Exploring mental workload via TLX: The case of operating a car stereo whilst driving

Various effects of using a high-end car stereo set on driving were investigated in the field. The experiment looked at driving with and without car stereo use. An instrumented car was used to carry out the investigations. Comparisons were made of primary driving variables (such as speed), measures of performance with the stereo on pre- defined tasks, and the NASA task load index (TLX). The TLX is an established subjective measure of mental workload (MWL). A further aim of the study was to investigate the effectiveness of the TLX as an MWL evaluation tool in a dual task situation involving driving. Focus of regard (direction of gaze) data were also collected. The main conclusions were that driving performance is significantly affected by stero operation, and that the TLX was a useful evaluation tool in this context, providing much insight into subjective mwl changes in an everyday situation, that of driving a car and operating a stereo system.