ABSTRACT
In Japan, a quarter million crossing collisions occur at intersections, accounting for one-fourth of the total accidents in 2008, which is the second most frequent pattern among traffic accidents. Three-fourths of crossing collisions occurred at urban intersections. Our previous studies revealed that the risk of collision depended on the quality of the visual environment at intersections, including direct and indirect visibility provided by traffic convex mirrors. Ergonomics guidelines for installing mirrors were proposed by authors to assure their performance in ensuring crossing safety. This study aimed to assess the quality of the visual environment at
intersections and discuss effective countermeasures for preventing collisions, especially safety enhancements related to direct and indirect visibility. Visibility simulation studies, applying 3-dimensional computer graphics software, were conducted at actual and hypothesized uncontrolled intersections. The visibility was assessed and optimal solutions were derived, which provided mirror images that ensure the maximum visible distance from the crossing road as well as minimal blind areas. We observed that the fine adjustment of the depression/horizontal angle of the mirror plate, horizontal position of the mirror plate, and width of major and minor roads were critical factors affecting indirect visibility. The visibility simulation approach was efficient and effective in demonstrating that direct and indirect visibility could be improved by installing mirrors or adjusting the angle and position of the mirror plate and pole, based on the ergonomics guidelines. Minimum ergonomics requirements for intersection visibility were proposed to prevent crossing collisions at urban intersections.
