A Study On Alignment Parameter Optimization And Safety Evaluation Of Interchange Loop Ramp

As an important part of high-grade road,interchanges have played a more and more important role.With poor road alignment,interchange loop ramps have high incidence of traffic accidence.Alignment combination of loop ramps is fatally important to the traffic safety of interchanges as well as expressways.While the present design specification for highway loop ramp alignment is imperfect,thus leading to the safety hazards of the built interchanges and setting a higher request for the alignment design of the loop ramp.Based on summarizing the domestic and foreign research status of ramp alignment parameters and road safety evaluation methods,alignment optimization of loop ramps is studied with ADAMS/Car,which is a kind of vehicle dynamics virtual simulation software.Integrated safety evaluation of loop ramp is finally carried out based on quantitative result of Loop ramp alignment?vehicle dynamics simulation indexes and accident data.Firstly,the road model containing road geometric alignment information,such as loop ramp radius,superelevation and longitudinal slope,and pavement friction coefficient is established through the Road Builder module of ADAMS/Car.While the vehicle models are the car model and semi-trailer tractor model that already established in ADAMS/Car.Then,the driver control strategy is specified in the Event Builder module,and the"driver--vehicle-road" system is built by using above established vehicle and road model.Secondly,radius of circular curve,length ratio of transition curve and circular curve,superelevation,longitudinal slope and vehicle speed are selected as the test factors of orthogonal test.While the seven dynamic indexes that respectively represent Rollover probability,vehicle trajectory consistency,driver workload are taken as the test indexes of orthogonal test.Car and semi-trailer tractor model are used to conduct the orthogonal tests respectively.According to the results of orthogonal test,the main influence factors of each dynamic index are analyzed.Then,the thresholds of each test indexes are calibrated using unfavorable vehicle through further simulation test,mechanical analysis and previous research experience.Then,according to the influence of the test factors on the test indexes,length ratio of transition curve and circular curve,superelevation,longitudinal slope of different loop ramp radius are quantified by means of vehicle dynamics simulation test and practice experience.In addition,the paper focuses on the influence of loop ramp widening method and road surface friction coefficient on traffic safety.The widen value and widen method of different loop ramp radius and safety speeds of different road surface friction coefficient are put forward.Finally,safety evaluation analysis of "MingHuang Interchange" G loop ramp is conducted by comprehensive use of quantitative application results of the loop ramp alignment parameters obtained in this paper,ADAMS/Car simulation test,statistical analysis of accident data.The results show that the safety evaluation method proposed can effectively find out the hidden hazards of established loop ramp and put forward the safety improvement measures,which may have great significance in engineering practice.