The absolute block system
(Extract from IR General Rules : Chapter 8)
A.Essentials
8.01. Essentials of the Absolute Block System
1. Where trains are worked on the Absolute Block System
(a) no train shall be allowed to leave a block station
unless Line Clear has been received from the block
station in advance, and
(b) on double lines such Line Clear shall not be given
unless the line is clear, not only upto the first Stop
signal at the block station at which such Line Clear is
given but also for an adequate distance beyond it;
(c) on single lines such Line Clear shall not be given
unless the line is clear of trains running in the same
direction, not only upto the first Stop signal at the
block station at which such Line Clear is given, but also
for an adequate distance beyond it, and is clear of
trains running in the direction towards the block station
to which such Line Clear is given.
2. Unless otherwise directed by approved special instructions,
the adequate distance referred to in clauses(b) and (c) of
sub-rule (1) shall not be less than-
(a) 400 metres in case of two-aspect lower quadrant
signalling or two-aspect colour light signalling, and
(b) 180 metres in case of multiple-aspect signalling or
modified lower quadrant signalling.
B. Conditions for granting Line Clear
8.02. Conditions for granting Line Clear at a class A station-
At a class A station on single line or double line, the line
shall not be considered clear and Line Clear shall not be
given, unless-
(a) the whole of the last preceding train has arrived
complete;
(b) all signals have been put back to `on' behind the said
train;
(c) the line on which it is intended to receive the
incoming train is clear upto the Starter; and
(d) all points have been correctly set and all facing
points have been locked for the admission of the train on
the said line.
8.03. Conditions for granting Line Clear at a class `B' Station
(1) At a class `B' station on double line, the line shall not
be considered clear and Line Clear shall not be given, unless-
(a) the whole of the last preceding train has arrived
complete;
(b) all necessary signals have been put back to `on'
behind the said train; and
(c) the line is clear-
(i) at stations equipped with two-aspect signalling,
up to the Home signal, or
(ii) at stations equipped with multiple-aspect
signalling or modified lower quadrant signalling,
up to the outermost facing points or the Block
Section Limit Board(if any)
2. At a class `B' station on single line, the line shall, not
be considered clear and Line Clear shall not be given, unless
(a) the whole of the last preceding train has arrived
complete;
(b) all necessary signals have been put back to `on' behind
the said train; and
(c) the line is clear
(i) at stations equipped with two -aspect signalling
up to the Shunting Limit Board or Advanced Starter
(if any) at that end of the station nearest to the
expected train, or
up to the Home signal if there is no Shunting Limit
Board or Advanced Starter, or
up to the outermost facing points if there is
Shunting Limit Board or Advanced Starter or Home
signal;
(ii) at stations equipped with multiple-aspect
signalling or modified lower quadrant signalling
up to the Shunting Limit Board or Advanced Starter(if
any) at the end of station nearest to the expected
train, or
up to the outermost facing points if there is no
Shunting Limit Board or Advanced Starter.
Note: At a class `B' single line station, this rule does not
forbid direct reception of a train from one side, when Line
Clear has been given to the block station on the other side
provided the distance between the Outer signal and outermost
facing points in two-aspect signalling, and between the Home
signal and outermost facing points in multiple-aspect
signalling, or modified lower quadrant signalling is not
less than sum-total of the adequate distances prescribed in
Rule 8.01 in regard to conditions for granting Line Clear
and Rule 3.40 in regard to conditions for taking `off'
Signal for the admission of a train even where Shunting
Limit Boards or Advanced Starters have not been provided as
prescribed in sub-rule (1) of Rule 3.32.
8.04 Conditions for granting Line Clear at a class `C' station
At a class `C' station on single line or double line in
two-aspect, multiple-aspect or modified lower quadrant
signalling, the line shall not be considered clear and Line
Clear shall not be given, unless
(a) the whole of the last preceding train has passed
complete at least 400 metres beyond the Home signal and
is continuing its journey; and
(b) all signals taken`off'for the preceding train have
been put back to `on' behind the said train:
Provided that on a single line, the line is also
clear of trains rnning in the opposite direction
towards the block hut from the block station at the
other end.
C. Obstruction-Double Line
8.05. Obstruction on double line at a block station when a train is
approaching
(1) Class `A' station-When Line Clear has been given, no
obstruction shall be permitted outside the Home signal, or, on
the line on which it is intended to admit the train, upto the
Starter pertaining to the said line.
