Study On Traffic Safety Evaluation Of Urban Expressway

While the urban expressway has satisfies the citizens’ travel demand,its traffic safety problem is becoming increasingly prominent.In order to enhance the management of the road safety,it is necessary to carry out a research regarding the evaluation of the urban expressway safety.First of all,based on the structural layout,the road condition and the road safety of the urban expressway,the traffic safety evaluation was carried out at the micro level.The urban expressway was broken down into basic sections and nodes(diversion area,confluence area and interweaving area),and these basic road sections and nodes were defined as “units” of urban expressway.The minimum section was composed of two section units and a node unit,which are called the "sub-section" of the urban expressway.The internal connection among the unit,the sub-section and the urban expressway had been established from the micro level.Subsection was taken as the objects in the evaluation of the urban expressway safety.The threelevel framework were based on for urban expressway safety evaluation.The evaluation cycle and methods were determined to establish a traffic safety evaluation framework.Secondly,based on the analysis of the internal relationship between the traffic accidents and the traffic conflicts,the severe conflict rate was taken as an evaluation index.Traffic safety influencing factors were selected preliminarily,relevant data were surveyed and disposed.Taking advantage of the characteristics of the severe conflict rate,a quantitative analysis of the influencing factors of the road safety was carried out objectively.Based on the descriptive statistical methods and correlation analysis,the influencing factors of the road safety in each type of the “unit” were determined to provide a theoretical basis for the construction of traffic safety evaluation model and the formulation of improvement countermeasures.Thirdly,the sub-section was composed of two section units and a node unit.In order to carry out the traffic safety evaluation of the sub-section,the road safety of the unit was necessary to be evaluated firstly,before integrating the evaluation results of each unit.Based on the severe conflict rate and the selected influencing factors,the traffic safety evaluation models of different types of units were constructed respectively by the Bayesian network as a modeling tool.The effectiveness of the model could be verified on the basis of the training data set and test data set.Making use of the conflict measurement method of the evidence correlation coefficient along with the information fusion technology of D-S evidence theory,the evaluation results of each unit were merged to realize the traffic safety evaluation of the sub-sections,thereby the traffic safety evaluation model of the urban expressway sub-sections had been established.Finally,the South Second Ring Road in Changsha City was taken as an example to conduct a case study to verify the effect of the evaluation model in a six-hour consecutive periods.A multi-factor inference analysis was conducted based on the evaluation results to propose control measures from both macro and micro perspectives.The results showed that the traffic safety evaluation model established could identify the road safety status of different types of the sub-sections.It was feasible and practical to use the sub-sections as the evaluation object to generate the thermal maps from the evaluation results,which could comprehensively reflect the road safety status of the urban expressway.The established traffic safety evaluation model could perform the analysis of causation based on the evaluation results in order to provide a basis for road safety control measures.