The Coordinated Control Of Urban Expressway On-ramp And Joint Intersection

With the rapid increase of urban traffic demand,traffic congestion in the area of expressway on-ramp and adjacent intersection is increasingly occurring.When the on-ramp traffic cannot be imported into the expressway mainline timely and the traffic flow in the adjacent intersection enters the ramp continuously,it is easy to cause the queue overflow of the on-ramp traffic and cause vehicles hoarding at the adjancent intersection and affects the normal operation of the traffic flow in the area.Based on the analysis of the characteristics of expressway on-ramp and adjacent intersection,heuristic coordination control method and optimal coordination control method are respectively established to alleviate traffic congestion in this area.Through setting the constraint of intersection queue length,the green time constraint of intersection signal control and the constraint of on-ramp queue length,combining the coordination strategy of restricting the intersection flow into the ramp and increasing the ramp flow into the mainline,the heuristic coordination control model of the on-ramp and the adjacent intersection is established.When the on-ramp occurs long queue,coordination method reduces the green time of the associated phase of the intersection and adopts the strategy of restricting the intersection flow into the ramp.When the on-ramp queue tends to the maximum capacity,coordination method restricts the minimum ramp rate threshold and adopts the strategy of increasing the ramp flow into mainline while reducing the flow into the ramp.The coordination strategies above can alleviate the queue congestion effectively and avoid queue overflow at the on-ramp while ensuring the normal passage of the intersection.Based on the cell transmission model theory,by setting the signal control parameter of the adjacent intersection and the ramp control parameter of the on-ramp,and through combining the analysis of the regional characteristics of the on-ramp and adjacent intersection area,the traffic flow model is established and its rationality is verified.Acquiring the evaluation indexs by the traffic flow model,taking the minmum average vehicle delay of the on-ramp and adjacent intersection as the objective function,and taking the green time,cycle time,queue length and mainline traffic capacity as constrains,optimal coordination control model is established,and the genetic algorithm is adopted to solve the signal timing parameters and ramp adjustment rate parameters.Through designing the process of optimal coordination control,the optimized control parameters can be used to update traffic status in the region,which achieves the bidirectional connection between the optimal coordination control and the traffic flow model.Based on the optimal coordination control,while reducing vehicle delay at the intersection,it can delay the generation of the queue in the on-ramp and accelerate the queue dissipation and improve the operation status of regional traffic flow.Taking the Chengdong Avenue expressway on-ramp and adjacent intersection(Chengdong Avenue and Zhenxing Avenue)in Xuzhou as an example,a simulation platform is built by using MATLAB and VISSIM software to realize the heuristic coordinated control method.The MATLAB software is used to establish the traffic flow model and realize the optimal coordination control method,and historical traffic volume in morning peak hour is used to evaluate the application of coordinated control method with the indexes of on-ramp flow,queue length and average vehicle delay.The simulation results show that compared with the uncoordinated control,the heuristic coordinated control reduces traffic volume into the ramp by 8.27%,which causes the queue length of intersection is increased by 0.16% and the average vehicle delay of intersection is increased by 2.59%,but the on-ramp queue length is reduced by 5.34%,the average vehicle delay of on-ramp is reduced by 4.46%.Optimal coordination control dynamically optimized the signal timing to reduce the average delay by 7.64% at the intersection.Through reducing the 9.28% of traffic volume into on-ramp,optimal coordination control reduces the average vehicle delay by 55.92% and reduces the queue length by 63.20% in the on-ramp,which is at the expense of the intersection queue length increased by 9.16%.Simultaneously,compared with the defects of excessive control and fluctuating adjustment of the heuristic coordination control,the optimal coordination control is more accurate and efficient.