Signal Aspects and Indications — Subsidiary Signals and Indicators


Main Signal Aspects and Indications are dealt in a separate section .

Calling-on signals

A calling-on signal is used to allow a loco or train to move into a block section or a track within station limits, which is or may be already be occupied by another train or loco. This is done for the purposes of coupling trains, for a train to enter a track for a long platform which already has another train stopped at it, for a train to enter station limits and wait behind another train on the section (thereby clearing the block section to the rear for another train to be received from the station in the rear), etc.

It always occurs in combination with a stop signal. It has only two positions, on and off. When on, the indication of the stop signal applies. The calling-on signal can be off when the stop signal is at Stop; this shows the indication of Proceed Slow, which allows the train to pass the signal at low speed, after stopping, being prepared to stop for any vehicle or obstruction ahead of it on the same track.

In suburban sections a calling-on signal is sometimes used to allow EMU trains to proceed with caution on to a section of track occupied by another train. Often, there is electrical circuitry in the tracks to ensure that the calling-on signal does not change to off unless the train has come to a complete halt first. A calling-on signal may in some circumstances also be used to allow a train to pass a defective stop signal.

The calling-on signal is not pulled off when the stop signal is not on; and if a shunt signal is on the same pole below it, the shunt signal and calling-on signal cannot be pulled off at the same time.

Semaphore: A calling-on signal uses a miniature semaphore arm which is square-ended, and which is white in front with a red stripe near the end, and white in the back with a black stripe near the end. In 2LQ and MLQ territory, the calling-on signal also works in the lower quadrant: on is horizontal, off is dropped by 60 degrees or so.

At night there is no lamp shown for the on position, and a miniature yellow lamp is shown for the off position. In MAUQ territory the calling-on signal works in two positions in the upper quadrant: (on is horizontal as usual (no lamp at night), off is at about 45 degrees above the horizontal (yellow lamp at night). The calling-on signal is always placed below the stop signal on the same pole. Semaphore calling-on aspects are shown below.

LQ Calling-on signals

 

MAUQ Calling-on signals

 

Colour-light: The calling-on signal consists of a single yellow lamp placed below the stop signal (2-, 3-, or 4-aspect) on the same post. It is lit only for the off position. A small circular plate marked "C" (black on white) is fixed to the post below the signal. Colour-light calling-on aspects are shown below.

Color light calling-on signals

Shunting signals and indicators

Shunt signals control shunting movements. A shunt signal may be placed on its own post or on the same post as a stop signal. If a calling-on signal is also placed on the same post, the shunt signal appears below the calling-on signal. A shunt signal has two indications; when on the indication of the stop signal applies, and when off, the indication is Proceed Slow for Shunting, which allows a loco to proceed past the signal with caution for shunting purposes.

A shunt signal mounted below a stop signal cannot be pulled off when the stop signal is not on. If a calling-on signal is also on the same post, the shunt signal cannot be pulled off at the same time as the calling-on signal. Even when a stop signal or shunt signal is pulled off, shunting operations are normally done only at a speed of at most 15km/h, and much lower depending on the composition of the shunted rake (some BOX / BOB wagons cannot be shunted at more than 5km/h singly or in small groups, and with transition couplers the limit is just 2km/h).

Multiple shunt signals may be mounted on the same post. In that case, the highest of them applies to the leftmost of the diverging routes, and the ones below it apply to successive routes moving to the right. However, just one shunt signal, with or without a route indicator, may be provided for diverging routes.

Disc: Disc signals used for shunting show a red stripe on a white background. (Black stripe on white background from the rear.) Aspects: The red stripe is horizontal for the on position and inclined at an angle for the off position. The inclination is upwards to the left in upper-quadrant or MACL territory, and downwards to the left for lower-quadrant or 2CL territory. Generally disc signals are used in semaphore territory. The aspects are as shown below.

LQ shunt signals

 

MAUQ shunt signals

 

Position-light: The most common position-light signals used for shunting show two white or yellow lights arranged horizontally for the on position, and two lights at an angle (the one to the left being higher) for the off position. These aspects are shown below.

2 aspect position light signals

 

3-aspect position-light signals: Some position-light signals used for shunting show three white (or yellow) lights arranged horizontally for the on position, three lights at an angle (sloping down to the right) for the proceed slow for shunting indication, and three lights in a vertical line for the proceed for shunting indication. These aspects are shown below.

3 aspect position light shunt signals

 

Semaphore: These are miniature semaphores, square-ended and coloured red with a white stripe at the end in the front (and white with a black stripe on the reverse side). They work in the lower quadrant in lower quadrant territory and in the upper quadrant in upper quadrant or MACL territory. In all, the horizontal position is on and the inclined position is off.

Except for the position-light signals, the others show their indications at night as follows: For the on position, the shunt signal shows no light if it is mounted on a post with a stop signal above it, and a red light if it is on its own post. For the off position, a green lamp is lit in 2-aspect territory, and a yellow lamp is lit in multiple-aspect territory.

A double-red colour-light signal, permanently lit, is sometimes used to indicate the shunting limit on a particular line. (It is more common to have a shunting limit board; see the section on signs). The double-red signal is used when it is especially important that no trains accidentally pass it -- e.g., at busy suburban stations with many automatic and semi-automatic signals which can normally be passed after halting for a specified time, hence a single red signal cannot be used. Normally the double-red signal also carries a board that says 'STOP'.

Shunt permission indicators

A Shunt permission indicator is used to indicate uninterrupted shunting movements past the indicator, in one or both directions.

