Surface run-off: a rainfall simulator for wash-off modelling and road safety auditing under different rainfall intensities

The great traffic and vehicle average speed increase in recent years have improved road pavements performance standards. Road surface must be designed, built and maintained to offer the highest active safety to drivers. This is very important during rainfall events, because the water collected on road pavements produces a drastic decrease of skid resistance and visual distance. So water film depth estimation is one of the most important factor on road safety. Moreover during rainfall events the rainfall wash pollutants collected on road pavements and dissolve them in urban drainage with an important environmental impact. In this paper has been studied and modelled the pollutants wash off on road pavements and the vehicle-road interaction in terms of water film depth. The laboratory equipment consists of an artificial rain system, capable of simulating variable rainfall intensities by different nozzles and by a controlled water discharge system to collect the water flowing from the road surface. To reproduce different rainfall intensities, three nozzles were used and calibrated according to rainfall intensity, drop dimension distribution and medium drop diameter. From rated flow calculation it has been investigated: - the effect of different rainfall intensity regimes on pollutants wash-off and safety; - the effect of different surface slope on wash-off and safety; - the effect of water film depth on skid resistance and safety. The data collected in this way have been submitted to an in-depth analysis, which has provided particularly interesting and significant results regarding design and maintenance of roads according to security and environmental standards.