Indirect visibility of mirrors has conventionally been measured according to an area of vision and there have been no appropriate methods to evaluate a degree of visual cognizance. This paper deals with a concrete evaluation of the visibility of the mirror based on the changeability of basic area and a rate of image distortion.

An evaluation better than the third level in the five ranks of evaluation scale can hardly be hoped for with the present outside-cross-view-mirror on current heavy-duty trucks in Japan.

To improve such situation, we have developed a periscope mirror system and succeeded in decreasing a number on the left side of confirming mirrors (from 3 to 2) and achieved the best evaluation (5th level).