This document discusses railway signaling and control systems. It begins by outlining the objectives of signaling such as regulating train movement safely and efficiently. Signals are then classified based on their characteristics as either audible (detonators) or visible (hand signals, fixed signals). Fixed signals include semaphore signals which use arm positions and colors to convey stop/proceed instructions. Permissive signals provide advance warning to drivers before stopping. Modern colored light signals use green, yellow and red lights to indicate track conditions both day and night in a way that ensures only one aspect is displayed at a time. The document focuses on different signal types, their purposes in controlling train movement, and maintaining safety.

1. Unit 3- Signaling & Control Systems
Lecture 3.1
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Objectives; Principles of signaling; Classification and types of
signals; Control of movement of trains and monitoring; Track
circuiting; Interlocking of signals & points: necessity and
functions, methods of interlocking, devices for interlocking
(names & figures)

2. Signaling
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Signalling consists of the systems, devices and means by
which trains are operated efficiently and tracks are used to
maximum extent, maintaining the safety of the passengers,
the staff and the rolling stock.

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Need/Objectives of Signalling
The purpose of signalling and interlocking is primarily to control
and regulate the movement of trains safely and efficiently.
(a) To regulate the movement of trains so that they run safely at
maximum permissible speeds.
(b) To maintain a safe distance between trains that are running
on the same line in the same direction.
(c) To ensure the safety of two or more trains that have to cross
or approach each other.
(d) To provide facilities for safe and efficient shunting.

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Objectives of Signalling
(e) To regulate the arrival and departure of trains from the
station yard.
(f) To guide the trains to run at restricted speeds during the
maintenance and repair of tracks.
(g) To ensure the safety of the train when it comes in contact
with road traffic at level crossings.

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Classification of Signals
Railway signals can be classified based on different characteristics as below
Audible-Detonators
Visual-Hand signal, fixed signal

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Classification of Signals
Characteristics
of operational
Signals-
audible and
visible signals.

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Classification of Signals
Audible Signals- (Also called detonating signals) are such as
detonators and fog signals placed on the rails in cloudy and foggy weather
when hand or fixed signals are not visible.
-sound of detonator draws attention of the
driver to the proximity of the signals.
They are placed 400-500m ahead of the
signal to enable the driver to stop the train.
Visible Signals-
These signals are visible and draw the attention of the drivers because of
their strategic positions.
1. Hand signals
2. Fixed signals

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Classification of Signals
Visible Signals-
1. Hand signals- done manually, given by flag or during night
using lamps with movable glass , guards or station master,
cabin man gives it. Red flag- STOP, Green flag- proceed, yellow-
proceed cautiously
2. Fixed signals

9. Functional characteristics-Fixed signals
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10. Functional characteristics-Fixed signals
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STOP or SEMAPHORE SIGNAL
The principle of design of semaphore signals is to show the stop
position of any failure that happens to be in the apparatus.
The signal mechanism is so arranged that in normal position it
indicates the Stop position.

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Fixed Signals
Semaphore signals-Greek word-
Sema' means sign and 'phor' means
to bear.
A semaphore signal consists of a
movable arm pivoted on a vertical
post through a horizontal pin as
shown in Fig.
Semaphore stop signals are normally
provided as outer signals, home
signals, starter signals, advanced
starter signals, and warner signals.

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Fixed Signals-
Semaphore signals-
• Lower quadrant semaphore signals
move only in the fourth quadrant
of a circle and have only two colour
aspects.
• In order to provide the drivers with
further information, multi-aspect
upper quadrant signalling (MAUQ)
is sometimes used on busy routes.
• These signals are operated by hand
levers or buttons located in a
central cabin near station master.

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Stop signal in MAUQ, Signaling-
In this system, the arms of the
semaphore signals rest in three positions and
the signals have three colour aspects, namely
red, yellow, and green associated with the
horizontal, 45° above horizontal and vertical
directions, respectively.
Fixed Signals- Semaphore signals-

14. Permissive signal/ warner
or distant signal
• In order to ensure that trains
speed up safely, it is considered
necessary that warning be given
to drivers before they approach a
stop signal.
• In the case of a stop signal, the
driver has to stop the train when it
is in the ‘on’ position, but in the
case of a permissive signal, the
driver can pass through even
when it is in the ‘on’ position.
• The warner signal is similar to
semaphore signal in shape except
a v-notch at free end.
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15. Permissive signal/
warner or distant signal
• Permissive signal—warner
Placed below outer signal
• In case a warner is fixed below
an outer signal the various
positions of the outer and
warner signals and their
corresponding indications are
given in Fig.
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• These signals use coloured lights to indicate track conditions to the driver both
during the day and the night. The lights are fixed on a vertical post in such a way
that they are in line with the driver’s eye level.
• The system of interlocking is so arranged that only one aspect is displayed at a
time. Coloured light signals are normally used in suburban sections and sections
with a high traffic density. Coloured light signals can be of the following types.
Two-aspect, namely, green and red
(b) Three-aspect, namely, green, yellow, and red
(c) Four-aspect, namely, green, yellow (twice), and red.
• In India, mostly three-aspect or four-aspect coloured light signalling is used. In
the case of three-aspect signalling, green, yellow, and red lights are used.
• Green indicates ‘proceed’, yellow indicates ‘proceed with caution’, and red
indicates ‘stop’
Coloured light signals

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Coloured light signals