Bus Rapid Transit Signal Priority For Large Four-leg Circular Intersections

BRT,a medium volume urban public transport system,can provide high service quality and efficiency with low pollution and cost.Up to June 2018,MBLs have been established in 38/48 worldwide cities with BRT systems.For increasing ridership attraction and facilitating traffic improvements,BRT routes often follow urban arterials.A large circular intersection has more than three lanes on multiple entries and wider circulatory roadway to accommodate vehicles traveling side-by-side,It can be found along urban arterials because of its landmark and network node function.Allowing median bus-only lanes(MBLs)to penetrate the central island will be a winwin approach,which gives advantageous to BRT vehicles without damaging the aesthetic and operational advantage.Under such design,this paper set two entry vehicle phases,one exit vehicle phase,two circulating phases and two pedestrian phases.Especially,this design can take control of BRT vehicle by adopting one BRT phase and sense arrival time of BRT vehicles through installment of four kinds of detections in MBLs.Additionally,it can also define green extension request,early green request and phase insertion request to offer more green time for BRT phase under five kinds of right-of-way assignment state.With the goal of accelerating the operation speed of BRT vehicles and serving conventional vehicles' demand efficiently,this research defined a number of traffic events which based on real-time collected data,as well as implemented BRT signal prioritization,Under the framework of isolated and coordinated control.The simulation results show that treatments in this paper have some advantages.Under isolated intersection control,The average delay of BRT vehicles was reduced by at least 33% after implementing priority,and the average delay of social vehicles was up to 9%;meanwhile,the average delay of both BRT vehicles and social vehicles in circular intersections are lower than those in conventional intersections,and the advantage of circular intersection is gradually increasing with the growing demand.However,stops of social vehicles in roundabout is much higher than those in conventional intersections.Besides,under coordinated control,the average delay of BRT vehicles was reduced by at least 26% after implementing priority,and the average delay of social vehicles was up to 7%.In conclusion,the signal control strategy in this study for large four-leg circular intersections can significantly improve the service quality of BRT systems without affecting the efficiency of social vehicles substantially.At the same time,such strategy can not only improve the efficiency of vehicles when they pass through circular intersections,but also provide a reference for traffic engineering practice.