Research On Evaluation Theory And Method Of Level Of Service Of Safety On Urban Expressway

In the megalopolis,urban expressway brought many convenient for the urban residents.But the safety issues are also increasingly concerned with the rising accident rate of the expressway.The city congestion is aggravated when accidents happened on the urban expressway,and convenient and efficient function of urban expressway are also reduced.The safety of urban expressway will be affected by the dynamic traffic flow characteristics,such as traffic volume,speed,density and occupancy under the condition of the existing traffic facilities.The level of service of safety on urban expressway in a certain period of time can be determined in real time by research on dynamic traffic characteristics of urban expressway.It can also provide some guidance for city traffic management to take corresponding measures timely,and reduce or prevent accidents,reduce or alleviate traffic congestion.The level of service of safety on urban expressway is studied in this paper from the aspects of definition,classification,quantitative and application.The main research contents include the following six aspects.(1)The paper analyzed the level of service of safety on highway and urban road,and intersection,traffic safety evaluation,traffic accident prediction and severity of traffic accident.The definition,classification description and relevant quantitative index of the level of service of safety on expressway are given in the thesis.(2)Based on the analysis on the influence of road alignment and entrance ramp on the safety of urban expressway,the accident probability models based on road factors are established respectively in the thesis.The accident probability model based on road alignment is affected by horizontal curve radius,vertical curve radius and longitudinal slope.And based on the analysis on delay of on-off ramp and off-on ramp,the delay model of off ramp,the delay model of on ramp,the delay model of expressway and the delay of side road are established considering the distance between on ramp and off ramp and traffic volume,and then the accident probability model based on entrance ramp is established.(3)Traffic flow varying characteristics of time and space on urban expressway are studied based on relevant data in Beijing expressway in the thesis.The mathematical model between traffic volume and speed,and between traffic volume and time occupation are verified.And then,based on study on traffic flow characteristics under congestion and smooth state on expressway,the influences on expressway safety of traffic volume are analyzed,and the accident probability model based on traffic volume is established.It is used to determine expressway safety under different traffic state.(4)Accident probability model and accident severity model are established through the analysis on the relationships between speed and the rate of traffic accident,traffic accident deaths and accident risk,and the influence of speed deviation on traffic accident based on the expressway data in Beijing.It can provide theoretical support for the construction of the model of level of service of safety in the end.(5)The definition of level of service of safety on urban expressway is given,and the evaluation system framework is constructed,including the basic functions,the establishment principle,the selection and analysis of evaluation index.And the safety evaluation system of urban expressway is determined,and the weights of influence factors and evaluation indexes are determined by fuzzy mathematics analysis and AHP evaluation method.(6)The division method of level of service of safety on urban expressway is proposed in the thesis,and the quantitative classification is determined by the classification index and the division criterion.The classification based on traffic volume and speed,and the overall classification are given.Finally the model level of service of safety is validated by an example.