Study On Key Indicators For Horizontal Alignment Design Of Double-crossover Diamond Interchange

Diamond Interchange has been widely used in the suburbs of cities because of its advantages of being small in construction area and low cost.However,with the accumulation of service life and the change of traffic flow characteristics,many Diamond Interchanges are saturated or even over-saturated.And the original design can not meet the current requirements,so it is of great necessity to rebuild them.Based on the traditional diamond interchange,American traffic workers have invented a new type of interchange,Double-crossover Diamond Interchange,which can achieve greater traffic capacity without changing land conditions.Since the first Double-crossover Diamond Interchange was built and operated in Springfield in 2009,it has been widely used in the United States with its advantages of greater left-turn traffic capacity,higher level of service and higher safety.It seems that this kind of interchange provides a new choice to solve the operation dilemma of over-saturated Diamond Interchange in China.Some problems have also been found during the promotion of this kind of interchange.At present,there is no norm for Double-crossover Diamond Interchange in the United States,and the states have different opinions on how to choose the key design parameters for the construction of such interchange.And researches on this kind of interchange by scholars mainly focus on micro-simulation,traffic operation evaluation and timing scheme,while there are few studies on horizontal alignment,which is different from the traditional diamond interchange and plays a decisive role in traffic organization.These problems have brought some difficulties to push this kind of interchange to China.The main object of study in this paper is the intersection road.Starting with the key points such as the setting of reverse curve,the angle of intersection and the length of weaving segment,the author tries to obtain the horizontal alignment of Double-crossover Diamond Interchange which is reasonable and feasible and meets the requirements of our country's norms,and provides certain guidance for design.Compared with the traditional diamond interchange and combined with the classification methods and relevant regulations of conventional Diamond Interchanges,the adaptability of the Double-crossover Diamond Interchange was analyzed.The suitable grade of road for this kind of interchange was determined,the relationship between the design speed of intersection and ramp and section design speed is clarified,and the lane design capacity under the recommended level of service was given.Geometric analysis and other methods were used to study the problem of the parameters of the reverse curve and the intersection angle of the route.The minimum length of the straight line inside the intersection was determined,and the relationship between the main parameters of the reverse curve was determined.According to the characteristics of the one-way traffic at the intersection,the general rule of 90 degrees of intersection as far as possible in our country's norms was negated,and the range of the intersection angle was given in combination with a large number of engineering facts abroad.And the restrictive relationship between the main parameters of the reverse curve and the intersection angle was given.Consulting the method of evaluating the LOS of weaving segment in HCM2010,the minimum length of weaving segment was studied in reverse,and the specific calculation process was determined.VISSIM was used to simulate the typical two-way four-lane Double-crossover Diamond Interchange.The operation of interchange under different traffic flow and length of weaving segment was studied,which supported the conclusion of applicability study again.Combined with the traditional layout method of Diamond Interchange ramps and speed change lanes,the horizontal alignment of Double-crossover Diamond Interchange can be basically determined through this study,which can provide technical support for the design of such interchange which both meets the requirements of China's specifications,and provides a new method for alleviating the predicament of oversaturated Diamond Interchange in China.