Survey the impact of different rainfall intensities on urban road traffic operations using Macroscopic Fundamental Diagram

This paper focuses on investigating the effects of different rainfall intensities on traffic operations of urban road networks. Macroscopic Fundamental Diagram (MFD) and Spearman correlation coefficient are used to quantitatively describe the network´s operation and measure the rainfall impact on it. Mastering the rainfall impact on urban road traffic operation is not only important for the traffic state evaluation in rainy days, but also for the development of effective management strategies under rainy conditions. An empirical analysis is carried out on a major arterial network located on Haizhu district of Guangzhou, China. The results indicate that the rainfall events increased the uncertainty in network performance, and the reduction is in an increasing tendency with the increase in rainfall intensity. Furthermore, the different rainfall intensities have divergent impacts on macroscopic traffic variables. The heavy rain and rainstorm have remarkable negative effect on macroscopic traffic parameters, which produced Critical Accumulation and Maximum Production reduction of 10.5%, 16.7% and 21.0%, 18.7%, respectively. While the light rain and moderate rain have relative small impact on network´s operation. What´s more, the precipitation resulted in a significant decrease effect on the parameters of weighted free-flow speed and weighted jam density of the study network, the average reduction is 9.7% and 12.3%, regardless of the intensity. The production and weighted speed are also reduced by rainy condition, but the parameter of accumulation is not rainy-sensitive.