Control Methodology Of Reducing Congestion At The Freeway Merging Area Under The Environment Of Intelligent Connected Vehicles

Freeways play an important role in the integrated modern transportation system in China,as well as in the national social and economic development.The merging area is a must for vehicles to enter any freeway.The main line traffic and on-ramp traffic flow in the merging area change lanes and switch speed frequently,which can easily lead to traffic congestion and bring safety and efficiency issues.A comprehensive information base and refined management methods are needed to deal with traffic congestion in the merging area.The technology of connected vehicles has become an emerging technology to cope with traffic congestion.Through information interaction technologies between vehicles or between vehicles and roads,traffic decision makers can form control strategies for the entire traffic flow based on real-time road traffic data.Hence it is of great significance to study the method of reducing congestion in the merging area of the freeway in the context of intelligent connected vehicles to reduce the probability of traffic congestion in the merging area of the freeway,and improve the operating efficiency and safety level of the freeway networks.The definition of intelligent connected vehicles and its connection with related concepts such as intelligent transportation and internet of vehicles are clarified.Intelligent connected vehicles technology system is summaried which includes three fields:vehicle,information interaction and basic support.The development status and future development trends and challenges of intelligent connected vehicless at home and abroad are analyzed,the principles of the three-stage division method are put forward,and the development stages are divided into three sections,including the non-connected environment,the primary connected environment and the advanced connected environment.The components of the merging area facilities are clarified and the merging area types are divided.Based on the video data of the multi-lane freeway merging area,the time distribution of the mainline and on-ramp traffic volume in the merging area,the distribution characteristics of the traffic volume in different lanes,the proportion distribution characteristics of each vehicle type on each lane,the main line traffic density and location speed distribution,and the distribution characteristics of the headways of vehicles on the on-ramp and 1^st-lane on main lane are analyzed.The results show that there was non-uniformity in the traffic volume of each lane of the mainline and the distribution of vehicle types in each lane,and the headway distribution characteristics follow the Weibull distribution.The specific connotation of the multi-lane freeway merging influence area is defined,and the spatial scope of the merge influence area is clarified.The location speed change of each lane in the merging area and the number of lane changes between vehicles were calculated during the congestion period.The speed reduction first appeared in 1^st-lane of the main line and gradually spread upstream and outward.A large number of inward lane changing behaviors were observed.It is considered that speed change and lane changing are the key factors that cause congestion in the merging area.The two different situations of time which the on-ramp vehicles take to finish the merging process under the intelligent connected vehicles environment are clarified.And the 3 levels ofcongestion caused by the merging process are divided by mild,normal and severe.The critical value of the headways and the method of determining the number of times and valus of speed reduction were given.A probability model of the convergence speed disturbance to propagate downstream the merging area in the intelligent connected vehicles environment is established.The smaller the headways of the main line and ramp traffic are,the higher the probability will be.The strategy of reducing congestion in the merging area under the condition of primary connect vehicles is proposed.The traffic flow environment is analyzed,and the necessary and sufficient conditions for traffic congestion on the freeway are deduced.The adaptability of the jam absorption driving in the merging area is analyzed,and three start-up discrimination conditions for the strategy are proposed.The calculation methods of key parameters such as the speed reduction value,and the location where the strategy should begin is proposed.A complete jam absorption driving strategy for the merging area of the freeway is formed.The SUMO simulation software is used to verify the effect of the strategy.The simulation results show that the strategy can be used to reduce congestion in the merging area of the freeway under the primary connected environment,and the effect of the strategy is obvious.A cooperative merging control strategy is proposed,the basic assumptions and boundary conditions in the control model are clarified.With the goal of minimizing the energy consumption of all vehicles and maximizing passenger comfort during the entire merging process,vehicle acceleration and jerk are selected as the modeling target functional.A method for determining the sequence of vechiles passing through the merge point is proposed,which includes two factors:the lane the vehicle is in and the time taken to reach the merge point.The established model is a functional extreme value solving model with both the initial and terminal ends determined,which can be solved by using the variational method.The MATLAB software is used to numerically simulate the situation of eight vehicles each on the main line and the ramp.The results show that the proposed model can make all vehicles pass the merging point at the same speed and headway,the average fuel consumption of the vehicle is reduced by about 15.7%,and the driving time is reduced by about 5.7%.