Pedal operation characteristics and driving workload on slopes of mountainous road based on naturalistic driving tests

Sloped sections are the basic road units of mountain roadways and often considered as high-risk positions. To verify the correlation between the slope and the physiological signals of drivers and thus acquire the mechanism of the influence of the slope parameters on the drivers' workload, this study conducted naturalistic driving tests on two-lane mountainous roads. The data of vertical alignment parameters, electrocardiographic signals of drivers, and accelerator/brake pedal forces were collected. The distribution pedal force as well as its relation with the heart rate increase (HRI) were analyzed. Furthermore, the mechanism of drivers' workload on slopes was identified in terms of the physical and mental burden. The main findings are as follows. (1) Brake pedal force are higher than those of the accelerator pedal force, and the amplitude of the brake pedal force corresponding to the maximum use frequency is higher than that of accelerator pedal force, i.e., greater physical load is required for foot-operated control on downhill segments. (2) The pedal force is positively correlated with the HRI, and the correlation between brake pedal force and HRI is stronger than accelerator pedal. (3) There is no significant correlation between gradient of sloped section, HRI and brake pedal use frequency. (4) When the HRI and pedal force data collected from different drivers on a slope were averaged, the correlation between HRI and pedal force was found to be even stronger.