Effect of rainfall intensity variability on highway capacity

Abstract

Traffic flow rate variability on road networks occurs when traffic decelerates on approach to a perturbation or accelerates away from it. This may be due to rainfall as well as physical bottlenecks. This study examines the effect of rainfall on a highway straight section operating under free flow conditions and to evaluate the effect of changes in rainfall intensity on the capacity of the section. Data for this study was collected from a two-way interurban arterial J5 near Pengkalan Raja in Johor Bahru State of Malaysia. The observation site was 750m away from a rain gauge station. A pneumatic loop detector was installed for 30 days during which 31 rainfall events were recorded. The data was filtered to obtain traffic flow information for both dry and wet operating conditions and these were analysed to see the effect of the rainfall. Rainfall intensity less than 2.5mm/hr. resulted in 8.14% capacity loss. Rainfall intensity between 2.5mm/hr. and 10mm/hr. substantially reduced the capacity by 50.30%. Under heavy rain condition (10mm/hr. and 50mm/hr.) 31.09% capacity loss was recorded. Roadways that lose 30% or more of their capacity in dry weather will generate instabilities that will persist for a long time. In adverse weather, the traffic state is unpredictable and could lead to similar situations as in dry weather. Resources could be placed from this point on to manage the resulting flow scenarios. On highway facilities where flow rates are higher and close to the capacity region, these effects could be more pronounced.