Safety at roadway intersections is of much interest to transportation professionals due to the design considerations that warrant attention in the context of the myriad movement conflicts that could potentially occur at intersections. A variety of collision types including head-on, sideswipe, rearend, and angle crashes may occur at intersections. There is a need to be able to model the number of accidents by collision type at intersections so that effective design strategies and countermeasures can be formulated to minimize accident frequencies by various collision types. At the same time, it is necessary to consider modeling accident frequencies of various collision types simultaneously to account for the possibility that there may be common unobserved factors affecting accident frequencies of various types. In this paper, a simultaneous equations model of accident frequencies by collision type is developed and presented using a data set of accident frequencies by collision type for rural intersections. The model estimation results support the notion that simultaneous equations models such as that presented in this paper should be considered for application in the safety field. The multivariate count data modeling methodology developed and presented in this paper is a significant methodological contribution to the field.
Abstract