Research and Design of Urban Intelligent Traffic Control System

introduction
According to China's current traffic situation and problems, it explains the important role of traffic control in economic development and urbanization, and proposes the important purpose and practical significance of developing intelligent transportation system. The intelligent transportation system is a research field that covers a wide range of areas and integrates various high and new technologies. The following focuses on the classification of intelligent transportation systems and the design of urban traffic control systems based on multi-agents.

1 Current status and problems of urban traffic in China The current situation of urban traffic in China is: the speed of urban transportation infrastructure cannot keep up with the rapidly growing traffic demand; the conventional public traffic is shrinking; the number of taxis and private cars is increasing rapidly; the rail transit is starting; Low level of management skills. The above problems have caused traffic congestion, traffic accidents, environmental pollution, and energy problems to become increasingly serious.
The problems faced are: complicated types of vehicles and serious mixed traffic; the number of non-motor vehicles such as bicycles is staggering; the urban layout and traffic are not compatible; the travel mode is single and there is no choice; the walking is difficult and the accidents are frequent.

2 The purpose and significance of urban traffic control With the development of social economy, the acceleration of urbanization and the rapid increase of motor vehicles, urban traffic problems are becoming more and more serious. Urban traffic congestion not only causes frequent traffic accidents, increased vehicle delays, but also further increases energy waste and environmental pollution. The adverse social consequences caused by this are even more difficult to estimate. At present, urban traffic problems have become the bottleneck of global economic development and one of the global “urban diseases”. The purpose of traffic control is to apply advanced technical means and ensure appropriate public transportation conditions for public and private transportation modes under the constraints of certain administrative regulations. Specifically, the purpose of traffic control is reflected in the following aspects:
(1) Reduce traffic accidents and increase traffic safety. By implementing traffic control, conflicting traffic flows can be separated from time and space, thereby reducing traffic accidents and increasing traffic safety.
(2) Alleviate traffic congestion and improve traffic efficiency. Reasonable traffic control can effectively guide and dispatch traffic flow, keep urban traffic flow in a stable operation state, thereby avoiding or slowing traffic congestion, shortening traffic delays of vehicles on the road, and improving the overall efficiency of transportation. .
(3) Reduce environmental pollution and reduce energy consumption. The implementation of good traffic control can reduce the number of stops on the road, keep the vehicle running in a better state, and greatly reduce exhaust emissions and energy consumption.

3 Classification of urban traffic control systems Urban road traffic control systems can be classified from different angles. Here, the urban road traffic control systems are simply classified from spatial relationship and control mode.
3.1 According to the spatial relationship , the urban traffic system can be divided into single intersection control (point control), coordinated control of traffic trunk (line control) and network control (surface control) of regional intersection. form.
(1) Point control of a single intersection The point control of a single intersection is one of the most basic control methods. The control parameters of the isolated intersection control are the signal period and the green signal ratio. The control targets are generally the vehicle delay and the traffic capacity of the intersection. In the ideal case, it is desirable to minimize the total delay time and maximize the utilization capacity of the intersection. Because the point control equipment is simple, the investment is saved, and the maintenance is convenient, it is still a kind of signal control method which is applied more. Technically, it is divided into offline point control and online point control. The former adopts timing signal timing technology, and is still the timing basis of other control methods; the latter is traffic response control or vehicle induction control, which is based on the actual distribution of traffic flow of each population at the intersection, and rationally allocates the green time to each Phase to meet traffic needs.
(2) Coordinated control of trunk traffic The traffic trunks in the urban road network bear a heavy traffic load, and ensuring the smooth traffic of the trunk line often plays a vital role in improving the traffic conditions in a region or even a city. In urban traffic networks, the intersections are sometimes very close together, and the distance between two adjacent intersections is usually not sufficient to allow a small fleet of vehicles to be completely evacuated for a limited time. When a single point signal is set to control the single point signal, the vehicle often encounters a red light, and when the vehicle stops, the vehicle is not smooth and the environment is seriously polluted. In order to reduce the number of vehicles parking at each intersection, especially when the trunk line vehicles are relatively smooth, the control scheme between adjacent intersections should adopt a coordinated control strategy. The method of coordinating signal timing is based on the concept of green wave. The same signal control period is performed at adjacent intersections. The green light on the main line phase is turned off for a certain period of time. The secondary trunk of the intersection obeys the traffic of the main line to a certain extent. .
When a train travels on a trunk line with many intersections, the coordinated control allows the vehicle to always arrive at the beginning of the green light as it passes through the main intersection, thus forming a green wave of traffic flow through the intersection without stopping. . The green wave control can effectively improve the driving speed and road capacity of the vehicle, ensure the smooth flow of the road, and reduce the delay time and energy consumption of the vehicle during driving. The control parameter of the trunk traffic coordination control is the cycle length. Green signal ratio and phase difference, the target of control is generally the average delay and number of stops of the vehicle. The design flow chart of the trunk signal coordination control method is shown in Figure 1.

