In a driving simulator experiment the effects of two information systems on workload were examined. It was also examined whether speed and swaying can be used as measures of on-line workload. Subjects drove the simulator car in both heavy and quiet traffic. Within each drive, subjects were exposed to five conditions: map; route guidance; traffic information with map; traffic information with route guidance, presented either simultaneously or separately (scheduled). Both subjective workload and heart rate were higher in map than route guidance conditions. Subjective workload showed significant differences for the `information system' factor, but the 'traffic density' factor was not significant. During map use, subjects' lateral position deviated more, and their speed was significantly lower than during route guidance conditions. Speed was also significantly lower in heavy traffic. This speed reduction was interpreted as subjects adapting to workload. It is suggested that this strategic speed reduction makes driving performance parameters difficult to use as measures of workload: drivers were observed to adapt their driving behaviour to task demands where possible. (A)
Abstract