Research On Bottleneck Control Strategy In Merging Area Of Expressway Based On Improved Cell Transmission Model

As the highest grade road that plays a skeleton role in the urban road system,the urban expressway are responsible for fast and smooth transportation of large-capacity traffic.The conflict between the main line and the ramp traffic at the merging area of the urban expressway makes it easier to form a traffic bottleneck compared to the basic road section.When the merging bottleneck occurs,the overall operating efficiency of the expressway will be affected.If it is very serious,it may also cause a wide range of congestion,and the expressway will lose its fast,smooth and comfortable characteristics.Therefore,the research on the control strategy for the merging bottleneck has important practical significance for improving the traffic state at the bottleneck,as well as the service level of expressway and the guarantee of overall transportation efficiency.First of all,based on the investigation of the actual operating sections on the expressway,this paper compares and analyzes the traffic data of the merging area and its upstream and downstream sections.It is found that compared with the basic road section,the traffic condition at the merging area during the peak period has a greater degree of decline,thus it is more likely to form a bottleneck that hinders the traffic.Then,based on the cumulative flow curve and the distribution data of on-ramp vehicles,the formation mechanism and basic characteristics of the merging bottleneck are studied,and it is concluded that the arrival rate of the upstream flow as well as the interference degree of on-ramp vehicles are the main factors affecting the traffic state of the merging area.After the merging bottleneck formed,the congestion induced by it will continue to spread upstream along the expressway,and the merging position of the onramp vehicles will gather near the transition section of the acceleration lane.Secondly,the paper analyzes the limitations of the traditional cell transmission model in predicting the traffic state of the merging area.According to the characteristics of the merging bottleneck,the traditional CTM model is improved based on the cell space division,the basic traffic diagram of the merging cell,and the on-ramp status update aspects.Based on the above improvements,an expressway traffic state prediction model considering the characteristics of the merging bottleneck is established,and the model’s parameter calibration and validity verification methods are given based on the GA and MAPE algorithm.Finally,the paper studies the variable speed limit and the ramp metering model at the merging bottleneck.According to the actual road state,the speed constraint conditions are set on the variable speed limit algorithm whose purpose is to control the mainstream traffic flow.Meanwhile,the expected occupancy update algorithm and queue control improvement are applied to the PI-ALINEA algorithm.Based on the model predictive control theory,the MPC algorithm is used to establish a merging bottleneck coordinated control strategy that combines the improved CTM model,the variable speed limit model,and the ramp metering model.The optimization goal of this strategy is set to traffic efficiency and safety level.The effectiveness of strategy is verified by simulation,and the results show that the coordinated control strategy proposed in this paper can significantly improve the traffic state at the merging bottleneck,and improve the overall operating efficiency and safety level of the expressway.