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Signal Aspects and Indications — Principal Running Signals

General information on signalling systems is found in another section. This section focuses on the main running signals and the aspects they display.

Stop signals

A stop signal governs access to a block section and ordinarily may not be passed when it is at its most restrictive indication (the on position, which shows the stop or danger indication for these signals). That is to say, when on, its interpretation is 'stop dead'.

Under some special circumstances, a stop signal may be passed at slow speed after the train has been brought to a standstill at the rear of the signal. This is commonly allowed in automatic block territory where the driver can proceed after waiting for a minute or two. In most other cases, the driver must obtain permission to proceed over a telephone callbox at the signal, or must have written authorization to ignore or pass the signal.

Automatic stop signals and delayed stop signals (see the section on block working) are provided with a circular plate marked 'A' (black on white)

Semaphore: The semaphore arm of a stop signal is red in front with a white stripe near the end, and white in the back with a black stripe near the end. The arm is square-ended. Signal aspects are as shown below.

 

Colour-light: The stop signal may have two (green above red), three (green-yellow-red), or four lamps (yellow-green-yellow-red) as described above. Aspects are as shown below.

 

Stop signal indication summary:

Usually the signals are set up at sufficient distances so that, for instance, a train arriving at a Caution signal at the maximum speed for the section can safely brake to a halt before the next signal which is at Stop. Older locos especially hauling vacuum-braked rakes or long freight rakes should be able to slow down sufficiently when they reach a signal at Attention so as to be able to halt after reaching the next signal at Caution; but the newer locos hauling air-braked rakes can reach a signal at Attention at the maximum speed for the section and proceed through it without slowing down and still brake safely if the next signal is at Caution.

If the distance between the signal at Caution and the signal at danger is less than the safe braking distance, the signal to the rear displaying Attention also serves to alert the driver that the train may have to be slowed to restricted speed when it reaches the next signal.

A signal that is to the rear of a signal protecting a divergence cannot show an indication less restrictive than Caution or Attention when the points are set at the divergence for any line other than the main line. (The divergence should normally also be indicated by the use of a route indicator.) This Caution or Attention indication may be repeated further in the rear if the distance to the divergence is insufficient to permit a train to slow down to the appropriate speed for the divergence. The Caution indication is also used to indicate track sections with speed restrictions. The Attention indication may correspondingly be displayed by the signal to the rear of the signal guarding the approach to a curve or a divergence or section with speed restrictions.

The starter signal (see below) may show Attention or Caution to provide permission for a train to leave a station, instead of the Proceed indication.

Stop signals are of the following types:

Home

This is the first stop signal on approach to a station without an outer home signal. It is not optional. The signal guards entry to the station limits ahead from the block section in the rear and appears before all connections to the line (branches, loops, etc.) at the station.

A home signal at Caution indicates that the train may have to stop on the line before leaving the block, or that the train has to slow down to a particular speed in order for the starter signal at the entrance to the next block to shift to Proceed. A home signal is also set at Caution for temporary or permanent speed restrictions within station limits. An optional (electric) numeric display on the post of this signal is usually an indication of the platform to which the train will be routed.

For stations with multiple lines where a train may be received (i.e., main running line and loop lines), normally home signals are provided either in sets in semaphore signalling (as many as the number of receiving lines), or with route indicators ('feathers') in colour-light signalling, just before the diverging points to the various lines, to indicate for which line the points have been set for the train to be received. In semaphore signalling, the main line home signal is placed above any others; the lower signals refer to lines diverging to the left or right of the main line according to their position with respect to the main signal.

Outer (Outer Home)

To increase track utilization, or to provide better control over approach to station limits, additional signals may be provided to the rear of the Home signal. An Outer Home signal (also known simply as an Outer), to the rear of the home signal, is very common. The outer may be at Caution to indicate speed restrictions further ahead, or if the home signal is at Stop.

Intermediate home

Intermediate home signals may be provided between the outer and home in some cases to provide finer control over train movements on approach to station limits.

