Research On The Values Of Key Design Elements For The Exit And Entrance On Expressway

In terms of easing urban traffic congestion, urban expressway plays animportant role and better meets the traffic demand of long-distance and rapid transit.But it always occurs traffic congestion at the exit and entrance, which has a strongimpact on expressway to play its function and utility. Therefore, to improve trafficefficiency and ease traffic congestion, research on the values of key design elementsfor the exit and entrance on expressway is conducted, it also has a very importantpractical significance.In this paper, based on the traffic investigation of expressway exit and entrance,the traffic flow operation, traffic volume and speed characteristics of that areanalysed. And combined with the influence factors of traffic flow at expressway exitand entrance, firstly the key influence factors of frequent traffic congestion areanalysed from the perspective of qualitative analysis. Then, the simulation test fortraffic congestion factors of different level is conducted by establishing a simulationmodel of expressway exit and entrance. With the significance test of simulation data,the four key design elements of expressway exit and entrance are determined fromthe perspective of quantitative, which are the length of acceleration lane, theauxiliary lanes of entrance, the prepositive distance of exit sign, the distancebetween the exit and entrance.Under the premise of minimizing the interference from exit and entrance on thetraffic operation of expressway mainline as far as possible, based on the principle ofguarantee the service level of mainline, with the traffic flow theory, probabilitytheory and kinematics, the calculation model of the length of acceleration lane andthe prepositive distance of exit sign is built based on three key factors, which aresaturation, design speed and the number of mainline lanes； four differentcombination forms of calculation models for minimum distance between exit andentrance are established. Meanwhile the code value in the Specification for Designof Urban Expressway (CJJ129-2009) is put forward suggestion for improvement,which just considered the mainline design speed as the single factor for the designvalue of minimum distance between exit and entrance. In addition, through theanalysis and calculation, the setting conditions of balanced lane of entrance whichdesigned to balance the number of lanes at entrance is obtained. Finally, the theoretical derivation calculation models for valuing the key design elements andthe setting conditions metioned above are proved to be rational by VISSIMsimulation.