Study Of Alignment Optimization Technique For Urban-Rural Fringe Road Based On Traffic Safety

With the further deepening of the reform and opening and the rapid development of national economy, the pace of urbanization of our country are accelerating. Starting From "The Twelfth Five-Year Plan", China will spend 20 years to resolve "peri-urbanization" problem, so that China's urbanization rate will reach 65% in 2030. With the acceleration of urbanization, road traffic safety issues of urban-rural fringe are becoming increasingly prominent. The roads of urban-rural fringe are the cohesive tie to connect the cities and villages, promoting the economic development of the surrounding greatly. However, the contradiction between the rapid process of urbanization and the relatively lagged road construction and traffic management of urban-rural fringe causes road traffic safety issues of urban-rural fringe particularly outstanding. Relevant data shows that about 50% of the urban road traffic accidents took place in the urban-rural fringe, and the consequences were serious. Further study of traffic safety of urban-rural fringe transition section and exploring improved approaches from the road alignment design to prevent and control accidents, are urgently need to be solved in front of us.The article firstly discussed the relationship between the general road alignment and traffic safety, including the general road horizontal alignment elements, such as length of straight line, circular curve radius, flat curve length, corner, curvature rate, stadia and gentle curve length. Moreover, this paper discussed the influence of the subgrade width and pavement width to traffic safety in the general cross-sectional arrangement, the relationship with accident rate per million vehicle kilometer are that the traffic accidents firstly reduces as the increase of width, when the width increases to a certain value, the accident rate begins to rise. Through the analysis and discussion, the author believed the urban-rural fringe transition section design, considering the premise of traffic safety, must carefully study the elements of horizontal alignment of transition section and the forms of cross-sectional decoration in order to reduce traffic accidents.Secondly, the scope of the urban-rural fringe has been defined based on the qualitative and quantitative description. Urban-rural fringe is a special economic geography unit with double feature of urban and rural as the urbanization developed to a certain stage. Then the traffic system composition and their features of urban-rural fringe were discussed, which included traffic participants, road condition, vehicles and the traffic environment. The paper defined the scope of the accident black spot, namely urban-rural fringe transition section, believed that the length of which was about 3-10 kilometers. The horizontal alignment of transition section was composed by curve and linear. This paper selected a kind of typical linear to research namely two circular curves connecting a straight line.During the optimization of horizontal alignment transition section, the circular curve radius and length of straight line were thought to be the most critical control targets. In this paper, theoretical studies on the possible speed in accordance with the arithmetic for the 5km/h values, respectively calculated six types of transition speed. Among them, the straight-line speed at the initial segment into the driving speed and the transition may be the average speed and was assumed to be uniform; the speed of circular curve near the city were the average value of straight line speed and the initial speed, and the speed of circular curve far from the city were the average value of straight line speed and leaving speed. By comparing the results, it was believed the general minimum radius of the rural-side was larger than urban-side. Meanwhile, the calculated general minimum radius was generally 1.2 to 1.5 times of the optimum minimum radius. The general minimum radius recommended nearly equaled to the maximum value of optimum minimum radius. In practical engineering, the design value should not be less than the recommended value.Moreover, this paper analyzed the problems existing in the design of cross-section of urban-rural fringe transition section, and pointed out the effects which produced by the nature of road, grade, design speed, layout of underground pipelines and other factors. By the analysis of the typical cross-section layout of urban roads and suburban highway, optimization design was made by using the three different graded smooth speed transition design concept, mainly including urban three width road and highway single road, double width road, urban four width road and highway single road, double width road.Finally, based on the analytic hierarchy process (AHP) multi-grade fuzzy evaluation method, alignment of transition section at urban and rural fringe was evaluated. Index system included four aspects 17 indexes in total, which were the linear index, speed index, stadia index and environmental index. The evaluation process was divided into the set of evaluation factors, the establishment of comments, the establishment of subordinate function judgment matrix, and the example was text and it showed correct conclusions, which would play a guide role on the road alignment design of transition section at urban and rural fringe.