Study On Capacity Of Continuous Auxiliary Lane Mode Of Urban Expressway Based On VISSIM

In according to two projects,which are ‘Wuhan City Entrance and Exit Road and Trunk Highway Network Development Research Project(Wuhan Transportation Commission Project Number: WHJT-CZH-2016-1C178)’ and ‘Preparation of Design Guidelines for Urban Road Intersections CJJ152(Engineering Construction Standards and Regulations Revision and Related Work Plan issued by Ministry of Housing and Urban-Rural Development in 2017),the author takes the adjacent "in-out" combination ramps and the continuous auxiliary vehicle road segment between them on the urban expressway as a case study.Based on the theoretical analysis and ‘standard value’ calibration,the research does a simulation with the VISSIM traffic simulation software and investigates the influence of the on-ramp merger ratio,the exitramp divergence ratio,the number of main lanes,and the number and length of consecutive auxiliary lanes on the capacity and average speed of the bottleneck in the case.First,the article systematically introduces the method and points of capacity analysis in terms of urban expressway sections,three-way intersections,and ramp entrance and exit.Then,four continuous auxiliary lane modes(i.e.mainline 3 + ramp 2 + auxiliary lane 1,mainline 4 + ramp 2 + auxiliary lane 1,mainline 3 + ramp 2 + auxiliary lane 2,mainline 4 + ramp 2 + auxiliary lane 2)and other two non-continuous auxiliary lane modes(i.e.mainline 3 + ramp 2 + no auxiliary lanes,mainline 4 + ramp 2 + no auxiliary lanes)are extracted based on the status quo of China’s existing expressway scale.Finally,simulate the extracted modes separately with the VISSIM traffic simulation software and conclude as follows:1.When the length of the continuous auxiliary lane(500m)equals to the minimum value and the saturated flow is input:(1)the traffic capacity and average speed of the interweaving section between the "inout" ramp entrances are not related to the entrance ramp confluence ratio,but highly negatively related to the exit ramp diversion ratio.The effect of setting one continuous auxiliary lane is significant,and there is no difference between setting two auxiliary lanes and one.(2)the traffic capacity and average speed of the interweaving section between the "inout" ramps increase with the increase of the number of lanes on the mainline,and the increase is obvious.Similarly,the effect of setting one continuous auxiliary lane is significant.Compared with the setting of two auxiliary lanes,there is no difference.2.When the length of the continuous auxiliary lane(300m)is less than the minimum value and saturated flow is input:(1)the traffic capacity and average speed of the interweaving section between "in-out" entrances are greatly affected by the number of continuous auxiliary lanes.When the number of continuous auxiliary lanes increases from one to two,the traffic capacity and average speed increase significantly.(2)the traffic capacity of the interweaving section between the "entrance-exit" entrances is related to the length of the continuous auxiliary lanes.The shorter the continuous auxiliary lanes,the smaller the traffic capacity and average speed.Compared with the condition that "in-out" ramp opening distance equals to 500 m,the capacity and average speed of two continuous auxiliary lanes are basically the same as the situation of setting one continuous auxiliary lane.In short,for the continuous auxiliary lane mode,when traffic congestion is resulted by the increase of the proportion of exit diversion,the capacity of intersection between the entrance and exit can not be improved by changing the "one continuous auxiliary lane mode" to the "two-lane continuous auxiliary lane mode".However,it is possible to improve the traffic congestion at the intersection between entrances and exits by increasing the number of lanes on the main road.Adding the exits on existing expressways to meet the needs of traffic may cause the distance between entrance and exit less than the minimum requirement of the standard and incur traffic jams.In this situation,the one continuous auxiliary lane mode between the entrance and exit can be changed to the two-lane continuous auxiliary lane mode,which can significantly increase the capacity and average speed of the interweaving section between the entrance and exit,thus relieving the traffic congestion.