Traffic Flow Characteristic Analysis And Signal Optimization Of Signalized Intersections In Rainfall Weather

With the acceleration of urbanization and the rapid increase of motor vehicle ownership,traffic congestion has become one of the important factors restricting the development of cities.Compared with sunny days,congestion occurs more frequently and lasts longer in rainy days.It is of great practical significance to grasp the law of traffic flow change in rainy weather in order to relieve traffic congestion.As the key node of urban road network,the intersections’operation efficiency is very crucial.At present,the control scheme of urban intersections mainly focuses on the traffic flow characteristics on sunny days,and seldom considers the rainfall weather.Most areas of China experience different degrees of rainfall every year.Especially in the south,rainfall days range from one-third to one-half of a year.Therefore,it is necessary to formulate a precise management and control scheme according to the traffic flow characteristics in rainy weather for improving the efficiency of intersection operation and reducing the adverse impact of rainfall on the transportation system.The traffic flow characteristics of signalized intersections under rainy weather are objects of study.The frequency distribution and discrete characteristics of saturated headway under different rainfall are analyzed.By regression fitting the relationship model between traffic flow parameters and rainfall is obtained.Its applicability and prediction accuracy are analyzed.The rainfall correction coefficients of traffic flow parameters are calibrated by comparing these in sunny days.On this basis,the signal timing scheme of intersection is optimized,and the simulation evaluation is carried out to verify the improvement effect.Firstly,a typical intersection is chosen to collect traffic flow data under different weather conditions,and the reduction degree of traffic flow parameters is analyzed.The saturated flow rate decreases by 12.5%in light rain,21.1%in moderate rain and27%in heavy rain.The degree of reduction raises with the increase of rainfall.Through homogeneity test of variance and multiple comparisons,it is found that the headway in rainy days is stable from the 5th vehicle,and the 1st saturated headway is determined.The frequency distribution of saturated headway obeys normal distribution and belongs to low peak value.The peak value increases with the increase of rainfall,but the degree of skewness has no obvious relationship with rainfall.Finally,the correlation between traffic flow parameters and rainfall is analyzed,which is found highly positive correlation.Through regression fitting,the relationship model between traffic flow parameters and rainfall is obtained.Saturated headway is directly proportional to rainfall,saturated flow rate is negatively exponentially correlated with rainfall,and starting loss time is directly proportional to rainfall.R~2 is greater than 0.9,which means it has high applicability and accuracy.According to the relative relationship between traffic flow parameters on sunny days and rainy days,the rainfall correction coefficient of traffic flow parameters is calibrated.Aiming at the change of traffic flow characteristics in rainfall weather,the signal control scheme is optimized.Through VISSIM simulation,it is found that signal timing optimization can effectively improve the overall service level of intersections and reduce the adverse effects of rainfall.But it can’t change the increase trend of delay and queue length compared with these in sunny weather.