Estimating number of Accidents Model for Urban Roads in Iran

In this paper, a statistical model has been offered to predict accident number in the segments of Iranian urban roads. The model was constructed on the base of traffic, geometric, environmental data and also the accident number for one hundred sixty five segments of urban road in Zahedan city, one of the biggest cities in Iran. Producing of a general model for several urban road types for evaluation of safety performance was the final aim of the applying of the model in this area. For production of the model a new methodology have been used. The most important features of this methodology are: selecting type of model on the base of characteristics statistical of data, applying of integral functions for selecting of variables functional form, the optimization on the base of improved gradient vector method, the goodness of fit models on the base of plot of cumulative residuals, and also no using of software statistical for running of modeling processes. On the other hand, this methodology can be extended to the other engineering subjects.The results showed that the independent variables, on the base of their character, imitate special functional form related to their data characteristics. The functional form can be liner, nonlinear or occasionally complex of them. Although the generalized linear models (GLMs) commonly use in develop accident prediction models, are not able to model probability of nonlinear relationship between dependent variables and independent variables, and on the other hand they usually divide independent variables and study their relationships separately. In this study following results related to road safety in Iran have obtaineda. Traffic flow is the strongest variable for increasing or decreasing the accidents. The relationships between this variable and number of accidents is nonlinear in the form of and the coefficients is about 1, which means for each 10000 transport means in day the accidents number increases to 15- 20 percent and show reduction process in high variations. b. Apart from traffic flow, there are some different variables can effect on the accident. On the base of Iranian cities condition, these variables are: percentage of curb parking using, the number of minor roads and junction’s number or access point density, and the lane numbers, one/two- way traffic and also lane width. The weight of these variables is different. In this study the percentage of curb parking show the biggest effect and being or inbeing of median have the little effects on accidents. c. The other variables such as road surface quality, being or not being of lane, speed and land use have a little effect or even ineffective on accident numbers.