scope:

All staff responsible for remitting or specifying works to the signalling system have an obligation to consider the 'reasonable opportunity' available for providing risk control measures as part of the works.

This module applies to ALL changes to the signalling system; including control systems, interlockings, trackside equipment, layout, functionality and trackside apparatus housings.

This module sets requirements and gives guidance to asset managers and project teams on the specific analysis required during the development of signalling schemes (renewals and enhancements) to identify:

• non-compliances to current standards;

• compliance with legacy standards of retained assets/arrangements;

• legacy non-compliances;

justify the reasonability of opportunities of:

• the extent to which current standards are applied to existing track layouts and signalling arrangements;

• where existing approaches (of principles of signalling) are to be retained in the control of operational risk;

• operational functionality and consider impact on data complexity and 'data safety';

• impacts of change on users of the system including human factors.

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.

This module supports Network Rail's policy for the adoption of current standards and the assessment and application of 'reasonable opportunity' to be taken when specifying and making any alterations to parts of the signalling system.

NOTE: There are some cases when current standards may be inappropriate for a renewal or improvement.

NOTE: This approach is consistent with the Common Safety Method for Risk Assessment [CSM] regulations and meets Network Rail's signalling policy. It also supports Network Rail's 'Safe by Design' commitment that requires the taking of reasonable opportunities to make safety improvement.