Driving Simulator Study for Driver Behavior Assessment while Driving on Downgrades with Different Gradients

This paper describes an investigation of driver’s behavior assessment while driving on downgrades with different gradients and effect of road safety countermeasures using a coloured pavement or a light-emitting delineator. The driving simulator used in the experiments consists of 300-degree fields of view screen, a hexapod motion platform, a sound system with spatial placed eight speakers, and so on. The target was two kinds of downgrades after curved and more gradual downgrade section: one is the existent downgrade with 8% gradient and with one traffic lane in each direction, and another has 7% gradient with two lanes that will be constructed for improvement of the existing downgrade. The existent downgrade has a temporary road structure and we investigated the effective countermeasures of the coloured pavement or a light-emitting delineator to reduce driving speed on the temporary downgrade. The simulator precisely represented these road structures using CAD data of the real and planned roads. Two downgrade sections were connected each other in one experimental route in order to compare the driving between on different downgrades and the driving with and without the countermeasures. The results of participated 31 drivers suggest that there are almost no differences in road safety between the existent and improved downgrades in terms of objective and subjective assessments. The evaluation results of the effect of the countermeasures imply the necessity of the interface design that affords drivers easy recognition of onset location of the steep downgrade.