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.

            


The material on this page is extracted from Indian Railways General Rules (Open Lines), 1976, published by the Government of India.
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