The road distance between two cities is not determined completely by the direct distance. The road network and the topography influence the road distance and make a difference in accessibility of cities in the traffic network.
In this paper the direct distance and road distance between two cities in Chugoku region, Kyushu region, and Shikoku region are measured and relation of the two distances is quantitatively aralyzed. As a result, the following anclusions are obtained:
(1) The ratio of the road distance to the direct distance is between 1.36 and 1.40 on the national highway network, the road distance is distributed in the range of about 100km. Therefore it is difficult to estimate the road distance by the direct distance.
(2) Kyushu region has small difference in the accessibility of cities not only in prefectural road network but also in national highway network. In Chugoku region there are some cities which are not high accessibility in national highway network. In Shikoku region the pretectural roads do not support national highway network and some cities have low accessibility in traffic network.
(3) The topographical barrier extends the road distance. The ratio of the road distance to the direct distance is between 1.5 and 3.0 in the road along the vallry, the mountain pass, and the coastline such as rias.
(4) In this paper the road distance is divided into three elements. The first element is the direct distance. The second element is the distance extended by the distribution of road network. The last element is the distance extended by the topographical barrier.
The ratio of the second element to the first element is 12_??_14%, the ratio of the last element to the first element is 18_??_30%. Therefore, the influence of topographical barrier is larger tham the influence of the road distribution.
