Overlaps ( Black & Signal )

Overlaps - block overlap - signal overlap

Adequate distance • As per GR 1.02 (2), Adequate Distance means the distance sufficient 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. Signal 1

For taking off Signal 1, portion shown beyond Signal 2 must also be clear. This portion is the Adequate Distance.

Signal 2

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.

GR 1.03 (2) defines C class stations where Line Clear may 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 assume off aspect unless the line is clear not only upto the next Stop signal in advance but also for an adequate distance beyond it

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 Home signal at terminal stations and also if the train has been brought to a stop outside the home signal.

Adequate distance In other words, The length of track in advance of a stop signal, which should be kept clear before the (stop) signal next in rear can be taken off is known as adequate distance.

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 that the adequate distance shall not be less than 120 metres.

Overlap • The adequate distance in advance of FSS of next station (for taking off LSS) is called Block 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 called Signal Overlap, and is 180m and 120 m respectively for 2 aspect and multi-aspect or MLQ signals.

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 be obstructed 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.

For 2 Aspect Signals

Station A

Station B Route of LSS of Stn A

Block Overlap

Portion to be kept clear for giving line clear by Stn B

For Multi-Aspect Signals

Station A

Station B Route of LSS of Stn A

Block Overlap

Portion to be kept clear for giving line clear by Stn B

For 2 Aspect Signals

For Multi-Aspect Signals

Loop Line

Main Line

Not for stabling