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The area traffic signal control is the traffic signal of all intersections in the city or a certain area. With the development of computer technology, optimization methods, automatic control and vehicle detection technology, people have studied to combine the traffic signals of all intersections in a city area or a local community to coordinate and control, so that the vehicles in the area are passing. The total loss incurred at some intersections is minimal. Under this control mode, the traffic signal transmits the traffic volume data to the upper computer through the communication network in real time. The upper computer continuously adjusts the ongoing timing scheme according to the real-time change of the traffic volume of the road network. The upper computer simultaneously controls multiple intersections in one urban area to realize unified coordination management between intersections in the area and improve the operation efficiency of the road network. Through this control method, it is easy to realize unified scheduling and optimization management of the traffic road network. The design of the regional signal coordination control timing optimization is shown in Figure 2.

3.2 According to the control mode According to the control mode, urban road traffic control can be divided into several types: timing control, induction control, adaptive control and intelligent control.
(1) Timing control The timing control method is based on historical traffic flow data to find out the different traffic flow changes of each day/week and time period, and prepare different days/weeks and different by manual methods or computer simulations. The timing scheme used in the time zone is open loop control, and it is not easy to adjust the control scheme in real time according to the traffic condition. Because the timing control has low requirements on traffic signals and does not require real-time traffic detection, it is still a widely used control strategy in urban road traffic systems.
(2) Induction control The principle of induction control is to adjust the length and time sequence of the corresponding green time according to the traffic flow data measured by the vehicle detector to adapt to the random variation of traffic flow. This approach has more flexibility than timing control.
(3) Adaptive control adaptive control is based on the detected relevant road traffic information, and based on the predicted future traffic demand predicted by the prediction model, select the corresponding optimization scheme from the system signal timing scheme library, or calculate correspondingly in real time. Optimize the control scheme to achieve automatic traffic control.
(4) Intelligent control In a strict sense, intelligent control is not only the control of traffic signals, but the control of the entire traffic system, namely the intelligent transportation system. Intelligent transportation system is the highest level of traffic control. It integrates advanced information technology, data communication technology, detection and sensing technology, automatic control theory, operations research, artificial intelligence and computer and its network into a series of high-tech applications. Each subsystem establishes a real-time, accurate and efficient comprehensive transportation management system with a wide range and all-round functions. The intelligent transportation system organically integrates all aspects of the transportation system such as people, vehicles, roads and the environment, so that the operation functions of the vehicles and roads are integrated and intelligent. Intelligent transportation system is the only way to solve traffic problems. Safe, efficient, environmentally friendly, low-cost, fast and comfortable green transportation is the development direction of intelligent transportation.

