The Longitudinal Operating Characteristics Of The Interchange Ramps Based On Naturalistic Driving Study

As an important road structure,the interchange ramps make the traffic flow on the planes of different heights,reduce or eliminate the conflict points,and guarantee traffic safety while improving the traffic capacity of the road efficiently.The setting of interchanges can also achieve the goal of access control and easy management.However,for the reasons of the complex alignment,the poor sight distance and the great speed difference between the ramps and the main alignment,the interchanges have been the hotspots of traffic accidents.How to improve the security of interchanges has attracted much attention in the traffic and transportation field.The road transportation system is made up of the following four basic elements,driver,vehicle,road and the environment.Only by combining the four elements and understanding the operating characteristics under the effect of different factors,can we identify the potential danger in road transportation system more efficiently and more accurately.This paper took three typical types of interchange ramps as the research objects,and studied their longitudinal operating characteristics by the means of Naturalistic Driving Study(NDS).This study involved 9 interchanges(23 ramps),the ramp types included ring ramps,U-Turn ramps and helical ramps.15 people from different industries volunteering as the drivers took part in this study,and a large amount of NDS data were obtained.At first,this paper summarized the longitudinal operating mode of each type of ramps.The mode of ring ramps is Four-Stage Mode: In-curve deceleration,Adjustment acceleration,Steady running,Ex-curve deceleration.The mode of U-Turn ramps is ThreeStage Mode: In-curve deceleration,Steady running,Ex-curve acceleration.And the mode of helical ramps is One-Stage Mode: approximately steady running.Then,the speed characteristics of the three types of ramps were analyzed.This paper studied the distribution of the start points,the end points and the travel distances in the stage of acceleration and deceleration.Comparing the running speed with the design speed and the limited speed,this paper figured out the serious problems of ramps in design and manage phases.And finally,the longitudinal acceleration characteristics of the three types of ramps were analyzed.There is no obvious connection between longitudinal gradient of the ramps and its longitudinal acceleration.This paper analyzed the distribution of acceleration and deceleration of ring ramps and U-Turn ramps,and built the accelerationdistance models.For the further simulation analysis of the ramps and the modeling of the running speed,this paper summarized the recommended acceleration values or ranges of the three types of ramps in different stages.At last,the ride comfort of drivers and passengers running in the ramps was evaluated based on the longitudinal acceleration.