Abstract
There is concern that the reduction of motorcycle accidents has stagnated in Nagano Prefecture, where most of region is a hilly and mountainous area. To further reduce traffic accidents, it is necessary to accurately identify true traffic accident causes unique to rural areas and take detailed countermeasures. In this study, the authors focused on single motorcycle accidents on hilly and mountainous roads in Nagano Prefecture, and analyzed statistical accident data and accident case studies regarding accident factors caused by road alignment. An analysis of 65 statistical data on fatal and serious single motorcycle accidents that occurred in Nagano Prefecture during the five-year period from 2015 to 2019 revealed that 54 （approximately 83%） of the accidents were on general roads, and 28（approximately 43%） were caused by motorcycle riders aged 45-64, accounting for the majority of accidents. It was found that most of these single motorcycle accidents were caused by middle-aged and older riders who came from outside Nagano Prefecture for sightseeing and driving, and who were overspeeding or careless in front on curved sections. Furthermore, an analysis of the road alignment of the accident locations using GSI maps for the 12 cases of accidents involving middle-aged motorcycle riders who intended to sightsee or drive, obtained from the characteristics of statistical accident data, showed that the section before the accident point had a downhill slope of -4.5 to -1.5% and a straight section of 50 m or more, and that the accidents occurred more frequently on slightly gentle curves of R120 m or more. In addition, the section before the curve also had characteristics that resulted in sudden changes in road alignment, such as changes in longitudinal slope and bridge joints. The results of these accident analyses indicate that the characteristics of the road alignment and the sudden changes in the road alignment caused excessive speed and failure to properly turn the curve as accident cause factors, and that proper deceleration behavior for the road alignment should be encouraged to prevent accidents.
