Abstract
Japan uses its limited land area intensely and many businesses are located along roads. Because of insufficient regulations in Japan, advertising signs such as billboards are more prevalent there than in Europe and America. Road signs, therefore, are more difficult to recognize, because they may be hidden among such commercial and other signs. The amount of information along roads that is not required for driving, such as billboards and signs on electric poles, is measured and the detectability of road signs is investigated quantitatively through actual road tests. The ratio of area of clutter signs to the total area of the field of view was called the visual noise ratio. Investigation of the relationship between the distance at which a driver first recognized a highway number sign and the visual noise ratio revealed a negative correlation. Differences between the sexes were also observed; for example, female drivers were less affected by the visual noise ratio, but their absolute visible distances were shorter than those of male drivers.
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