4 Urban intelligent traffic control system design intelligence is an ability to apply knowledge to a certain environment, or to measure the target criteria. Another definition is the ability to efficiently acquire, process, and utilize information for a specific purpose to successfully achieve its goals in a given environment. The intelligent transportation system is a comprehensive system that solves traffic problems by using the theory and method of artificial intelligence. The achievements of artificial intelligence in recent years have provided a solid theoretical basis for the study of intelligent transportation systems, and these results can be used to solve problems that cannot be solved by traditional methods. This is because: on the one hand, the transportation system is a system with complex structure, many influencing factors and strong randomness. It is very difficult to solve the traffic problem by mathematical methods. The established model is often too complicated, difficult to solve, and difficult to use. One or several models to summarize the diversity of traffic flow systems. On the other hand, the transportation system is a dynamic time-varying system, and the real-time requirements for traffic management and control are very high. Therefore, from the actual situation, the traffic management control method based on mathematical description is difficult to meet the requirements of online real-time control, and the operability is poor. The artificial intelligence method, referring to the human problem solving method, solves complex problems through knowledge expression, reasoning and learning, and transforms the previous description of the transportation system into pure knowledge to combine knowledge or knowledge with mathematical models. Continuously improve management and control by gradually adapting to the learning ability of the environment.
Multi-agent system is a frontier discipline in artificial intelligence today. It is an important branch of distributed artificial intelligence research. Its goal is to build large complex systems into small, easy-to-manage subsystems that communicate and coordinate with each other. Solve complex system control problems through the autonomy and coordination of subsystems. Due to the complexity of road traffic scale and the real-time nature of traffic flow dynamics, urban regional transportation networks have applied multi-agent systems to the research topics of urban traffic network control. Based on this, this paper designs the urban intelligent traffic control structure diagram, as shown in Figure 3.

In Figure 3, the left side is a multi-agent based urban traffic flow system, and the right side is a signal control system. In the traffic model, the road segment intelligent agent not only has the ability to update the traffic of a single road segment in real time, but also provides traffic flow data for the connected communication ports to carry out and optimize the signal timing; according to the upper regional traffic flow information, the traffic flow regulation is performed simultaneously. The data is exchanged with other road sections through the intersection; in the corresponding signal control model, according to the information provided by the segment agent, the signal timing is performed, and the dynamic balance of the traffic flow between the road segments is coordinated.
The regional agent has the same functions as the road segment agent, such as obtaining traffic flow information, supporting signal control data, independent of each other, and being able to operate separately. The regional agent can also operate according to the traffic flow of the area. Signal coordination of traffic intersections, to optimize the traffic target of the corresponding road network operation, determine the corresponding control strategy autonomously, and timely report the signal timing results to each signal in the parrot area, and transmit the traffic demand and control effects simultaneously. Give the decision-making layer, the traffic management center. The regional agent plays a role between the road segment agent and the central management agent, and transmits the traffic flow information with the entire road network of the single road; and exchanges information with other regional agents at the same level to provide services for traffic control. The central management agent consists of an urban traffic control decision system. Its function is to evaluate the operation status of the entire traffic network according to the road network structure, traffic detection and traffic congestion. The purpose is to seek the best performance index of the whole system, and use its superior reasoning and planning ability to make the system run. In an optimal state. In the signal control system, the intersection level signal control gives the intersection signal timing according to the traffic flow information of the connected link agent. The intersection level signal control controls the intersection traffic flow information and the signal timing layer, while the upper area control feeds back the control command. If a certain intersection in a certain area is crowded in the application research of the urban traffic network area control in a certain direction, the area is crowded. Control gives the purpose of relieving congestion and reducing the overall delay time of the area by giving control commands and adjusting the timing of other intersections on the same road segment. What is transmitted between the regional control is the traffic flow information in the area. If there is a crowded intersection in a certain area, the signal distribution time in the adjustment area and the adjacent area is guided, the traffic flow is dispersed to alleviate the congestion, and the roadside information sign or traffic is passed. The radio signal directs the vehicle to shunt. The regional traffic control information is transmitted between the regional control and the traffic control center. Adjust the dynamic balance of road network traffic flow and provide information to the central traffic control center to achieve centralized and decentralized control of urban traffic.

5 Conclusion Intelligent transportation system is a research field that covers a wide range of areas and integrates various high and new technologies. Due to space limitations, this paper discusses some measures to improve the safety of urban roads from the perspective of urban intelligent traffic control, but does not carry out research from the perspective of vehicles and passengers. Improving the overall level of intelligent transportation systems requires coordinated development of various industries to jointly promote the improvement of urban transportation levels.