Page 179 - IRSEM_Main Book

Section 6: Interlocking of Signals with Points and other
Equipments

7.6.1 Essentials of Interlocking: Equipments provided for the operation and
control of signals, points, etc., shall be so interlocked and arranged as to
comply with the following essentials;
(a) It shall not be possible to take 'OFF' a Main stop signal or a Subsidiary
signal, unless all 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 road, and relevant tracks
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 points nor unlock the route, including overlap and isolation,
nor to open any interlocked gates until the concerned signal is replaced
to 'ON' position.

(c) It shall not be possible to take 'OFF' any two signals simultaneously,
which can lead to conflicting movements.

7.6.2 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 Counters from the signal up to the
end of the route at all class of stations.

(b) Overlap shall be released with, either the passage of Train or with
specified Time delay on arrival of Train on berthing Track or Emergency
Route Release.

(c) Approach locking and back locking shall be provided for all routes
governed by Main Stop signals and Subsidiary signals. Approach and
back locking shall be continuously effective from the approach track which
shall commence from an adequate distance in rear of the signal. In the
absence of approach track circuit, Dead Approach Locking shall be
provided with suitable Time Delay.

7.6.3 Route Locking/Holding at Stations having Lever Operated Points &
Signals

(a) Points shall be so interlocked where feasible, as to avoid any conflicting
movement.

(b) At a station, where trains run through at speeds more than 50 kilometers
per hour, such arrangements to hold the route are also required in case of
trailing points situated more than 180 meters from the signal controlling
them. However, such arrangements are not required, if the Points are
locked in either position by the signal in advance.

Chapter 7: Essentials of Signalling Page 148 of 535