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Visibility Effectiveness of Hemisphere and Corner Cube Retroreflective Pavement Markers on Curved Roads

This research investigated the visibility effectiveness of hemisphere and corner cube pavement markers on various curved road driving conditions. The study consisted of a field experiment to investigate visual threshold and an evaluation study to investigate visibility effectiveness. In the field experiment, a U-shaped test track with a curvature of 30 m radius was set up to investigate the visibility threshold. Two marker types, the hemisphere and the corner cube, and 2 directional driving conditions, right-turn and left-turn conditions, were considered. The results indicate that there is no difference between marker types, but there are differences between turning directions. The left turn has a significantly higher value and is therefore determined to be the resultant visual threshold. The resultant visual threshold is 1.70 X 10sub6 lx, and this is significantly higher than the recommendation of the Commission Internationale de l'Eclairage (CIE). The evaluation study was to evaluate the visibility effectiveness of these 2 markers on 8 curved roads with different radii based on the resultant visual threshold. The evaluation indicates that both pavement markers meet the 3 s preview time as suggested by CIE. However, it also suggests that the corner cube is superior on roads with radii greater than 60 m, whereas the hemisphere is much better for the roads with radii smaller than 60 m.