Single-vehicle accidents, especially collisions with roadside hazards are a major highway safety problem in many countries. Accidents statistics indicate that the probability of occupant fatality in these accidents is significantly higher than most other accident types. However, this problem has been paid little attention in the highway safety research in Japan. In this paper, therefore, some attempts are made to identify the magnitude and nature of the problem by reviewing the findings of recent studies in many countries, to perform some statistical analyses on the collisions with roadside object in Hokkaido, and to develop a simple roadside hazard model for estimating the hazard for particular roadside object. A limit study on the roadside accidents in Hokkaido reveals that nearly two-third of the fatalities are caused by a striking a utility pole and a longitudinal guardrail. The effects of alignment on roadside accidents and departure location are defined. In discriminant analysis, it is found that the most important factor contributed to the fatal accident potential is an impact speed, and the second contributor is the kind of vehicle. Based on the results, logit model is developed for estimating the probability of fatal accident in roadside impacts. The simple roadside hazard model is developed for the conditions that vehicles will encroach to the left-side and collide with particular object on a tangent section of two-line highway. This model consists of accident model, encroachment model and fatal probability model. This model is applied for the simulation in case of electric pole and the results suggest that an estimated accident rate is almost similar to an actual one on National highway system in Hokkaido.
Statistical Analyses on the Collisions with Roadside Obstacles and Development of Roadside Hazard Model
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