n Ergonomics SA : Journal of the Ergonomics Society of South Africa - A systems approach to the assessment of mental workload : development of a mental workload index : research article

Volume 18, Issue 2
  • ISSN : 1010-2728



The objective of this study was to develop a scientific method for determining the mental workload imposed on train control officers (TCOs) which is objective and quantifiable and stands up to tests of validity and reliability. The method solves an existing operational shortcoming, and could be used as a tool for predicting the mental workload imposed on an operator at a particular train control centre. The method could be applied to manage and improve operational safety in the rail transport environment. A participative approach was followed in the development process. A work group comprising expert users of the system was involved in identifying task factors and assigning weights for task and moderating factors. The newly developed Mental Workload Index (MWLI) consists of three task factors and eleven moderating factors, each with a different weight in terms of its contribution to overall mental workload. The work group performed several iterations to reach final consensus and acceptance of the factors and their respective contributions to the MWLI. The development process is discussed, and the final index with the task and moderating factors is presented. In closing, the value and application of the MWLI is discussed. The MWLI provides an objective method for the assessment and prediction of mental workload in the train control environment.

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