Abstract
　A road hazard database for the National Road No.307 in Ujitahara Town of Kyoto Prefecture, Japan, is analyzed to extract the topographic factors affecting the potential of road hazards, especially landslides. The four sections of the road as defined according to the administrative boundary reflect a characteristic topographic variation between the lowland and mountains. Analysis of the thirty years of road construction works in these sections by this database reveals historical changes in the hazard environment in this period including a senous flood hazard in 1953 and intensive improvement works accompanying the change from a local road to a national road. A statistical analysis of the cost of the restoration, particularly caused by landslides of the upper slopes, suggests that the cutting of the upper slopes for the road widening causes an increase of hazard potential. Meanwhile, the disaster prevention potential of a road depends largely on the social environment including technical improvements and financial conditions, which makes the assessment of the risk in human lives and traffic interception complicate. It is concluded that the software of road management including the database of road hazards is essential to overcome such difficulties, as well as hardware constructions.

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*京都大学防災研究所
Disaster Prevention Research Institute, Kyoto University
**富山県立大学短期大学部環境工学科
Department of Environmental Technology, College of Technology, Toyama Prefectural University