Since it became operational in 2005, RAIB has investigated numerous incidents in which signaller decision-making has been pivotal, and where the safety of the railway system was heavily dependent on those decisions (that is, scenarios in which there were no, or limited, engineered safeguards).

Under its remit, RAIB also collected industry data on several similar incidents over a five-year period which again highlighted the vulnerable nature of such decision-making. In the light of these incidents, the RAIB undertook a class investigation into what affects those decisions, recognising that they may be influenced by a variety of systemic factors.