Research On Freeway Graded Speed Limits Control Considering Accident Risk Control And Prevention

The scale of freeway transportation network in China is huge.The growing demand for transportation not only increases the road load,but also highlights the problems of operation risk.The traffic accidents have brought immeasurable losses to the society and the economy.With the improvement of freeway detection system and the popularization of intelligent transportation system(ITS),the research on intelligent and humanized risk prevention and control technology is the future development trend.The research on accident risk prevention and control methods have also changed from passive experience mode to active prevention and control mode.Variable speed limits control of freeway is a relatively mature control method at present,which plays an important role in improving road traffic efficiency and safety.From the perspective of accident risk control and prevention,this paper proposes the freeway graded speed limits control method.First of all,the traffic data of Whitemud Drive in Canada and the accident statistics of Yongtaiwen freeway are calculated.The influence of variable speed limits control on efficiency and safety indicators such as road capacity and vehicle speed dispersion is analyzed,and the necessity of implementing variable speed limits control is verified.According to the needs of the graded speed limit control strategy for traffic flow prediction,on the basis of the classic METANET macroscopic traffic flow model,the variable speed limits control parameters and the compliance rate of the driver to the speed limit measures are introduced,and the model improvement and parameter calibration methods are proposed.The causes and locations of bottlenecks in freeway are discussed,and they are divided into fixed bottlenecks caused by road infrastructure and mobile bottlenecks caused by the influence of traffic disturbance waves.Spatiotemporal influence range of traffic waves after static speed limit control and variable speed limits control are analyzed respectively under smooth and congested traffic conditions,which provide a theoretical basis for the optimization of graded speed limits control.In the design of the graded speed limits control optimization model,the strategy and process steps are firstly proposed.The division method of the control area upstream of the bottleneck road section represented by sudden accidents,as well as the rear-end collision accident risk discrimination method is defined.In order to achieve the purpose of accident risk control and prevention and smooth congestion,this paper abstracts the graded speed limits control problem of freeway into a multi-objective problem,and uses the linear weighting method to construct the optimization objective function to meet the need of the real-time calculation and easy-to-solve requirement.A method for determining the number of grades of speed limits is proposed.Constraints to ensure traffic operation and safety are added,and the optimal speed limit scheme is obtained according to the actual road and traffic environment.In the verification link of the simulation experiment,the MPC algorithm is used to integrate the traffic flow model and the speed limit model,and the speed limit series and speed limit value are optimized in a rolling manner.Under different traffic conditions,the operation results of static speed limit control and graded speed limits control are compared and analyzed.The results show that the research on the graded speed limits control considering accident risk control and prevention proposed in this paper is feasible,and it can play a role in alleviating congestion and improving safety.