Freeway Safety Evaluation Based On Accident Prediction And Level Of Safety Service

Freeway safety is crucial, effective freeway safety evaluation is an essential part of work for insuring traffic safety. The keystone of this paper is to explore the method of freeway safety evaluation based on accident prediction and level of safety service.Six freeways of Liaoning province and one freeway of Guangdong province are selected as research freeway. The basic data including geometric alignment data, traffic accident data and traffic volume data of the seven freeways is arranged and analyzed. On this basis, the unequal length segment division method of dynamic cluster analysis based on the concentration and dispersion degrees of traffic accident point is determined, to divide freeway segment and provide basis segment unit for freeway safety evaluation.The freeway traffic accident statistic distribution property, the main type and application condition of generalized regression models are analyzed. The accident prediction model based on negative binomial distribution is determined. The geometric alignment independent variable and traffic volume independent variable which influence freeway safety are selected. The accident prediction models of four types which classified by design speed and number of travel lanes are established. On this basis, accident prediction upper limit model and lower limit model are established based on 95% confidence level. The freeway safety evaluation based on accident prediction is proposed, and accident prediction evaluation models are provided, which divide freeway safety into four levels.The basic concepts and classification purposes of level of safety service are confirmed. The unit length traffic accident number is selected as classification index of level of safety service. The level of safety service classification evaluation criterions of four types which classified by design speed and number of travel lanes are established. The three boundaries which divide level of safety service into four levels are determined; they are upper limit value boundary, mean value boundary and lower limit value boundary. The freeway safety evaluation based on level of safety service is proposed, and evaluation models of level of safety service are provided.The similarities and differences of two freeway safety evaluation methods are contrasted and analyzed. One freeway is selected for case analysis. Advantages, disadvantages and application condition are of two freeway safety evaluation methods are confirmed.The researches show that the freeway safety evaluation method based on accident prediction considers geometric alignment and traffic volume, which is more suitable for mountain terrain and hilling terrain freeway with compelx geometric alignment conditions, focus on detailed evaluation. And the freeway safety evaluation method based on level of safety service considers the relationship of accident number and traffic volume, which is more suitable for plain terrain freeway with better geometric alignment conditions, focus on rapid evaluation.