Dependence of Visibility of a Fallen Object in a Tunnel on Vehicle Moving Speed

We evaluated the visibility of fallen objects on the road while a vehicle is moving in a tunnel and evaluated its speed dependence. The experiments were done in the national full-scale tunnel for experimental evaluation. The results show that the distance from a subject to a fallen object on a road when the subject recognised the fallen object is proportional to the natural logarithm of the luminance ratio between the fallen object and the background road surface. The slope of the logarithm line is constant, independent of the vehicle speed. The slope is larger in the reverse silhouette-view condition than in the silhouette-view condition. Consequently, at least in the speed range of 40-80 km/h, the visibility depends on the luminance ratio between the fallen object on the road and the background road surface. Improving the visibility of a fallen object on a road in a tunnel by increasing the ratio of luminance between the surface of the fallen object and the road surface is more effective for silhouette viewing than for inverse silhouette viewing. We conclude that from the viewpoint of visibility, the asphalt road, which gives a reverse silhouette view, is better than the concrete road.