Method And Application Of Traffic Safety Evaluation For Freeway Climbing Section

There are a lot of climbing sections in the existing freeways in China. The design technical indicators of these sections are in full compliance with "road design specifications" (JTG_D20-2006) and "Highway Technical Standards" (JTG B01-2014) and other relevant norms and standards. But these sections tend to be accident-prone and high-risk when operation, So it is urgent to develop effective traffic safety evaluation method and specific safeguards for climbing sections. This paper attempts to explore the relationship between traffic flow characteristic and traffic safety under certain traffic conditions and road conditions from macro and micro perspective.The limitations of the existing research are summarized based on literature review about traffic safety evaluation of freeway. Then this research was conducted from two aspects of theory and application. Theoretically, the relationship between traffic safety and the traffic flow characteristics of climbing sections was constructed and the proposed traffic safety evaluation method was applied on the Donglushan climbing sections of Nanjing-Hangzhou freeway. The research details are as follows:(1) Traffic data collection and simulations of climbing sections. The specific object of this study was determined based on reasonable classification of climbing sections. Basic data required for this study was obtained with field observation and traffic simulation(2) Analysis of traffic flow characteristics and influencing factors. Several traffic flow characteristics such as the average speed of cars and large vehicles, average speed difference between cars and large vehicles and headway of different cross-section were analyzed. The impact of road conditions and traffic conditions on above indicators was discussed with statistical analysis.(3) Definition of affected zone and featured sub-sections division of climbing sections. On the basis of the traffic flow analysis, a suitable indicator of traffic flow was used to determine the scope of upstream and downstream of the climbing sections. And the affected zone was divided into several featured sub-sections according to the change law of traffic flow indicators.(4) Evaluation index system of traffic safety. Some evaluation index were considered based on the present literature and traffic flow characteristics and screened with correlation coefficient. Then the selected indexes were validated with traffic conflict technique and the relationship between the evaluation index and traffic safety was constructed indirectly through TTC (Time To Crash).(5) Evaluation method of traffic safety. For the entire affected area, traffic safety macroscopic evaluation method based on Bayesian network was proposed. For the upstream and downstream of the climbing sections, threshold method of traffic flow indicators was used to evaluate the traffic safety microscopically.(6) Application of traffic safety evaluation method. The proposed method was applied on the Donglushan climbing section of Nanjing-Hangzhou Expressway. Traffic safety measures were carried out based on the evaluation results. And the effects of traffic safety measures were evaluated with before-after study of the traffic accident data and traffic flow data.