(2) Class`B' station-When Line Clear has been given, no
obstruction shall be permitted outside the station section but
shunting within the station section may go on continuously,
provided the necessary signals are kept at `on'.
(3) When signals have been taken `off' for an incoming train on
to a line which is not isolated, no shunting movement shall be
carried on towards the points over which the incoming train
will pass.
8.06. Obstruction on double line in the block section
(1) When Line Clear has been given, no obstruction shall be
permitted in the block section in rear.
(2) Shunting or obstruction for any other purpose shall not be
permitted in the block section in rear unless it is clear and
is blocked back.
(3) Shunting or obstruction for any other purpose shall not be
permitted in the block section in advance unless it is clear
and is blocked forward:
Provided that when the block section in advance is occupied
by a train traveling away from the station , shunting or
obstruction may be permitted behind the train under special
instructions taking into consideration the speed , weight
and brake power of trains and the gradients on the section,
and as soon as intimation has been received that the train
has arrived at the block station in advance, the line shall
be blocked forward if it is still obstructed.
Note: See rule 8.14 also
D. Obstruction -Single Line
D.1. Class A stations
8.07. Obstruction on single line at a class `A' station when a
train is approaching
When Line Clear has been given, no obstruction shall be
permitted outside the Home signal, or, on the line on which it
is intended to admit the train, upto the Starter which controls
the train.
8.08. Obstructing the block section at class `A' station on single
line
The block section shall not be obstructed for shunting
purposes, unless-
(a) the Station Master has received Line Clear from the Station
Master at the other end of the block section, or
(b) the block section is blocked back, or
(c) is occupied by a train traveling away from the block station
at which the shunting is to be performed which shunting may be
permitted under special instructions taking into consideration
the speed, weight and brake power of trains and the gradients
on the section. As soon as intimation has been received that
the train has arrived, the block section shall be blocked back,
and
(d) the Driver or other person in charge of the shunting
operations has received distinct orders from the Station Master
to shunt in a manner directed by special instructions.
D.2. Class B Stations
8.09. Obstruction in the face of an approaching train at a class `B'
station on single line
The line outside the Home signal in two-aspect signalling
territory or outermost facing points in multiple-aspect or
modified lower quadrant signalling territory in the direction
of a train for which Line Clear has been given, shall only be
obstructed when a Shunting Limit Board or an Advanced Starter
is provided and under speical instructions which take into
consideration the speed, weight and brake power of trains, the
gradients, the position of the first Stop signal and the
distance from which that signal can be seen by the Driver of an
approaching train.
8.10. Obstruction within station section at a class `B' station on
single line
(1) If the necessary signals are kept at `on', shunting may be
carried on within the station section, provided the provisions
of Rule 8.09 are complied with for shunting upto Shunting Limit
Board or Advanced Starter, where provided.
(2) When signals have been taken `off' for an incoming train on
to a line which is not isolated, no shunting movement shall be
carried on towards the points over which the incoming train
will pass.
8.11. Obstruction outside station section at a class `B' single line
station equipped with two-aspect signals
The line outside the station section and upto the Outer signal,
shall not be obstructed unless a railway servant specially
appointed in this behalf by the Station Master is in charge of
the operations, and unless-
(a) the block section into which the shunting is to take place
is clear of an approaching train and all relevant and necessary
signals are at `on' position, or
(b) if an approaching train has arrived at the Outer signal,
the Station Master has personally satisfied himself that the
train has been brought to a dead stand at the signal:
Provided that the line shall not be obstructed under
clause(b) in thick, foggy or tempestuous weather impairing
visibility, or, in any case unless authorised by special
instructions.
8.12. Obstruction outside station section at a class `B' single line
station equipped with manually operated multiple-aspect signals
The line outside the station section and upto to the first Stop
signal shall not be obstructed unless a railway servant
specially in this behalf by the Station Master is in charge of
the operations, and unless the block section into which the
shunting is to take place is clear of an approaching train.
8.13. Obstruction outside the first Stop signal at a class `B'
station on single line
The line outside the first stop signal shall not be obstructed unless
the line has been blocked back.
E General Provisions
8.14. Block back or Block forward
Block back or block forward shall be done only in accordance
with the procedure prescribed by special instructions.
8.15. Authority for shunting or obstruction in block section
While permitting shunting or obstruction in the block section,
the Driver shall be given authority for shunting in the block
section as prescribed under special instructions which
authority may be-
(a) either a shunting arm of prescribed size and design on the
same post as and under the last Stop signal, or
(b) a token of prescribed design, or
(c) a written permission to shunt.
