Analysis Of Highway Sight Distance Based On Reliability Theory And Alignment Design

Road traffic plays an important role in China’s economic development due to its fast and convenient features. And it has become a significant part of the way of traffic at this stage. However, with the increase in the number of vehicles and new type cars usage, traffic safety in China shows a continued deterioration trend. Sight distance, as a key factor affecting the highway alignment design, is an important indicator to guarantee the traffic safety, especially in the tunnel. But currently the analysis of sight distance tends to rely on the de deterministic approach, which ignores the three-dimensional nature of highway alignment. Therefore, taken the city tunnel as an example, through analyzing driver stopping sight distance based on the reliability theory and three-dimensional highway alignments and its application in traffic safety evaluation, this paper researched the influence of road parameters on driver stopping sight distance. And in addition, the paper also analyze the highway design framework based on reliability theory, and proposed the highway design framework in the short term and in the long term, respectively based on reliability theory. The contents of this study are as follows:(1) Reliability theory was introduced to analyze the driver stopping sight distance. By establishing reliability performance function of different alignments, this study analyzed the impact of running speed, reaction time, road surface friction coefficient, curve radius, clear distance and the design height on stopping sight distance when the driver travels in the tunnel. And the result shows that when the value of horizontal curve radius is larger than the general minimum curve radius, or the driving speed is less than the design speed, then the sight distance is less affected. And the sight distance has a higher failure probability if the clear distance is small. The vertical curve radius has little impact on the sight distance, while it is sensitive to the design height of the tunnel.(2) Three-dimensional (3D) sight distance model was constructed in this paper. And 3D sight distance and 2D sight distance were analyzed when the driver travel on universal conditions of combination of horizontal and vertical alignments, especially on convex vertical curve with small radius horizontal curve in the top point. In addition, the difference between the 3D sight distance and 2D sight distance when the driver travel in the tunnel also is analyzed. The study shows that the 3D sight distance tends to smaller than 2D sight distance when the driver travel on convex vertical curve with small radius horizontal curve in the top point, and sight distance was dominated by horizontal parameters indicators. Compared with the horizontal radius, the vertical radius has little impact on sight distance when the driver travels in the combination of horizontal and vertical alignments. But for a single vertical curve, the radius should be the main factors affecting the sight distance. In addition, through analyzing the sight distance in the urban tunnel, the study finds that top wall of the tunnel could affect the driver’s line of sight, and 3D sight distance had relationship with the travel direction.(3) The design process of traditional highway alignments and its shortcomings were analyzed, and then general design process of highway alignments based on the reliability theory was proposed. In addition, from the perspectives of the short-term and long-term development, the paper also provides the highway alignments design framework based on the reliability theory.