Alireza Jafari Anarkooli - Post Graduate Student, Dept. of Transportation Engineering, K.N. Toosi University of Technology
Mansour Hadji Hosseinlou - Assistant Professor, Dept. of Transportation Engineering, K.N. Toosi University of Technology
Mehdi Hosseinpour - Assistant Professor, Dept. of Civil Engineering, Islamic Azad University, Tehran Central Branch

Ran off the road (ROR) crashes contribute to a significant amount of fatalities in the world. Although a great portion of ROR fatalities occurs in collisions with fixed objects at the roadside, including roadside hardware, current studies focusing on these collisions are scarce. The main objective of this study is investigating the effects roadway, driver, collision, and environmental factors on the injury severity of fixed object-related crashes. Using 2-year crash data of the state of Washington for two-lane rural roads, separate ordered-probit models were developed to predict the effects of a set of factors expected to influence injury severity for two major fixed object-related crashes; collision with ditches and striking to a roadside object. The modelling results revealed that injury severity in these two types of collisions is associated with contributing factors in different ways which such differences can not be uncovered by focusing merely on one aggregate model. Key differences include speed limit, shoulder width, crash location, and curved segments. This study also highlights the two variables of alcohol or drug usage and vehicle rollover as the most significant factors increasing the probability of severe crashes in both collisions with ditches and roadside objects.

Injury Severity, Fixed Objects, Ordered-Probit