Driver Perception of Superimposed Horizontal and Vertical Road Curves for Bi-Directional Roads

With additional dimensional elements, the road appearance gets complicated and hence there is a possibility of erroneous reactions from drivers, which can cause a safety hazard. This paper assesses the perception abilities of the drivers for different roads with superimposition of horizontal and vertical curves. The questionnaire of the survey has been designed as a set of slides, each containing two 3D images of simulated roads having different values of vertical and horizontal curve parameters at various staggering levels arranged successively. The renderings during the design are made with a camera set in congruence with the eye level of the driver on the road. Sixty drivers have been interviewed with this questionnaire, and their ability to distinguish between the curves is recorded as a categorical variable (Yes or No). The responses are modeled using logistic regression wherein the curve parameters and driver demographics are explanatory variables. From the model, it has been observed that the ability to differentiate between the curves decreases with higher radius of the horizontal curve, and higher staggering of the superimposed horizontal and vertical curves. Furthermore, drivers can perceive differences in vertical geometry better than in horizontal geometry. The drivers can distinguish two successive similar curves if the geometric parameter difference is higher, as evident from the model. With the lack of field models, results from this experimental study can be a cue for transportation planners for designing overlapping geometry.