Cooperative Control Of Ramp Metering And Variable Speed Limit For Expressway Considering Accident Risk

Expressway is the main skeleton of urban road network,and its operation efficiency is closely related to the overall traffic efficiency of the city.Ramp metering and variable speed limit are commonly used expressway control methods,which have been widely proven to relieve congestion,improve traffic efficiency and safety.With the continuous increase of traffic pressure,the effect of single control method is limited,and the cooperative control of ramp metering and variable speed limit has become an emerging research hotspot.Although there have been some researches on cooperative control at home and abroad,most of them are based on the relevant control theories and experiences of foreign highways,and take the optimal traffic efficiency as the control objective unilaterally.However,expressways are quite different from freeways in terms of road structure and traffic flow characteristics.Its traffic environment is complex and changeable,and traffic accidents are frequent and easy to cause large-scale traffic congestion,resulting in great social cost waste.Therefore,the cooperative control strategy for expressways should not unilaterally pursue the optimal traffic efficiency,but should take into account the active prevention and control of accident risk while improving efficiency.Based on the traffic characteristics of expressways with frequent accidents and large involvement,this paper proposes a cooperative control method of ramp metering and variable speed limit considering accident risk.Firstly,the traffic characteristics of the expressway are analyzed,and the necessity of expressway accident risk prevention and control is clarified through the analysis of the characteristics of the expressway accident and the impact of the accident.Secondly,the principle,method,advantages and disadvantages of ramp metering and variable speed limit are analyzed.On this basis,the necessity of cooperative control is discussed,and the realization method and overall idea of cooperative control considering accident risk are proposed.In order to adapt the basic METANET traffic flow model to the cooperative control scenario and better conform to the traffic characteristics of the expressway,this paper improved the METANET model,which took into account the driver’s level of compliance to the speed limit,the characteristics of reaction time,the structural characteristics of multiple bottlenecks of the expressway and the mechanism of ramp metering.Then,the parameter calibration method of the improved METANET model is given,and the effectiveness of the improved METANET model is verified by an example of a real expressway.On the basis of the above research,a cooperative strategy of ramp metering and variable speed limit based on accident risk prediction is designed,aiming at alleviating traffic congestion and realizing the monitoring and prevention of expressway accident risk.The collision probability model is introduced to quantify the real-time accident risk of the expressway,and the traffic state is determined by the speed threshold and the collision probability threshold.The implementation process of cooperative control is proposed.Considering both efficiency and safety control objectives comprehensively,a cooperative control optimization model was established with the basic laws of driver safety,comfort and traffic flow as constraints.Finally,taking the western expressway of Changchun City as an example,the simulation verification of the proposed cooperative control strategy is carried out.The results show that the proposed cooperative control strategy not only improves the overall traffic efficiency of the expressway,but also can better improve the safety level of traffic operation,which has certain reference significance for the management and control of the expressway.