Study On Risk Propagation And Control After Freeway Accident Based On Macroscopic Traffic Flow Model

With the constant increase of motor vehicle total quantity and the expansion and promotion of freeway network in our country,the traffic safety problem is becoming more and more serious,which has brought great test to road users and managers.Under the background of the strategy of building a powerful traffic country,scientific and effective analysis of risk communication of traffic accident and corresponding control methods are of great significance for improving freeway traffic safety and reducing the loss of national economic property.However,the current research on freeway traffic accidents mainly focuses on the analysis of the factors affecting the accident and the evaluation and prediction of the accident risk,and the research on the communication and control of the traffic risk after the accident is relatively few.After the accident,the traffic risk spreads to the upstream section,and within the scope of its temporal and spatial influence,the traffic flow accident risk on the section will be in an uncertain and fluctuating process.If the communication process of traffic accident risk on the road can be accurately described and the accident risk can be quantified,it will provide a theoretical basis for traffic safety warning and traffic risk control.Therefore,this paper takes freeway accident sections as the research object to study the risk transmission after traffic accidents and the corresponding control methods.First of all,the risk transmission behavior of the freeway after the accident is studied.Freeway accidents are often accompanied by lane occupancy and the resulting vehicle lane change phenomenon,and these two phenomena are the main risk factors inducing secondary accidents.The influence of these two risk factors on traffic flow is analyzed,and based on this,the classic macro traffic flow model is improved,and a traffic flow model under accident risk is established to simulate the traffic flow operation in the accident section of the freeway.Combined with the concept of change rate of fluid kinetic energy in fluid mechanics,the accident risk was represented by the change rate of traffic flow energy,and the calculation model of risk propagation time and influence range based on the change rate of traffic flow energy was proposed to simulate the propagation process of accident risk on the road section.Secondly,a freeway control method to inhibit the spread of accident risk is proposed.The influence of lane change guidance control and variable speed limit control on the basic traffic flow diagram is analyzed,and the basic cell transmission model is improved.On this basis,a lane change guidance control model is constructed with the goal of optimal traffic flow density distribution and minimum lane change times,and a variable speed limit control model with the goal of minimum total speed difference,minimum total travel time and maximum total turnover of traffic flow in the speed limit section.The control logic of MPC is analyzed,and the lane change guidance-variable speed limit cooperative control method based on MPC framework is proposed.Finally,the proposed collaborative control method is verified by simulation.According to the traffic simulation scenario set in this paper,various parameters in the collaborative method are calibrated,and genetic algorithm is used to optimize the collaborative control model based on MPC framework.The control effect of the collaborative control proposed in this paper is compared with that of no control and lane change guidance control.The simulation results show that the collaborative control method proposed in this paper can effectively improve the running condition of the traffic flow in the freeway accident section and restrain the spread of the accident risk.