Interlocking

 Essentials of Interlocking ( SEM -7.6.1)-

Equipments provided for the operation and control of signals, points etc. shall be Interlocked and arranged as to comply with following essentials,

A) It shall not be possible to take OFF a Main stop signal or subsidiary signal, unless all the Points in the route, including overlap and Isolation (as applicable),are correctly set and locked and all interlocked level crossing are closed and locked against public,and all the relevant track circuits are unoccupied by vehicles and clear for the line on which the train will travel.

B) After such Signal has been taken off, it shall neither be possible to move any point in the route,including overlap and Isolation, nor to open any interlocked gates until the concerned signal replaced to ON.

C) It shall not be possible to take 'OFF' another signal which can lead to conflicting movement.

Route Holding (Approach Locking & Back Locking)-

A) The route ( including overlap, isolation as applicable),locked by a signal,shall be released normally on passage  of train or by Emergency Route Release with specified time delay.For such route Holding, it is essential to provide continuous track circuit/Axle counter from  Signal to end of the route at all class of stations.

B) Overlap shall be released with,either passage of train or with specified time delay on arrival of train on birthing Track or Emergency Route Release.

Approach locking is rear of Signal and back locking is ahead of Signal.For Home signal back locking is used and for Starter Signal both approach and back locking can be used

If the track ckt/Axle counter in rear of Home  Signal is minimum 1 km and track detection is provided,  we can use Approach Locking.After taking off a Home signal,if signal  cancellation is carried out,signal will go to danger without any time delay but route will not cancel immediately because driver need  some time to stop the train.in this case route can be canceled in two ways

1) If approach track/ Axle counter ( 1 km length) is clear,  route will be canceled immediately without any time delay.

2) If approach track/ Axle counter ( 1 km length) is occupied, a timer of 120 seconds will start and after 120s route will be released and driver will get 120 s to control his train.

3) If approach track is not provided, it is called dead approach and route will be released after 120 s time delay after signal cancelation process.

Back locking tracks start from foot of the Signal to Last point zone track excluding birthing track.

For Home Signal., length of Approach track is 1 km. To avoid making a track ckt of 1km,we prefer Dead Approach Locking.

For other stop signals, length of Approach track is not mentioned so take sufficient distance according to need.

Approach Locking and back locking shall be provided for all routes governed by Main stop signals and subsidiary signals.In absence of approach track circuit, dead approach shall be provided with suitable time delay.

At LC gates in , Approach Locking to be provided if continuous track circuit available. In other sections dead approach with 60 sec time delay to be provided.

Continuous Track Circuit -

Where continuous track circuiting/Axle counter are  provided, the occupation by a vehicle of any track circuited/Axle counter section shall also control the signals leading to same line and shall also lock the points on the route.

At Stations where points and signals are operated through Relay interlocking/ Electronic Interlocking, track circuiting/ Axle Counters shall be provided.

Note-  If a signal is flashing at panel, it's route will come if other conditions are satisfied but signal will not lower.For cancellation of this route,you have to first cancel the signal then route will be cancelled through super emergency cancellation.

Length of overrun shall be 120 m.

Emergency Crossover point

It is located in either up or down side in double line section. Generally it is kept in Normal.Used in Reverse when we need to receive a train on common loop line. Platform line is made common loop to get the facility of receiving a train from both directions.


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