Several Problems About The Trattic Safety Of Expressway

Taking the requirements for theory and method of expressway safety designing and assessment as the starting point, while the spot investigation data and field test as the fundamental basis, this paper use the method of combining mathematical statistics, theory and analysis and simulation to study in depth several important key problems about traffic safety of expressway. The study includes median type and its safety, climbing lane for specific upgrade segments, safety assessment for area of small interchange spacing on expressway and 3-D sight distance assessment.Through the investigation of expressway median accidents data, collision simulation test and road safety lateral clearance measurement, safety analysis for expressway median type is carried out and reasonable median structure suitable for expressway in China is put forward. Based on ADAMS soft, it is set up that 3-D vehicle model,3-D carrier model and curb model are suited to simulation test of carrier crash. The test result of different collision angle and speed shows that the driving speed with the median having curb beside carrier should be less than 60km/h, and the curb should not be the hurdle type. According to the operating speed of different vehicle types and its corresponding inside clearance measured at the passing lane of different testing roads, the relevant model of inside clearance and speed is established. Under studying the impact of curb type to inside clearance, the safety lateral clearance value is set up. Considering different choice of drainage patterns, w-beam guardrail types and antidazzle types, the narrowest reasonable median structure and its width composition are given both for combination-type and grouped-type w-beam guardrail.The key to safety designing for specific upgrade segments is to determine the key parameter of designing longitudinal slope and set up climbing lanes reasonably. By means of surveying about characteristics of trucks upgrade, the calculation model and test method are obtained, which take the ratio of truck power and weight as the key parameter of designing longitudinal slope. Taking the test of about expressway in Northern Shaanxi for example, in this area, the ratio of typical truck on expressway longitudinal slope design is about 8.0-8.33kw/t caused by 15% of the ratio of truck power and weight. With the traffic composition surveying and the truck developing trends, a truck whose load is 12t was selected as the longitudinal gradient design typical truck at Northern Shaanxi area, whose ratio of power and weight is 8.05kw/t. Then, it can be made certain the climbing performance curve diagram of the typical truck, and also put forward the value of critical slope length under different speed reduction. With the speed loss which allowed and the average operating speed of trucks on near-level grade road section, and based on speed loss in different gradient and grade length, this study also brought forward grade length limit of the expressway at Northern Shaanxi. By the way of analyzing traffic flow factors and the capacity calculating demand, the capacity algorithm is used to simulate the passenger-car equivalents at the specific upgrade segments. By providing a simulation environment of the specific upgrade segments and selecting representative non-standard leading vehicles models such as heavy vehicles and trailers as the study objects, passenger-car equivalents under different design speeds,different longitudinal slope and different traffic composition are put forward. Furthermore, both the simplified model of calculating the equivalent composite grad and slope length at composite grade segments and the condition and index for setting the climbing lane of specific upgrade segments are proposed.Taking the area of small interchange spacing as a research object, it is used traffic conflict technique to establish traffic conflict simulation procedure based on VISSIM as micro traffic simulation soft. According the traffic characters at the area, conflict ratio is taken as the safety assessment index. Considering the incompletion of traffic safety information and lack data at the area, by means of gray cluster theory, it is put forward the traffic safety assessment method at the area of small interchange spacing and the measures to ensure the area safety.On the basis of the existing research analysis of visual range assessment method, it is derived 3-D visual range formula to set up a new 3-Dvisual range model, by using principles of spatial analytic geometry and horizontal, vertical and cross line on expressway. Through checking up the elevation relations between any points at the 3-D sight and their corresponding points at the expressway, it can be determined that whether the road or road-side kept the sight out, then the assessment procedure of checking 3-D visual range is gained. This model and method is simple and easy to implement. It can not only help to achieve auto-testing 3-D visual range, but also use 3-D visual range to carry out safety assessment.