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
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:
||train on immediate block
||train on the block after the next, prepare to stop at the next signal
||line clear for the next two or more blocks
4.1.2 Automatic Approach Signal
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
||train on the section ahead
|AMBER over AMBER
||controlled signal ahead is Danger
|AMBER over GREEN
||going on the loop line
|GREEN over AMBER
||going on the main line
The upper unit (three aspects) refers to the main line and the lower unit
refers to the loop line.