Study of Local Traffic Flow Fluctuation under Rainfall and Waterlogging with Characteristics of Dynamic Spatiotemporal Changes

It is common knowledge that rainfall and rain-induced waterlogging have negative impacts on urban road traffic in that they could cause decreased traffic flow capacity and induce traffic congestion from a macroscopic view. What is the ultimate cause behind the phenomenon from a micro perspective, however, is still unclear. This paper proposes a variable cell transmission model (VCTM) considering the influence of rainfall and waterlogging on traffic parameters based on the key findings from a previous experiment-simulation study. A typical local traffic network in a city with seven road sections was chosen as a study area, and a case study was conducted in a scenario of rainfall and waterlogging based on the proposed model. The results comprehensively profile how rainfall and waterlogging induce flow fluctuation and density fluctuation. It is found that road capacity is a dominant factor influencing the flow fluctuation, and the flow fluctuation tends to be much more violent near the ponding areas. It is also found that density increases with increased rainfall intensity and water depth, and the density increase caused by waterlogging seems to be more significant. Another important discovery is made that density of some roads could increase violently due to insufficient capacities of downstream roads. These valuable findings from this study help better understand the influence of rainfall and waterlogging on urban traffic flow. This work can also help guide the emergency response by the corresponding government department when encountering rainfall and waterlogging.