| As a special section of expressway network,the long longitudinal slope section of expressway is the key area for road operation safety management.Among them,the proportion and severity of traffic crashs in downhill direction are higher than that in uphill direction.Therefore,it is of great significance for improving the safety level of the whole road network to analyze and study the traffic crashs on the long downhill sections of expressway,and then to formulate specific safety improvement programs.Firstly,the basic data is the starting point of this paper,so a detailed database of "one file for one slope" is established.The data types mainly include traffic infrastructure data,such as road alignment,marking,traffic crash data,such as crash time,crash type,traffic data,such as traffic flow,vehicle speed and so on.Secondly,in order to understand the characteristics of traffic crashs in long downhill sections of expressways,the factors influencing traffic crashs are qualitatively analyzed from four aspects: people,vehicles,roads and environment.On this basis,the distribution law of traffic crashs is quantitatively studied from five aspects: time,space,vehicle type,crash form and crash climate.It is concluded that road factors account for a large proportion in the causes of crashs.The conclusion that the peak of traffic crashs occurs between 9:00-10:00 and 16:00-17:00 and that the risk of freight car operation is greater than that of car operation provides a basis for the analysis of the causes of traffic crashs.Then,in view of the fact that traffic safety has many attributes,this paper determines five traffic safety attributes according to the actual demand: crash rate of millions of car kilometers,number of casualties,number of vehicles involved,duration of crashs and duration of major crashs(fire crashs,bus crashs,dangerous chemicals crashs),etc.Based on which,the long downhill sections studied are handed in turn.General safety assessment.In order to judge the traffic safety situation of the studied slope more comprehensively in recent years,the above five individual traffic safety evaluation indexes are weighted and synthesized,and the TSI index of traffic safety comprehensive evaluation for long downhill sections is put forward,and two sets of weight calculation models,entropy weight model and analytic hierarchy process model,are established.Through case analysis,it is found that the application of comprehensive evaluation index of traffic safety can give priority to the slope with poor operation safety.Then,the causes of traffic crashs are analyzed for the slope with poor safety conditions.Combining the results of field investigation and traffic crash characteristics analysis,it is found that road factors are the main causes of traffic crashs,and different road alignment combination will lead to different forms of traffic crashs.Therefore,traffic crashs are divided into three types: vehicle-vehicle collision,road-vehicle collision and vehicle itself.Taking road alignment index as independent variable and number of traffic crashs as dependent variable,three traffic crash regression models are established respectively.Elastic analysis of the model is carried out to obtain the main and secondary causes of three traffic crashs.Taking the ideal state of slope 0,deviation angle 0 and not near the entrance and exit,the crash correction coefficient of the model is studied and the reference value of the crash correction coefficient is obtained.According to the reference value,the change direction and degree of the number of traffic crashs can be determined when the unit change of road alignment index occurs.The research results lay a theoretical foundation for formulating reasonable and targeted road safety countermeasures.Finally,based on the analysis of the distribution of traffic crashs and the causes of crashs,a series of countermeasures for improving traffic safety are formulated from the aspects of adding escape lanes and channelizing entrances and exits. |
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