Study On Calculation Of Net Distance Of Expressway Interchange And Lane Line Setting Of Net Distance Section

The density of interchanges close to the city is increasing,and the spacing is becoming smaller and smaller,so the net distance needs to be controlled.If the net distance is too small,it is easy to lead to road congestion and frequent traffic accidents,while if the net distance is too large,it is not convenient for vehicle conversion.Considering the shortcomings of previous studies,this paper,based on the calculation model of minimum net distance of expressway interchange by predecessors,fully considers the lane changing behavior of drivers,and further improves the calculation model.At the same time,considering that the road section controlled by the net distance usually has the characteristics of large traffic volume,many lanes and high degree of traffic flow interweaving,the vehicle driving environment is more complex than the interworking section that meets the minimum spacing requirement,combined with the above net distance calculation improvement model,this paper proposes a traffic organization method for the net distance section of adjacent interchanges to reduce interleaved flow,improve the clean distance section driving environment,improve the clean distance section traffic efficiency and safety level.The main research results are as follows:Based on the definition of net distance of expressway interchange,the factors affecting net distance determination of expressway interchange were selected and analyzed,including traffic flow state,traffic sign setting,lane changing behavior of drivers and driving characteristics of merging vehicles.According to the lane changing behavior characteristics of drivers,road traffic conditions and the setting of traffic signs,considering the most unfavorable way for a vehicle to exit the main line,the minimum net distance composition of adjacent interchange is determined.Based on the traffic flow theory,the minimum net distance calculation model of freeway interchange was established,and the limit,ideal and conservative net distance values of interchange under different design speeds and number of lanes were calculated.Among them,under the design speed of 120km/h oneway four-lane,the net distance of interchange limit is 1600 m,the ideal net distance is2000 m,and the conservative net distance is 2900 m.The collision rate was selected as the safety evaluation index,and the sections with different distance lengths were simulated by VISSIM software,and the safety level was analyzed by clustering analysis and fuzzy evaluation method.The results show that under the design speed of 120km/h one-way four-lane,the safety level of 1600 m interchange limit net distance segment,2000 m ideal net distance segment,2900 m conservative net distance segment and the minimum net distance segment of 1200 m stipulated in "Rules for Interchange Design" are respectively critical safety,relatively safe,safe and dangerous.The calculation model of minimum net distance is proved to be reliable.Based on the calculation model of minimum net distance of interchange,considering the behavior characteristics of drivers and the most unfavorable condition of vehicle exiting the main line,the spatial position and form of lane line setting in clear distance section were determined,and the calculation models of dotted line segment,virtual and real gradient segment,solid line segment and gradient distance were constructed.At the design speed of 120km/h,100km/h and 80km/h,the length of gradient section of lane separation line is 500 m,400m and 300 m respectively,and the number of gradient section is 10,8 and 6 respectively.The change of line spacing between adjacent sections and adjacent lanes is 80 cm,100cm and 120 cm respectively.From two aspects of traffic efficiency and traffic safety,the average speed of section and the number of conflicts are selected as evaluation indexes,using VISSIM software,the clean distance section with or without special lane lines is simulated,according to the traffic collision trajectory diagram,the traffic safety and traffic efficiency of the clean section under the design speed of 120km/h,the limit distance length of one-way 4-lane and different interleaved flow ratio are compared and analyzed respectively.The results show that lane separation is beneficial to restrain lane change behavior of vehicles,reduce the degree of interweaving,improve the safety level of road sections,help vehicles pass,and improve the adaptability of the calculation model of the clean distance.When the design speed is 120km/h and the interleaved flow ratio is greater than 0.30,it is suggested to set auxiliary lanes at the same time to relieve the carrying pressure of the traffic volume on the outermost lane in order to avoid the traffic volume on the outermost lane exceeding its bearing range.