Study On Accident Characteristics Of Weaving Area And Traffic Flow Simulation Of Expressway Ramp

Highway has now become an indispensable part of Chinese comprehensive transportation system because of its fast,efficient,convenient,comfortable,low transportation cost et al.As an important part of highway,ramp weave section is also the bottleneck of its.When the distance between on-ramp and off-ramp is relatively close there will form a weave area between them which is prone to conflicts between vehicles.Vehicles in the weave section usually need change their lane,when there is no proper gap,some drivers will choose compulsory lane-changing.Both mandatory lane changing and free lane changing will cause interference to the traffic flow in the weave area and make traffic in disorder,lane-changing easily caused traffic accident,made the highway congest,it also endangered life and property security of people.So the study of the traffic flow and the characteristics of the traffic accident in the weave section is of great significance to the reduction of expressway traffic accident.This paper takes the cellular automata theory,traffic conflict theory and traffic flow theory as a guide,base on the classic NaSch model,take the Matlab computer platform as the main simulation method by reviewing the relevant achievement at home and abroad,and the freeway ramp weave section cellular automata model is established,and the relationship between total system traffic flow and a1 is simulated when the parameters a2 = 0.2 and Poff =0.2;then this paper respectively study the relationship between a1 and continuous brake rate/lane changing rate/ forced lane changing proportion in the condition of free flow and saturated flow when the system traffic flow is taken into consideration.The main achievement is:(1)Firstly,traffic accident type in the highway ramp weave section is analyzed on the basis of traffic conflict theory,and divide it into three types,namely collision,side impact and collision fixed objects.Secondly,traffic accidents on expressway ramp weaving area are collected and the reasons of them are analyzed through network.Finally,it makes some suggestions to drivers and managers according to the traffic accident causes.(2)The freeway ramp weave section cellular automata model is established.By analyzing the relationship between a1 and the weave section traffic flow qall under the condition of different ramp import and export probability,it can be found: the system total flow starts to saturation when the main imports probability a1 = 0.4;under the same probability of on-ramp,the system saturated flow value increases when the probability ofoff-ramp increases.(3)On the basis of analyzing the change rules of the system total traffic flow,the relationships between a1 and continuous brake rate/ lane changing rate and forced lane changing proportion in the condition of free flow and saturated flow are researched.It is shown that under the condition of fixed the on-ramp probability: a.When the system flow is in a free state: the probability of the continuous braking of the different ramp exit probability increases slightly,but the continuous brake rate corresponding to the high ramp exit rate is higher than that of the lower;the mandatory lane changing proportion under different off-ramp probability is equal to zero.b.The system flow is in a state of saturated flow: After a sharp rise,the continuous brake action tends to a stable state under different off-ramp probability,the continuous brake value corresponding high value off-ramp probability is also higher than that of low value;the mandatory lane changing proportion also rose sharply and then tends to stable state,and it increases with the increase of the off-ramp probability.Under the condition of fixed off-ramp probability: a.The system flow is in a state of free flow: the continuous brake rate is rising along with the different off-ramp probability,but the influence of different off-ramp probability is not seriously;the mandatory lane changing proportion under different off-ramp probability is equal to zero.b.The system flow is in a state of saturated flow: continuous braking rate corresponding to different ramp entrance probability increased rapidly after the steady state,but the value of the continuous braking rate corresponding to the ramp inlet rate is lower than it corresponding to the low probability of exit ramp;at this time,the ratio of forced lane change also increased sharply and then became stable,but the high rate of import ramp corresponding to the continuous braking rate is lower than the ramp exit probability low when the continuous braking ratio and it increases with the increase of ramp entrance probability.