Relationships between drivers’ mental stress and cars steering manoeuvre on mountain roads environment

Steering manoeuvre is a major part of driving tasks that drivers have to implement to complete a travel on a highway. Existing studies speculate that a faster rotation of steering wheel cause a larger psychological burden. To confirm the correlation between steering wheel operation and driver’s mental stress, field driving tests using real vehicles under natural driving condition were performed on four complex two-lane mountain highways with long-distance. Drivers’ electrocardiosignal, steering wheel input, vehicle speed and trajectory were collected along the distance travelled. Using heart rate increase (HRI) of the driver as an intermediary, the relationship between the angular speed of the steering wheel and driver’s mental stress was analyzed. The results demonstrated that: first, drivers’ heart rates were significantly higher during overtaking than under normal driving conditions. Furthermore, HRI was significantly higher when overtaking large vehicles than that when overtaking small passenger cars, and drivers’ heart rates had already substantially increased before the start of overtaking. Second, drivers’ heart rates increased when traveling on horizontal curves. The sharper the curve was, the higher their heart rate increased. Finally, drivers’ HRIs had a strong positive correlation with the maximum angular velocity of steering wheel, for both the conditions of overtaking and driving on curves. Therefore angular speed of the steering wheel input can be used as a predictor of driver’s mental stress when travelling on a mountain road with complex geometric features.