Intermediate block

his stop signal is provided on intermediate block sections which are block sections created by subdividing a long block section between stations; there isn't necessarily a separate station or route junction at the point. (If there is a station, it is an intermediate block post or halt station.) An intermediate block signal simply protects the block section ahead of it in a manner similar to a starter signal. A circular marker with 'IB' (black on white) is fixed to the post below the signal. The signal is controlled by the cabin of the station to the rear if the intermediate block post is not manned.

Routing

This indicates which of two or more diverging routes have been set, especially in cases where the corresponding Home or Outer or other stop signals before the facing points do not provide such indication.

Starter

This governs exit from the most advanced section within station limits, and entrance to the block section ahead. Normally it is the last stop signal on departing from a station unless an advanced starter is present. If an advanced starter is provided, the starter may protect facing points to another running line at the same station. Starter signals are provided at most stations, but there are some without them. If the starter is not provided station working rules prescribe when trains may proceed to the next block section; usually tangible authority to proceed such as a Neale's ball token or paper line clear ticket are needed.

If a starter is provided for each of several converging lines exiting a station, they are provided so as to protect each line from fouling the adjacent lines. If a single starter is provided for several converging lines exiting a station, it is placed beyond the trailing points of the convergences. In some areas, a starter signal may be set up so that it does not shift to the Proceed indication unless the train slows down to a particular speed (or stops) before reaching it (in such cases the home signal at the entrance to the block is usually at Caution). Shunting cannot take place without special instructions beyond the starter if it is the last stop signal at the station.

Normally the starter signal shows a 'Proceed' indication (green signal) to indicate that a train may leave the station, but in some cases an 'Attention' or 'Caution' indication (double yellow / yellow) may be used to allow the train to leave the station (and make the platform available for another train) but at a reduced speed. On Konkan Railway lines it has been observed [4/01] that the 'Attention' indication (double yellow) is routinely used for the starter signal.

A starter signal may have additional lamps or signs such as 'M', 'B', etc. to indicate which tracks the train will depart on (mainline, branch line, etc.).

Advanced Starter

This is an optional signal. It is a stop signal provided ahead of the starter signal, and therefore if present it is the last stop signal on departing station limits. The advanced starter allows shunting operations beyond the starter. Normally shunting may not take place beyond the advanced starter. Otherwise the advanced starter, if present, functions just like the starter signal to control exit from station limits and entrance to the block section ahead. It is placed ahead of all trailing points for converging lines exiting the station.

Intermediate starter

Intermediate starters may be provided between the starter and advanced starter to split up the section into smaller sub-sections and provide finer control over train movements and shunting operations. Intermediate starters are placed to the rear of the fouling points of the points they protect.

Gate

A gate stop signal guards interlocked (or sometimes non-interlocked) gates at level crossings. A circular plate marked 'G' (black on yellow) is fixed on the post below the signal. A gate signal may be passed after the train comes to a standstill to the rear of the signal and after waiting for a minute or two. The train may then proceed slowly up to the level crossing, and must then wait for the gateman to direct the train across the level crossing with hand signals.

A gate signal may be placed on the same post as an outer signal, or the two may be combined. If an outer signal is ahead of the gate signal and there is insufficient visibility of the outer signal, the gate signal and the outer signal can be slotted to work together so that the gate signal is never pulled off when the outer is on. In such situations, the distant signal pertaining to the outer home acts as the gate distant.

Note: In very rare instances, if the distance between stations is really short, and the station to the rear needs an advanced starter which would appear in about the same place that the outer home for the station ahead, the two may be combined into one stop signal controlled from both stations. Thus the train effectively moves directly from the station limits of one station into the station limits of the next.

Note: For class 'C' stations, the Home signal is both the first stop signal and the last stop signal, as starter signals are usually not provided.

Warner Signals

A warner signal is used only in two-aspect signalling (2LQ, MLQ, 2CL). Its purpose is to warn of an approach to a stop signal further ahead, or to advise a driver of the condition of the block section being entered. As such, it is a permissive signal and may be passed when it is in its most restrictive (on) indication, although when it is on the train must reduce speed.

