Freeway crashes in wet weather: the comparative influence of porous and conventional asphalt surfacing

This paper analyses the correlation between the number of crashes on freeways and weather conditions on dense and porous asphalt before and after road modernization operations. The data were collected along 43 km of the A3 freeway, located in Southern Italy from the Tarsia road interchange to the South Cosenza interchange. Crash data were made available by the Police Station of North Cosenza, with traffic data from the ANAS Compartment in Cosenza, and the rainfall measurements were provided by the ARPACAL centre in Calabria. Data were collected over two periods: before the modernization operations with existing dense asphalt and after modernization using porous asphalt. A porous pavement system is a structural and environmentally mindful alternative to the traditional pavement system. Safety tests were carried out correlating the number of crashes to the rainfall detected using two rain gauges and the traffic data. The results show that crash frequency depends considerably on the intensity of rainfall, both for porous and dense asphalt. In the first case, the accident rate increases to a rainfall of 0.5 mm/h, and then decreases due to probable greater prudence adopted by drivers in adverse meteorological events. The use of porous asphalt allows a reduction in the accident rate both in adverse meteorological conditions and for light rain, and confirms that, in terms of risk, the psychological effect on drivers increases with the amount of rain on the road rather than a reduction of adherence on a wet road surface.