Crossing collisions at intersections have been accounted for one-fourth of the total accidents for the last two decades in Japan. This type of accidents could be caused by poor visual environment at intersections, including indirect visibility provided by traffic convex mirrors. No available desk methods, however, has been reported so far on how the mirror shall be installed properly. This paper discussed the appropriate conditions of the mirror installation. They include mirror visibility simulation technology which was developed applying three-dimensional computer graphics software. The simulated mirror images were found to be in high consistency with actual images. In this way, the mirror visibility obtained by optimal mirror installation was assured to be desirable both in simulation as well as in the field study. The simulation demonstrated that a slight change of the mirror plate angle influenced greatly the visible distance. In conclusion, the 3DCG simulation method was effective to examine conditions of good direct and indirect visibility at intersections.