A warner is always set to the on position for a train which is scheduled to stop ahead at the station. A warner may also be provided in 2-aspect territory on the approach to a gate stop signal. Normally warners are pulled off only when the stop signal they refer to is pulled for the main line (highest permissible speed), and not if a stop signal for a divergence is pulled off. There are some other considerations, see below.

Combination Warner

The warner is often paired with a stop signal (for example, an outer-warner combination is very common), in which case the warner's indication is never less restrictive than that of the stop signal, and if the stop signal is on, the combination cannot be passed. When the stop signal and the warner are both clear (in the case of outer home signals this is known as 'home double' or 'double home'), the signal may be passed at the maximum speed for that section.

In a combination warner, the stop signal may show Proceed and the warner may be on, to indicate that the next stop signal ahead (usually the home signal, in the case of an outer+warner combination) is on (at Stop).

In some cases, the warner may not be pulled off (see distance considerations below) at all. Allowed combinations are outer+warner, starter+warner (if no advanced starter), or last stop signal + warner (i.e., advanced starter + warner). The mechanical interconnection between the stop signal and the warner in semaphore signalling, which prevents the warner from being less restrictive than the stop signal is known as slotting.

Lone Warner

If the warner is by itself, a fixed green lamp is usually placed above it on the same mast (so that technically it is equivalent to a warner below a stop signal which is always clear).

Unworked warners

A warner signal may be set up to be permanently in the on position (caution indication). In this case the warner merely advises the driver of a train of the approach to a stop signal ahead or possibly a permanent restriction or problem with the track ahead.

Illustrations covering aspects in both semaphore and color-light systems are shown below.

Semaphore: The semaphore arm of a warner signal has a vee-notch at the end; it is red in front with a white stripe (V-shaped) at the end, and white at the back with a black stripe (V-shaped) at the end. Aspects are as shown below.

 

Colour-light: The warner consists of a two-lamp signal (green above red) fixed below the (2-aspect) stop signal on the same post. A warner without a stop signal has a single green lamp (always lit) above it on the same post, and a small circular plate marked 'P' (black on white) below it.

 

Warner signal indication summary:

Distant Signals

A distant signal (also known as a pre-warner) indicates approach to a more restrictive signal further ahead. In IR terminology, the distant is said to 'pre-warn' the driver of the indication of the next signal ahead. Examples: The distant signal shows Caution, and the next stop signal ahead is at Stop. Or, the distant signal shows Attention, and the next stop signal is at Caution.

A distant signal may be at Attention if the following signals guard a divergence and the points there are set for a route other than the main line. A distant signal to the rear of signals at a divergence will be at Proceed if the points are set for the main line at the divergence. In that case, the stop signal for the main line may be at Caution. Of course, both the distant and the next stop signal may be at Proceed.

A distant signal is a permissive signal and may always be passed even in its most restrictive indication. A distant signal is analogous to a distant signal that occurs by itself in UK practice. A distant signal is typically at a distance of 1km or so from the stop signal it protects, but this may vary depending on the particular track requirements.

Outer and Inner distants

In some sections two distant signals may be provided to the rear of a stop signal. In that case, the one further to the rear of the stop signal is known as the outer distant or the second distant, or simply as just the distant signal and the one just before the stop signal is known as the inner distant signal. In such a case, the outer distant can only show two indications, Attention and Proceed, while the inner distant can show Caution as well. Two distants are standard on routes with speeds above 100km/h and where goods trains run which require braking distances over 1km.

A distant signal is usually placed far enough (2km or so) to the rear of the stop signal it protects that when it is at Caution a train at the maximum speed for the section can brake safely to a halt before the stop signal. Otherwise, the Caution indication may be replicated further back by using more than one distant until the rearmost distant at Caution is at sufficient distance from the stop signal.

Gate distant

Distant signals may also be provided to the rear of gate signals, in which case they are known as gate distant signals and have the 'G' marker just like gate stop signals. However, a distant signal may act as a distant signal for both a normal stop signal as well as a gate signal.

n rare cases distant signals may be mounted on the same mast as the last stop signal of a station or a gate stop signal. In such cases the distant signal operates with the additional restriction that its indication can never be less restrictive than that of the stop signal.

