# Research on a Collaborative Control Strategy of an Urban Expressway Merging Bottleneck Area
## 1 Introduction
In recent years, some scholars have begun to focus on the coordinated control strategy of on-ramp [18; 19; 20] and variable speed limit [21; 22; 23], with a view to improving traffic flow efficiency and accelerating the feedback rate. Model Predictive Control (MPC) [24; 25] has achieved great success in the field of industrial control. Then, model predictive control is introduced to combine the macro traffic flow model, on-ramp control, and variable speed limit control for collaborative control design. However, most of the macro traffic flow models used are second-order METANET [26; 27], which confirms the effectiveness of the collaborative control strategy. At present, research on the bottleneck control of expressway merging areas has made some achievements. Scholars have improved the traditional macroscopic traffic flow model, ramp control, and variable speed limit control model and proposed control ideas based on different optimization objectives. However, there are still some problems in the improvement of the macroscopic traffic flow simulation model and the design of cooperative control strategy for expressway merging bottleneck, as follows:  
1. The expressway capacity often changes when the merging bottleneck occurs, and there are queues and overflows of on-ramp merging vehicles. Research on the improvement of macro traffic flow has little consideration of the complex traffic characteristics of expressway merging bottlenecks, which means the macro traffic flow model may have low simulation accuracy when applied to the research of expressway merging bottlenecks. 2. At present, a lot of research has been obtained for the cooperative control of expressways, but most control strategies have little research on the mutual feedback between control algorithms and traffic flow models. 3. The existing expressway control strategies based on the macro traffic model are mostly based on unilateral considerations, such as traffic efficiency, safety, environment, etc. The research on comprehensive optimization objective functions under multi-objective constraints needs to be improved. This paper introduces the problem of urban expressway merging bottleneck area, focusing on the coordinated control of safety and efficiency. The existing expressway control strategies based on macroscopic traffic models are mostly based on unilateral considerations, and most control strategies have less research on the mutual feedback between control algorithms and traffic flow models. The main motivation for this research is to introduce the current methods for solving the cooperative control strategy of urban expressway merging bottleneck areas with the goal of efficiency and safety. The rest of the paper is organized as follows. Section 2 proposes an improved CTM and gives the parameter calibration and validity test method. Section 3, MTFC-VSL (Mainline Traffic Flow Control-Variable Speed Limit) is used for speed limit control, PI-ALINEA is used for ramp merging control, and MPC is used to establish a merging bottleneck cooperative control model. Section 4 takes Xi'an Expressway in Shaanxi, China as an example to build a VISSIM simulation model to analyze the control effect of the collaborative control strategy. Section 5 presents the conclusion and suggestions for future work.