NR NR/L2/SIG/11201/MODA22 ISSUE 4 PDF

The requirements of this module apply to both Network Rail and its design contractors.

This module applies when sequential design processes have to be compressed to run in parallel, including the special case when the programmes for consecutive design alterations overlap. The concurrent design processes specified shall be employed only after all other methods of achieving the required design output have been considered and then only in conjunction with the mitigating control measures described in section 5.1.

The benefits of running parallel processes decline rapidly as the following situations are approached:

a) the time spent on assessing the risks and devising and implementing additional controls outweighs the time saved by process compression;

b) it is likely that the amount of rework generated by a change in one process (requiring rework in all the concurrent processes) will outweigh the time saved by process compression.

Parallel processes shall not be used unless the safety risk resulting from the above considerations is controlled with appropriate mitigation (e.g. unless the business cost of not compressing timescales is grossly disproportional to the safety cost of doing so).

Purpose

This module, sets out the mandatory requirements that apply when it is necessary to produce signalling design detail in reduced timescales, so that risks are adequately controlled. The process for authorisation of such relaxations is defined.