Study On Route Signal Control Strategy Of Emergency Traffic

In order to improve the efficiency of emergency traffic response and reduce its travel time,it is of great significance to formulate an efficient and reasonable signal timing strategy of emergency traffic along the route of rescue OD.Therefore,oriented to the characteristics of emergency traffic and route signal control,this study combined the preemption signal control of emergency traffic and the coordinated signal control of the route,and a green wave preemption signal control of emergency traffic was proposed.Furethermore,considering the fairness efficiency of the intersection along the route after the preemption signal control of emergency traffic,a reasonable signal transition strategy was studied.Firstly,aiming at the urban emergency events,the characteristics and demands of emergency traffic were analyzed in detail.Starting with the characteristics of emergencies,such as the little probability,irresistible influence and contagion,as well as the harmfulness of the consequences,the concept of emergency traffic was brought forward.Moreover,the frequency of emergency traffic and significant traffic characteristics were analyzed,and the priorities of different types of emergency vehicles were divided afterward.Then the objectives of emergency traffic control were given as least delay of emergency traffic,least impact on social vehicles and lowest safety risk index.Secondly,aiming at the least delay of emergency traffic,a two-level based emergency traffic route coordinated control model was established.Based on the analysis of route categories and features,the classical route was selected,which was,the stepped route including left turning and right turning.Then,a route correlation model was brought out based on the modification of classical Whitson model,which was used to define the coordinated range of the two-level programming model.Then a detailed analysis of the upper and lower model were carried out.The upper level was the dynamic phase offset model for emergency traffic,and the lower level was the route green wave model for emergency traffic.The upper level analyzed the relationship among arrival time of emergency,current phase time and the time of queuing,and established a reasonable strategy which could adjust the timing and the phase offset dynamically.The lower level calculated the turning bandwidth and the total bandwidth of the route,according to the different turning capabilities.Furthermore,in view of the disturbance of the emergency signal preemption to the social traffic flow,a scientific and reasonable signal transition strategy was studied which also considered fair and effective.Taking into account the great delay of other phases that influenced by the emergency signal preemption,the difference of queue length and the vehicle delay were selected as the objectives.Then emergency oriented multi-objective signal optimization transition model was established with the method of power function score,whose weight was determined by the coefficient of variation,and solved by genetic algorithm.Finally,the multi-objective signal optimization transition model proposed in this study was compared with traditional immediate transition scheme the two-cycle and the three-cycle transition scheme,and the Mixed Logit discrete selection model was used to establish the utility functions of the four schemes and their selection probability was also calculated.Finally,based on the survey data from the typical route network in the Lion Mountain area of Suzhou City,relative case analysis and simulation verification were carried out.For the emergency traffic two-level programming route coordinated control model,the simulation results showed that,compared with the single-point signal preemption strategy and the non-signal preemption strategy,the signal coordinated preemption strategy brought in this study can reduce the number of stops of emergency vehicles' to 0,the emergency vehicle delay was reduced by 4.7%,11.6%,the travel time was reduced by 6% and 18%,the queue length was reduced by 9.1% and 16.8%,and total delay of vehicles was reduced by 8.8% and 7.1% respectively.For the emergency signal transition strategy,the results of Mixed Logit discrete choice model showed that the average selection probability of emergency multi-objective transition model in this study was 50.23%,from which we can see that compared with the classical immediate transition,two-cycle and three-cycle transition,transition strategy in this study has significant benifits.And related TSIS simulation results also proved that the transition model in this study had a lower delay than the other three schemes which was same conclusion as the Mixed Logit Discrete Choice Model.