Abstract
Motorcycle accident is one of traffic accidents types in Nagano Prefecture, where most of the population lives in hilly and mountainous areas. Motorcycle accidents, particularly single-vehicle accidents, are common in the prefecture, suggesting the influence of road alignment in causing the accidents. In this study, the authors analyzed the effect of road alignment on single motorcycle accidents in comparison with four-wheeled single-vehicle accidents, using statistical data on traffic accidents in Nagano Prefecture. The analysis covered 134 single motorcycle accidents (excluding mopeds) and 1,169 single four-wheeled vehicle accidents that occurred on general roads in Nagano Prefecture during the 11-year period from 2010 to 2020. The classification of road alignment was based on traffic accident statistics. The results showed that motorcycles were most frequently involved in accidents on downhill road alignments, accounting for approximately 40% (four-wheeled vehicles: approximately 27 %), and approximately 35 % (four-wheeled vehicles: approximately 16 %) of these accidents involved left/right curves, indicating that fatal and serious injury accidents were more common on downhill road alignments with curves. Furthermore, the fatal and serious injury accident rates for motorcycles were higher when the road alignment was a downhill left curve and an uphill right curve, at approximately 95 % (four-wheeled vehicles: approximately 55 %) and 91 % (four-wheeled vehicles: approximately 32 %), respectively. These results indicate that motorcycles are more susceptible to the effects of road alignments with gradients and left/right curves, and the unique road alignments such as downhill left curves and uphill right curves are particularly the contributing accident factors.