A distant signal showing the Proceed indication (clear) is also known as a 'distant green' from its colour-light indication.

Illustrations covering aspects in both semaphore and color-light systems are shown below.

Semaphore: A distant signal has a vee-notch at the end; it is yellow in front with a black stripe (V-shaped) at the end, and white at the back with a black stripe (V-shaped) at the end. At Caution and Attention the semaphore spectacle displays a yellow lamp at night; for the Proceed indication a green lamp is displayed. In upper quadrant territory, an additional yellow light is placed below the signal, on the same post, and is lit when the distant is in the Attention indication, so that at night two yellow lamps are seen.

 

 

Colour-light: Distant signals have a small circular plate marked 'P' (black on white) mounted on the same post, below the signal (this marker is omitted if the distant signal is mounted on the same post as the last stop signal for a station). The signal itself has 3 lamps, of which the top and bottom are yellow. Aspects: For Caution only the bottom lamp is lit; for Attention both yellow lamps are lit, and for Proceed just the green lamp is lit. The aspects are shown below.

 

Distant signal indication summary:

Placement of Signals

Visibility requirements

Two-aspect signalling: Outer signals have to be visible for 1200m if train speeds exceed 100km/h; 800m otherwise. If a warner signal is provided to the rear of the outer signal, the visibility can be 400m. Lone warners, home signals, and main starter signals must have a visibility of 400m. All other running signals have to be visible for at least 200m. When this cannot be complied with, repeating signals are provided.

3- or 4-aspect signalling: All running signals must be visible for at least 200m. If this is not possible speed restrictions are imposed to the rear of the signal for which visibility is impaired, and repeating signals may also be provided.

Distance requirements

Outer and home signals: In lower-quadrant territory, the outer signal, or the home signal if no outer home is provided, is at least 400m to the rear of clearing point for the tracks it guards. In modified lower-quadrant, upper-quadrant, and MACL systems, the distance requirement is 180m. If outer signals are near interlocked level-crossing gates, usually they are placed 400m to the rear of the gates in lower-quadrant signalling (180m in other systems).

Starter signals are usually at least 400m ahead of home signals. In lower quadrant territory, an advanced starter is at least 180m ahead of the outermost trailing points for converging lines exiting the station on single line sections; and 180m ahead of the starter on double-line sections (corresponding distances are 120m in modified lower-quadrant, upper-quadrant, and MACL signalling).

Gate signals in lower-quadrant territory are placed at least 400m to the rear of the gates they protect (180m in upper-quadrant and MACL signalling).

Warner signals – distance considerations: If a warner is to the rear of a gate stop signal, it is usually never pulled off unless the first stop signal of the next station is at least 1200m ahead of the gate stop signal, regardless of the indication of the gate stop signal. If a warner is provided in a station whose last stop signal is less than 1200m to the rear of the first stop signal of the next station, the warner is pulled off only when the first stop signal of the next station is pulled off.

Distant signals – distance considerations: As above for warners, but the distance in question is 1km instead of 1200m.

Q. What signals are provided at different kinds of stations?

Generally, fixed signals have to be provided at all block stations (i.e., classes A, B, and C), except those operating trains under the One Train Only system. The minimal signal provisions for block stations with manual absolute block working are described here. Additional signals may be always be provided based on local requirements. Note that the requirements below are for each direction of approach to the station.

In automatic block working, manually operated Home and Starter signals are provided at a block station. Minimally, an automatic stop signal is also provided to the rear of the Home signal. Additional automatic stop signals may be provided between any two block stations.

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Continue to the section on aspects and indications of subsidiary signals.

Related Sections

• Signalling Systems
• Signal Aspects and Indications: Subsidiary signals
• Train Working Systems
• Signs and Symbols
• Whistle Codes
• Hand & Flag Signals

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• Wikipedia: Railway signalling

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