Determining the Accident Modification Factors Based on Iranian Road Accident Models

Road accident models are the mathematical equations of various attributes in road environment which may not be directly applicable in economic appraisal and optimization procedures in road safety projects. There is a need to use a mediator variable to estimate the amount of decrease in traffic accidents as a function of improvements in geometric features and environmental condition of the road. This mediator variable, known as "Accident Modification Factor (AMF)", converts the initial form of a raw statistical accident model to an indicator applicable in economic appraisal models. Numerous equations have been established before by various researchers to estimate the AMF quantities. In this paper, the AMF factors applicable in road safety economic appraisal and optimization models are developed using the valid statistical accident models in Iran. In accordance to the validity of the models existing and currently used in Iran, AMF factors are suggested for three types of geometric features consisting of: (1) road width and surface condition, (2) horizontal curves, and (3) roadside hazards. The proposed equations of AMF factors have been utilized in the recently established resource allocation algorithm for road safety projects in Iran.