47.Overlap,Adeqate distance ,fouling mark

 Block overlap  SEM .7.1.8-.  180 meter - Adequate distance ahead home signal only ( used for line clear).

(i) Where there is a continuous down gradient towards station steeper than 1 in 260 between Distant and Home signal in single distant territory and between Inner Distant and Home Signal in Double Distant territories, the Home signal may be placed at a distance of sum of Block Overlap and Signal Overlap from BSLB (Block Section Limit Board) or the outer most Facing Point, as the case may be (i.e 180 + 120 = 300 m in MACLS).   

(ii) If there is rising gradient in between or there is no emergency crossover for criss-cross movement cutting across the main line, then this shall not be applicable.                 

Signal overlap SEM 7.1.9. -120 meter- Adequate Distance ahead starter signals only if we are lowering Home Signal to receive a train.

Where a sand hump of approved design,or under approved special instructions a derailing switch ,has been provided for the line on which a train is to be received,they shall be deemed to be efficient substitute for the adequate distance.

IB signal overlap -400 meter

No Block overlap in  Automatic Block system.Only signal overlap 

Automatic signalling possible in singal line but it is rare.

Adequate distance- distance to ensure safety 

Block overlap and signal overlap are two types of Adequate distance 

Fouling mark -

Fouling means the marks at which the infringement of two fixed standard Dimensions Fouling Block  occurs,where two lines crosses or join each other. 

It shall be placed at a location,where centre to centre distance :-

Minimum 4265 mm ( for existing line)

Minimum 5300 mm ( for New construction)

Glued joint should be placed more than 3m distance from Fouling mark to avoid side collision because in guard compartment the distance between wheel and last part of vehicle is around 3m.