Abstract
　Construction, improvement, repair and restoration works carried out between 1962 and 1988 on the mountainous roads besides the Amagase reservoir, Kyoto Prefecture Japan, have been recorded on a card type database. Detailed analyses prove its usefulness for the assessment of road hazards.
　Damage of human lives on roads and failure of traffic capacity can be quantitatively expressed by a function of the hazard potential and the social preparedness against road hazards. It is demonstrated that the weathering conditions, which constitute major factors affecting hazard potential, can be explored by the hydrochemical analysis, even if systematic geological survey is difficult. It is also demonstrated that the database can be effectively used to evaluate the hazard potential of any site which has experienced frequent landslides.
　Historical analysis of the database is carried out to reveal changes in the hazard potential, social environment of the road and engineering methods for road protection. In 1960's and the earlier half of 1970's, concrete retaining walls, mortar covering and removal of debris were the major countermeasures to the repeated occurrence of small scale debris slides. In the later half of 1970's and the beginning of 1980's, facilities for preventing rock-fall hazards were extensively installed. Meanwhile, increased traffic posed a heavy demand for road widening at some sections, which resulted in a higher hazard potential. Radical improvements of slope stability were undertaken in the later half of 1980's and thereafter in order to minimize the risk to human lives, because occurrence of rockslides had become a major source of the risk, infrequent as it is.
　The result of the historical analysis of road hazard database can be used to assess the hazards for a section at which much experiences of hazards and engineering works are not recorded. It can be a basis for analysing the safety of a road network and for its improvement, as well.

【キーワード】：道路災害，斜面災害，道路環境，データベース，防災力
Key words: road hazard, landslide, road environment, database, social preparedness, disaster prevention

*京都大学防災研究所
Disaster Prevention Research Institute, Kyoto University