4.1 Automatic Signals
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Automatic Signals can be identified by the circular number plate bearing the distinctive number of that signal post and the gray color mast. They may contain one, two or three aspects of one or more units. Only one aspect can be lit in a unit at a given time. The automatic signals are approach lit; i.e. light up only when a train approaches. This arrangement is used to conserve power. The automatic signals operates according to the track conditions ahead and are not controlled by the controller.

4.1.1 Automatic Block Signal

Automatic block signaling is used to control trains between two stations. A detailed discussion about automatic block signals  can be found here. These signals have one unit of three aspects and have the following meanings:

RED Danger; train on immediate block
AMBER  Caution; train on the block after the next, prepare to stop at the next signal
GREEN Proceed:  line clear for the next two or more blocks

4.1.2 Automatic Approach Signal

These signals are placed immediately before the controlled signals. These signals have one unit with three aspects on the main post and  another unit with two aspects on a support bracket below the main unit.

These signals indicate that a controlled signal is being reached and show the route that will be taken at a controlled speed. These are also called distance signals or outer home signals.  The aspects of the signals are as follows.

RED Danger;  train on the section ahead
AMBER over AMBER  Caution;  controlled signal ahead is Danger
AMBER over GREEN Proceed;  going on the loop line
GREEN over AMBER Proceed;  going on the main line

The upper unit (three aspects) refers to the main line and the lower unit refers to the loop line.


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[ 4.1 Automatic Signals ] 4.2 Controlled Signals ] 4.3 Call-on Signal ] 4.4 Typical Signal Layout ]

R. Jayanthan
Last updated on 01 January, 2002