Study On Vehicle Running Velocity And Technical Indexes On Collector-distributor Lane Of Cloverleaf Interchanges On Freeway

Interchanges inevitably occur at the intersection of expressway with the construction of a large number of highways.Cloverleaf interchanges,as one of the most important interchanges forms,have both attractive appearance with relatively low cost on the construction and good functionality that can allow the vehicle run continuously.However,in cloverleaf interchanges,the interweaving of vehicles entering and leaving ramps may affect the normal operation of vehicles on the outside lane of the main line,therefore,a collector-distribution lane is set outside the main line to eliminate the influence of the interweaving on the main line caused by the vehicle's entering and exiting the ramp.But the research on the vehicles running velocity and technical indexes of the vehicles on the collector-distribution lane is not yet mature and it will cause adverse effects on scientific research and design,thus,it is necessary to study the vehicle running velocity and technical indexes of the collectordistribution lane.This research use police traffic radar to collect the vehicles running velocity at each entrance and exit ramp of collector-distribution lanes to select the key feature point vehicle speed of three collector-distribution lanes on the different cloverleaf interchanges as analysis samples and to establish a prediction model for the running velocity of vehicles entering and exiting the main line through the collector-distribution lane.Continuous running data of vehicles entering and exiting a collector-distribution lane is collected by using on-board high-precision RTK equipment.And then the prediction model is carried out to the verification,it turns out that the relative error and the average relative error of model predictive values and measured values are less than 10%,which means the data's accuracy meets the requirements.The traffic flow simulation model of the collector-distribution lane is established by using VISSIM software to output the relevant parameters in the evaluation file.In simulation model,the traffic density meet the top level of traffic service when it's stabilized.It verified that when the traffic flow in the collector-distribution lane is in the state of free flow,the average running velocity trend and acceleration are basically consistent with the experimental data which proved the feasibility of the running velocity prediction model.Meanwhile,the technical indicators of the cross-section of collector-distribution lane's separation strip,lane width,and hard shoulder are analyzed and calculated.It propose that the length of the deceleration lane of the collector-distribution lane should include the nose distance between the collector-distribution lane and the first exit ramp and the length of the acceleration lane should include the nose distance between the second entrance ramp and the collector-distribution lane.According to the actual measurement data,the recommended values of the minimum length of the direct-type single deceleration lane and the parallel single acceleration lane of the collector-distribution lane are calculated with the guidance of the vehicle secondary deceleration theory and the pluggable gap theory respectively.At last,the formula for the calculation of the length of the waving sections in the "Highway capacity Manual" of the United States and the provisions for the various key parameters of the collector-distribution lane in the existing regulations in China are used to calculate the recommended values of the minimum length in the weaving area of the collector-distribution lane at different design speeds under the limit conditions of traffic operation that satisfies the four-level of service.This research provides a strong theoretical basis for vehicle running velocity and technical indexes of the collector-distributor road on cloverleaf interchanges.Through the establishment of running velocity model and the determination of technical indexes on the collector-distribution lane,it offers new ideas for perfecting the regulation on the collector-distribution lane of interchanges on expressway in the existing specifications.It also provides reference for the determination of the minimum length and overall minimum length of each component of the collector-distribution lane as well as providing convenience for scientific researchers and designers which will have great value in application.