System Research On Connection Problem Of Urban Expressway

With the development of cities and the rapid increase in traffic demand, the urban expressway system of big cities in China is under planning and construction in succession to meet the rapid growth of the urban motor vehicles. However, the expressway in China is built through new construction and/or reconstruction based on the old urban road network already with a certain scale, which is different from that in west countries such as America. There remain a lot of traffic problems for a long time for the inadequate consideration of the coordination of the urban expressway with other urban roads (collectively called conventional roads), and the lack of professional expressway planning theories and design standards. The poor traffic flow conversion between the two systems have caused the traffic congestion and frequent accidents that give rise to the traffic bottleneck, especially at the exit and entrance of expressway and adjacent intersection. What is more serious, these traffic problems in the traffic bottleneck will spread quickly throughout the neighbouring unban traffic network. Nowadays, China’s development of expressway in most big cities but Beijing and Shanghai is still in its start stage, which makes it urgent to do system research on the connection problem of expressway, for assuring the two systems form an organic whole.With the aim of efficient coordination of urban expressway with the other urban roads, the paper discusses the connection problem of expressway from different aspects, such as expressway system planning, design, system control, and so on, based on the theoretical research and practical experience at home and abroad.1. The paper conducts an analysis of the background of expressway planning, discusses some known methods dealing with the connection problem of expressway, and based on which, points out a planning method of combining node with line and network. As for the problem that the existing assignment model fails to take into consideration minor roads and the road functions, the basis of avoiding or decreasing short-distance travel on expressway are put forward. Based on multi-path assignment model, the calculation method, considering short-distance travel on expressway, and its algorithm design are presented. The traffic flow assignment serves as the basis on devising road construction standards, identifying roads parallel to expressway and the connection point of expressway and conventional road. Some main problems, such as orginal road network, computing method, and weight modified function are discussed. It’s simultaneously parsed in this paper the joint section planning of expressway with the other urban roads, and the index system to evaluate the two systems’coordination.2. The paper goes into the three levels of urban network (common municipal road, urban expressway and suburban road) and their relationships, pointing out that expressway system is important part of urban outbound traffic, that exits and entrances are critical to the coordination of expressway with urban road network, and the improvement should be made of the exit and entrance road network, with its specific requirements presented.3. Based on the understanding of "Urban expressway design standard (CJJ129-2009)" it’s suggested in this paper that the design of exit and entrance of expressway should provide basic conditions for the coordination of expressway with the other urban roads. As for the existent main problem in expressway construction, it’s proposed here some design requirements for designing the exit and entrance of expressway, with a major discussion on the design elements and traffic flow management of joint sections. Furthermore, as for the common problem of the restricted space of expressway in the off-ramp joint section, it’s put forth an optimal design and control method, which proves to be effective through the simulation of Vissim.4. From the perspective of traffic management control and based on the existing mature optimal control methods of expressway system and the conventional road system, the paper forwards a multi-layered heuristic coordinated integrated control method as per the blocking index. The key links of integrated control are elaborated on, such as the definition of blocking index, the integrated control, the integrated control principle of passageway of expressway and adjacent intersection, and the integrated control of the passageway of expressway and adjacent intersection with their subsystems. Furthermore, the technical conditions required for integrated control, application of the control methe and the optimization goal at different traffic state are analysed. Taking the coordination of on-ramps with adjacent intersections as an example, the paper verifies the effectiveness of the control idea through the simulation of Vissim. For the expressway with the cross section of the main road and auxiliary lane, the coordinated integrated control idea of Auxiliary Lane and adjacent intersection was been proposed.5. The paper analyses the traffic flow management of expressway, such as the signs and lines of management, vehicles and their operation rules management, urban access management. Combined with the existing problems of management, the paper proposes some management requirements. In this part, the paper focus on a quantitative analysis of impact of large-scale trucks on the traffic flow of expressway with traffic flow wave theory which provides the basis for making clear division of large-scale truck lanes, limiting the minimum speed and strictly controlling the proportion of large-scale trucks on the expressway, and doing good job for coordination of expressway with other urban passageway. Meanwhile, the management measures are discussed on avoiding/decreasing short-distance trip on expressway and traffic flow of city entrance.Only with a multilevel urban road network system of efficient coordination of urban expressway with other urban roads, rational in functions and clear in structure, can its traffic function and capacity be fully exploited. The integrated control of expressway and other urban road system is the technical support for improving the efficiency of urban road network. In view of this, the research result can provide important references for urban expressway system construction in our country.