Study On The Lenghth Of Speed-change Lane And Minimum Net Distance Between Interchanges On Freeway

The short length of speed-change lane and net distance between interchanges may cause the high accident rate and low traffic capacity on freeway,and reasonable length and distance are guarantee of safe lane-change timely,confluence and shunt orderly.Firstly,the definition,components,influencing factors of the interchange,and function,classification and characteristics of speed-change lane are introduced.Then,the capacity of parallel acceleration lane and probability of merging onto mainline are analyzed,and a model for length of acceleration lane on the basis of merging probability is established.Considering transition's alignment and deceleration characteristic,a computing method for tapered section of parallel deceleration lane is established.Then,considering longitudinal grade and pavement adhesion coefficient,computing methods for parallel/tapered deceleration lane are established,and lengths of them are got.Secondly,taking the car from the acceleration lane to the most inner lane and then to the most outer lane for example,a whole driving process for lane-change inwards,sign recognition and lane-change outwards is analyzed.The conditions of speed and gap for safety lane-change are respectively analyzed by speed coordination principle and dynamic principle.Considering number of main lane's lanes,maximum service traffic volume,operating speed,the driving distance combination for waiting lane-change on multi-lane is structured.Using probability theory and traffic flow theory,a related model for safety lane-change probability and net distance between interchanges is established,and result is got by Matlab.Research shows that the probability presents a ladder-like increase with the increase of net distance between interchanges;the whole driving distance of lane-change inwards is greater than lane-change outwards;and at the first service level,for the probability threshold being 0.95,the minimum net distances between interchanges are respectively 2083m(3 lanes one-way,100km/h),2193m(3 lanes one-way,120km/h),2833m(4 lanes,120km/h).Finally,according to the research results,the obvious accident characteristic of the short net distance between interchanges on freeway in Tianjin is confirmed.The optimization strategies are put forward,including design of auxiliary lane and collector-distributor lane,additional setting of ground traffic signs/ concussion marking,additional setting of advance exit sign at the starting point of the previous interchange's acceleration lane,and lower extent of speed limit.The results can provide references for planning design and optimization of freeway interchange.