Process and Task Analysis of Signaller and Crossing Keeper roles to support Human Factors Assurance – A Subject Matter Expert's Perspective

A variety of human factors assurance activities are carried out to support the safe and efficient operation of both existing and proposed signalling and level crossing control facilities. However their effectiveness can be... [ view full abstract ]

A variety of human factors assurance activities are carried out to support the safe and efficient operation of both existing and proposed signalling and level crossing control facilities. However their effectiveness can be limited by a lack of detailed understanding of the operator’s role by Human Factors practitioners and a corresponding lack of understanding on the part of operators and design engineers of the value that a systematic Human Factors approach can bring to railway signalling operations.

Assurance activities range from the assessment of operational demand associated with existing control facilities and the operator’s ability to take rest in naturally occurring gaps between planned activities through prediction of operational demand associated with proposed control facilities to the interdisciplinary design review of proposed user interfaces.

A key challenge has been to gain the acceptance of Human Factors practitioners, the operations community and signalling and telecomms design engineers alike that a systematic approach to process and task analysis using cognitive task analysis facilitated by a Subject Matter Expert can add significant value.

Another key challenge has been to develop an approach to cognitive task analysis which can capture and record those findings relevant to the Human Factors assurance process in a sufficiently detailed but understandable way to support conclusions and any recommended design changes.

This paper seeks to show how cognitive task analysis of the steps involved in signalling and level crossing control tasks can be used to inform Human Factors assurance activities. Such analysis has the potential to drive the optimisation of signalling control systems to support the operator in operating the infrastructure in a safe and efficient manner. It includes identifying monitoring and checking activities the operator is carrying out to reduce the likelihood of making an error and identifying how controls and indications can be better presented to remove or mitigate potential error traps for the operator.

The approach taken has identified that the tasks carried out by signalling and level crossing staff can be characterised as a series of interrelated and overlapping process cycles which place the operator's cognitive demand in an operational process context.

It also considers the human factors implications of usability issues by identifying their operational consequence, and impact on safety and performance so that potential mitigations can be assessed.

This approach is applicable to any operational scenario regardless of the state of the railway. These include:
• emergency scenarios where the signaller is required to take immediate action to prevent a catastrophic incident
• degraded scenarios where the signaller is unable to signal trains normally or is required to give operational instructions to the driver before giving movement authority
• perturbed scenarios where the signaller is required to implement significant changes to planned services
• normal working where the signaller implements the planned timetable and deals with trains running outside their planned path.

The flexibility of the approach also enables its use across the full range of signalling control systems, methods of working and configurations of geographical area in use across Network Rail infrastructure.