CHAPTER - XX

AUTOMATIC BLOCK SIGNALLING

20.1 Installation

20.1.1 General

20.1.1.1 The installation and wiring shall be carried out as per approved plan and Circuit Diagrams.

20.1.1.2 All fail-safe circuits shall work on continuously energized principle such that any open circuit in wiring, relay contacts, etc. or loss of power supplies shall not cause an unsafe condition.

20.1.1.3 The circuits and equipment shall be so installed as to cause minimum failures while ensuring maximum safety.

20.1.1.4 Triple pole double filament electric signal lamps shall be used, as far as possible. In case double pole lamp is used, 'ON' aspect lamp must have two filaments in parallel.

20.1.1.5 All external circuits shall be provided with double cutting arrangements.

20.1.2 Signals

20.1.2.1 The aspects of a signal shall be controlled by the signal in advance through lamp proving relays, in addition to the controlling relays.

20.1.2.2 The circuits shall be so designed that if an automatic signal which must display red aspect  does not do so for any reason whatsoever, the signal in rear shall display a red aspect.

20.1.2.3 An automatic signal on a double line shall require all tracks to be clear upto the next signal and an adequate distance beyond, before it can display 'OFF' aspect. In case of Single Line, after establishment of favorable direction of traffic, an automatic signal shall require all tracks to be clear up to the next signal in advance and in case the next stop signal in advance is a manual stop signal, the line is clear for an adequate distance beyond it before it can display 'OFF' aspect.

20.1.2.4 The lamps of the signal shall be so wired that if the lamp of the aspect displayed fails, the signal shall immediately assume the next restrictive aspect.

20.1.2.5 (a) The circuit for illuminated 'A' marker shall be such that the 'A' marker lights up only when the signal is working as an automatic signal.

(b) The circuit for illuminated 'AG' marker where provided shall be such that the 'AG' marker lights up only when the conditions for 'A' Marker to light up are satisfied except for the level crossing gate which may either be open to road traffic or may have failed.

20.1.2.6 The illumination of the 'A' marker shall prove the correct setting and locking of the points as required and ensures the back-locking of the route. Level crossing gates, if any, on the route shall be proved closed to the road traffic.

20.1.3 Level Crossings

20.1.3.1 Level Crossing gates in automatic sections shall be worked by lifting barrier gates operated mechanically or electrically and shall be interlocked with signals. The gates shall be both approach locked and back-locked by track circuits. They shall also be provided with audible warning on both sides of the road, actuated by approaching trains. In addition, road-warning lights shall be provided on both sides of the road, which will be lit when there is any train on the approach or whenever the gate is not in the open condition.

20.1.3.2 (a) The approach locking shall be effective from the moment the train occupies the track circuit in rear of the signal which assumes clear aspect when the Gate Signal is taken 'OFF' and the backlocking shall be effective until the train clears the level crossing. The audible warning shall stop when the gate is closed and locked but the red warning lights for road users where provided shall be exhibited till the gates are re-opened for traffic.

(b) Approach locking should be effective from a distance not less than braking distance required for maximum permissible speed on that section.

20.1.3.3 The audible and visual train approach annunciation shall be such that the Gateman gets adequate warning time. This time shall normally be 60 seconds for the fastest train, for closing the level crossing gates before the train approaches within the sighting distance of the relevant gate signals.

20.1.4 Track circuits: - Provision contained in Chapter XVII shall be adhered to.

20.1.5 Power Supply: - Provisions contained in Chapter XVI shall be adhered to.

20.1.6 Installation in 25 kV AC electrified areas: - Provisions contained in Chapter XXII shall be adhered to.

20.1.7 Installation of Cables: - Provisions contained in Chapter XV shall be adhered to.

20.1.8 Electrical signalling arrangement: - Provisions contained in Chapter XIX shall be adhered to.

20.2 Maintenance

20.2.1 The triple pole electric signal lamps shall be replaced as early as possible, after the fusing of its main filament.

20.2.2 The double pole electric signal lamps used in colour light signals and marker lights shall be replaced on a regular schedule as prescribed by the Railways to avoid failures due to burning out of lamps. The interval between replacement of lamps for the various aspects will depend on the intensity of traffic on the section and the anticipated life of lamps.

20.2.3 The following shall be tested by the SSE (Signal) at-least once in a year.

(i) Track Circuit control on signal and aspect control by signals in advance;

(ii) Automatic Cutting-in of the next restrictive aspect when the lamp of one aspect burns out;

(iii) Interlocking equipment and circuits for level crossings and points;

(iv) The circuits that establish the direction of traffic and prevent clearing of conflicting signals on sections provided with Automatic block Signalling on Single Line.

20.2.4 All failures reported by the Drivers shall be promptly attended to.

20.2.5 Track circuits

20.2.5.1 Adequate precautions should be taken after every track renewal work to ensure proper working of track circuits.

20.2.5.2 Provisions contained in Chapter XVII shall be adhered to.

20.2.6 Power Supply: - Provisions contained in Chapter XVI shall be adhered to.

20.2.7 Electrical signalling arrangements: - Provisions contained in Chapter XIX shall be adhered to.

20.2.8 Cables: - Provisions contained in Chapter XV shall be adhered to.