Different kinds of route guidance systems for use within vehicles are being developed these days. Apart from achieving a more optimal traffic flow, decision support is seen as one of the major functions of these systems. A beneficial effect on traffic safety can possibly be attained when a decision support system reduces the mental workload of the car driver. The aim of this experiment was to find out whether route guidance decreases mental workload in car drivers. The effects of route guidance on other sub-tasks of car driving, such as vehicle control, and paying attention to the surrounding traffic, were also investigated. How the driver regulates his speed and mental effort at different levels of mental workload was investigated as well. Speed has been used as a measure for compensating driver behaviour. The average interbeat interval of heartrate and the .10 hz component of heartrate-variability have been used as indicators of mental effort. mental workload has been manipulated by decision support and familiarity of the route as independent variables. The main results were: (1) when decision support was given and/or when driving on a familiar route, the amount of mental effort as measured by physiological indices was lower than when no support is given and/or the subject drove on an unfamiliar route. (2) decision support and familiarity of the route did not influence the quality of vehicle control. (3) the quality of paying attention to the surrounding traffic was dependent on the amount of mental workload. When decision support was given traffic was better observed by the subjects. (4) average speed depended on the amount of mental workload. When the workload was high the speed reductions tended to be insufficient to keep the performance of attention to traffic on an acceptable level.
Samenvatting