scope:

The content of this module is pertinent to the implementation of signalling logic to fulfil the requirement to implement the required functional requirements, whether that is to be achieved in the interlocking itself, or at the trackside, or within the signaller's control system or other related system.

This module applies to all command and control equipments (see the typical listing in NR/L2/SIG/30009/A060 Section C1.2) for new provision and, subject to consideration of "using reasonable opportunity" and practicability, all alterations to signalling where the changes appreciably alter the risk associated with the layout and with any of the signals within the scheme. 

Changes to layout risk are likely when any of the following apply: 

a) alterations are made to a layout; 

b) lines become designated as passenger; 

c) layouts are re-signalled or relocked (or re-controlled, though it is recognised that the opportunity to mitigate existing risk is generally limited); 

d) additional routes are provided; 

e) platforms are added; 

f) permissible or attainable speeds are changed, whether raised or lowered; 

g) an overrun or timetable risk assessment (or similar) identifies the need to review protection. 

Purpose

This module forms part of the Signalling Principles Handbook (NR/L2/SIG/30009) and is to be read in conjunction with the other modules of the handbook. Its purpose is to record the legacy practices which exist within the signalling asset but which are generally no longer considered as being the first choice approach for new applications. Their use in alterations may remain applicable. (Refer to each individual entry).