NR NR/L2/SIG/30009/E420 ISSUE 1 PDF

This specification applies to all alterations to signalling installations.

SPAD alarms, in accordance with NR/L2/SIG/11130, shall be provided whenever a panel or VDU based system is provided. Retrospective application is required when signalling is substantially upgraded.

Overrun management is a combination of automatic overrun (SPAD) detection and signalling system controls; the signalling and associated operational systems support the signaller in the management of unauthorised moves. Overrun Management shall be adopted when power operated signals are provided or substantially altered. It is mandatory except where:

1. minor alterations or enhancements are made to existing signals which do not otherwise materially relate to the likelihood or consequence of overrun*;

2. the works are temporary in nature (e.g. stageworks);

3. an assessment of the intended operational use demonstrates that the complexity is not justified (typically low speed layouts of 15mph)*;

4. the works consist of a "like for like" renewal* of a junction in accordance with NR/L2/SIG/19803;

5. the works consist of a "modern equivalent form" renewal of a junction in accordance with NR/L2/SIG/19803;

6. an interlocking(s) is renewed in "like for like" form and it is not reasonably practicable to modernise the controls.

Items 3, 5 and 6 additionally require that all controlled signals shall be replaced to danger by train detection located at or immediately just beyond the signal.

Those cases above marked with an asterisk * do not require any form of overrun detection. The remainder (items 2, 5 and 6) require the adoption of Simple Overrun Detection as a minimum.

Any projects which adopt a risk-based approach (items 3 and 6 above) are required to agree their approach with the Major Scheme Review Panel (NR/L2/SIG/30035) and to obtain a non-compliance to this Signalling Principles Handbook standard. This shall form the record of justification for the approach taken.

Movement authorities given by signals which are mechanically operated do not require any form of detection of overrun.

Guidance to achieve the minimum requirements of Overrun Management is given in section 6.2; preferred arrangements for installations are tabulated in Appendix A

To support one of the requirements of the Ladbroke Grove accident inquiry an overrunning train shall not apply any additional locking to points; see also section 7.

The requirements for point flank protection are described in NR/L2/SIG/30009/E710.

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 detecting overruns and the controls to be applied to protect the overrun. It 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).

This handbook section also establishes the principles for future designs of control system with integrated SPAD detection and management systems.