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Overlaps in Indian railways
#1
Hi,
        As of my experience I had found three types of overlaps in absolute block working system under colour light signalling for Indian Railways i.e., Signal O/p - 120m, Block O/p - 180m, Intermediate Block O/p - 400m. Can anyone explain me why these are different and how these distances are kept

Unlike in UK a fixed overlap distance of 200yards (183m), why in IR fixed overlap is not followed

Thanks in advance
KKD
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#2
(20-05-2016, 07:24 AM)karundeepu Wrote: Hi,
        As of my experience I had found three types of overlaps in absolute block working system under colour light signalling for Indian Railways i.e., Signal O/p - 120m, Block O/p - 180m, Intermediate Block O/p - 400m. Can anyone explain me why these are different and how these distances are kept

Unlike in UK a fixed overlap distance of 200yards (183m), why in IR fixed overlap is not followed

Thanks in advance

Don't know about India, but in UK with Absolute Block signalling, the block overlap is 400m, but if the distant is colour light can be reduced to 180m.
The UK does have other overlap lengths- 225m where can be provided particularly on highest speed lines, conversely if speeds are low can justify a reduced overlap less than 180m.
PJW
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#3
(20-05-2016, 10:39 AM)PJW Wrote:
(20-05-2016, 07:24 AM)karundeepu Wrote: Hi,
        As of my experience I had found three types of overlaps in absolute block working system under colour light signalling for Indian Railways i.e., Signal O/p - 120m, Block O/p - 180m, Intermediate Block O/p - 400m. Can anyone explain me why these are different and how these distances are kept

Unlike in UK a fixed overlap distance of 200yards (183m), why in IR fixed overlap is not followed

Thanks in advance

Don't know about India, but in UK with Absolute Block signalling, the block overlap is 400m, but if the distant is colour light can be reduced to 180m.
The UK does have other overlap lengths- 225m where can be provided particularly on highest speed lines, conversely if speeds are low can justify a reduced overlap less than 180m.

Well I had got the answer.

Signal O/P - It refers to the overlap to be provided beyond any other stop signal other than the outermost stop(home) signal for the station; the term is especially used for the overlap provided in advance of starter signal. It is normally 180m for lower quadrant or 2-aspect colour light signalling, and 120m for MAUQ (Multi-aspect Upper Quadrant Semaphopre) or MACL (Multi-aspect Colour Light) signalling

Block O/P - It is associated with reception stop signal of a station(home or outer), and is the distance to be provided from that signal to the first facing points of the station. It is usually prescribed to be 400m for lower quadrant or 2-aspect colour-light signalling and 180m for MAUQ and MACL signalling.

Intermediate Block O/P - It is a different scenario from the above two, where the classes of stations to be known to get this. Basically in Indian railways, stations are classified as classes like Class -A, B, C and D. Since Intermediate block overlap is for Intermediate block signals where they come under Class-C station. In Class-C stations permission to approach(i.e., approach to the Intermediate block signal) may not be given for a train unless the whole of the last preceding train has passed complete at least 400m beyond the home signal(Intermediate block signal) and is known to be continuing on its journey. So, the Intermediate block overlap is kept as 400m. 

May be this is helpful to understand.
KKD
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