Page 474 - IRSEM_Main Book

Chapter 20: Automatic Block Signalling

Section 1: Automatic Signalling - General

20.1.1 Automatic Block System on Double Line/Single Line: General

(a) Automatic Block is a system in which the movement of trains is controlled by
Stop Signals which are operated automatically by the passage of trains past
the Signals.
(b) The automatic Stop Signal which governs entry of Train into an Automatic
Signalling section is a multiple aspect colour light signal which is not
dependent upon manual operation but is controlled automatically by the
passage of a train into, through and out of the Automatic Signalling section
which the Signal governs.

(c) The line between two adjacent crossing stations shall be divided into a
series of Signalling sections and entry into each signalling section shall be
controlled by a Manual Stop Signal or an Automatic Stop Signal or a Semi-
Automatic Stop Signal which must assume 'ON' position on entry of a train
into the section and be maintained in that position until the train has passed
clear of the next Automatic Stop Signal in advance and also for an adequate
distance beyond it.

(d) No automatic signal shall assume 'OFF' position unless the Line is clear not
only up to the next Stop Signal in advance but also for an adequate distance
beyond it. Except under approved special instructions, this adequate distance
shall not be less than;
(i) 120 meters, if next Stop signal in advance is an automatic signal.

(ii) 180 meters, if *next Stop signal in advance is a Manual stop signal or
Semi-automatic signal.
(*Note: if such signal is a Home signal or LC gate signal)

(e) Signals shall be so spaced as to meet the operational requirements of the
section. At the same time the distance between signals shall not be so high
as to cause serious repercussions during failures or so small as to provide
inadequate braking distance. If the distance between the Caution and Stop
Aspects in the case of three aspect signalling or Attention and Stop Aspects in
the case of four aspect signalling, is less than the Emergency braking
distance of a train, the speed of that train shall be so regulated as to bring
the Emergency braking distance within the above mentioned signal spacing.

(f) The Signal that governs entry into the Block section shall be Manual or
Semi-Automatic Stop Signal, which are explained below.

20.1.2 Manual Stop Signals and Semi-Automatic Stop Signals

(a) Manual Stop Signals: Fixed Signals which require manual control each
time they are taken 'OFF' are called Manual Stop Signals. Manual stop
signals shall be manually operated multiple aspect colour light signals which
shall assume ‘ON’ position automatically on the occupation of the section
ahead but shall assume ‘OFF’ position only when on clearance of the
relevant section and they are operated manually.

Chapter 20: Automatic Block Signalling Page 420 of 535