the UK uses route signalling. Most railway systems around the world, however, use speed signalling.

Under route signalling, the driver is informed which route has been set by an illuminated Junction Indicator mounted on the signal post. The signal will display a restrictive aspect to make the driver reduce the train’s speed. Once the train has slowed down to the required speed the next signal may step up to a clear aspect, but the driver must be prepared to slow down further if it does not.

Under speed signalling, the driver is not told which route the train will take, but the signal aspect informs him at what speed he may proceed. Speed signalling requires a far greater range of signal aspects than route signalling, but less dependence is placed on drivers’ route knowledge.

Bidirectional signalling

Many double or multiple track railways have a designated direction of travel assigned to each track. Signals will only be installed to permit traffic to flow in one direction on each line (i.e. uni-directional signalling).

Bidirectional signalling is the provision of signalling that allows one or more tracks on a multiple track railway to be operated in either direction, whether for regular or emergency use. Bidirectional signalling intended for regular use will generally allow traffic to flow at similarly high frequency in one or other direction. If intended for emergency use, running in the opposite direction might only be possible at reduced frequency. Typically, ‘reduced capacity’ bidirectional signalling only provides a signalled route onto and off the other line for ‘wrong’ direction running, without any intermediate stop signals that would improve capacity.

Bidirectional signalling is more expensive to implement as it requires more equipment than uni-directional operation, so it is not always provided. In the absence of bidirectional signalling, ‘wrong direction’ movements may still be made on a uni-directional line at times of disruption, through a procedure known as single line working.

Bidirectional signalling is easier to implement when under the control of one signal box. Before power-operated signalling became widespread, track layouts tended to be designed to avoid bidirectional arrangements as much as possible.

Single track railways must necessarily have signals for both directions.

Signals for special purposes

Train order signal

Used in conjunction with the American train order system, a train order signal advises the engineer of the need to pick up a train order at a station.

Hump shunting signal

In a hump yard, special signals may control the speed of trains propelling vehicles towards the hump.

Loading and unloading signals

Signals may be installed to control the movement of freight trains through a facility for loading or unloading minerals, for example coal. Unlike ordinary signals, there may be a series of identical signals installed along the track so that at least one is always visible to the train driver at any time. All signals in the same group display the same indication simultaneously. A ‘stop’ indication means «stop immediately«, even if the train is not at the signal. The signals can also instruct a train to reverse.