Target signal: When shunting is permitted, a black disc with a yellow cross on it is visible from the direction(s) from which shunting is permitted; if shunting is not permitted, the discs of the signal are edge-on. At night, when shunting is permitted a yellow cross-shaped light is visible, and no light is visible otherwise.

Lamp: A lamp close to ground level may also be used. It displays a yellow cross-shaped light when lit to indicate shunting permitted, and no light if shunting is not permitted.

Points indicators

Points indicator
Points indicator
(Click for a larger view.)

Where points are not interlocked with signals, and there are no other indications to a driver of the position of facing points, a point indicator signal is used. This is always of the target type, placed close to ground level, which shows a white disc (white lamp at night) when the points are set for the main or straight-ahead line. When the points are set for a divergence, the disc is edge-on (and a green lamp is lit at night). In some cases where a green lamp might be confusing, a red lamp may (rarely) be used.

Trap indicators

Where points are not interlocked with signals, and there are no other indications to a driver of the position of facing points, a point indicator signal is used. This is always of the target type, placed close to ground level, which shows a white disc (white lamp at night) when the points are set for the main or straight-ahead line. When the points are set for a divergence, the disc is edge-on (and a green lamp is lit at night). In some cases where a green lamp might be confusing, a red lamp may (rarely) be used.

Repeaters

A repeating signal or repeater is one placed to the rear of a signal in order to provide early indication of the indication of the signal. It is an advisory signal and therefore permissive and may always be passed. A repeater has only two positions, on and off. In the on position it indicates that the signal ahead which it repeats is in the on position or most restrictive indication. In the off position it indicates that the signal ahead which it repeats is off, i.e., not on (but not necessarily clear).

Banner or Disc: A disc type repeater consists of a white disc with a band across it that consists of three parallel stripes: black, yellow, and black. (This is also known as a banner signal in IR terminology.) The band is horizontal for on and inclined (upwards to the left) for off. A circular plate with "R" on it (black on white) is fixed below it to the post. Banner signals usually don't have lamps for indication at night, but where provided the on indication is given by a yellow lamp and the off indication by a green lamp.

Disc repeaters

 

Semaphore: This has a square-ended arm which is yellow with a black stripe at the end in front (and white with a black stripe near the end in the rear). This is used in 2-aspect territory, and works in the lower quadrant; horizontal for on and inclined downward for off. A circular plate marked "R" (black on white) is fixed to the post below it. At night, a yellow lamp is shown for on and a green lamp for off.

semaphore repeaters

 

Colour-light: This has two lamps, green above yellow. The yellow lamp is lit for on and the green one for off. A circular plate marked "R" (white on black) is fixed to the post below the signal.

color light repeaters

 

Konkan Railway uses repeater signals that are different from those on the rest of IR. These are 2-lamp assemblies, with lenses about the size of a shunt signal, placed close to the ground. There is a red lamp below a green lamp. The red lamp is is lit for on and the green one for off.

A starter indicator is a special type of repeater provided to show the indication of a starter signal to the guard of a train who, being at the rear of a train, may not be in a position to see the starter signal directly. It consists of a single miniature yellow lamp which is lit when the starter is off and unlit when the starter is on. It may have additional lamps showing signs such as "M" (mainline) "B" (branch) to indicate the particular track for which the points have been set.

Unusual signalling situations

Signals that control access to some bridges or other structures sometimes have additional interlocking with devices that ensure safety. For instance, the Pamban sea bridge (Manmadurai - Rameshwaram section) has a lower quadrant semaphore signal that controls access to the bridge. This signal is coupled with a wind speed measuring device that tracks the wind over the bridge, and does not allow the signal to be pulled off even if the station clears the signal, if the wind speed is too high. In case the device is suspected to have failed, the station master is supposed to ensure that wind speeds are not abnormal, and then issue written authority to trains to pass the signal at danger. There is (was?) another similar signal just before Kudalasangama Road Station (?) on the Bagalkot-Bijapur MG section between Gadag and Solapur set up to be dependent on the wind speed across the Krishna river (Upper Krishna project).

Home signals without loop line indication

Some stations on the Maliladuthurai-Tiruvarur-Karikudi (MG) section in lower quadrant semaphore territory have outer and home signals that control access to the station limits, but do not provide any indication of which line (main line or loop line) the train will be received on. A single home signal is provided, not the usual combination of a main line signal placed at an elevation with respect to the loop line signal. The driver of the train with a clear signal is expected to slow down to about 15km/h or less near the diverging points and examine the points indicator at ground level. A green display (edge-on) indicates the points have been set for the loop line and a white display (face-on) indicates the points have been set for the main line. Depending on this the driver adjusts his speed to proceed (at normal speed if on the main line, reduced speed for the loop line). As there is no interlocking, pointsmen usually wait near the points to ensure the points are set correctly, and sometimes provide additional hand signals to the driver.

The same stations as mentioned above also are notable for not having starter or advanced starter signals. Tangible authority to proceed in the form of a Neale's ball token or paper line clear certificate is sufficient for the train to proceed to the next block section, except if stopping at the station in which case the guard's signal is required.

Starter signals shared by lines: Thiruturipondi station has two lines (for two platforms) and is also a junction with lines diverging to Karikudi and Agaisthianpalli. The platform lines share a common starter signal; nor does the signal indicate which route the points are set for. Hence, drivers of trains awaiting departure at the platforms are expected to first obtain tangible authority to proceed (Neale's ball token or paper line clear ticket), and additionally, specific written authority to proceed which mentions that the starter signal that is pulled off is intended for that particular train on that line and headed on one route or another.


Return to the section the principal running signal aspects and indications.

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