Emma Lowe

The role of situation awareness for understanding signalling and control in rail operations

Rail signalling is typical of a complex control task where situation awareness (SA) has been thought to play a significant role. Taking into account the main theoretical positions, and through reviewing cognitive accounts of signalling, it is apparent that SA is a useful construct in describing and understanding rail signalling at both a cognitive and a system level. Development and maintenance of SA is complex, requiring much expertise and knowledge on the part of the signaller to extract and synthesise relevant information from the environment. The display and other artefacts and actors in the system also play a major role in the construction and maintenance of SA. This suggests that it is not sufficient to consider SA purely as an individuals product of knowledge. Instead, the active use of SA, such as in design, must reflect the distributed nature of the signalling environment, as found in other command and control-type domains. Rail signalling has not yet been subjected to in-depth analysis in terms of SA and has characteristics that make it distinct from other areas where SA has been analysed (e.g. air traffic control). This paper reviews the validity of SA and associated concepts to this safety-critical function, as well as highlighting some of the characteristics of SA (multiple tasks, display-based and distributed SA, role of local knowledge and expertise) that must be considered to use the construct in an operational context.

The Operational Demand Evaluation Checklist (ODEC) of workload for railway signalling.

This paper is concerned with the interpretation and assessment of mental workload, and in particular assessment of the load imposed by the work system. It highlights a framework created to direct the development of workload assessment tools capable of assessing the dimensions most relevant to the population being studied, in our case railway signallers. A tool to capture the operational demands on the rail signaller was required to evaluate the load from the system they operated. This paper justifies the need for, and describes the development of, the Operational Demand Evaluation Checklist (ODEC), using techniques like repertory grid with active signallers. The practical experience of the development, evaluation, live use and validation of ODEC is discussed and the paper concludes by suggesting that the approach could be adopted to interpret the concept of workload in other work domains.

Management of Personal Safety Risk for Lever Operation in Mechanical Railway Signal Boxes

Despite increased implementation of computer control systems in managing and regulating rail networks, mechanical signal boxes using lever operation will be in place for years to come. A rolling risk assessment programme identified a number of levers in mechanical signal boxes within the UK rail network which potentially presented unacceptable personal safety risk to signallers. These levers operate both points and signals and the risk is primarily the weights which have to be moved when pulling and pushing the levers. Operating difficulties are often compounded by the design and condition of lever frames, the linkages to the points/signals, maintenance regimes, the workspace and the postures and strategies adopted by signallers. Lever weights were measured as from 15 kg to 180 kg at over 160 boxes, using a specially designed and constructed device. Taken together with examination of injury and sickness absence data, interviews and field observations, and biomechanical computer modelling, the measurement programme confirmed the potential risks. A risk management programme has been implemented, comprising lever weight measurement, training of operations staff, a structured maintenance regime and renewal or redesign for boxes/levers where, after maintenance, a criterion weight level is still exceeded. For a feasible management programme, the first alert (or 1st action) value for further assessment is 55 kg, a second action level requiring specified maintenance is 80-99 kg, and a third action level requiring the lever to be signed out of use is 100 kg.