scope:

This specification applies to all signalling schemes and detailed design where the interlocking is renewed without alteration to the trackside equipment, layout, functionality or trackside apparatus housings.

NOTE This specification is to apply for projects where the interlocking is renewed or replaced with an interfaced SSI (or equivalent technology).

Purpose

This section 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 Section details Network Rail's policy on the replacement of interlockings and continuing the application of the principles in force when the interlocking was originally commissioned and comprises mandatory sections, statements of best practice (which shall be followed unless an alternative can be demonstrated to be beneficial to the company and no less safe), and guidance on historical practices (which are not to be applied to new works but provide information on previous standards or their interpretation.