The objective of this study is to develop a quantified method for determining the mental workload imposed on train control officers (TCOs) and to express this mental workload by means of an index that is objective and can stand up to the tests of validity and reliability. The method addresses an existing operational shortcoming in Spoornet train control operations and could be used as a tool for predicting the mental workload imposed on operators at particular train control centres. The method could be applied to manage and improve operational safety in the rail transport environment. A participative systems approach was followed in the development of the measuring methodology. A work group comprising expert users of the specific train control 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 on the following task factors and their respective contributions to the MWLI: the number of data transactions, the number of authorisations, and the number of communications via telephone and radio. The systems approach used in the development process is discussed, and the final index with the task and moderating factors is presented. In conclusion, the value and possible application of the MWLI are discussed. The MWLI is shown to provide an objective method for the assessment and prediction of mental workload in the train control environment. / Thesis (PhD)--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / unrestricted