| In recent years,to ease traffic pressure and improve vehicle speed,China’s major citieshave started to build expressway.There are two common forms of expressway,they arehorizon expressway and high rack expressway.There are two types of expressway exit.Onekind of the exit is in contact with the road intersection,the other is in contact with thesecondary roads.In Xi’an,most of the expressway is in the form of the horrizon expressway incontactwith interchanges.These interchanges’s off-ramp always locate near theintersection.The length and geometryof the connecting portion is often the bottleneck of theentire road network.although there are not many studies about the connecting portion,butthere are still many papers achievements made manymeaningful insights,such as summing upthe characteristics and classification of freeway and urban road,analyze the relationship fromthe form of road construction and function,as well as the interaction between the freeway andthe urban form of transit modes.Analyze the system from the traffic characteristics ofconvergence lines and functional aspects.In the aspect of connecting portion’s functionalposite,build the computing capacity of the model of the connecting portion.From the servicefunctions rationality,bridging organizational rationality,economic rationality andenvironmental impact in four areas,build a comprehensive evaluation index systemconvergence program.But the study about the length of the connection portion is very rare nomatter in the country but also abroad.Because our countris’ road network is large,sothe lengthof the connecting portion is often determined in accordance with the road network planwithout a basis.This has resulted in the completion of the expreeway connecting portion tobecomethe bottleneck of the road capacity.In this paper,we use vissim as a tool to simulatedifferent length of connecting portion,then get the right length og connecting portion.Providea new reference todetermine the length of connecting portion.In the same time,provide someoptimization measures for the connecting portion which have been build. |
