Constraints on Positioning of Stop Signals

Constraints on Positioning of Stop Signals


Position of Signals relative to Hazardous Locations,Position of Signal relative to Platforms,Where practicable stop signal shall be so placed,Overhead Electrification Systems,Conductor Rail Electrification Systems,Overhead Electrification Systems,IDENTITY OF SIGNALS 

Constraints on Positioning of Stop Signals

1.Position of Signals relative to Facing Points

Where a signal reads over facing points, it shall be positioned not more than 800m from the first set of facing points so that risk due to following is minimised:

I.Likelihood  of the driver forgetting the indicated route

II.The ability to accelerate to more than permissible speed over the diverging route.

 The 800m limit does not apply for:

I.Points which are operated from G/F

II.Facing points which are secured out of use

III.Facing points which are in same position for all movements from signal

IV.A signal which is positioned parallel and one of the parallel signal is within 800m from facing points.

1.Position of Signals relative to Facing Points



2.Position of Signals relative to Points & Level Crossings

 Where practicable stop signal shall be so placed

  1. a) so that the associated overlap is clear of points & level crossings.
  2. b) trains stopped at the signal do not stand over points or level crossing or foul any other line.

3.Position of Signal relative to Platforms

Stop signals shall be positioned to minimise the risk arising from passenger train without central door locking or power operated doors stopping with a platform adjacent to only part of the train.

  1. Position of Signals relative to Hazardous Locations

         Where practicable, stop signals shall be positioned to avoid the risk of passenger train stopping in a hazardous location (e.g. on a viaduct or in a tunnel)

  • Where signal is required at such location, e.g. for maintaining headway, signalling control shall be applied to the previous signal to minimise the risk of train stopping at such location.
  • It is not necessary to apply such control where risk has been controlled by other means such as central door locking on all trains, trackside walkways, secure communication between trains and signallers and train protection systems fitted on signal and trains etc.
  1. Other Constraints

     Stop signals shall, where practicable, be positioned such that trains are not required to stop:

  1. a) on severe rising or falling gradients.
  2. b) at known sites of poor adhesion.

6.Overhead Electrification Systems (25KVor 1.5KV)

      Stop signals shall be appropriately positioned in relation to neutral section or section gap to minimise the risk of:

a.An electric train with only one pantograph being brought to rest with pantograph in neutral section or section gap

b.An electric train restarting from a signal stalling in neutral section or section gap.

Constraints on Positioning of Stop Signals

Overhead Electrification Systems:

     Stop signals shall be appropriately positioned in relation to relevant overhead line sectioning locations, so as to minimise likelihood of an electric arc being drawn when a pantograph bridges the sectioning point when train is traveling slowly or stationary.

   This makes it mandatory to maintain certain minimum distances between a signal and OLE booster overlap, insulated overlap and section insulators.

Conductor Rail Electrification Systems

     Stop signals shall be positioned to minimize the likelihood of trains stalling in conductor rail gaps.


  • Main signals shall be designated passable or non passable for the purpose of specifying whether or not driver is permitted to pass a signal at danger under his own authority.
  • The term ‘passable or non-passable’ apply for operating purposes and ‘automatic/ controlled’ for signal control purposes.
  • Non-Passable: A signal that protects an area of conflict or other infrastructure such that a significant hazard would arise in the event of it being passed at danger without authority. Such signals can not be passed at danger w/o specific authority from signaller.
  • Passable: A signal which is able to be passed at danger without specific authority of signaller, in accordance with rule book, without a significant hazard arising.


  • Each signal should have an unique identity that is unique to its controlling signal box or locality, comprising the signal box prefix code, the signal number and where required a suffix.
  • All signals including automatic and distant signals except distant signals worked by same lever as stop signals shall be individually numbered as part of a sequence.
  • A separate sequence shall be used for running signals and for shunting signals.

Main Rules for determining the sequence of numbers:

I.Separate sequence for each numbered functions

II.Odd numbers for down direction and

III.Even numbers for up direction

IV.Odd numbers usually ascend and

V.Even numbers descend in the direction of traffic flow

VI.In multiple line section each line – separate sequence


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