Effects of Geometric Features on Rear-End Crash Incidence on Mountainous Two-Lane Highway

In order to improve the safety level of mountainous two-lane highway, this paper investigated the relationship between highway geometric features and rear-end crash incidence. By using negative binomial generalized models and separating the 139 kilometers highway segment into 94 successive vertical slope units, the statistical software Stata9.0 was used to evaluate the effects of 8 variables which were based on roadway geometric characteristics on the incidence of rear-end crashes occurred from 2003 to 2005 on mountainous two-lane highway in Gansu Province. Unrelated geometric variables were dropped one by one by using step regressing method. Finally, the variables found to influence the incidence of rear-end crashes significantly was accumulated vertical slope length. The regression analysis results suggest that there are strong positive relationship between the incidence of rear-end crashes and accumulated vertical slope length. So it is wise to avoid too long successive down slope when designers are engaged in fresh highway designs on considering safety effect.