NR NR/L2/SIG/30009/E420 ISSUE 2 PDF

These requirements apply to all alterations to signalling installations. A decision contrary to this module specifically requires the approval of Network Rail's Professional Head (Signals and Controls). The provision of protection from overruns 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 and short duration in nature (e.g. stageworks) and are low risk;

3. an assessment of the intended operational use demonstrates that the benefit of detecting and acting on an overrun is not justified (typically low speed layouts of 15mph);

4. the works consist of a "like for like" renewal (overall footprint of the S&C and its associated signalling is unaffected) of a junction in accordance with NR/L2/SIG/19803;

5. the works consist of a "modern equivalent form" (point operating mechanism is to be replaced or the rail section is changed) renewal of a junction in accordance with NR/L2/SIG/19803.

Cases 1, 4 and 5 above do not require ANY change to the pre-existing form of overrun detection.

Signals which are mechanically operated (wires & pulleys) do not require any form of detection of overrun.

Simple Overrun Management shall be provided for small-scale alterations to existing installations on the grounds that Overrun Management would be disproportionate. Cases 2 and 3 require consideration of Simple Overrun Detection as a minimum.

Overrun Management shall be adopted when power operated signals are newly provided or substantially altered:

a) all re-signalling projects should adopt a solution where the primary data resides in the control system, reflecting migration to ROCs and future Traffic Management;

b) all re-control projects should adopt a solution where the primary data resides in the control system;

c) all re-lock projects should formulate and submit their case for their chosen solution [noting that any new data will readily accommodate the form of Overrun Management described in this Module], see section 6.1 & 6.2;

d) panel-controlled route relay (RRI) and computer based solutions can adopt an interlocking or control system solution taking account of how SPAD alarms are to be provided and should formulate and submit their case, see section 6.1.

The decision on the method of protection from overrun shall be taken before achievement of AiP is granted: each project shall consider the extent of compliance to this module of SPH which shall be recorded within the assessment required by NR/L2/SIG/30009/E810. This shall particularly include the capability for detecting SPAD at signals and whether data or circuitry should be removed from existing interlockings due to the double handling of signal replacement.

All projects and especially those which adopt a risk-based approach (items 2 and 3 above) are required to agree their approach with the Major Scheme Review Panel (NR/L2/SIG/30035) and to agree onward submission to the Professional Head (Signals and Controls) to obtain any required deviations¹ to this Signalling Principles Handbook standard.

The circumstances when SPAD alarm systems shall be provided² are described in section 5.3.

To support one of the requirements of the Ladbroke Grove accident inquiry³ an overrunning train shall not apply any additional locking to points; see also section 8.

The associated requirements for point flank protection are described in NR/L2/SIG/30009/E710 [Notice Board 125/3 provides guidance on sufficiency].

Purpose

This level 2 standard forms part of the Signalling Principles Handbook (SPH: NR/L2/SIG/30009) and is to be read in conjunction with the other modules of the handbook and the reference documentation.

This module details Network Rail's policy on the provision of SPAD alarms, the detecting of overruns and the controls to be applied to protect the overrun. These principles have been endorsed by operations and risk specialists and shall be applied for new and altered installations, wherever reasonably practicable.

This module 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 can be retained only in prescribed circumstances, see section 2.

¹ These shall form the record of justification for the approach taken.

² Recommendation 47 of the Ladbroke Grove Rail Part 1 Report, ISBN 0 7176 2056 5 dated 2001

³ Recommendation 48 of the Ladbroke Grove Rail Part 1 Report, ISBN 0 7176 2056 5 dated 2001