Research on calculation model of minimum net distance between interchanges on eight-lane expressway

According to traffic operation characteristics and lane changing maneuvers, combining with the export notice signs and considering the worst driving conditions, the gap acceptance theory and kinematics are employed to establish the length of lane change operation between interchanges with probability theory. To operating speed as the premise, the necessary length that drivers change to the inside lane from the nearside lane is analyzed in terms of waiting for the gap acceptance, and the necessary length that drivers change to the nearside lane from the inside lane is also analyzed in terms of running for the gap acceptance, then calculation model of minimum net distance between interchanges on eight-lane expressway is constructed. The recommended value is then put forward. With the rapid development of economy and continued growth in traffic volume, domestic four-lane expressways that were built in early days present scarcity in the aspects of traffic capability, service levels and safety, etc, therefore they have been extended into eight-lane expressways in some areas. Because eight-lane expressways have characteristics of wide subgrade, several lanes, large traffic flow, drivers need to look for the gap and change lanes repeatedly in order to achieve vehicles' diversion or merging. If the distance between interchanges is too short, which lead to weaving traffic flow frequently and causing traffic accidents. At present, each component of interchange area has been researched extensively at home and abroad. Based on analysis of urban expressway, the calculation model of minimum interchange distance has been proposed by He Yu-long([1]); From the viewpoint of interchange system, using the gap acceptance theory, the model of minimum interchange distance has been constructed by Xiao Zhong-bin([2]); Basic expressway sections, weaving section and ramp junction are all studied detailedly in Highway Capacity Manual released in 2000 by American Association of State Highway and Transportation Officials([3]); The path management of intersections around interchanges has also been examined in detail by National cooperative highway research program in 2004; To export notice signs as the premise, the minimum distance between interchanges has been studied and standardized by German research; Due to the definition of minimum distance is different in countries, its corresponding standard values are quite different. Without systematically researching and referring to the Japanese Road Design Specifications, the minimum net distance is defined as 1km for four-lane expressway by Highway Route Design Standard([4]) in China, and it hasn't been studied on eight-lane expressway. From the traffic flow theory, taking merging, lane change and diversion into consideration, the calculation model of minimum net distance between interchanges is established in this paper. The recommended value is then put forward.