The purpose of this project is to develop the start of a more objective and standard methodology for the measurement of mental workload during driving. In this study we look at the best way to measure the expected differences in mental workload on a busy and quiet motorway. Thirty-four participants drove the instrumented car of TNO Human Factors (INCA) on the A27 motorway in the vicinity of Almere (expected workload: low) and on the A10 motorway around Amsterdam (expected workload: high). The participants were divided into one of three groups that each performed a different secondary task: a visual continuous memory task, an auditory continuous memory task and a peripheral detection task. Several driving behaviour measures were recorded with 10 Hz. Participants also gave a subjective rating about their experienced mental workload. None of the secondary tasks shows a significant difference in performance between the A27 motorway and the A10 motorway. We did find a difference, especially on the visual continuous memory task, between stationary performance and during driving performance. For example, the percentage missed responses and the percentage wrong answers increased from stationary to driving conditions. This was the effect that was also expected from the A27 motorway to the A10 motorway, but that we didn’t find. The driving behaviour measures did not show unambiguous results either. The subjective mental workload, however, did show a clear effect of type of road. Driving on the A27 motorway is experienced as less loading that driving on the A10. It is concluded that this study is not a solid enough basis to choose for an unambiguous standard methodology for the measurement of mental workload during driving. The reason for this is not that we chose to test the wrong measurements during the experiment, but because the mental workload was not different enough between driving on the A27 motorway and the A10 motorway. On both of these two roads the mental workload of the driver is probably still that low that performing an extra secondary task can easily be done by the driver without having to decrease his driving performance. The effects on driving behaviour are not large enough to speak of compensatory behaviour for the higher mental workload on one of these motorways. (Author/publisher)
Abstract