| The urban expressway is the main artery of the urban transportation system,carrying a large amount of transit traffic and greatly relieving the traffic pressure in the city.However,with the frequent occurrence of traffic accidents,resulting in the rapid loss of the original "fast" ability of the expressway,and even caused a long period of extensive traffic congestion.In order to improve the operational efficiency of urban expressways and reduce traffic delays caused by accidents,it is important to study the accident characteristics of expressways from expressway accident traffic accident data,develop expressway accident risk prediction,determine the scope of accident impact after an accident occurs,and take control measures in a timely manner,so as to achieve early warning in advance and response in the event,and to reduce the negative impact of accidents.Based on the existing domestic and foreign research results,study the accident characteristics,prevention and control strategies of expressways,explore the potential relationship between prior traffic flow and the type of vehicles involved in accidents and accident risks according to the impact of traffic accidents on the traffic operation status of expressways,analyze the factors and mechanisms of accident spatial diffusion,and classify accident impact areas and accident levels.For the expressway,a safety evaluation model of the accident risk of the expressway and the prediction of the accident impact range are proposed,and the corresponding control measures are adopted for different accident impact ranges.Firstly,we analyze the characteristics of expressway traffic accidents by combining the data of expressway traffic accidents,analyze the accident pattern,time distribution and spatial distribution,etc.,and explain the mechanism of the formation of this characteristic according to the analysis results.Secondly,for the purpose of expressway accident prevention,we construct an expressway accident risk safety evaluation model by mining historical accident data and combining traffic flow data to find the regular characteristics between traffic flow,accident involving vehicle types and traffic accidents.Two indicators of vehicle ratio and traffic flow in different time periods before the accident were selected,and the accident involved vehicle ratio and traffic flow were analyzed based on the color-order diagram procedure to obtain the accident risk evaluation table.Determine the standard traffic flow conversion coefficient,convert the natural traffic flow into standard traffic flow for downscaling analysis,and perform density detection,which conforms to the normal distribution.The standard traffic flow is curve-fitted and verified by a two-dimensional scatter plot to derive the critical accident flow,and the upper and lower alert values of traffic flow are obtained from the law of normal distribution.Classify accident risk level and propose accident prevention measures according to alert value and critical flow.Through the expressway accident risk safety evaluation model,the safety risk of expressway traffic operation can be assessed in real time and effectively.Again,analyze the impact of accidents on expressway traffic operation,summarize the factors related to the spatial diffusion of traffic accident impact,divide the diffusion state of traffic accident impact into three cases,point diffusion area,line diffusion area and surface diffusion area,and select indicators such as accident duration,remaining capacity of the incident section,prior traffic conditions,weather conditions,evacuation capacity of the affected area road network,etc.,and use hierarchical analysis to determine the indicator weights.Based on the accident impact range,the accident level is divided into incident point accident,local accident and regional accident,combined with the fuzzy comprehensive evaluation and analysis method to determine the accident level,providing traffic managers with accurate and reliable accident spatial impact range.Finally,the accident impact range is used as the basis for regional division of the accident level,and the impact area is divided into protection zone,control zone and buffer zone according to the spatial impact range of the accident.Incident point accidents are divided into protected areas,local accidents are divided into protected and controlled areas,and regional accidents are divided into protected,controlled and buffer areas.For the spatial spread of traffic accidents on expressways using the main line regulation control,ramp control,traffic induction three aspects of control,combined with the control measures of each impact area,to take targeted control measures for different levels of traffic accidents.Accident risk evaluation analysis is conducted for the real-time traffic flow of an expressway section in Jinan,and the accident rate of the section is predicted according to the accident risk safety evaluation model of the expressway,and the accident risk warning level is determined and targeted accident prevention strategies are proposed.For the occurred traffic accident using fuzzy comprehensive evaluation method to determine the accident level as local traffic accident,combined with vissim simulation software and the implementation of the ramp control and variable speed limit joint control for simulation,these two joint measures can reduce the total delay by 60.3%,but the reduction effect on the average vehicle delay is not obvious. |
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