Track Circuit Block 

Track Circuit Block 

Indian Railway Signalling Network Rail Thales

Track Circuit Block 

Block Signal

  • A Stop signal that controls the entrance to or signifies the termination of a block or signal section (and any other stop signal)
    within station limits.

Signal Section

  • In a track circuit block area, the line between two consecutive block signals (whether or not these are within the area of control of the same signal box) in the same direction of travel.


Non-block Signal

  • A mid-section stop signal specifically provided for the protection of a level crossing or other hazard and without block or signal section controls.


  • The distance ahead of a stop signal up to which the line must be clear, and where necessary locked, before the signal in the rear can clear.

Track Circuit

  • A Portion of the railway line having fixed boundaries and providing information on its state of occupancy to the signaling system. This traditional name does not preclude alternative forms of train detection.



  1. Maybe Employed on both uni-directional and bi-directional lines.
  2. Level of traffic and types of vehicles to be suitable for reliable operation.
  3. Integrity level to be sufficient for the application.
  4. Not necessary for the signaller to directly observe trains.
  5. No restriction on the location of signal boxes.
  6. Block signals may be automatic, semi-automatic, or controlled.
  7. Controlled signals may work automatically on selection.

Following Facilities may also be used :

  1. Mechanically operated Controlled signals and distant signals.
  2. Permissive and shunt working
  3. Automatic stepping up of warning facilities.
  4. Train-operated route release i.e. automatic route release.
  5. Automatic route setting.
  6. Automatic working of distant signals and/or aspects.
  7. Fixed distant signals and (reflectorized) distant boards.



  1. Signals for all normal train movements.
  2. Signals at the point of reversal for reverse movement.
  3. Only one train in a signal section at any time except where permissive or shunt working allowed.
  4. Promotion of correct sequence of events.
  5. Block signal without a separate overlap track circuit not to prove its own overlap clear provided the overlap is proved clear in the procedural aspects of the block signal in the rear.
  6. Where there are automatic or semi-automatic signals for both directions, opposing signals shall clear for one direction only at anyone time.
  7. The Clear direction selected by the operation of the controlled signals, or by the operation of direction or acceptance controls if there is more than one signaller.



Train Detection

  1. Indications to the signallers – the presence or absence of trains in each signal section.
  2. Track Circuit indications to correspond to the actual controls applied to signals, especially where overlaps at automatic signals are part of the rear section.
  3. Appropriate indications of approaching and conflicting trains.

Bi-directional Control

  1. Maybe co-operative if there is more than one signaller or overall control by a single signaller by additional switches or levers.
  2. Directional control for un-limited number of trains or restricted to a single train.
  3. Direction Controls to be suitably indicated to all associated signallers.

Signal Controls

  1. Signal section and the overlap at the exit signal to be clear.
  2. Automatic replacement of signal aspects, where practicable.
  3. Except for mechanical signals, signal sticks for all controlled block signals.
  4. Signal Sticks overridden by the selection of automatic working.
  5. If no automatic replacement of aspect, the replacement to be proved before clearance of block signal in rear. This replacement proving shall be lever or control plus aspects.

Replacement by lever only if –

  1. The signal is mechanically operated, and
  2. An arm repeater is not provided, and
  3. The signal does not give entry to a bi-directional Line worked by any non-token system, and
  4. The block signal in the rear controlled from the same signal box and
  5. The block signal in the rear cannot work automatically.

Semaphore signals

  1. Semaphore stop signals at either end of a signal section or semaphore distant signals that apply to these stop signals –
  2. the overlap controls to be suitable for fog conditions.

(GK /RT 0078)


Communication between Signal Boxes

  • Emergency alarm facility and voice communication.

Stop signal communication

1 . Signal Post Telephone.

Identification of Signal

  • Signal identification plates
    (GK / RT 0009)

Permissive and shunt working

  • Where authorized, under the authority of a position light signal, semaphore subsidiary signal, or a semaphore shunting signal.

Switching out of signal boxes

  1. Controls to be transferred to another signal box including the ability to replace each or all block signals.
  2. Transfer of all indications and communications.



  1. Maybe block or non-block signals
  2. Block signal to be a controlled signal by the gate-operator
  3. Or a semi-automatic signal

System Failure

  • Any failure not to result in the clearance of the signals. (Failures to be on the safe side)


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