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Overlaps

- block overlap

- signal overlap

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Adequate distance

As perGR 1.02 (2), Adequate Distance means the distancesufficient to ensure safety.

This is the length of track in advance of a signal which

must be kept clear before the signal next in rear can be

taken off.

For taking off Signal 1, portion shown

beyond Signal 2 must also be clear. This

portion is the Adequate Distance.

Signal 1 Signal 2

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Adequate distance (contd.)

Conditions for taking off various Stop Signals reflect this

requirement:

GR 3.40: The Home signal (except at a terminal station or unless the

train has been brought to a stop in rear of it) shall not be taken off

unless, on a double line the line is clear for an adequate distance

beyond the starter, or on a single line, line is clear for an adequate

distance beyond the trailing points.

GR 3.42: The LSS or IBS shall not be taken OFF for a train unless

Line Clear has been obtained from the block station in advance.

GR 8.01 (1) (b) & (c ) : Such Line Clear shall not be given unless the

line is clear not only upto the FSS but also for an adequate distance

beyond it.

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GR 1.03 (2) defines C class stations where Line Clearmay not be given for a train unless the whole of the last

preceding train has passed complete at least 400 metres

beyond the Home Signal.

GR 9.01(c ) ( i ): The (automatic) signal shall not assumeoff aspect unless the line is clear not only upto the next

Stop signal in advance but also for an adequate distance

beyond it

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Adequate distance

We can therefore say that:

A Stop Signal shall not display Off aspect

unless the line is clear not only upto the

next (stop) signal but also an adequate

distance beyond it.

Important:This condition does not apply for Homesignal at terminal stations and also if the train has

been brought to a stop outside the home signal.

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Adequate distance

In other words,

The length of trackin advance of a stop

signal, which should be kept clear before

the (stop)signal next in rearcan be taken

off is known as adequate distance.

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Adequate distance - how much?

GR 3.40 dealing with conditions for taking off Home Signal lays

down in sub-para (c) that the adequate distance shall not be less than

180 metres for 2 Aspect signals and not less than 120 metres for

multiple aspect or MLQ signals. GR 8.01 read with GR 3.42 dealing with conditions for taking off LSS

lays down in sub-para (2) that the adequate distance shall not be less

than 400 metres for 2 Aspect signals and not less than 180 metres for

multiple aspect or MLQ signals

GR 9.01 dealing with automatic signals in sub-para (2) lays down thatthe adequate distance shall not be less than 120 metres.

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Overlap

The adequate distance in advance of FSS of next station

(for taking off LSS) is calledBlock Overlap, and is 400m

and 180 m respectively for 2 aspect and multi-aspect or

MLQ signals.

The adequate distance in advance of Home Signal at a C

class station (for taking off LSS at station in rear) is

always 400m for 2 aspect as well as for multi-aspect and

MLQ signals.

The adequate distance for taking off all other signals is

calledSignal Overlap, and is 180m and 120 m

respectively for 2 aspect and multi-aspect or MLQ signals.

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Overlap

For taking off Home signal for reception on loop lines,

overlap may be provided:

either by providing a dead end siding of 180/120

metres, or

by providing a sand hump or a snag dead end, or

by setting the points for the main line.

GR 5.19 (2) A sand hump or a snag dead end shall not beobstructed for any purpose and when it has become

obstructed, it shall cease to be a substitute for the adequate

distance for the purpose of taking off signals.

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Route of LSS of Stn A Block Overlap

For 2 Aspect Signals

Route of LSS of Stn A Block Overlap

For Multi-Aspect Signals

Station A

Station A

Station B

Station B

Portion to be kept clear for giving line clear

by Stn B

Portion to be kept clear for giving line clear

by Stn B

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For 2 Aspect Signals

For Multi-Aspect Signals

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Main Line

Loop Line Not for stabling