Study On The Evolution Law Of Road Network Traffic State Under Rainfall Condition

Under unfavorable weather conditions such as rain and snow,urban traffic congestion intensifies.Large cities like Beijing and Tianjin often experience multi-section regional traffic congestion under rainfall conditions.Therefore,based on the traffic flow data of the road network in the downtown and suburban areas of Tianjin,this paper studies the impact of different rainfall on the macro traffic flow of the road network and grasps the traffic flow characteristics and its distribution and variation rules of urban traffic under further rains.And design management and control measures to alleviate the impact of rainfall on the traffic flow of the road network and ensure the stable operation of the road network traffic system.The specific research contents are as follows:Firstly,according to the actual traffic data of the road network in the urban and suburban areas of Tianjin,this paper takes the macroscopic fundamental diagram(Macroscopic Fundamental Diagram,MFD)model of road network traffic flow as the research basis,the comparison of the traffic flow time sequence and macroscopic fundamental diagram characteristics of non-working days and different road networks in the road network,and the analysis of the effect of different rainfall(light rain,moderate rain,and heavy rain)on the macro traffic flow of the road network in the urban area and suburban areas of Tianjin.The research show that: compared with the rainy weather conditions,the average traffic flow of the road network increases,the average speed decreases,and the average density increases under the light rain and moderate rain conditions.The average speed of the road network decreases during the rainfall period,and the greater the rainfall per unit time,the faster the average rate of the road network decreases.Compared with no rain,the traffic flow changes of the road network under heavy rain conditions do not have a more uniform law.For the road network MFD,when the rainfall grades are light rain and heavy rain,the distribution of flow-density scatter points is more concentrated.In contrast,the spread point distribution of MFD under moderate rain is more discrete,and there is a "hysteresis".Under different rainfall,after the MFD of the road network reaches the critical density,with the increase of the average thickness,the average flow begins to decrease,the average speed decreases rapidly,and the road network becomes congested.On non-working days,the higher the rainfall level,the greater the impact on the traffic flow of the road network;under the same rainfall level,the effect on the traffic flow of the road network on non-working days is smaller than that on working days;the MFD of the road network on non-working days has rain not much has changed from no rain.Secondly,to compare the impact of rainfall on different road networks,this paper also conducts an in-depth study on the traffic flow characteristics of the road network in the suburban areas of Tianjin under rainy weather conditions.Compared with the urban area,the overall average traffic volume of the road network in the suburban area is smaller,the average speed is more prominent,the speed fluctuation is also more apparent,and the average density is smaller at the same time.When the rainfall grade is light rain and moderate rain,the traffic flow of the suburban area and the urban location with showers is similar to that without rain.The average traffic flow of the road network increases,the average speed decreases,and the average density increases.The changes in traffic flow on the road network are even more remarkable.Compared with no rain,the average speed of the overall road network in the suburban area increases,and the average flow and average density change irregularly under heavy rain conditions.There are also apparent differences between the change characteristics of the road network MFD and the urban area.The distribution of flow-density scatter points in the suburban area is relatively discrete in different periods of rainfall.The morning and evening peak of moderate rain appears to be "hysteresis".According to the comparative statistical analysis of traffic flow in suburban areas with different rainfalls,light rain has the most significant impact on the road network in suburban areas,followed by moderate rain and heavy rain.Finally,based on the change law of macro traffic flow of the road network in the urban area and the suburban area under different rainfall,the dynamic evolution model of the road network in the urban area and the suburban area is constructed,the model parameters are calibrated,and the validity is verified.Aiming at the regional congestion problem of the road network under rainfall conditions,based on the perimeter control of MFD,the control strategies of the road network in the urban area and the suburban area under different rainfall were designed,respectively.Feasible strategies for alleviating road network congestion in major urban and suburban areas are presented.