Development of a mental workload index: a systems approach.

The objective of this study is to develop a method for determining the mental workload imposed on train control officers that is objective and quantifiable and can stand up to the tests of validity and reliability. This technical note reports on the methodology used in the development process, as well as the assessment of the criteria considered for the mental workload index (MWLI). The MWLI aims at solving 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 MWLI consists of three task factors and 11 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 criteria and development processes are discussed and the final index with the task and moderating factors is presented.